Luminous Landscape Forum
Equipment & Techniques => Medium Format / Film / Digital Backs – and Large Sensor Photography => Topic started by: Theodoros on December 26, 2015, 02:26:42 pm
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Can one please provide an article on how to calculate how much image circle expands when a lens is focused to its minimum focusing distance if compared to infinity? If there is no article, but one knows the theory behind the subject, can he please comment?
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What you’re looking for is a rather basic sine function, based on a right-angled triangle.
(https://upload.wikimedia.org/wikipedia/commons/6/6f/Rtriangle.svg)
Your initial image circle at infinity would be 2*a - so if we assume that the image circle is 90mm, a = 45mm.
b would be your focal length / bellows extension at infinity, so if you're using a 80mm lens, your (initial) bellows extension (at infinity) b = 80mm.
The angle at A (alpha) would be about 26.57 degrees and that's all we need to know to calculate the rest.
If we get closer to the subject our bellows extension grows but the angle on A stays the same (as you don't change the focal length) - if we know the bellows extension it's pretty easy to calculate the projected image circle.
I think the problem with medium and small format lenses is that through complex lens designs with internal focussing and moving lens elements the whole calculation won't be correct any more...
Edit: However I'm pretty sure you can actually calculate the theoretical bellows extension through the focal length and your magnification. But that would only work if potential moving lens elements don't interfere with the image circle!
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What you’re looking for is a rather basic sine function, based on a right-angled triangle.
(https://upload.wikimedia.org/wikipedia/commons/6/6f/Rtriangle.svg)
Your initial image circle at infinity would be 2*a - so if we assume that the image circle is 90mm, a = 45mm.
b would be your focal length / bellows extension at infinity, so if you're using a 80mm lens, your (initial) bellows extension (at infinity) b = 80mm.
The angle at A (alpha) would be about 26.57 degrees and that's all we need to know to calculate the rest.
If we get closer to the subject our bellows extension grows but the angle on A stays the same (as you don't change the focal length) - if we know the bellows extension it's pretty easy to calculate the projected image circle.
I think the problem with medium and small format lenses is that through complex lens designs with internal focussing and moving lens elements the whole calculation won't be correct any more...
Edit: However I'm pretty sure you can actually calculate the theoretical bellows extension through the focal length and your magnification. But that would only work if potential moving lens elements don't interfere with the image circle!
Hi, thanks for the reply but maybe I should put it practically so that people understand better my question... What I'm looking for, is to use MF lenses on a view camera, but the lenses will be focused to their min focusing distance (instead of infinity) so that their image circle is the maximum possible, then there is provision for enough space so that the lens will be focused back to infinity (or other) by recessing the front standard to the desired focusing distance, what you describe above, does apply when one is recessing the lens... but I'm looking on how much the image circle of the lens itself will be increased (with the lens fixed at its platform's mounting distance) if it is focused to its minimum distance (using the lens focusing ring)... is there a way for one to (accurately) calculate that?
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No maths but a test:
FPS + IQ180 + lenses w/ 12mm shift to left side
left parts of pictures shown
upper row: Canon TSE 24f3.5 II @ f11
lower row: Contax 645 35f3.5 @ f11
findings:
- Contax has larger image circle than Canon
- enlargement of image circle towards shorter distances with Contax (longer focal length) less pronounced than with Canon (shorter focal length)
- enlargement of image circle from infinity to 1m not very pronounced, only towards 0,25 shortest distance of the Canon TSE
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Hi, thanks for the reply but maybe I should put it practically so that people understand better my question... What I'm looking for, is to use MF lenses on a view camera, but the lenses will be focused to their min focusing distance (instead of infinity) so that their image circle is the maximum possible, then there is provision for enough space so that the lens will be focused back to infinity (or other) by recessing the front standard to the desired focusing distance, what you describe above, does apply when one is recessing the lens... but I'm looking on how much the image circle of the lens itself will be increased (with the lens fixed at its platform's mounting distance) if it is focused to its minimum distance (using the lens focusing ring)... is there a way for one to (accurately) calculate that?
