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My truth about some Minolta MD and Canon fifties
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PostPosted: Thu Mar 30, 2023 10:46 am    Post subject: Reply with quote
RokkorDoctor wrote:
[

In general, the longer the focal length of the lens, the closer the diameter of the entrance pupil will be to the diameter of the front lens.



But long focal telephoto lenses can go beyond that I guess. I found it interesting that with 45mm lenses salvaged from fixed lens rangefinders the asymmetry, arm length view of the front and rear, the aperture set at 8.0, some were symmetrical, some a bit tele. Where standard SLR lenses show almost all the asymmetry of some retrofocus design. No measurements but just the impression of the aperture size, front and rear.


PostPosted: Thu Mar 30, 2023 1:13 pm    Post subject: Reply with quote
Ernst Dinkla wrote:
RokkorDoctor wrote:
[

In general, the longer the focal length of the lens, the closer the diameter of the entrance pupil will be to the diameter of the front lens.



But long focal telephoto lenses can go beyond that I guess. I found it interesting that with 45mm lenses salvaged from fixed lens rangefinders the asymmetry, arm length view of the front and rear, the aperture set at 8.0, some were symmetrical, some a bit tele. Where standard SLR lenses show almost all the asymmetry of some retrofocus design. No measurements but just the impression of the aperture size, front and rear.


Indeed. Given that the entrance and exit pupils are the virtual images of the aperture as imaged by resp. the front and rear lens sections, they do not even need to be inside the physical confines of the lens:

https://www.rp-photonics.com/entrance_and_exit_pupil.html

E.g. when composing a panoramic shot from multiple images, it is important to know the location of the entrance pupil. For the most common lens designs, to avoid a parallax shift of near subjects as the setup is rotated in general the camera setup should be rotated around the location of the entrance pupil of the lens (or the nodal point for rotating lens systems), certainly not the front element of the lens or camera tripod mount. Less critical these days with smart stitching software but essential when working with film/darkroom and still good practice.

https://www.panoramic-photo-guide.com/finding-the-nodal-point.html

Some lenses (notably fish-eye lenses) have peculiar behaviour of the entrance pupil, in that it doesn't have a fixed position or shape/orientation for off-axis imaging rays. Even if you could de-fish the constituent images effectively, stitching those would be a nightmare if it contained near-camera subject matter due to the inconsistencies in parallax.

https://wiki.panotools.org/Special_issues_with_fisheye_lenses#Entrance_Pupil_.28No-Parallax_Point.29

http://michel.thoby.free.fr/Fisheye_history_short/Beyond-the-pupil.html

EDIT: This is getting a bit off-topic; apologies. If there is enough serious interest it might be worth opening a new topic for entrance/exit pupil associated discussions (f/# stops, stitching, parallax, dedicated vs generic teleconverters, sensor illumination, etc); I can only find two very old threads...


PostPosted: Thu Mar 30, 2023 5:05 pm    Post subject: Reply with quote
Thank you, Ernst!

So the sticklers can learn from these graphs that no 50mm lens is a 50mm lens.


PostPosted: Thu Mar 30, 2023 5:48 pm    Post subject: Reply with quote
kathala wrote:
Thank you, Ernst!

So the sticklers can learn from these graphs that no 50mm lens is a 50mm lens.


I suspect that non-consumer scientific lenses intended for industrial/laboratory/military use may be a bit closer to their stated FL. (maybe)


PostPosted: Thu Mar 30, 2023 6:58 pm    Post subject: Reply with quote
I struggled with determining the real T-Stop or F-Stop of a lens too. I can tell you from comparing multiple 50ies it is complicated and you can make a lot of mistakes that will invalidate your whole test result.

I started the same as the TO. But even with spot metering the result is not reliable. It helps to have one benchmark lens. Take a modern lens with modern glass and use it as base for all your comparisons. Best would be a bright lens. F.e. if you want to measure F1.8 lenses than take a F1.4 as your benchmark lens. Chances are high that this lens will show the correct behavior when stopped down to F1.8 or F2.

