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M lens performance on the SL


IkarusJohn

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 But the sensor in Sony is optimised for different angle  than a Leica M lens.

Yes indeed - I quite agree that this MIGHT have another effect.

My point has just been that it simply isn't simple :)

It's easy to pinpoint one factor and then take images to bear it out . . . . . . . but that doesn't mean that there aren't lots of other factors playing at the same time. 

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Shorter Flange distance requires steeper angle. The sensor is optimised for this and the Sony Fe lens design.  Mechanically moving the rear element away by 1 cm (approx.) by an adapter for M lens does not equate optimal angulation of light rays reaching the sensor. As I mentioned it just may be part of the reason, I am not sure. But cannot be dismissed either, even though it give K-hawinkler great joy :)

 

Sven, the shorter flange distance when used with native lenses means there's more room in the lens body for corrective elements to steer the ray trace to be orthogonal to the sensor plane, that's all. It doesn't matter how much glass is in front of the sensor if the ray trace is properly orthogonal.  

 

When used with adapted lenses, the adapter sets the mount registration to the same value those lenses were designed for; the lens design and resulting incidence to the sensor remain as the lens was originally designed. This is when the thickness of the sensor stack has an influence, because light passing through the stack at an angle refracts from its intended path. A thin stack imposes the smallest change in the ray trace, a thick stack imposes larger changes. 

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Sven, the shorter flange distance when used with native lenses means there's more room in the lens body for corrective elements to steer the ray trace to be orthogonal to the sensor plane, that's all. It doesn't matter how much glass is in front of the sensor if the ray trace is properly orthogonal.  

 

When used with adapted lenses, the adapter sets the mount registration to the same value those lenses were designed for; the lens design and resulting incidence to the sensor remain as the lens was originally designed. This is when the thickness of the sensor stack has an influence, because light passing through the stack at an angle refracts from its intended path. A thin stack imposes the smallest change in the ray trace, a thick stack imposes larger changes. 

 

A lot of what you say is very true and I totally agree. My only point is that the sensor and lens need to be optimised.

 

In theory if the cover glass is the only issue and refraction is reduced, it should make the kolari mod Sony A7 equal to the M240 atleast in the corners. But its not. The kolari mod A7 is not even equal to the M240 in the center (this is with lux 50). Thats why I believe there are other factors at play rather than a simple cover glass issue.

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The kolari mod A7 is not even equal to the M240 in the center (this is with lux 50).

 

Actually, according to Jim Kasson, there does not seem to be any difference all over the frame (if any, I like the Kolari mod better):

 

http://blog.kasson.com/?p=10967

Edited by CheshireCat
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A lot of what you say is very true and I totally agree. My only point is that the sensor and lens need to be optimised.

 

In theory if the cover glass is the only issue and refraction is reduced, it should make the kolari mod Sony A7 equal to the M240 atleast in the corners. But its not. The kolari mod A7 is not even equal to the M240 in the center (this is with lux 50). Thats why I believe there are other factors at play rather than a simple cover glass issue.

 

I'm sure there are other factors at work too; the lens to sensor match is finely nuanced thing and is all important to getting what I want out of a camera. What I said before is assuredly just a first order approximation. 

 

This is why I've been completely uninterested in modifying cameras in an attempt to achieve what I feel the manufacturers should be doing. I never expected Sony to tune their cameras for Leica lenses, I just hoped that it might work. I do expect Leica to do that tuning, between the sensor hardware and software massaging the data afterwards, as it is in their best interest to do so to the limits of what is possible and reasonable for the camera's intent. Since they've marketed this camera to be the 'use all Leica lenses' body, I expect they've addressed compatibility for their lenses to as great an extent as can be managed. 

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I am slowly coming to a possible conclusion for me, i.e. that I have to use only those M lenses that have a basic design that makes them less susceptible to changes in sensor cover glass optical thickness.

 

The WATE and 50/2 APO seem to work just fine on an unmodified stock A7r2 with minimal, but nevertheless ever so slightly detectable, insignificant corner degradation, unless one pixel peeps.

I suspect the new 28/2 Summilux falls into the same categorie, as do pretty much the 21/1.4 and 24/1.4 Summiluxes.