I'm pretty sure that won't work that way for multiple reasons.
If you focus on a closer subject and then move the lens to get it back to infinity you'll face two problems:
On a lens with internal focusing you'll degrade the image quality by a huge amount and by moving closer you'll reduce the image circle again.
On a lens without internal focussing you'll end up with the same image circle as you did before.
You can't trick optics into providing a bigger image circle for free. Physics doesn't work that way.
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Hi,
On most medium format lenses, focusing just moves the lens. So image circle at infinity will be the same, whatever the focus setting on the lens is. The only question is where you are adding extension, inside the lens or in the bellows of the camera.
Modern macro lenses are often using floating elements. Focusing them close moves a lens group in order of reducing field curvature at close distances. Not clear how that would affect image circle but focusing close would cause field curvature at longer distances.
Some older lenses, like Hasselblad FLE-s have an extra focusing ring using variable airspace between the two front groups to achieve a similar effect.
Best regards
Erik
I'm pretty sure that won't work that way for multiple reasons.
If you focus on a closer subject and then move the lens to get it back to infinity you'll face two problems:
On a lens with internal focusing you'll degrade the image quality by a huge amount and by moving closer you'll reduce the image circle again.
On a lens without internal focussing you'll end up with the same image circle as you did before.
You can't trick optics into providing a bigger image circle for free. Physics doesn't work that way.
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Well not quite... sure the principle of extension stays the same but(!) as the extension happens inside the lans barrel you're not guaranteed to have a bigger image circle at a macro setting. The image circle may very well be cut off by internal elements or simply by limitations of the length of the lens barrel itself.
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Thanks!
A good point!
Best regards
Erik
Well not quite... sure the principle of extension stays the same but(!) as the extension happens inside the lans barrel you're not guaranteed to have a bigger image circle at a macro setting. The image circle may very well be cut off by internal elements or simply by limitations of the length of the lens barrel itself.
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No maths but a test:
FPS + IQ180 + lenses w/ 12mm shift to left side
left parts of pictures shown
upper row: Canon TSE 24f3.5 II @ f11
lower row: Contax 645 35f3.5 @ f11
findings:
- Contax has larger image circle than Canon
- enlargement of image circle towards shorter distances with Contax (longer focal length) less pronounced than with Canon (shorter focal length)
- enlargement of image circle from infinity to 1m not very pronounced, only towards 0,25 shortest distance of the Canon TSE
Thanks for the response Chris... your contribution here is of most importance as it is Contax lenses that will be used on a (highly modified) Rollei X-Act2 camera both with 37x49mm MFDBs as well as with a mirrorless... Please follow this thread as your experience with Contax lenses will be needed (there are more detailed questions coming).
EDIT: By the way, is that tested on an ALPA FPS? I ask this because on a view camera the image circle will expand considerably more as the lenses will be focused much nearer to the sensor... Also... I noticed that the Canon lens vignettes more to the lower corner...
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I'm pretty sure that won't work that way for multiple reasons.
If you focus on a closer subject and then move the lens to get it back to infinity you'll face two problems:
On a lens with internal focusing you'll degrade the image quality by a huge amount and by moving closer you'll reduce the image circle again.
On a lens without internal focussing you'll end up with the same image circle as you did before.
You can't trick optics into providing a bigger image circle for free. Physics doesn't work that way.
I think you may be right to some extend with what you state for an IF lens (although Chris's example above shows some image area expansion even with the Contax 35mm f3.5 lens which is an IF lens but less so than the Canon he also posts)... But on a lens without IF, wouldn't "focus breathing" increase the image circle? (without affecting image quality)... it should, shouldn't it? ...I mean the frame on the sensor will look the same with no movements applied (as of constant focal length), but the total image circle projected should be one of wider focal length (due to focus breathing) ...shouldn't it?
EDIT: At least Chris's results on the Canon 24mm above, (which is not IF) show some considerable image circle expansion when the lens is focused to its minimum... Now as far as IQ is concerned, one can't be certain that it will be less... It will be altered to some degree alright, but it has as much chance to be better as much as to be worst (depending on how near to the "optimum" image circle one is)... but in any case, it can't be much different as to seriously be considered to be a problem.
