Leica M-Adapter L - Image Circle and Focal Length Diffs

[bluehoursky]

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This is my first post on the forum. Please forgive me in advance if I inadvertently dash the eyes of any norms of the Forum.

Being familiar with the image circle of a lens from large format photography, and, similarly, being familiar with moving a lens farther from the film plane indicator, I'd expect some changes in the image circle when using the Lecia M-adapter. At least, I'd expect to read comments about the effective change in focal length of the lens. Yet, I've never read any comments about the image circle nor about changes in focal length. Same with video posts on the world's most popular site for posting videos.

What I mean by changes in focal is if I use the Leica M-adapter L with a 50MM mounted, I end up getting the equivalent of a 55mm on the SL (just making up the 55mm).

Moving the M lens farther from the film plane indicator seems like it would lengthen the effective focal length because you are capturing a smaller area of the image circle.

Am I missing something rudimentary? Perhaps the Leica M-adapter to L is to keenly engineered that the change in focal length is hardly noticeable?

[Sandokan]

No changes. the L mount has a shorter distance to M mount (rear of lens to sensor) and the adaptor simply sits the lens further away, so that it focuses the image on the plane of the sensor

[frame-it]

Please Read the Manual.

 

madapter_l.pdf

[dpitt]

Any adapter on the SL will bring the lens at the exact native flange distance. So it operates as if it is on an M body.
That is why the R-L adapter adds even more distance than the M-L adapter to accommodate R lenses.

Edited January 11, 2023 by dpitt

[Sonnelacht]

"Being familiar with the image circle of a lens from large format photography, and, similarly, being familiar with moving a lens farther from the film plane indicator, I'd expect some changes in the image circle when using the Lecia M-adapter."

Really???

If you really would be familiar with optics, you would know, moving the lens farther from the film plane does nothing else do than focusing closer.

[Photoworks]

11 hours ago, bluehoursky said:

Moving the M lens farther from the film plane indicator seems like it would lengthen the effective focal length because you are capturing a smaller area of the image circle.

every adapter has been built to focus on the film plane or sensor, another way you would not be able to focus.

Increasing any lens distance from the film plane with result in macro photography with use of extender or bellow.

image circle of the lens does not change, you can only change what format "film size" you can use. Medium and large format lenses cover an area for does related film sizes, on a 35mm camera you only use part of the image circle.

[Stuart Richardson]

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4 hours ago, Sonnelacht said:

"Being familiar with the image circle of a lens from large format photography, and, similarly, being familiar with moving a lens farther from the film plane indicator, I'd expect some changes in the image circle when using the Lecia M-adapter."

Really???

If you really would be familiar with optics, you would know, moving the lens farther from the film plane does nothing else do than focusing closer.

This is incorrect. Image circle increases the closer you focus, a phenomenon that is well known by large format photographers, and probably the source of the confusion. You also lose one stop of light for each multiple of the focal length (so 1 stop for 1 to 1, two for 2 to 1 etc. Diffraction also increases at the same rate (so a lens at 5.6 and 1 to 1 has the light transmission and diffraction of a lens at f8 at infinity).
But as noted above, the adapter places the lens as close as possible to the native distance from the sensor/film plane. Sometimes depending on the tolerances the lenses might focus slightly past infinity. 

[Sonnelacht]

"I'd expect some changes in the image circle when using the Leica M-adapter." said the thread opener - and this is wrong without doubt.

Your exact description of what happens when you go into the macro range has nothing to do with his worries. There will be no change of the image circle of a lens using an adapter which is only adapting the different focal flange distances of the camera bodies.

[BernardC]

23 minutes ago, Sonnelacht said:

"I'd expect some changes in the image circle when using the Leica M-adapter." said the thread opener - and this is wrong without doubt.

Your exact description of what happens when you go into the macro range has nothing to do with his worries. There will be no change of the image circle of a lens using an adapter which is only adapting the different focal flange distances of the camera bodies.

Technically, some longer lenses might vignette a little bit because of the limited inner diameter of the adapter. If I recall it's only an issue with old Telyts (long focal length, non-telephoto).

Edited January 11, 2023 by BernardC
typo

[John Smith]

There is a difference between my 75SL and 75Noctilux, comparing them on a tripod.

Edited January 11, 2023 by John Smith

[Photoworks]

5 hours ago, Sonnelacht said:

"I'd expect some changes in the image circle when using the Leica M-adapter." said the thread opener - and this is wrong without doubt.

