Help needed on lens image circle expantion when focused to its min..

[Christoph B.]

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."

[Petrus]

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.

[Theodoros]

 ....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...

[Christoph B.]

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.

[Christoph B.]

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.

[Theodoros]

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...

[Christoph B.]

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.

[Theodoros]

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...

[Petrus]

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.

[Theodoros]

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...