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I think you may be right with what you state for an IF lens... But on a lens without IF, wouldn't "focus breathing" increase the image circle? (without affecting image quality)... it should, shouldn't it? ...I mean the frame on the sensor will look the same with no movements applied (as of constant focal length), but the total image circle projected should be one of wider focal length (due to focus breathing) ...shouldn't it?
In general, focusing closer will create a larger image circle.
The easiest way to calculate such things is with the Magnification factor, which becomes easier and more accurate to calculate with the closer we focus.
The image circle diameter at infinity focus gets magnified by a factor: 1 + MagnificationFactor / PupilFactor
If we assume symmetrical lens design (with PupilFactor=1), at infinity that would be 1+0/1 = 1, and at 1:1 magnification factor it would be 1+1/1 = 2.
The magnification factor can be calculated from the focus distance (measured from the front principle plane of the optics), or measured from a shot (# pixels x senselpitch, divided by the original subject size). If measured from focus distance it's :
MagnificationFactor = focallength / (subjectdistance - focallength).
The pupil factor for asymmetrical lens designs is the Exit / Entrance Pupil diameter ratio. Focus, and then look at the lens at arms length from the front and the rear to estimate the entrance and exit pupil diameters.
That's not the whole story if you need very high accuracy, since aperture number and barrel design can change things a bit, but the main principle is as mentioned above.
Cheers,
Bart
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In general, focusing closer will create a larger image circle.
The easiest way to calculate such things is with the Magnification factor, which becomes easier and more accurate to calculate with the closer we focus.
The image circle diameter at infinity focus gets magnified by a factor: 1 + MagnificationFactor / PupilFactor
If we assume symmetrical lens design (with PupilFactor=1), at infinity that would be 1+0/1 = 1, and at 1:1 magnification factor it would be 1+1/1 = 2.
The magnification factor can be calculated from the focus distance (measured from the front principle plane of the optics), or measured from a shot (# pixels x senselpitch, divided by the original subject size). If measured from focus distance it's :
MagnificationFactor = focallength / (subjectdistance - focallength).
The pupil factor for asymmetrical lens designs is the Exit / Entrance Pupil diameter ratio. Focus, and then look at the lens at arms length from the front and the rear to estimate the entrance and exit pupil diameters.
That's not the whole story if you need very high accuracy, since aperture number and barrel design can change things a bit, but the main principle is as mentioned above.
Cheers,
Bart
Great Bart, this is spot on what I wanted to be informed! It is also much in agreement with the pictures that Chris posted above...
Can you please comment on these conclusions please? Do you agree with them?
1. If one is to use MFDB with MF lenses, he better choose a view camera than a technical camera so that the image circle is first widen to the maximum by focusing the lens at its minimum possible distance and then expanded even more proportionally as the lens is focused towards infinity using the (rear) distance focusing knob of the view camera.
2. It's best for one to choose (or modify appropriately) a view camera so that there is as much space as possible between the front and the rear standard and additionally take care that the standards can be recessed as to touch one another without a bellows on...
3. For optimum image quality (depending on the movements used) one is best to frame and focus with the lens focused to its minimum focusing distance and then (after framing) re-focus the scene by readjusting the focusing ring and the camera's focusing knob as to work with an "optimum" image circle (if aiming to optimize sharpness).
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No maths but a test:
FPS + IQ180 + lenses w/ 12mm shift to left side
left parts of pictures shown
upper row: Canon TSE 24f3.5 II @ f11
lower row: Contax 645 35f3.5 @ f11
findings:
- Contax has larger image circle than Canon
- enlargement of image circle towards shorter distances with Contax (longer focal length) less pronounced than with Canon (shorter focal length)
- enlargement of image circle from infinity to 1m not very pronounced, only towards 0,25 shortest distance of the Canon TSE
Chris, could you (or any other that might have checked) please comment on the image circle of the 45-90mm vario-sonnar zoom? Also... is it ALPA FPS you used for checking the image circle? (I've asked this before as it is important to know as to judge the lens behavior on a view camera where the image circle will be further increased). Any other Contax 645 lens image circle experience will be highly appreciated...
