DoF is determined by the lens, not the converter. So if you put a 2 stop converter behind an f/2.8 lens, you'll have the DoF of the f/2.8.
When using a teleconverter, there is a focal length conversion factor (1.4x, 2x, etc) and an accompanying f-stop drop f/4 -> f/5,6, etc.
Does the f-stop drop relate only to drop in light intensity (making it more of a T-stop adjustment) or does it also represent depth of field?
When using a teleconverter, there is a focal length conversion factor (1.4x, 2x, etc) and an accompanying f-stop drop f/4 -> f/5,6, etc.
Does the f-stop drop relate only to drop in light intensity (making it more of a T-stop adjustment) or does it also represent depth of field?
OK, let's start afresh: 400mm f/5.6 and 200mm f/2.8 with 2X teleconverter will produce exactly the same optical result full open. That is really all there is to it.
However, there will likely be minor discrepancies due to resolution differences. A poor teleconverter will possibly result in a slightly greater DoF, and an excellent teleconverter in a slightly shallower DoF. But that's pixel-peeping. ;DWhat about 5 teleconverters (http://petapixel.com/2015/02/05/stacking-five-2x-teleconverters-create-ridiculous-9600mm-lens/)!
What about 5 teleconverters (http://petapixel.com/2015/02/05/stacking-five-2x-teleconverters-create-ridiculous-9600mm-lens/)!
(http://petapixel.com/assets/uploads/2015/02/IMG_9419.jpg)
Any resolution advantage is often negated by the higher ISO required, or the slower shutter speed required due to the higher F/stop number of the lens when converter is attached.
That is assuming you are using an inapporpriate shutter speed for the magnified focal length or increasing the ISO. .
I shoot daytime sports with the AF-S Nikkor 70-200mm f/2.8 VR II and 1.4x TC-14EIII and find the results acceptable. And since I shoot a D810, I find a 1 stop increase in ISO not a problem, when I might need it, as I might have when I was shooting the D300.
Inappropriate? Do you mean, if conditions were such that one would use an unnecessarily fast shutter speed at base ISO without the converter, then one could reduce shutter speed instead of increasing ISO when using a converter which requires a stopping down of F/stop?
I'd be wary about this approach, especially when using a 36mp camera. Maximum resolution is often dependent upon using a reasonably fast shutter speed, despite the benefits of VR. The higher the pixel count, the faster the shutter speed needs to be, except when using a tripod.
Even with a so-called ISO-less camera, such as the D800 or D810, increasing ISO by one stop whilst doubling shutter speed, results in approximately a 1-stop reduction in DR and a 1-stop reduction in SNR at 18%. You can't get away from this, except by using Canon cameras where DR at low ISOs is approximately equally bad from ISO 100 to 400 and only about 1/2 a stop down at ISO 800.
You might well find the results acceptable when using a high quality zoom with teleconverter, such as the 70-200/F2.8. I would think the main advantage would be the ability to see the action more clearly because of the greater magnification. However, if you were to compare two shots of the same scene, with and without teleconverter, either using the same ISO but a faster shutter speed for the shot without converter, or using the same shutter speed but a higher ISO for the shot with converter, I doubt that you would find any meaningful benefit outside of pixel-peeping.
You should see a marginal increase in resolution when using the converter, if the lens is good. However, if the image without converter was shot at a lower ISO, it can be sharpened more, thus narrowing any resolution differences. If the image without converter was shot at the same ISO but using a shutter speed twice as fast, there will likely be some increase in resolution due to that faster shutter speed.
I mean shooting at an appropriate shutter speed for the magnified focal length. And yes, you do incur a small penalty for increasing ISO. Since I usually don't require all the DR the D810 has at base ISO for sports, that isn't even a penalty and the images up to about ISO 800 are Excellent and up to about 3200 are still very good.
What ISO do you suspect indoor sports shooters use, though they do not usually need the extra reach of a TC or super telephoto lens. Everything in photography is about trade offs. Give something to get something of higher value. The trick is making smart choices. The good shot you get is always better than the great shot you didn't!
I mean shooting at an appropriate shutter speed for the magnified focal length.
Actually, there's an interesting aspect of this perceived need to increase shutter speed due to the longer, effective focal length of a lens used with teleconverter. The concept is, the enlargement of the scene unavoidably includes the enlargement of any movement in the scene, and/or the movement from camera shake, therefore, one should increase shutter speed to compensate for this.
However, if one is comparing the technical quality of images taken with and without converter, the image without converter is cropped and enlarged through a different process of interpolation, but enlarged nevertheless.
in order to achieve the maximum 'freezing of movement' in the image without converter, I would speculate that one should use the same shutter speed that is appropriate for the image produced with the converter, but I'm not certain about this.
If I'm wrong on this point, then in order to get an image with both equivalent DoF and equivalent (or better) sharpness when using a 1.4x converter, one not only has to raise the ISO one stop because of the increase in F/stop number, but also raise ISO another stop in order to get the faster shutter speed required to freeze the enlarged movement. That's a 2-stop difference in ISO. Quite significant I'd say.
If one is using a 2x converter, then in order to achieve maximum sharpness and the same DoF, one might have to increase ISO by 4 stops. Am I right or wrong on this point? ;)
I'm just trying to be clear here as to the real benefits of the teleconverter. It seems to me that in the interests of reduced weight and cost, one is accepting the performance of a poor quality, or at best a mediocre quality lens.
In other words, an excellent 200mm lens used with a 2x converter becomes a mediocre 400mm lens, and a mediocre 200mm lens used with a 2x converter becomes a poor quality 400mm lens.
