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Author Topic: Using teleconverters  (Read 48953 times)

Ray

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Re: Using teleconverters
« Reply #20 on: February 10, 2015, 11:15:50 pm »


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. 


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.
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Ray

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Re: Using teleconverters
« Reply #21 on: February 10, 2015, 11:20:47 pm »

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.

I'd rephrase that along the lines that some primes have such superb performance at wide apertures that even when used with a good teleconverter they can produce results that equal or exceed the performance of a normally good lens of the same, extended focal length.

The bottom line is, whatever the quality of the prime one is using, the attachment of a teleconverter degrades the quality compared with a lens of similar quality designed with a 'native' longer focal length.
In other words, a superb 200mm lens when used with an excellent quality 2x teleconverter will never result in a superb 400mm lens.

This difference is important when comparing the resolution advantages of the teleconverter with the same scene shot without the teleconverter. If the teleconverter is the best available, and if the scene is static, and if one is using a tripod so that raising ISO is not necessary, one should see a worthwhile improvement in detail and resolution, at 100% on screen or print. Otherwise not, especially if one has to raise ISO by 2 stops or more to get the equivalent DoF and freezing of movement.
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spidermike

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Re: Using teleconverters
« Reply #22 on: February 11, 2015, 09:43:46 am »

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.
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dwswager

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Re: Using teleconverters
« Reply #23 on: February 11, 2015, 09:54:31 am »

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.


Different for every combo, but the Nikon 80-400mm f/4.5-5/6 VR is sharper at 400mm than the Nikkor 70-200mm f/2.8 w/ TC-20EII 2x teleconverter.  I waited 5 years for Nikon to update the 80-400mm because the original was designed for precision so it focused really slow.  Hence not good for sports.  That is how I ended up replacing the 80-200mm f/2.8 (which is a spectacular bargain in comparison at $1100) for the 70-200mm f/2.8 VRII with TCs.  They released the update 80-400mm about 9 months late! Doh!
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kers

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Re: Using teleconverters
« Reply #24 on: February 11, 2015, 09:55:51 am »


Converters are a waste of time, in my very, very humble opinion.  ;D
in most cases i think you are right... I agree with Erik:
I bought the 2x Nikon converter VII; i did not realize that it has to be matching a specific lens...
of all my lenses it only works on the new 300mm F4 PF and presumably the 300mm f2.8 VrII for it was designed to match it.
on my 70-200 it is indeed a waste...but on the 300F4 PF it becomes a very good F8 600mm VR ...
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dwswager

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Re: Using teleconverters
« Reply #25 on: February 11, 2015, 10:11:44 am »

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.  Backgrounds at sports tend to be either significantly lighter or darker than the field.  And since you lose DR and get more noise as ISO goes up, metering is even more critical.  You could dial in exposure compensation, but as the action moves toward you filling the frame, the exposure compensation becomes overcompensation one way or the other.  Of course, if someone made a great 80-300mm or 80-400mm f/4 lens I could afford, that would be a better solution.

« Last Edit: February 11, 2015, 10:15:05 am by dwswager »
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Ray

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Re: Using teleconverters
« Reply #26 on: February 11, 2015, 10:35:02 pm »

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.  

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.

If one doesn't do this, then one can achieve almost any result that one's biases lead one to. To take an extreme example, one could shoot a high-resolution image with a telephoto lens at F2.8, producing a very noticeable shallowness of DoF on a large print, then reduce the print size to that of a postage stamp and claim, "Who said that wide apertures result in a shallow DoF?"  ;D

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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.

In my opinion these would be the main advantages of using a teleconverter, which are similar to the advantages of using any telephoto lens of equal focal length.

One the other side of the coin, let's look at the advantages of using a 70-200/F2.8 without 2x teleconverter, shooting the same scenes.

First, one gains that very significant advantage of the rangefinder camera where the scene one sees through the viewfinder is larger than the shot one intends to capture. One is thus able to anticipate events more easily, as they unfold, which should enable one to do a better job at 'capturing the moment', which is surely a very important factor when photographing sports. Henri Cartier-Bresson used this quality of the rangefinder camera to great effect.

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.

Thirdly, I would think that anyone who buys a rather expensive and rather heavy lens such as the 70-200/F2.8 does so because image quality, sharpness and resolution are important to him. Is it not contradictory that such a person would be satisfied with effectively a lower quality lens of double the focal length?

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.