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Can you please comment on this conclusions please?
1. If one is to use MFDB with MF lenses, he better choose a view camera than a technical camera so that the image circle is first widen to the maximum by focusing the lens at its minimum possible distance and then expanded even more proportionally as the lens is focused towards infinity using the (rear) distance focusing knob of the view camera.
To me, a View camera and a Technical camera are the same thing. Moving the rear standard changes perspective, so I'd not consider using that for only focusing. Focusing close up will already cause the largest (bellows) extension. Subsequent infinity focus, either with the front standard or with the rear standard will reduce the bellows extension (and image circle diameter).
2. It's best for one to choose (or modify appropriately) a view camera so that there is as much space as possible between the front and the rear standard and additionally take care that the standards can be recessed as to touch one another without a bellows on...
I do not follow what that is supposed to do for the image circle. Longer focal lengths can have larger image circles, and require more distance between front and rear standards. But longer focal lengths need longer bellows, which need to be exchanged for a wide angle version if short focal lengths are used.
3. For optimum image quality (depending on the movements used) one is best to frame and focus with the lens focused to its minimum focusing distance and then (after framing) re-focus the scene by readjusting the focusing ring and the camera's focusing knob as to work with an "optimum" image circle (if aiming to optimize sharpness).
I do not follow what that's supposed to achieve. There is only one image circle dimension at optimal focus. If a lens is used with its own focus mechanism, it might be more accurate than the rail focus knobs allow, especially if the lens focus ring has a large throw (large rotation angle for small adjustment).
Cheers,
Bart
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Hi,
The TSE II changes image circle size with focusing and it has internal focus, which I know as I have such a lens.
The Contax has the same image circle regardless of focus. Correct?
Best regards
Erik
No maths but a test:
FPS + IQ180 + lenses w/ 12mm shift to left side
left parts of pictures shown
upper row: Canon TSE 24f3.5 II @ f11
lower row: Contax 645 35f3.5 @ f11
findings:
- Contax has larger image circle than Canon
- enlargement of image circle towards shorter distances with Contax (longer focal length) less pronounced than with Canon (shorter focal length)
- enlargement of image circle from infinity to 1m not very pronounced, only towards 0,25 shortest distance of the Canon TSE
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To me, a View camera and a Technical camera are the same thing. Moving the rear standard changes perspective, so I'd not consider using that for only focusing. Focusing close up will already cause the largest (bellows) extension. Subsequent infinity focus, either with the front standard or with the rear standard will reduce the bellows extension (and image circle diameter).
I do not follow what that is supposed to do for the image circle. Longer focal lengths can have larger image circles, and require more distance between front and rear standards. But longer focal lengths need longer bellows, which need to be exchanged for a wide angle version if short focal lengths are used.
I do not follow what that's supposed to achieve. There is only one image circle dimension at optimal focus. If a lens is used with its own focus mechanism, it might be more accurate than the rail focus knobs allow, especially if the lens focus ring has a large throw (large rotation angle for small adjustment).
Cheers,
Bart
Sorry... my bad! I forgot to explain that I modify a Rollei X-Act2 as to accept both MFDBs and Sony mirrorless on it... (starting with an α7ΙΙ). The requirement of the design (and hence the modification on the rear standard) is for one to be able to use the mirrorless instead of the MFDB without any further modification on the rear standard other than just unplug the MFDB and plug the mirrorless instead (on the same MFDB hinges via an appropriate plate)... So the requirements in my case change as one has to count for the extra space needed as to compensate for the 18mm sensor depth and the extra recessing of the mirrorless sensor because of the grip size...
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I think you may be right to some extend with what you state for an IF lens (although Chris's example above shows some image area expansion even with the Contax 35mm f3.5 lens which is an IF lens but less so than the Canon he also posts)... But on a lens without IF, wouldn't "focus breathing" increase the image circle? (without affecting image quality)... it should, shouldn't it? ...I mean the frame on the sensor will look the same with no movements applied (as of constant focal length), but the total image circle projected should be one of wider focal length (due to focus breathing) ...shouldn't it?