Some lenses are good enough that they don't become mediocre when using teleconverters (assuming a good teleconverter). I recently saw a comparison of the Leica 400mm f/4 APO with the Leica 280mm f/4 APO plus Leica APO 1.4x teleconverter. The 280+TC was spectacular (my own experience as well) and the Leica 400mm f/4 APO didn't catch up to the 280+TC until about f/8.
Hi,
I would say that a case may be made for a converter matched to a lens. In that case the converter can actually be designed so it further reduces some aberrations in the lens it has been designed for.
Alternatively a lens can be designed to be used with a given extender. So a single 1.4X extender may be shared between several lenses.
Best regards
Erik
Because the angle of view is narrowed with the TC on the same sensor, you have an apparently longer lens. Hence, any camera shake is also magnified.
Some lenses are good enough that they don't become mediocre when using teleconverters (assuming a good teleconverter). I recently saw a comparison of the Leica 400mm f/4 APO with the Leica 280mm f/4 APO plus Leica APO 1.4x teleconverter. The 280+TC was spectacular (my own experience as well) and the Leica 400mm f/4 APO didn't catch up to the 280+TC until about f/8.
With an interest in bird photography I have been reading about the relative merits of the 70-200 f2.8 L with 2xtc vs 100-400 f4-5.6 and the 70-200 holds up extremely well - so unless you start with the assumption that the 100-400 is 'mediocre' it would call into question your broad-brush comment on the effect of tcs. A lot of this will depend on the 'generation' of the lens and how different people describe the same differences as irrelevant in practice, evolutionary or 'night and day'.
As a general caution of 'no magic cure' I think your comments are useful but that does not mean the differences cannot be reduced to negligible with careful component-matching.
in most cases i think you are right... I agree with Erik:
Converters are a waste of time, in my very, very humble opinion. ;D
Of course. My point was, if you crop the image captured without the use of a teleconverter, you've also narrowed the angle of view to the same degree as the teleconverter did. If you then enlarge that cropped image, through interpolation in Photoshop, to the same size as the uncropped image that resulted from the use of the teleconverter, then you have also enlarged the effect of any camera shake or subject movement, just as you did using the teleconverter lens.
If this is not true, and there are other issues involved, such as the consequences of the higher native pixel count of the teleconverter image, then I would say that unless one is shooting in very bright light where underexposing due to a higher shutter-speed requirement is not an issue, and/or unless one is happy with a shallower DoF when using the teleconverter (by using the same F/stop), then the circumstance of the shot might result in there being no worthwhile technical improvement at all, when using the teleconverter.
Give and take. At the lower focal length there will be less DOF blur, but you have to enlarge it so what the shot gives you the enlargement taketh away. And that is different from movement blur. Once captured, movement blur is locked in.
One reason shooting with a TC is preferable is framing and focusing. Just easier to get and keep the focus spot on the target. In addition, metering is better.
But the 70-200 with tc offers a far cheaper alternative (and a lighter gear bag) to having the 80-400 and the 70-200. But again the question is how significant is the loss in quality - both subjectively and objectively.
Fourthly, there is no weight-saving when using a 70-200/F2.8 with 2x converter instead of the new Nikkor AF-S 80-400 G. In fact, after taking the trouble to look up the weights on the internet, I see the 70-200 with converter is about 300gms heavier.
But the 70-200 with tc offers a far cheaper alternative (and a lighter gear bag) to having the 80-400 and the 70-200. But again the question is how significant is the loss in quality - both subjectively and objectively.
I made a quick test with Nikon D800e and 70-200mm f/2.8 Nikkor with and without 1.7X teleconverter, at f/5.6. Picture shot with 1.7X converter was sharper than the plain 200mm shot enlarged 1.7 times, even if the ISO was 1 1/3 faster with the converter. Apparently the 1.7X Nikkor converter is quite good.
This was not a scientific and precise test, but at least it showed that worrying about drastic quality failure is unfounded. 2X converter might be different, at least with Canon it was not good when I still had Canon system, but I have no experience with Nikkor 2X converter.
The original question posed by Dreed, as I understand it, asked if the unavoidable f/stop drop resulting from the use of a teleconverter changed the effective DoF of the resulting image as well as the effective focal length, or was such a drop in F/stop merely equivalent to a drop in T/stop (transmission loss).
After some initial confusion on this issue, and with the help of the authoritative Bart, it was decided many posts ago that there is effectively no change in DoF as a result of the use of a teleconverter. In other words, the drop in F/stop corresponds with the increase in focal length to maintain the same DoF, broadly speaking.
Now, when comparing the technical qualities of two images, whether such qualities be resolution, detail, noise, DoF, or even perspective, it is essential to compare equal size prints, or equal size monitor images, of the same captured scene viewed from the same distance.
Secondly, that 2-stop advantage in noise is always there, when using the lens without 2x converter. The issue of a possible requirement for a faster shutter speed due to the longer focal length, makes that a 3-stop advantage. The noise differences between ISO 100 and ISO 800 are very significant for me.
In your experiment, did you apply slightly more sharpening to the image shot without teleconverter? Whenever I do such tests, I always apply a degree of sharpening that results in equal noise in both images.
Although the loss of 1 or 2 stops of light with the use of a 1.4x or 2x focal length extender is a given, I think that with a good matching extender, the optical quality takes a much lower hit that upsampling would cause. I base that opinion on practical experiments with relatively recent Canon Extenders on relatively recent version zoom lenses (Canon have been releasing second generation versions of many lenses during the past years).
