FF Lens on APS-C camera and APSC on FF camera

[M11 for me]

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Bad example. I do not think. Leica publishes MTF curves that are of course compared with other lenses' MTF curves across brands. Fact is: Leica publishes that for each single lens. I have no problem with that. 

Look: You can be against any numbers that are published to any camera or lens. How relevant is any number for your daily photography?

Edited December 15, 2019 by M10 for me

[jaapv]

Yes, but comparing them across brands is not very useful for precision, as they are all arrived at differently. Of course people compare, if only for an indication. But precise and exact? No way.

Better to use OTF diagrams.

 

 

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Zitat Laney und Richter Leica Objective in der Praxis

[ramarren]

5 hours ago, M10 for me said:

Bad example. I do not think. Leica publishes MTF curves that are of course compared with other lenses' MTF curves across brands. Fact is: Leica publishes that for each single lens. I have no problem with that. 

Look: You can be against any numbers that are published to any camera or lens. How relevant is any number for your daily photography?

The numbers are basically useless, although many people assume they are significant and use them to do pre-purchase evaluation and later to say how good a thing they have in their hand. And marketers use them to promote their products to those people. 

I find all of this debate over published numbers and curves a complete waste of time when it comes to anything I want to do with my photography. 

[lct]

5 hours ago, jaapv said:

Leica doesn't even measure MTF curves, as they find that too imprecise.

Are you sure?

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[FrozenInTime]

23 minutes ago, lct said:

Are you sure?

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Computed  MTF curves ...  simulation not measurement.

But do these calculations account for sensor cover glass and micro lenses ? for what camera ?

[JonPB]

DXO's perceptual megapixels attempts to summarize a lens' merit with a single number that uses a lens-camera combination (which immediately defeats the purpose of talking about the lens as a thing unto itself) to measure sharpness (which is an image trait that is influenced by, but not determined by, the lens and camera system), weighted (in an unspecified manner) across the frame, weighted (in an unspecified manner) across apertures, and weighted (in an unspecified manner) across focal lengths. Measurements aren't meaningful to me unless they are reproducible, which these scores aren't based on published information. Measurements aren't meaningful to me unless they accurately represent some variable that I care about, and I cannot see a way of mapping a "perceptual megapixel" value to what I care about in how a lens-camera combination performs, even if I trusted the values in the first place. I can give DXO credit for trying to simplify a complex topic, but, in my mind, the complexity of the topic is where the meaningful information is. "Perceptual megapixels" is a lot like estimating how many calories were in someone's lunch without knowing anything about what they actually ate. It is merely a marketing tool -- pseudo information to make consumers feel like they are making an informed purchase without having to do the heavy lifting of informing themselves.

MTF graphs, whether measured or calculated, indicate the contrast level as a fraction of subject contrast of specific image frequencies in sagittal and tangential patterns drawn by the lens at specific distances from the image axis using a specific lens (ignoring the effect of the camera) at a specific focal length and aperture. This is in no way a score of merit. However, it suggests a lens' overall contrast, resolution, focus shift, focal plane curvature, and astigmatism at the nominal focal plane, all of which is useful information when applied against what I desire from a lens for a given purpose. Of course, MTF says nothing about what causes the reductions of contrast or what that looks like, and those matters are more important to final image quality than the MTF curves themselves. But I know what MTF curves tell me and so I can use that as meaningful information.

As far as I know, Leica used optical measurements of their lenses for MTF charts until their lenses were designed to have distortion correction applied in camera, at which point the optical corner resolution would be misleading, so they have since used calculated values for at least those lenses. But I don't have a cite for that.

Edited December 15, 2019 by JonPB
Original said that MTF measured subject frequencies; this was corrected to /image/ frequencies.

[jaapv]

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Leica has been using computed MTF graphs for a long time. Puts mentions it in his Lens Compendium which predates digital photography. Another problem with MTF graphs is that they describe the plane of focus only, which means that they say absolutely nothing about the way a lens draws. A lens can have perfect MTF performance and absolutely horrible OOF rendering. 

[jaapv]

58 minutes ago, lct said:

Are you sure?

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Yes. 

[JonPB]

From Leica M-Lenses: Their soul and secrets, by Erwin Puts with technical support by Peter Karbe, dated September 2002 and published by Leica. Page 16:

Quote

How are MTF measurements actually obtained?