EDIT: At least Chris's results on the Canon 24mm above, (which is not IF) show some considerable image circle expansion when the lens is focused to its minimum... Now as far as IQ is concerned, one can't be certain that it will be less... It will be altered to some degree alright, but it has as much chance to be better as much as to be worst (depending on how near to the "optimum" image circle one is)... but in any case, it can't be much different as to seriously be considered to be a problem.
On a lens without IF there is 100% no focus breathing, if you just move the lens back and forth you don't change the angle of the lens.
If you have a lens that's affected by focus breathing, the image circle may also change - for better or worse. Without testing the lens one can't tell you that for sure, it depends on which element moves where.
The image quality will definitely be worse if you use an IF lens at close focus and then back-focus to infinity with the camera. The internal focusing is (or rather should) be set to achieve the best performance at the adjusted focus point, at close focus position certain elements will most likely be moved back and/or forth to improve the quality at a larger magnification - whether that affects field curvature, central or corner sharpness or any other aspect of the image.
As I already mentioned there's another possible problem with the technique you want to use: depending on the lens design, internal elements or the length of the lens barrel could possibly reduce the image circle more than expected. Normally that wouldn't be an issue as they're not made to be used in tech cameras with movements - but in your case you could get a smaller image circle than you expect.
Not trying to get you down, I just want you to be prepared for that.
Now after reading your last comment I think I understand what you're trying to do but either I'm completely wrong or you've mixed up some things:
If you set the lens to its closest possible focus setting, the point where infinity focus lies is CLOSER to the lens. Not further back.
If you put the camera on an adapter (which increases the distance) and your cameras sensor is another 18mm further back - then it's like introducing a bunch of extension rings. You won't get closer to infinity, you'll do the opposite.
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On a lens without IF there is 100% no focus breathing, if you just move the lens back and forth you don't change the angle of the lens.
If you have a lens that's affected by focus breathing, the image circle may also change - for better or worse. Without testing the lens one can't tell you that for sure, it depends on which element moves where.
The image quality will definitely be worse if you use an IF lens at close focus and then back-focus to infinity with the camera. The internal focusing is (or rather should) be set to achieve the best performance at the adjusted focus point, at close focus position certain elements will most likely be moved back and/or forth to improve the quality at a larger magnification - whether that affects field curvature, central or corner sharpness or any other aspect of the image.
As I already mentioned there's another possible problem with the technique you want to use: depending on the lens design, internal elements or the length of the lens barrel could possibly reduce the image circle more than expected. Normally that wouldn't be an issue as they're not made to be used in tech cameras with movements - but in your case you could get a smaller image circle than you expect.
Not trying to get you down, I just want you to be prepared for that.
Now after reading your last comment I think I understand what you're trying to do but either I'm completely wrong or you've mixed up some things:
If you set the lens to its closest possible focus setting, the point where infinity focus lies is CLOSER to the lens. Not further back.
If you put the camera on an adapter (which increases the distance) and your cameras sensor is another 18mm further back - then it's like introducing a bunch of extension rings. You won't get closer to infinity, you'll do the opposite.
Christoph, I don't question your knowledge on the subject here... to the contradict, I find your posts very helpful indeed...., but out of my testing (and as Chris posted with pictures and Bart explained) all lenses expand their image circle if focused to their minimum focusing distance, additionally, the phenomenon is more pronounced (I find) with non IF lenses rather than with the IF ones.... Now, about my camera project... by converting the rear standard of the X-act2 as to be able to accept both an MFDB & a mirrorless, it doesn't mean that the two image areas will be positioned the same... There is 3.2cm of difference between the two (up to now) and I'm working further as if I 'll be able to redesign the rear standard as to avoid the mirrorless (only) being recessed by the grip...