The greater the magnification, the poorer the quality of the equivalent focal length of lens that results. My owns tests have confirmed that even a very modest 1.4x converter provides little resolution advantage over an image without converter, cropped to the same FoV as the image with the converter. Any resolution advantage is often negated by the higher ISO required, or the slower shutter speed required due to the higher F/stop number of the lens when converter is attached.If you'd read the link included, they demonstrate how stacking teleconverters works out. Not as bad as one would have thought. But I reckon the shots with more converters suffer more from poor tripod placement, i.e. on camera body.
Converters are a waste of time, in my very, very humble opinion. ;D
In other words, an excellent 200mm lens used with a 2x converter becomes a mediocre 400mm lens, and a mediocre 200mm lens used with a 2x converter becomes a poor quality 400mm lens.Maybe you should test excellent lenses with excellent convertors instead. :P
If what I write is true, and I believe it is as a result of my own tests, then the real benefits of the teleconverter are reduced weight and cost, and the facility to see any action more clearly through the viewfinder, due to the greater magnification.
Maybe you should test excellent lenses with excellent convertors instead. :P
You are also forgetting the advantage they really give you. Not having to carry a much bigger and heavier lens. I'd be surprised if upping ISO a bit with current cameras makes for a poorer quality image rather than cropping to get the magnification. Plus I'd rather frame shot correctly in camera.
Hi,
I didn't want to mention it, but I agree. Mediocre lenses with mediocre extenders are a bad mix.
That, and if used with a sort of image stabilization system (IS/VR/etc.), allows more accurate focus, and the stabilization is performed at the level of the magnified image. Of course one can come up with a low light scenario where every stop of shutterspeed or aperture is welcome, but then one should use higher quality equipment rather than an extender.
Cheers,
Bart
Maybe you should test excellent lenses with excellent convertors instead. :P
Hi,
I didn't want to mention it, but I agree. Mediocre lenses with mediocre extenders are a bad mix.
That, and if used with a sort of image stabilization system (IS/VR/etc.), allows more accurate focus, and the stabilization is performed at the level of the magnified image.
Of course one can come up with a low light scenario where every stop of shutterspeed or aperture is welcome, but then one should use higher quality equipment rather than an extender.
Are you sure about this, Bart? Here's an extract from the USA Canon site at http://learn.usa.canon.com/resources/articles/2014/ef_extenders_pt2.htmlp
"Change in lens AF speed with EF Extenders
Because AF systems are essentially computer-controlled to read and react to focus distance changes, the information must be modified so that the focusing movement (or sensitivity) compensates for the added presence of the extender. In the Canon EOS system, this is done by deliberately reducing drive speed when an extender is detected.
Before you immediately conclude that this is a problem, understand that this reduction in drive speed now corresponds to the effective speed you would achieve with the same EF lens alone. It compensates, automatically, for the reduced distance lens elements in the lens’s focusing group(s) need to move to refocus on a subject, with either EF Extender in place. Accordingly, overall AF performance remains essentially unchanged with an EF Extender attached, versus the lens’s AF speed without an extender."
OK, let's start afresh: 400mm f/5.6 and 200mm f/2.8 with 2X teleconverter will produce exactly the same optical result full open. That is really all there is to it.DOF comparisons get controversial partly becuase different people assume different comparison conditions, so I can see tha 2x covertor either halving DOF or not changing it:
DOF comparisons get controversial partly becuase different people assume different comparison conditions, so I can see tha 2x covertor either halving DOF or not changing it:
a) If you print the entire image recorded by the sensor at the same total size, the 2x TC image will have half the DOF: the image of the subject will be twice as big, and the circle of confusion at each point of the image will also be, so you only have to look at something half as far from the plane of critical focus in order to see OOF effects.
b) If for some reason you display the images with the subject the same size (TC print half as big in each dimension, so as if you had just cut down the print of the non-TC version) and view from the same distance, DOF will appear the same.
c) But if you then view those different size prints at distance proportional to print size, yo are back half the DOF with te TC version.
c) And in the new-fangled style of comparing at equal PPI and equal viewing distance, it is again half the DOF with the 2x TC.
So to my preferred way of comparing (version (a)), a TC reduces DOF by the magnification factor of the TC.
I appreciate the argument that a very high quality lens used with a high quality converter may rival the quality of a mediocre telephoto lens of the same equivalent focal length
Is the Leica 400mm f/4 APO a mediocre lens? Compared with the Leica 280mm f/4 APO (a very high quality lens) used with the Leica 1.4x APO extender (a high quality converter), the only advantage of the 400mm f/4 APO is one stop faster maximum aperture. The 280mm lens with 1.4x extender out-resolves the 400mm f/4 until the 400 is stopped down to f/8.
This is a crop from a photo made with stacked extenders - the 280/4 APO with 1.4x and 2x APO extenders. I won't make big prints of this photo; I think this is where the prime plus extender(s) rivals the quality of a mediocre 800mm lens.(http://www.wildlightphoto.com/birds/picidae/melanerpes/lewood04.jpg)
I have no experience with those Leica lenses you mention, Doug.
You've said it all right there.
A 400mm lens shot at f/5.6 and location X focused on subject at location Y on a camera with sensor W will have the same DOF as a 200mm lens shot at f/2.8 with a 2x TC (effective aperature of f/5.6) and location X focused on subject at location Y on the same camera with sensor W.Agreed: a TC changes both the focal length and the aperture ratio from that marked on the lens by the same factor, because the aperture ratio is focal length divided by effective aperture diameter (= entrance pupil size) and the latter is not changed by the TC. But ...