I rest my case.  ;)
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spidermike

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Re: Using teleconverters
« Reply #27 on: February 12, 2015, 04:23:38 am »


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.


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Petrus

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Re: Using teleconverters
« Reply #28 on: February 12, 2015, 05:23:11 am »

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.
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Ray

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Re: Using teleconverters
« Reply #29 on: February 12, 2015, 08:36:13 am »

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.


That's true. I guess if had already splashed out money on an excellent quality 70-200/F2.8 or 300/F2.8 prime, I'd certainly be investigating the usefulness of a teleconverter if I needed a longer reach. The issue is not so much a comparison between a 70-200/F2.8 with 2x converter, and the 80-400, because I wouldn't want to carry two such heavy lenses in my bag, but rather a comparison between the 70-200/F2.8 with teleconverter and without teleconverter, after cropping, interpolating and sharpening the image without teleconverter.
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Ray

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Re: Using teleconverters
« Reply #30 on: February 12, 2015, 08:41:16 am »

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.

I hope I haven't given the impression there is a drastic quality failure. I would expect the image with teleconverter to be at least as good, on average, as the image without teleconverter, and always at least marginally better if shooting a static subject using a tripod.

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.
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Bart_van_der_Wolf

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Re: Using teleconverters
« Reply #31 on: February 12, 2015, 09:40:19 am »

Now that the thread has drifted this far from the original topic...

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 than 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).

Especially in the case of lenses with image stabilization (IS or VR), the amount to increase the shutterspeed can be less than the extender factor. Of course at marginal light conditions life becomes more challenging whichever way one twists ...

I also took the opportunity a while ago to test the lens+extender combination (in both center and extreme corner) with the Canon Digital Photo Professional Raw converter, which offers a Digital Lens Optimization (DLO) option. That DLO uses a downloadable lens profile (for the lens or lens+extender, generations I/II, or III), and corrects the residual lens aberrations (based on focal length and used distance). It writes an improved version of the Raw data to the Raw file (which becomes twice as large but remains compatible with other converters) and demosaics that. I can only say that it works very well. The quality, especially in the corners, jumps to a higher level and it also equalizes the sharpness in the focal plane across the image (corners can and will be improved more than the center).

This shows that it is better to optically magnify the image than to attempt doing it afterwards via software. Concerns like noise, low shutterspeed (not only impacts camera shake but also subject motion), and such, are secondary to the sharp in focus image one can achieve with good quality lens+extender. Not that these auxiliary effects are not important, but rather that they just demand better technique, rather than a smaller image that e.g. can't even resolve the blur. The blur from motion can perhaps be cured with deconvolution, because the inherent detail is present. Lack of actual resolution can not really be cured.

Cheers,
Bart
« Last Edit: February 12, 2015, 04:37:46 pm by BartvanderWolf »
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dwswager

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Re: Using teleconverters
« Reply #32 on: February 12, 2015, 09:57:58 am »

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.

Depth of field is the same for a 400mm at f/5.6 as a 200mm with 2x TC at f/2.8.  Assuming all modern components the camera will read f/5.6 as the aperture with a f/2.8 and 2x TC.

And the output target size always has to be the unifying standard.  Otherwise, no comparison makes sense.  Plus knowing the output target size lets you choose the best option among those available.  Basically, it will tell you if the lens w/o TC will give you enough to start with.

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.

Shooting soccer, I'm normally shooting 1/500th and f/4-f5.6.   If I get desperate I will drop the aperture down to f/2.8 if available.  As I mentioned shooting soccer the other day, my starting light was 1/800, f/5.6 and ISO 64.  The 1 stop of light lossed from the TC doesn't hurt from an ISO boost.  But by the end of the game, I was regularly seeing ISO 2500-6400.  I had already dropped the shutter speed down to 1/500th and moved the aperture to f/4 to stay below ISO3200.

But I will say this is a massive difference shooting the D810 or the D7100.  If I set the D810 to 1.2X mode, it gives me the same frame rate as the D7100 and roughly the same 24MP image.  But the difference is the D810 produces usable images with very little objectionable noise at IS0 6400.   Similar to what the D7100 produces at about ISO 2500.  The D7100 is unusable, at least without a lot of post processing work, at ISO 6400, even though by that ISO they both (and most cameras) are exhibiting the same limited DR.
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Petrus

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Re: Using teleconverters
« Reply #33 on: February 12, 2015, 12:33:22 pm »

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.

