[SunnyG.]

I have been reading articles regarding how sensor stack thickness and exit pupil affect adapted glass. Especially film era lenses.
I was curious to know the sensor stack thickness of the Pentax FF twins.
Any info?

[stevebrot]

Stack thickness and exit pupil diameter are not particularly important for SLR lenses.


Steve

[UncleVanya]

I have been reading articles regarding how sensor stack thickness and exit pupil affect adapted glass. Especially film era lenses.
I was curious to know the sensor stack thickness of the Pentax FF twins.
Any info?

If you cite the source maybe we can give more context to our answers. I think I've read something about how this impacts mirrorless designs but I can't recall the details.

[stevebrot]

I think I've read something about how this impacts mirrorless designs but I can't recall the details.

Yep...The matter is specific to designed-for-mirrorless lenses and is somewhat controversial even in that context. It was discussed in detail here several years ago. There was a blogger who was frequently referenced, but my memory is that example images showing poor performance were hard to come by.


Steve

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Last edited by stevebrot; 09-01-2020 at 10:24 PM. Reason: readability

[leekil]

I believe there have been articles about sensor stack thickness and lenses on the lens rentals blog in the past?

[PJ1]

It can't be much of an issue or third party lens manufacturers would have a problem. Samyang, Sigma, Tamron and others can offer a range of mounts but I don't think they adapt the optics to specific systems.

[Rondec]

Yep...The matter is specific to designed-for-mirrorless lenses and is somewhat controversial even in that context. It was discussed in detail here several years ago. There was a blogger who was frequently referenced, but my memory is that example images showing poor performance were hard to come by.


Steve

I think @pinholecam shoots with one of the Sony mirrorless (along with a K-1) and mentioned that he had to change the sensor stack in order to adapt certain lenses to his Sony camera. As I recall the issue is primarily seen with wide angels and a short registration distance, but I am no master of the MILC universe.

[UncleVanya]

I think @pinholecam shoots with one of the Sony mirrorless (along with a K-1) and mentioned that he had to change the sensor stack in order to adapt certain lenses to his Sony camera. As I recall the issue is primarily seen with wide angels and a short registration distance, but I am no master of the MILC universe.

What appears to be the case is that this is mostly a non issue when using adapted SLR or DSLR lenses on Sony. It is more of an issue with Leica M lenses on m4/3. Basically if the sensor glass thickness is significantly different, there can be an optical effect.

Sensor Stack Thickness: When Does It Matter?

Oh and the closer the exit pupil to the sensor, the more impact this has. Slr wide angles with their retrofocal designs are typically less impacted than rangefinder wide angles.

[UncleVanya]

And a better detailed article, part three of a series:
Lens Rentals | Blog

Summary: larger aperture, closer exit pupil showed a difference, at and above about f2.8, limited effect on axis, Corners can be a lot worse.

[pentaxus]

My understanding is that sensor stack thickness affects mirrorless cameras using wide angle lenses designed for film.

[UncleVanya]

My understanding is that sensor stack thickness affects mirrorless cameras using wide angle lenses designed for film.

Read the details above in the linked articles. The wide angle issue is mostly a problem with wide aperture lenses that aren't retrofocal.

[MJKoski]

Sensor stack thickness affects the optical path. When my K-1 was modified to full-spectrum, the stack thickness changed enough so that most of my K-mount lenses have severe issues reaching infinity focus. I have managed to remove shims from two lenses and use a modified Leitax adapter to bring my Zeiss lenses closer which has worked.

[SunnyG.]

Stack thickness and exit pupil diameter are not particularly important for SLR lenses.


Steve

It affects the performance on modern DSLR. The refractive index and optical thickness affects performance. Coma, color fringing, sharpness.
Also one of the many reason some cine glass makers have started redesigning their vintage lenses for Digital cameras

---------- Post added 09-02-20 at 10:12 AM ----------

I believe there have been articles about sensor stack thickness and lenses on the lens rentals blog in the past?

Yes, true. Their experiments were completely scientific in nature considering the graphs and readings they posted

---------- Post added 09-02-20 at 10:14 AM ----------

If you cite the source maybe we can give more context to our answers. I think I've read something about how this impacts mirrorless designs but I can't recall the details.

I read the article on lens rentals, this guy testing lenses in a lab. If you want I can post the links to his articles

---------- Post added 09-02-20 at 10:17 AM ----------

Yep...The matter is specific to designed-for-mirrorless lenses and is somewhat controversial even in that context. It was discussed in detail here several years ago. There was a blogger who was frequently referenced, but my memory is that example images showing poor performance were hard to come by.


Steve

It affects DSLRs too. And the difficulty in designing for digital sensors. Considering the fact that, the glass infront of the sensor contain multiple filters, it, uv. It affects mostly wide angle, super fast, and with exit pupils less than 70mm

---------- Post added 09-02-20 at 10:39 AM ----------

It can't be much of an issue or third party lens manufacturers would have a problem. Samyang, Sigma, Tamron and others can offer a range of mounts but I don't think they adapt the optics to specific systems.