All the rest is useless mubmo jumbo.... given that the original question was about how attaching a TC affects DOF, the rest is actually relevant to answering that question! Especially since there is so much confusion about how DOF (how visible OOF effects are) is affected by choices of how to view the image (how big, from how far away, etc.), not solely by traditional "guideline" formulas using only focal length, aperture, subject distance and such.
...I'm still waiting for someone to post comparison images showing how much sharper hand-held shots can be when using a teleconverter, than the same scene shot without teleconverter, after cropping, interpolating and appropriately sharpening the image without teleconverter, or downsampling the image from the teleconverter...
I would say that extenders make a lot of sense with high quality optics that are outperforming the sensor. In real world I would say that shooting a cropped sensor camera without extender could be better than using an extender on full frame.Yes, or just using a sensor that allows such cropping: having a sensor with twice the pixel count than one needs for long telephoto shots allows a 1.4x crop (to half the image area) as an alternative of using a 1.4x TC. And with a lot of modern sensors, the full resolution is mostly of value with stationary or very brightly lit subjects (landscapes, architecture, studio portraits, etc.) so for telephoto shots of wildlife, sports and such, half the total pixel count is often enough. This cropping approach allows "loose framing", to be able to correct the framing in the case that a bad prediction of subject motion causes subject to ends up framed poorly. On the the hand (as indicated in Reply #25 above by dwswager) the cropping approach can have the problem of a far smaller OVF image of the part of the scene that you actually care about, and can mess up light metering. That is why I like the "digital teleconvertor" mode of some EVF cameras like the EM5, which can in principle also do light metering based only on the intended crop (but I do not know if the EM5 meters this way). This mode only crops the in-camera JPEG to what is seen in the EVF; the raw file still records the whole image, so preserves the ability to correct the framing if needed. Unfortunately the EM5 only offers a 2x digital TC; I would like a 1.4x option.
i do not exactly know what you mean, but if a converter is made for the specific lens ussually the quality of the lens is very good and the converter makes sense...
In all other cases it does not work...at least that is what i have noticed with this specific converter: the nikon 2x versionII.
I have found out it works really well with the new Nikkor 300PF ; a lens that is very sharp and the center can handle a 135MP full frame.
I have added some 100% crop-samples ....
PS
i have used a dNikon d810..
the lens is only 755 ; gram the converter is about 450 gram... a 600mm F8 at about 1200 gram... not bad...
Ray: that 4 stop increase is correct in the worst-case scenario of a 2x TC and hand-holding (with no or insufficient IS), which is the scenario where the shutter speed would also need to be doubled. If instead the shutter speed needed is dictated mainly by subject motion, there is not necessarily any need to increase shutter speed. For example, the same shutter speed that works to freeze motion of a subject with a 200mm focal length at 50 meter range also works with a 400mm focal length at 100 meter range (these alternatives giving about the same framing of the subject). So in the best-case scenario of 1.4x TC and camera on tripod, or with any stabilization system good enough that only subject motion is a problem, then only a doubling of exposure index is needed, and the increased noise effect from that is probably comparable to getting the same pixel count on the subject by halving pixel area instead of using a 1.4x TC.
Thanks,
In the examples you show above, the EXIF data indicates that both shots are at F16. That suggests you used the 300mm lens at F8 with 2x converter, then compared the result without converter, with the lens set at F16. The fine detail in the F8 shot is of course sharper, as you would expect any good lens to be sharper at F8 than at F16.
If you are going to be objective with such tests, using this approach, you should choose a scene with great depth, and then also compare the out-of-focus parts. You might then see that the OoF parts in the shot without converter are more significantly sharper than the in-focus parts are sharper in the teleconverter shot. ;)
But ...
... given that the original question was about how attaching a TC affects DOF, the rest is actually relevant to answering that question! Especially since there is so much confusion about how DOF (how visible OOF effects are) is affected by choices of how to view the image (how big, from how far away, etc.), not solely by traditional "guideline" formulas using only focal length, aperture, subject distance and such.
If you want to know how the shots are taken please ask me and i will tell you ..
The shot with the 300mm PF is made at 1/13 sec; f/16; ISO 64
the shot with the 300PF + 2x converter is made at f5.6 1/400 64 asa...
I tried to get the shots as steady as possible- because i was interested in the optical performance.
As you can see the d16 shot + converter contains much more information..
That is the point ( my unbiased opinion) i was trying to make... and i believe i made that clear to anyone but... ;) ;)
We hear a lot about the additional shutter speed that a high-resolution sensor requires to take full advantage of that increase in pixel count. Michael mentioned this in relation to the D800 when it first became available.
A 2x converter effectively quadruples the pixel count, compared with the same FoV from the lens without converter. Regardless of whether the movement is due to subject movement or camera shake, I would think that in order to get the maximum resolution advantage when using a converter, one should always increase the shutter speed beyond what one would use shooting the same scene without converter, when the camera is hand-held.
The question is, by how much? Imagine using a particular lens on a 9mp camera, then upgrading one's camera to 36mp and using the same lens. In order to see the full advantage of the increased resolution potential of the 36mp camera, would one not be advised to quadruple shutter speed?
It's been explained over and over again in this thread that a 300mm lens at F5.6 will have the same DoF as that same lens used at the same aperture with a converter. The effect of a 2x converter is to unavoidably drop the aperture by 2 stops, ie. F5.6 becomes F11, but the aperture of the 300mm lens is still physically F5.6 despite the reading being F11. The converter does not go in front of the lens but behind it. You must have noticed that. ;)
...