Your exact description of what happens when you go into the macro range has nothing to do with his worries. There will be no change of the image circle of a lens using an adapter which is only adapting the different focal flange distances of the camera bodies.

harsh tone! we are all friends here .

most M lenses are not corrected for focus breathing, like a cinema lens would, so when you rack focus from 0.7 to infinity there is a minor change. the border go image circle is still outside the frame and won't make a visible difference on SL cameras.

[Sonnelacht]

Harsh tone???

Things should be named clearly. But in this thread some things are getting mixed up.

Of cause different optics of nominal same focal length differ in their real world focal length, not to mention the different image charactericstics. But what has this to do with the adapter?

Of cause even Leica lenses show focus breathing. But what has this to do with the adapter?

And what has a lot of optical wisdom in this thread to do with the questions of the thread opener?

Again: harsch tone???

[bluehoursky]

Thank you!

[jaapv]

17 hours ago, Stuart Richardson said:

This is incorrect. Image circle increases the closer you focus, a phenomenon that is well known by large format photographers, and probably the source of the confusion. You also lose one stop of light for each multiple of the focal length (so 1 stop for 1 to 1, two for 2 to 1 etc. Diffraction also increases at the same rate (so a lens at 5.6 and 1 to 1 has the light transmission and diffraction of a lens at f8 at infinity).
But as noted above, the adapter places the lens as close as possible to the native distance from the sensor/film plane. Sometimes depending on the tolerances the lenses might focus slightly past infinity. 

The change in angle of view/ focal length when focusing away from infinity is of course well known. However this is only correct for lenses that focus by moving the optical cell.  Lenses with internal focusing or even floating elements can behave anomalously. 

[Stuart Richardson]

13 hours ago, John Smith said:

There is a difference between my 75SL and 75Noctilux, comparing them on a tripod.

This is most likely variations on the true focal length of the lenses, not on the difference between SL and M. Lenses are not always exactly the same field of view implied by the number on the lens. Leica M lenses typically have (or at least had) a series of small numbers on the lens barrel that indicate the true focal length. So if you have a 50mm lens that says "25" on the barrel, it is actually a 52.5mm lens. The SL lenses don't have this, and also feature optical corrections which could also slightly alter the field of view. All these are small technical details, however. The original poster's main question as to whether adapting a lens would cause changes in focal length is a pretty resounding no.

[01af]

The Leica M-Adapter L doesn't move the M lens farther away from the image plane. Instead, it just restores the proper flange distance required for M lenses — which is 27.8 mm, as opposed to the L mount's 20.0 mm. In other words, it turns the camera's L mount into an M mount, so the M lens will feel at home.

[John Smith]

5 hours ago, Stuart Richardson said:

This is most likely variations on the true focal length of the lenses, not on the difference between SL and M. Lenses are not always exactly the same field of view implied by the number on the lens. Leica M lenses typically have (or at least had) a series of small numbers on the lens barrel that indicate the true focal length. So if you have a 50mm lens that says "25" on the barrel, it is actually a 52.5mm lens. The SL lenses don't have this, and also feature optical corrections which could also slightly alter the field of view. All these are small technical details, however. The original poster's main question as to whether adapting a lens would cause changes in focal length is a pretty resounding no.

I agree.m

[bluehoursky]

@01af, It's the flange distance of the M lens! I totally understand now. Thank you for the answer.

[dem331]

On 1/12/2023 at 1:07 AM, Sonnelacht said:

Harsh tone???

Things should be named clearly. But in this thread some things are getting mixed up.

Of cause different optics of nominal same focal length differ in their real world focal length, not to mention the different image charactericstics. But what has this to do with the adapter?

Of cause even Leica lenses show focus breathing. But what has this to do with the adapter?

And what has a lot of optical wisdom in this thread to do with the questions of the thread opener?

Again: harsch tone???

It also struck me as harsh. Specifically, your phrase: “If you really would be familiar with optics…” 

The guy is a first time poster, and hardly claims world class expertise in optics. I am familiar with many things -Lightroom, photography, and with how my motorcycle engine works-, but I continually have doubts and questions about things I probably know but just didn’t think through properly.

 

 

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Hallo,

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[Photoworks]

8 hours ago, bluehoursky said:

@01af, It's the flange distance of the M lens! I totally understand now. Thank you for the answer.

Every camera has a flange distance, M lenses are designed to function on M camera, no on every camera can you adapt lenses. Lenses for DSLR have the space of a mirror to deal with and they are designed to focus on the sensor/film place with that size. Every camera has a different number, canon 5d, Leica R, Nikon d810. with a small adapter you can mount a Leica R lens on Canon 5d and still get focus at infinity, you would not be able to do the reverse.