I was lazy: I just compared the backup JPEGs on the SC card without any post processing.
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Ray

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Re: Using teleconverters
« Reply #34 on: February 12, 2015, 04:11:04 pm »

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).

Hi Bart,
Canon also have an advantage, compared with Nikon, in this respect of losing 1 or 2 stops of light within the range of ISO 100 to 400. There will be no noticeable loss of DR because it's equally bad at all 3 ISOs settings, and at ISO 800, DR might be only 1/2 a stop worse.  ;D

I agree that in ideal conditions, using either a tripod to shoot a static subject or using the camera hand-held in bright light where there is no need to raise ISO, the image that has been magnified with a converter should always be more detailed.

However, in my experience when using the Canon 100-400 and Nikkor 80-400, I find that I'm very rarely in circumstances where I'm able to use base ISO with the required shutter speed at 400mm, without underexposing, so these secondary considerations (as you put it) become primary considerations for me, which tend to negate the benefits of the teleconverter.

Even if it is the case that despite such secondary considerations the image with teleconverter is still marginally better, I would have to consider if such marginal improvement justifies the inconvenience of not being able to quickly use the 70-200 at F2.8 or F4 if circumstance were to quickly change. One could easily miss the opportunity for an interesting shot whilst stuffing around removing the converter.  ;)
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jjj

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Re: Using teleconverters
« Reply #35 on: February 13, 2015, 11:05:47 am »

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.

Converters are a waste of time, in my very, very humble opinion.  ;D
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.
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jjj

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Re: Using teleconverters
« Reply #36 on: February 13, 2015, 11:12:12 am »

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.

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.
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Bart_van_der_Wolf

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Re: Using teleconverters
« Reply #37 on: February 13, 2015, 11:47:33 am »

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.

Quote
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.

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
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ErikKaffehr

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Re: Using teleconverters
« Reply #38 on: February 13, 2015, 03:53:01 pm »

Hi,

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.

Best regards
Erik


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
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Ray

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Re: Using teleconverters
« Reply #39 on: February 15, 2015, 08:42:12 am »

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.

It's understood that high quality lenses produce better quality images than mediocre and poor quality lenses. Who could possibly disagree with that?  ;D

Any high quality lens, with or without any converter, will of course produce a better quality image than a lower quality lens with or without the same quality of converter.
Naturally, the best image quality results from the best quality lens used with the best quality converter, and one would certainly expect that the image quality from such a combination would be on a par with, and hopefully better than that of a mediocre lens of the same focal length.

If one is comparing the image through the converter with the interpolated cropped image without the converter, then both images will be better whenever the lenses are better.
The issue of whether or not to buy a converter for use with a particular lens is often related to the comparison with the alternative lens of the same focal length. Does the Canon 70-200/F2.8 with 2x extender produce results which are as good as the Canon 100-400 IS? Maybe it does, but probably not. Does the same lens with extender produce a quality equal to that of the new Canon 100-400 IS II. It's doubtful.

Comparisons are also affected by the quality-control variability of all the lenses under comparison. Comparing any two lenses of the same model can result in a noticeable variation in the test images.

Take half a dozen 70-200/F2.8 lenses from different batches; choose the best and the worst. Take half a dozen 2x extenders from different batches; choose the best and the worst. Take half a dozen 100-400 lenses from different batches; choose the best and the worst.
Combine the best of the 70-200 lenses tested, with the best of the 2x extenders and compare with the worst of the 100-400 zooms tested; then do the opposite. Post your results here.  ;D

Quote
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.

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."


I get the impression that focus accuracy when using a teleconverter is sometimes reduced, at least in the past, partly also because the contrast of the scene is reduced. One frequently sees comments on the internet about the problem of focus-hunting when using a teleconverter. Early Canon 'prosumer' DSLRs wouldn't autofocus at all when an extender was attached to an F5.6 prime.

Are you referring to manual focussing, perhaps? I've agreed earlier in the thread that a magnified view of the scene has advantages in one being able to see more clearly what you are shooting and focussing on.

Quote
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.

It is the extender that creates the low-light scenario, Bart. One doesn't have to 'come up with it', just attach the extender.  ;)

As I've mentioned before, if the light is very bright so that the faster shutter speed required with the longer 'effective' focal length, in combination with the unavoidable drop in F/stop, allows one to continue to use base ISO, or, if the subject is static and one uses a tripod, then that's the best scenario that might produce a worthwhile improvement in image detail resulting from the extender.
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