We can now concentrate on other factors that have to do with getting the shot, and that's about technique, not about the extenders per se. BTW it helps some folks to reduce the caffeine intake before shooting handheld telephoto shots, although image stabilization does also help in that case.
....
Cheers,
Bart
The physical aperture is the same, I agree. But the 'f stop' is the ratio of physical aperture size to focal length, so if you add a teleconverter to go from 400mm to 800mm, the physical aperture is constant so the f value changes accordingly.
Are you sure?Indeed.
The physical aperture is the same, I agree. But the 'f stop' is the ratio of physical aperture size to focal length, so if you add a teleconverter to go from 400mm to 800mm, the physical aperture is constant so the f value changes accordingly.
Regardless of whether the movement is due to subject movement or camera shake, I would think that in order to get the maximum resolution advantage when using a converter, one should always increase the shutter speed beyond what one would use shooting the same scene without converter, when the camera is hand-held.
I'm not sure why you are comparing in your above comment, a 200mm lens at 50metres and a 400mm lens at 100 metres. If one uses a 200mm lens with 2x converter it is presumably to get an enlarged image (greater pixel count) from the same distance.
It's been explained over and over again in this thread that a 300mm lens at F5.6 will have the same DoF as that same lens used at the same aperture with a converter.That has been _claimed_ over and over again, but it has also been explained that this is not true if you make the traditional comparisons of images displayed at equal size and viewed from equal distance.
The effect of a 2x converter is to unavoidably drop the aperture by 2 stops, ie. F5.6 becomes F11, but the aperture of the 300mm lens is still physically F5.6 despite the reading being F11.Ray, if you are ging to enter vigorously into technical debates, you should learn to use technical terms correctly. A value like f/5.6 or f/11 is not the "aperture", it is the aperture _ratio_; the ratio of focal length to entrance pupil diameter, a.k.a effective aperture diameter.
Are you sure?
The physical aperture is the same, I agree. But the 'f stop' is the ratio of physical aperture size to focal length, so if you add a teleconverter to go from 400mm to 800mm, the physical aperture is constant so the f value changes accordingly.
So in a lot of cases, the most relevant alternative to using a TC is not a lens of greater focal length and of equally low minimum f-stop; it is either cropping or accepting the higher minimum f-stop in order to get the arrow FOV desired.
Since many photographers (those lacking infinite budgets for gear and sherpas) use long telephoto lenses f/5.6 and slower, I do not see a fatal flaw in achieving a long focal length at about f/5.6 by the relatively cheap and light addition of a TC to an existing f/2.8 or f/4 lens.
Ray, if you are ging to enter vigorously into technical debates, you should learn to use technical terms correctly. A value like f/5.6 or f/11 is not the "aperture", it is the aperture _ratio_; the ratio of focal length to entrance pupil diameter, a.k.a effective aperture diameter.
Adding a TC does not change the effective aperture diameter, but it really does change the aperture ratio, so that 300mm f/5.6 lens + 2x TC is for _all_ purposes a 600mm, f/11, with no sense of it really being still f/5.6.
Indeed.
This thread is beginning to seem like the one where Ray insisted that perspective was changed by lenses.
That's what I wrote, the physical aperture of the 300mm lens remains the same. The light passes through a 300mm lens at F5.6 before it reaches the converter. Imagine a completely manual lens with no automatic read-out of F/stop, and no automatic adjustment of F/stop. Imagine you have to change the aperture by twisting a ring on the lens.
You manually set the f/stop on the 300mm lens to F/5.6. You add a 2x converter. The 300mm lens still shows a reading of F5.6 on the barrel. However, if you then take a shot on the assumption that the two combined lenses are F5.6, the shot will be underexposed by 2 stops. This is because the 2x converter grabs one quarter of the image, or light, that has passed through the 300mm lens at F5.6 and spreads it over the entire sensor, so that each pixel receives only one quarter of the light that it would have received without the converter.
This also, perhaps, explains more clearly why the DoF does not change. The image that has passed through the converter is an F5.6 image with the DoF of an F5.6 image (in relation to the 300mm lens). Although the automatic f/stop readout on a modern camera changes to F11 when the converter is added, to ensure correct exposure, the qualities of that F5.6 image (what's sharp, what's not sharp, what's in focus, what's out-of-focus etc), remain unchanged, ideally, if the converter is a perfect lens.
If you print an image at two different sizes, DOF changes if you view both from the same distance -
- The tc is like taking a crop of a much larger image so the DOF narrows.
- The effective aperture drops which increases DOF
At least I gave some specific examples which even Bart couldn't sensibly refute. My claim was that if all factors involved were kept constant, such as use of the same camera, no cropping, same print size and same viewing distance to print, then different focal lengths of lens would result in a different perspective from the position of the viewer of the print.Sigh! Lenses do not change perspective, only the position where image is taken from relative to subject does. Lenses only alter the field of view captured.
As I recall, your argument was, if one crops the wider-angle shot to the same FoV as the shot from the longer lens, then the perspective in both images will be the same, which I never disputed because I understand very well that cropping produces a result which is effectively equivalent to a longer focal length of lens. Any two lenses of the same 'effective' focal length will of course exhibit the same perspective, just as any two lenses of the same 'actual' focal length will.
Have you still not got it, Jeremy? ;D
Exactly! That's why it makes sense to compare DoF only on same-size images or prints viewed from the same distance, and viewed at a distance close enough for one to be able to discern the sharpest parts in the images.