My problem with the later, (allowing for the mirrorless grip) is that (after having the first conversion made) the mirrorless leaves only 6mm of space for the front standard (lens set to infinity) which is too close to the rear standard to allow serious tilts... I believe I can gain another 2cm (!!!) if I redesign the rear standard and overcome the recessing because of the grip (with the mirrorless only)... Actually I already thought how this can be done (it requires a totally different approach though) and I'll start working on it by tomorrow... Still the MFDB will be at the same distance as before (which is plenty with the lens set to infinity) and it will have a focal plane shutter included on the (MFDB) adapter too...
Please, keep an eye on this thread as your comments can be very helpful to me...
EDIT: 6mm of space (mentioned above) is with a Contax lens on, it means that a Mamiya 645 lens would be (about) 5mm & a Hassy-H only 3mm... Of course a 35mm lens won't be usable at all... If I "gain" 2cm with the mirrorless, 35mm lenses will be usable...
LOL ;D I think my view camera will end up with an L-bracket rear standard and the adapters slotted on the L-bracket from its "free" side..., as not having rotate-able by 90 degs image sensors on it (either MFDB or mirrorless) is out of the question... ;)
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Yes, the image circle expands with close focus - but if you move the sensor closer to the lens you re-focus again. You lose the image circle and get back to where you started from.
As I understand it with your setup you're trying to get more distance between the two standards in order to have a little bit of movement. But when you're using the min focus setting for your lens, you're actually losing distance. Your method for the mirrorless is like adding extension rings, meaning your lens will move forward as will the focus point to infinity.
In short - not only do you not gain anything, you actually have to put the camera even closer to the lens to get to infinity than you would otherwise.
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On a lens without IF there is 100% no focus breathing, if you just move the lens back and forth you don't change the angle of the lens.
I thought what you are describing is called focus breathing: changing the angle (framing) when focusing a lens without IF, as the lens moves closer or further away from the sensor. For that reason cine lenses are designed so that they actually slightly change the focal length during focusing to keep the angle/framing constant while being focused.
Lenses with internal focus systems can behave whichever way they choose. They often also actually focus by changing the focal length instead of moving the lens away or towards the sensor, but they do not do it as precisely and controlled way as a $$$$$ cine lens does.
The idea OP suggests to squeeze more image circle out of a lens is a brain dead one anyway. Take a flashlight with a tight beam, move it twice as far to make the beam twice as large, then move back to half distance to get the same brightness again? What was gained?
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Lens breathing only applies to some lenses with internal focusing:
https://en.wikipedia.org/wiki/Internal_focusing
"One issue internal focusing lens can have is that the true focal length of the lens is reduced when not focused at infinity."
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Lens breathing only applies to some lenses with internal focusing:
https://en.wikipedia.org/wiki/Internal_focusing
"One issue internal focusing lens can have is that the true focal length of the lens is reduced when not focused at infinity."
I do not understand your quote. Changing the focal length to focus is not a breathing issue, but just one method of focusing; keeping the distance from the image plane constant, but slightly changing the focal length. This, if done to perfection, actually prevents "breathing" by keeping the image angle the same no matter where the lens is focused. This is highly desirable in cine lenses.
Article about "lens breathing" from Wikipedia: "Breathing refers to the shifting of angle of view of a lens when changing the focus. Some (often higher quality) lenses are designed to lessen the degree of this effect. Lens breathing does not prevent one from racking focus or following focus with this lens, but it lessens the desirability of any type of focus adjustment, since it noticeably changes the composition of the shot."
https://en.wikipedia.org/wiki/Breathing_(lens)
Many of you seem to have this backwards. A normal old fashioned lens breathes when focus is changed (image angle changes), while IF lens can be designed so that the angle remains constant, i.e. focus is done by changing the focal length, not distance from the sensor.
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....Take a flashlight with a tight beam, move it twice as far to make the beam twice as large, then move back to half distance to get the same brightness again? What was gained?
If the scene requires both shifting and tilting, you gain more shifting ability...
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I do not understand your quote. Changing the focal length to focus is not a breathing issue, but just one method of focusing; keeping the distance from the image plane constant, but slightly changing the focal length. This, if done to perfection, actually prevents "breathing" by keeping the image angle the same no matter where the lens is focused. This is highly desirable in cine lenses.