 

All my R lenses are great as well.

 

So to fit into this thread I would say, if a lens works fine on a stock A7r2 it certainly should work without any problems on the SL. :-)

 

And as Leica is the only one to match their lenses to their cameras, more of their existing M lenses should work just fine on the SL.

 

My 2 cents.

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Actually, according to Jim Kasson, there does not seem to be any difference all over the frame (if any, I like the Kolari mod better):

 

http://blog.kasson.com/?p=10967

 

I beg to differ from Mr. Klasson, though I have not heard about him. I am speaking from personal experience and extensive testing. I repeat, the 50 lux, when used with the kolari mod a7, even the center lags behind the M240. Also this is unpredictable as Jono was stressing. With some images, the difference is not much but with others significant.

 

Anyway I will have the SL in the last week of November hopefully. I will be very happy if it works well my Leica 21 SEM as its confirmed to work great with my other lenses, thanks to this thread. If the 21 SEM has issues, will consider trading for WATE.

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[...] if a lens works fine on a stock A7r2 it certainly should work without any problems on the SL. :-)

 

So because it works on the Sony it should work on the Leica for sure... Wonder how we managed to live w/o Sony when they concentrated on Betamax... 

Edited by lct
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Actually, according to Jim Kasson, there does not seem to be any difference all over the frame (if any, I like the Kolari mod better):

 

http://blog.kasson.com/?p=10967

 

 

Thanks for mentioning Jim Kasson.

 

He also has posted here on LUF, as he also shoots Leica gear.

I wouldn't be surprised at all if he also had an SL on order.

In that case one can be certain he would explore it fully once he has recovered from his surgery.  http://blog.kasson.com

I certainly appreciate the unique qualitative and quantitative insights he has gained from his experiments.

 

All the best to Jim Kasson and I wish him a complete and speedy recovery.

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Okay - quick and dirty - this is 100% crops from the bottom right hand corner of the image (slightly compressed to fit in the teeny tiny attachment limit)

28 elmarit on this message

 

attachicon.gif28 elmarit at f4.jpg

This one at F4

 

attachicon.gif28 elmarit at f8.jpg

This one at F8

 

For a comparison between a stock A7r2 and a Kolari modified A7r2 please, see here:

http://www.fredmiranda.com/forum/topic/1392833/2#13289493

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I did an informal test with the SL and 21lux, 35lux (FLE) and the 50 APO yesterday. The 21 and 35 struggled with corner sharpness fully open, but seemed OK from 2.0 and higher. The APO, which I was most worried about, seemed to do OK.

I would be very interested in a more formal test, though, but have not seen any so far.

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I did an informal test with the SL and 21lux, 35lux (FLE) and the 50 APO yesterday. The 21 and 35 struggled with corner sharpness fully open, but seemed OK from 2.0 and higher. The APO, which I was most worried about, seemed to do OK.

I would be very interested in a more formal test, though, but have not seen any so far.

Did you do informal test on brick wall or more realistic 3D subject? I would imagine fast 21 or 35 M lens at max aperture would be unsharp in corners even on M240 or M9 in most situations.

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Just a big thank you to Jono for posting so many helpful comments about in this thread, and the related SL subsections.  :)

 

You answer so many questions a shooter has (particularly one who uses WA and puts the motif well off center), and you provide the insight without the burden of technical spinning (that is always reads like a caveat rather than a conclusion).

 

Well done!

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Did you do informal test on brick wall or more realistic 3D subject? I would imagine fast 21 or 35 M lens at max aperture would be unsharp in corners even on M240 or M9 in most situations.

 

A shop front, brick wall, but also some plants and signs. You may be right, I don't currently have an M to compare

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A shop front, brick wall, but also some plants and signs. You may be right, I don't currently have an M to compare

Hmm - well I agree with Mladen - wide open several lenses will show slightly unsharp corners on the M as well (mostly due to curvature of field).

Also worth mentioning that if you want a torture test you're better to do a distant subject (where the rear element of the lens is closer to the sensor). 

I've got some proper tests I'm hoping to put together into an article (but I'm not sure which is more boring, taking the pictures or writing about them!

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