If you crop an image, the image as a whole changes, obviously. Objects are removed and the cropped image becomes smaller as a result, but the objects within the crop do not change. What was blurred in the cropped part of the image before cropping, remains blurred after cropping, and what was in focus in the cropped part of the image before cropping, remains in focus after cropping.The bit in bold I agree with...but only at the plane of focus. Anything outside tha plane of focus is de facto out of focus and this is a gradual variation. Depth of field is all about what is acceptably sharp which means we all know it is out of focus but ask ourelves the question 'does it look sharp enough'. We are all familiar with the phenomenon that an image looks woderfully sharp on your camera LCD screen but is total pants when you load it up (whether it is a focus issue or a camera shake issue), so let us expand on that: assume focussed on one person in a crowd:
That is why the most important comparison is between the cropped image from the lens without converter, with the full-sensor image through the converter.OK, so you are comparing the two options of
No, I said more than that. ;)
I said I would like to see comparisons of the lens with and without converter. Your picture of the bird is very nice and certainly acceptably sharp at the size presented, but gives me no idea of the relative quality of images with and without converter in circumstance when one cannot avoid the f/stop disadvantage with the converter.
… here's the problem. There's no such thing as a perfect lens.
...the CaNikon equivalent 300mm f/4 lenses are a cruel joke in comparison....
Ray - also of note.
If you shoot with a 200mm and crop to a 400mm FOV instead of using a TC, then you also need to up the minimum shutter speed just as if you used a teleconverter.
Well the new 300 f4 PF nikkor is really good and has a very usefull VR... nothing cruel or funny about it...just good.
As long as you use Nikon's PF-compensating software, which if the examples mean anything, is inadequate.OK i understand...
EDIT: The PF lens may well be the equal of the Leica 280mm f/4 but that's not why I brought up the Leica lens. The issue I was bringing up is that Ray hasn't used the 280/4, nor the 300mm PF so it seems unlikely he's used a really good lens with a really good TC so IMHO his blanket statement that a lens plus TC will produce mediocre image quality is likely based on experience with lenses that aren't as good.
.
About the usefulness of converters.. i think the success is based upon two things- the original lens must have a very sharp centerpart and the converter has to be made for that lens.
About the usefulness of converters.. i think the success is based upon two things- the original lens must have a very sharp centerpart and the converter has to be made for that lens.Optics experts might want to jump in and correct me, but from the little I have read, matching a teleconverter to lens just depends on compatibility with the exit pupil height of the lens. This is, roughly, the distance at which the aperture diaphragm appears to be when seen from the focal plane at the back of the lens. In a telephoto lens, this is typical higher than reality; for example, in a perfectly telecentric design, the exit pupil height can be infinity!. So one TC can work well with several lens, so long as they have (roughly) the same exit pupil height.
EDIT: The PF lens may well be the equal of the Leica 280mm f/4...........
The issue I was bringing up is that Ray hasn't used the 280/4, nor the 300mm PF so it seems unlikely he's used a really good lens with a really good TC so IMHO his blanket statement that a lens plus TC will produce mediocre image quality is likely based on experience with lenses that aren't as good.
Here is another way to think about DoF with teleconverters. Suppose your camera sensor was perfect, with infinitely small pixels. Suppose also that your lens was perfect, limited only by diffraction. Then there would be no reason to use a TC at all -- you could achieve exactly the same result by cropping the image from the original lens. This includes all DoF considerations.
Whenever I've investigated this issue on the internet, the consensus of opinion seems to be, to quote just one example, that the 70-200/F2.8 lenses, whether of the Canon or Nikon variety, when used with the latest 2x converter from Canon or Nikon, do not produce as good an image quality as the latest Canon 100-400, or Nikon 80-400 zooms used at 400mm.
If this situation has now changed with recent technological advances, and teleconverters for use with the 70-200/F2.8 have become so good that image quality now exceeds, or even equals, that from the latest Nikon AF-S 80-400 G, then I have made a big blunder in buying the new Nikkor 80-400. I would have preferred to have spent a bit more for the 70-200/F2.8 plus 2x converter. >:(
I ended up selling the spectacular 80-200mm f/2.8D and buying the 70-200mm f/2.8G VRII and TC-14EIII. But there are advantages and disadvantages to both setups. From 70-200mm, the 70-200mm f/2.8 is much better than the 80-400mm. And to 280mm it is the equivalent. Only getting to 400mm does the 80-400mm outperform. (I have no experience with the 1.7x TC-17EII).
Surely not! Didn't you claim earlier that the Leica 280/F4 was close to being a perfect lens? ;D
I think you've misunderstood my blanket statement. There are a limited number of common words to describe general lens performance. Words and phrases such as excellent, very good, good, quite good, average, mediocre, poor, very poor and so on, are approximate and imprecise. It's the relativity I was trying to get across. In other words, my blanket statement that a good lens becomes a mediocre lens of longer focal length, when a teleconverter is attached, was merely a way of describing the fact that whatever the quality of the lens used with a teleconverter, the longer focal length that results will effectively be a reduced quality lens of longer focal length compared with the quality of the shorter lens, when each lens is used within its focal length range. In other words, the effectively longer lens will have a reduced MTF response, compared with the actual, shorter lens.
Now, if this is not true, then I would be one of the first to be overjoyed at such news. Who wants to carry around more weight and more lenses than they need, in order to achieve their desired image quality?? ;)
Whenever I've investigated this issue on the internet, the consensus of opinion seems to be, to quote just one example, that the 70-200/F2.8 lenses, whether of the Canon or Nikon variety, when used with the latest 2x converter from Canon or Nikon, do not produce as good an image quality as the latest Canon 100-400, or Nikon 80-400 zooms used at 400mm.