Article about "lens breathing" from Wikipedia: "Breathing refers to the shifting of angle of view of a lens when changing the focus. Some (often higher quality) lenses are designed to lessen the degree of this effect. Lens breathing does not prevent one from racking focus or following focus with this lens, but it lessens the desirability of any type of focus adjustment, since it noticeably changes the composition of the shot."
https://en.wikipedia.org/wiki/Breathing_(lens)
Many of you seem to have this backwards. A normal old fashioned lens breathes when focus is changed (image angle changes), while IF lens can be designed so that the angle remains constant, i.e. focus is done by changing the focal length, not distance from the sensor.
Sure you _can_ change the focus by changing the focal length but then you're normally talking about the normal function of a zoom lens - but focus breathing happens at the same focal length setting and changes to focal length even on fixed focus lenses.
With old fashioned lenses the image angle doesn't change, only the position of the lens in relation to the film/sensor changes. Focus breathing means that an IF lens changes its image angle i.e. the focal length when you change its focus. The focal length on the old fashioned lens does _not_ change, it remains the same no matter what - that means that when you make big adjustments you may have to reposition the camera. Or you move the rear standard or both standards and then _nothing_ changes and you won't have to reposition anything.
In any case, the focal length (!) remains the same and that's what matters, so we're not talking about focus breathing/lens breathing.
I've not found a single source on the web or in my library that says focus breathing happens with old fashioned lenses or that the normal act of incasing or decreasing the bellows draw counts as focus breathing.
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If the scene requires both shifting and tilting, you gain more shifting ability...
But if you want to use the lens at infinity and you move the rear standard to the font again - the image circle reverts back to normal... So you have no advantage.
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But if you want to use the lens at infinity and you move the rear standard to the font again - the image circle reverts back to normal... So you have no advantage.
In that case... You would have no advantage only if you aim to focus back to infinity... on all the rest of focusing distances you do gain some... small the further away you focus, more as you focus closer...
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In that case... You would have no advantage only if you aim to focus back to infinity... on all the rest of focusing distances you do gain some... small the further away you focus, more as you focus closer...
Sure. But the gain at "normal" distances is pretty much negligible. It only really gets interesting at closeup/macro work. I used a 28mm lens for small format to take some interesting 4x5" macro (or micro?) shots a few years ago.
But for normal usage (which I assume is part of what you're doing) you won't be able to gain additional usage - especially if you use it at the min focus setting right away.
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Sure. But the gain at "normal" distances is pretty much negligible. It only really gets interesting at closeup/macro work. I used a 28mm lens for small format to take some interesting 4x5" macro (or micro?) shots a few years ago.
But for normal usage (which I assume is part of what you're doing) you won't be able to gain additional usage - especially if you use it at the min focus setting right away.
The closer the lens is to the sensor, small tilts can provide great additional shifting ability by comparison, especially with WA lenses... Applying some tilts (even if there is no need for them) as to gain on shifts is a known "trick" as to find solutions in difficult situations... Having the lens closer to the sensor helps further...
Anyway, the camera is mainly needed to be used with a mirrorless (Sony for the time, others will be considered instead whenever there will be more FF offers) the MFDB ability is primarily needed because both my MFDBs are with multishot ability (that's why I include a focal plane shutter in the design) and thus, the camera will be great for close focus still life as well as copy work...
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I've not found a single source on the web or in my library that says focus breathing happens with old fashioned lenses or that the normal act of incasing or decreasing the bellows draw counts as focus breathing.
Trust me Christoph, when you focus an old-fashioned lens which is moved back and forth as one unit, the framing changes for obvious reasons. This is called focus breathing.
Any framing change due to focusing is focus breathing. Motion picture lenses spare no expense to construct them so that this does not happen. In practice it means that that they have to do the actual focus not by changing the back focus distance, but changing the focal length slightly. There is no way around it.
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Somebody that has tried the Contax 45-90mm vario sonnar on a camera with movements (ALPA FPS?), please comment on the image circle of it at various focal lengths, all other Contax lenses information will also be highly appreciated. Thank you...