Actually it's a really big issue. The recently released CV 50mm f1.2 in two different mounts, perform different from eachother. The FE mount version performs poorly than the m mount version on other mirror less cameras. Leicas version was optimised for a stack thickness of 1mm and performs better on fuji x mount and canon RF mount. Because both of them have stack thickness equal to 2 mm.

Some of my friends, who are professionals in the cinema industry told me about the mount variations.

---------- Post added 09-02-20 at 10:42 AM ----------

I think @pinholecam shoots with one of the Sony mirrorless (along with a K-1) and mentioned that he had to change the sensor stack in order to adapt certain lenses to his Sony camera. As I recall the issue is primarily seen with wide angels and a short registration distance, but I am no master of the MILC universe.

No not the registration distance, I think he meant the exit pupil distance from sensor. Anything below or near 70 will not perform good on Sony and m4/3 cameras. The super takumar 50mm f1.4 Has exit pupil distance of 70.xx mm

---------- Post added 09-02-20 at 10:47 AM ----------

My understanding is that sensor stack thickness affects mirrorless cameras using wide angle lenses designed for film.

Not just mirrorless, DSLRS too. Both use the same sensor. It comes down to stack thickness and f stops below 2

---------- Post added 09-02-20 at 10:53 AM ----------

What appears to be the case is that this is mostly a non issue when using adapted SLR or DSLR lenses on Sony. It is more of an issue with Leica M lenses on m4/3. Basically if the sensor glass thickness is significantly different, there can be an optical effect.

Sensor Stack Thickness: When Does It Matter?

Oh and the closer the exit pupil to the sensor, the more impact this has. Slr wide angles with their retrofocal designs are typically less impacted than rangefinder wide angles.

The article also states that it affects lenses with exit pupil closer than 70mm

[stevebrot]

I read the article on lens rentals, this guy testing lenses in a lab. If you want I can post the links to his articles

Excellent idea. It the "guy" is Roger Cicala, he is usually very thorough and very readable.

To save you the trouble...

The 2014 three-part series:

Lens Rentals | Blog: The Glass in the Path: Sensor Stacks and Adapted Lenses

Lens Rentals | Blog: Sensor Stack Thickness: When Does It Matter?

Lens Rentals | Blog: Sensor Stack Thickness Part III: The Summary

The part III summary is the most useful, but it helps to read the other two. I am familiar with the series based on the earlier discussion here a few years back.

The 2015 followup:

Lens Rentals | Blog: A Thinner Sensor Stack

The last is quite telling in regards to adapted rangefinder lenses.

We should all be on the same page now.


Steve

[stevebrot]

The article also states that it affects lenses with exit pupil closer than 70mm

OK...this is the part I am not seeing in any of the four Cicala articles. In fact, he appears to avoid drawing any lines in the sand. Going forward, all Pentax SLR lenses will have exit pupil distance (at infinity) 45.46mm or longer, simply to allow for the mirror box. According to the Part II article (LINK), the sole Pentax lens measured (Super Tak 50mm f/1.4) measured at 70.5mm. This does not surprise me since traditional Pentax normals are mildly retrofocus.

Going to the Part III article (LINK), his comments regarding SLR lenses begin with a simple statement:

Most SLR lenses have exit pupil distances of 50mm to 100mm.

In regards to Pentax physical stack thickness, the Part II article has the K10D at 1.6mm. Removing the AA filter, as with all current model Pentax dSLRs, I would expect the same or thinner on those. It is probably enough that Cicala basically lumped dSLRs together as having about 2mm filter stacks. I take Cicala's Summary from Part III as a reasonable guide for practical matters:

Summary

While I don’t have a mathematical formula to predict how well a given lens will work on a given camera, it should be apparent that wide-angle rangefinder lenses designed for film are going to struggle, especially on m4/3 cameras, but to some degree on other cameras. Longer focal length rangefinder lenses tend to have longer exit pupil distances and should do better. Stopping down to f/4 or f/8 should reduce the problem significantly, although it isn’t guaranteed to eliminate it near the edges of the frame.

SLR lenses may also have some troubles on m4/3 cameras, since there’s nearly a 2mm difference in stack thickness. They shouldn’t have as much of a problem as rangefinder lenses, though, since they are designed for a 2mm sensor stack and they tend to have longer exit pupil distances. Older lenses designed for film cameras will tend to have more issues, of course, since they were designed for no sensor stack.

Obviously, these are generalizations and suggestions. There are going to be exceptions. But, if nothing else, hopefully we can help a few people stop trying one adapter after another, hoping to make their 15mm rangefinder lens look great on the m4/3 camera.

As for shooting designed-for-film SLR lenses on any recent model Pentax dSLRs, the simple answer is that the results we get are the results we get. Whether poor results are a result of sensor stack depth is hard to say, though the more usual culprits are missed focus and camera movement.


Steve