Before I use any converter on a regular basis, I would want to know how much sharper or more detailed the image which has been enlarged by the converter is, compared with the crop of the same scene without the converter, after interpolation and sharpening.
I think this is something you'll have to try for yourself with the specific combinations of lens and extender you have in mind. Results that may be completely acceptable to someone else may be unacceptable to you or vice versa… and there's more to it than measurebating.
Exactly why I carry the 280/4 and 1.4x extender. I sold my 400mm lens.
Here is another way to think about DoF with teleconverters. Suppose your camera sensor was perfect, with infinitely small pixels. Suppose also that your lens was perfect, limited only by diffraction. Then there would be no reason to use a TC at all -- you could achieve exactly the same result by cropping the image from the original lens. This includes all DoF considerations.On one hand I agree, and will even go a bit further: a TC can be discarded in favor of cropping to the same FOV (or using a different body with a smaller sensor) with essentially the same results including DOF, _if_ that crop:
But what about other focal lengths between 200 and 280? For example, to achieve a focal length of 240mm with the 70-200, with 1.4x converter, one would use the lens at 172mm, approximately. Surely it would be better to remove the converter, take the shot at 200mm, then crop slightly to get the equivalent 240mm focal length.
Bottom line is that every decision is a case of making trades.Indeed. Plus, what one thinks worthwhile to trade is a very individual choice. One which also depends, as you nicely illustrated on the individual shooting circumstances.
My tests have always compared images from the same lens, with and without converter, and I've always found that the converters (an older Canon 1.4x and a newer Nikon 1.4x) provided slightly improved detail. The problem is, the improvement has been too marginal and tends to be cancelled by the f/stop disadvantage, and sometimes a noticeable resolution fall-off at the edges, which one doesn't get when cropping the image from the shorter lens.
But haven't you deprived yourself of a 560/F5.6 by selling that lens? As a 'birder' surely you would find a 560mm lens very useful; or was that 400mm lens not really good enough for use with an extender? ;)
2) Using all the sensor area via the TC potentially improves dynamic range when abundant light can be gathered, by gathering and counting more photons by using all the photo-sites instead of only one half (1.4x TC) or one quarter (2x TC) of the sensor area.
However, the situation is different when comparing two separate lenses, as in Doug's example of the Leica 280/F4 with 1.4x extender, compared with the Leica 400/F4. He claims that the 280 with extender is slightly sharper than the 400/F4 at F5.6.
In both cases, the full sensor is used to record the images. The disadvantage is that Doug has deprived himself of the benefits of the 400/F4 used at full aperture, which will allow either a lowering of ISO, and the corresponding increase in SNR and DR, or the use of a faster shutter speed without any SNR disadvantage, and possibly a sharper image to boot. ;)
Other features of the 400mm f/4 APO I'm missing out on include much greater weight, the need to use a tripod (vs. the shoulder stock/monopod rig I often use) and the impossibly shallow DOF at f/4
Ray I think you can resolve many of your questions by just going outside (or wherever you typically make photographs) and take some pictures.
Except that in the (perhaps rare) situation when the TC option can get adequate shutter speed at the sensor's base-ISO speed setting; then the non-TC option is stuck with that same setting, and so avoiding blown highlights potentially requires halving the exposure time; that is the case where less light is gathered, and so shadow handling could be worse without the TC than with. (Equal per pixel DR with fewer pixels means worse overall IQ and DR, as has been often discussed!)
You might turn up your nose and think that no Canon lens could match the quality of a Leica prime
... We are always trying to get them to understand that "You can't score if you don't shoot. You don't want to waste opportunities taking bad shots, but the good shot you take is ALWAYS better than the great shot you didn't"I totally agree (also with the bits I edited out); I was pedantically talking about a probably rare edge case, and in fact I am a big advocate of using "excessive pixel counts" to eliminate the need for TC's.
It is the same with photography. You want to get the shot with the best possible quality you can by choosing between all the available, viable, options. But the good shot you get is ALWAYS better than the great shot you didn't!
When comparing the use of a TC to the alternative of cropping to the same final FOV, the shutter speed needed to control image blurring due to motion of either subject or camera is the same, when judged by final images displayed at the same size, etc. The "1/f" guideline goes out the window when one is going to crop and thus enlarge more, just as it does when one changes to a smaller format (which is what cropping is, effectively). So when comparing use of a 1.4x TC to a 1.4x crop, the f-stop change with the TC dictates a _doubling_ of exposure index (not quadrupling).
Nope
For example, let's consider the effects of a 1.4x converter. The converter doesn't add any light.
It enlarges the image with a corresponding reduction in light per pixel.Reduction in light intensity, yes
Each pixel receives just half of the number of photons it would have received without converter,Only if you force the camera to use the same shutter speed. If you are using auto-metering the shutter speed lengthens to accommodate the reduced aperture
comparing images of the same FoV.This is where it could get interesting anmd is something I had not considered before: if you crop an image and blow it up, you are taking a fixed amount of light information and spreqding it over a larger area. Is this analogous to the teleconverter taking a smaller amount of light from the 'lens output' and spreading it over a larger area? It makes sense but I hardly see my images fading on cropping but maybe the computer program accounts for it? I guess one way to look at it is how did it used to work in the days of film processing - I never processed my own stuff so don't know.