There are two methods: one method computes MTF data, the other method measures MTF values. Basically, there are no differences, and Leica uses either method, whichever is most appropriate: the optical design department computes the MTF values, and the manufacturing department uses an MTF-measuring instrument to obtain MTF data (see the diagrams).

I want to add that computed MTF data can indeed differ from measured MTF data if the computations do not take into account all aspects of optical transmission. I've seen MTF charts from other manufacturers that indicate a 100% contrast ratio, which is only sensible if they neglect a few of the more confounding aspects of optics -- which is fine for designers in their process of optimization, but which does not reflect the total, real-world performance of a lens as do Leica's graphs. I have seen nothing to make me doubt that Leica (or Zeiss) publish anything other than realistic MTF charts, even when the charts are computed rather than measured.

[nicci78]

What we should know is simple : 

A bad lens on 24x36 will be worst on APS-C. Because, we are magnifying the defects. 
An excellent lens in 24x36 will stay excellent on APS-C. 
 

A good but flawed lens at the corner on FF can be excellent on APS-C. Because we are throwing away the bad corners. 
 

That’s why every manufacturers chose to transition from analog to digital with crop sensor : APS-C or APS-H (Canon or Leica M8 and DMR) 

 

To sum up make your own tests. And make your own conclusions. 
We do not have the same relationship with image quality. Some some it is okay, but for others it will be horrible. 
That’s why I never trust, when someone say that such lens is nice on this body. Then finding that I hated it. I have to see it myself. 
 

[jaapv]

The reason for the M8 was different: insufficient microlens technology for the corners AKA sensor vignetting and IR colour shift.  

[lct]

32 minutes ago, nicci78 said:

A good but flawed lens at the corner on FF can be excellent on APS-C. Because we are throwing away the bad corners. 

... provided the sensor stack of the APS-C camera is as thin as that of the FF camera, which is rarely (never?) true.

[jaapv]

10 minutes ago, lct said:

... provided the sensor stack of the APS-C camera is as thin as that of the FF camera, which is rarely (never?) true.

That is incorrect. The filter stack of a smaller sensor is less demanding through lack of the corners where the problem lies. 

[nicci78]

48 minutes ago, lct said:

... provided the sensor stack of the APS-C camera is as thin as that of the FF camera, which is rarely (never?) true.

Thin sensor stack is only a goal for Leica, due to M lenses support.
R support is less of a problem, being SLR lenses, they are way more telecentric than M ones. Especially the wide angle. Due to retro focus design. 

Telephoto or long focal length lenses are by design almost telecentric. That’s why they are not a challenge for digital sensors. Even the one with thick sensor stack. 
 

AA filter is actually desirable for videos. Not so much for photos, except for fashion maybe. 
 

Just keep in mind. That all of that are only theories. We have to test them to be sure. There are so many exceptions to the rule. 

Edited December 17, 2019 by nicci78

[sector99]

Northrup has a following based mostly on his smooth video deliveries and his decent photography. He is just the latest pundit to illuminate the sensor stack/third party lens performance issue. Having never designed a lens, he unfortunately with the others, venture into indefensible areas.

Fuji X-TRANS has no AA filter but a sensor stack (SS) approximating 2mm according to measurements made by the current source of information–Lens Rentals. It isn't a secret that the designer must accommodate the SS dimension in order to optimize a final design. In the CL case as well as M cameras, we don't have official values other than empirical results (which appear to be excellent especially for flagship models e.g., Summilux 50 f/1.4 asph). Diglloyd is also a ventilating fanboy of SS issues.

Northrup was apparently edging viewers to avoid non-brand lens use per se. His supporting manufacturer's do, after all, provide more than a modicum of his revenue and now wish 100% brand lens loyalty.

Regarding CL performance in general, you may observe the Leica CL fares about an ISO 100 stop better in dynamic range vs. the flagship model SONY A9 in (APSC mode). The fact that the A9 has larger photosites should have give a superior DR result. It appears the CL has a class-competitive sensor and works well with M-lenses. The sensor stack (M or CL) seems to be a non-M-lens issue

http://www.photonstophotos.net/index.htm

 

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