Only if you force the camera to use the same shutter speed. If you are using auto-metering the shutter speed lengthens to accommodate the reduced aperture
This is where it could get interesting and is something I had not considered before: if you crop an image and blow it up, you are taking a fixed amount of light information and spreqding it over a larger area. Is this analogous to the teleconverter taking a smaller amount of light from the 'lens output' and spreading it over a larger area? It makes sense but I hardly see my images fading on cropping but maybe the computer program accounts for it? I guess one way to look at it is how did it used to work in the days of film processing - I never processed my own stuff so don't know.
vs teleconverter then when you crop and blow that crop to the same size as the teleconverter image you are also desaturing the amount of light available?
the process of interpolation essentially duplicates each correctly exposed pixel with its full DR and noise characteristics. There is no desaturation nor any fading.
Whilst there's some confusion about the necessity to increase shutter speed
There's no confusion - if you are using a tc you need to shorten shutter speed to reduce the effect of camera shake. Just like an image cna look wonderfully sharp on the camera LCD only to find it is blurred to heck when viewed on the computer monitor. As ever, the combination of image viewing size and viewing distance dictate what it looks like - the tc gives you a 'crop' and magnifies it like looking at a billboard from 20 feet and 100 feet.
So far, according to the points you have raised or agreed with, BJL. it's looking very favourable for the converter.That does not sound so amazing; it is just a list of some respects in which there is a _rough_ equivalence between what you get with the TC vs what you get by cropping instead. If that were the whole story, one would be better off cropping: one less piece of gear to buy and carry, and no time spent swapping the TC on and off. (which is why I have yet to find a reason to use a TC.) The main potential advantage of a TC lies elsewhere, in increased resolution by using more pixels: twice as many with a 1.4x TC. (And my preferred alternative to that would be having a sensor that out-resolves the lens!)
(1) No loss or change in DoF despite the drop in f/stop number.
(2) No requirement for a faster shutter speed than what you would use without a converter, for a given size image/print of same FoV.
(3) No increase in noise, or reduction in DR, as a result of increasing ISO to accommodate the drop in f/stop, because the larger area of the recorded image offsets such increase in noise.
Wow! Everyone should get a teleconverter. These are amazing devices.
(3) No increase in noise, or reduction in DR, as a result of increasing ISO to accommodate the drop in f/stop, because the larger area of the recorded image offsets such increase in noise.
...
However, (sorry to introduce a bit of negativity), I'm still not sure about point #3. ...
For example, let's consider the effects of a 1.4x converter. The converter doesn't add any light. It enlarges the image with a corresponding reduction in light per pixel. Each pixel receives just half of the number of photons it would have received without converter, comparing images of the same FoV. ...
Using a teleconverter means you need to raise the shutter speed to minimize camera shake induced blur. If you make the same crop in post, you also need to raise the shutter speed just as much, as you are using the same picture angle, "equivalent" focal length, so to speak. Simple.
It is the image angle which determines the slowest "safe" shutter speed, not focal length.
... possibility that sensor noise is worse with a TC than with a crop, due to spreading the same light over more photo-sites at lower intensity of illumination: same signal (photons gathered from the subject), so same photon shot noise, but likely more dark current and read noise, due to having a greater area of silicon involved and more photo-sites to read out.Spreading the light across more pixels is a *good* thing, not a bad thing. In fact, that is a nice summary of the entire benefit of a TC. Assuming the sensor does not out-resolve the lens (which is the situation where a TC is better than cropping), spreading the light across more pixels clearly increases overall resolution. As you point out, if exposure is kept the same, there is no overall light loss, only a light loss per pixel, and there will be some increase in readout noise from the extra pixels. But in this situation you can improve the result by increasing exposure, providing more total photons and hence less overall noise. So spreading the image across more pixels is a win-win situation, unless you are constrained to under-expose the larger image.
Spreading the light across more pixels is a *good* thing, not a bad thing.As I tried to explain, using more pixels can be a good thing is some ways (resolution) but possibly a bad thing in others (more sensor noise in situations that call for an elevated exposure index, so giving the sensor far less than full exposure). As you say:
... there will be some increase in readout noise from the extra pixels. ... spreading the image across more pixels is a win-win situation, unless you are constrained to under-expose the larger image.Agreed, but such a constraint to underexposing is rather common when using a TC, due to the combination of the higher minimum f-stop it gives with the high shutter speeds often needed with the narrow image angles that TCs are typically used to achieve.
Using a teleconverter means you need to raise the shutter speed to minimize camera shake induced blur. If you make the same crop in post, you also need to raise the shutter speed just as much, as you are using the same picture angle, "equivalent" focal length, so to speak. Simple.
It is the image angle which determines the slowest "safe" shutter speed, not focal length. It is just that with 135 systems the rule of thumb used to be 1/focal length. If we use crop factor 1.4x (compared to 135 size) there same rule is 1/(1.4xfocal length). It does not matter if we use teleconverter or cropping or smaller sensor. With a TC it becomes 1/(1.4xoriginal focal length).
Thank you; this should be bookmarked, especially the part that I underlined! So simple, yet so often misunderstood.
BJL, you should know that this is true only with regard to the concept of a "safe' shutter speed, ie. one that gets you a traditional size print of, say, A4 or A3 or A3+ size that is acceptably sharp.Agreed; and that is the most relevant criterion here: we are comparing the two alternatives of cropping vs using a TC, so IQ comparisons should indeed be done on the basis of equal [apparent] image size, and for that, the same shutter speed gives the same degree of visibility of motion blurring.