I noticed that the quality of light might interfere with your test results. Testing a lens in bright daylight might create other results than testing on a cloudy day or in a dimm room. It will not turn all your results upside down but sometimes one lens that shows good and correct transmission in good light might stick with average lenses in dimm light. This might be important when comparing lenses with a close aperture range. Your F1.8 lens might show a small advantage in good light but behave like an F2 or F2.2 lens in darker conditions.

Even your camera might trick you. Do not fall into the trap to compare native lenses with manual lenses. Since the camera can talk with the native lens it might increase the images brightness when the lens is used at F1.8 or F1.4. My Voigtlander Nokton 40mm F1.2 SE tricked me with this. It has electronic contacts and so the Sony Alpha camera knows the used aperture setting of the lens. If you go from F4 to F1.2 the camera uses perfect shutter speeds and a bright image with all settings. It is to perfect! If you slightly turn the lens the camera looses contact to the lens and the image gets darker on <F2. The camera compensates all lenses under F2.

You can try a different approach. Use a fixed light, a fix shutter time, and a fix ISO and shoot a white or gray target. Take the images and look how dark your white target is compared between different lenses and aperture settings. You can use the color picker in lightroom to see the RGB numbers. If you have a benchmark you see how off the result of your test lens is or how accurate.

Good luck. If someone finds a good approach to test T-Stops please let me know.


PostPosted: Thu Mar 30, 2023 7:07 pm    Post subject: Reply with quote
kathala wrote:
Thank you, Ernst!

So the sticklers can learn from these graphs that no 50mm lens is a 50mm lens.


Within 5% deviation of the focal length is acceptable. The Rollei Planar touches that 5% though.


PostPosted: Sat Apr 01, 2023 8:43 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
Sorry for quoting myself but I wanted to illustrate MD 50 1,7 @f2,0. Do you need anything sharper?

lumens pixel wrote:


On a side note, MD 50 1,7 is rather week wide open, at true 1,7. It is a little bit difficult to select f2,0 due to the lack of stop on the aperture ring so you have to start from f2,8 and locate the point on the aperture ring that will provide you with twice the speed, surprisingly physically close from the f2,8 stop.

So now you have true f2,0 on the MD 1,7 and you can compare with the famous 50 2,0 MDIII considered the best full open. Same results.

So the 1,7 is not the lesser lens, it just provides you with a weaker wider aperture you are free to use.

H


Cerisier - Printemps 2023 by lumens pixel, sur Flickr


PostPosted: Sat Apr 01, 2023 9:01 pm    Post subject: Reply with quote
Same lens, close-up f2,8 probably

Rosier | Rosebush by lumens pixel, sur Flickr


PostPosted: Sun Apr 02, 2023 12:49 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
lumens pixel wrote:


On a side note, MD 50 1,7 is rather week wide open, at true 1,7. It is a little bit difficult to select f2,0 due to the lack of stop
on the aperture ring so you have to start from f2,8 and locate the point on the aperture ring that will provide you with twice the speed,
surprisingly physically close from the f2,8 stop.

So now you have true f2,0 on the MD 1,7 and you can compare with the famous 50 2,0 MDIII considered the best full open. Same results.

So the 1,7 is not the lesser lens, it just provides you with a weaker wider aperture you are free to use.

H


The MD 1.7/50mm variants (MD-I, MD-II, and MD-III) all have a bit more astigmatism than the MD-III 2/50mm, at corresponding
f-stops (just tested wide open, at f3.5 and at f5.6). In addition the MD-III has virtually zero distortion (in the 0.1% range).

On 43 MP FF sensors, using f5.6, the MD-III 2/50mm images are perfect, even in the corners: No astigmatism, no lateral CA,
no distortion Wink

S


PostPosted: Sun Apr 02, 2023 6:18 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
stevemark wrote:
lumens pixel wrote:


On a side note, MD 50 1,7 is rather week wide open, at true 1,7. It is a little bit difficult to select f2,0 due to the lack of stop
on the aperture ring so you have to start from f2,8 and locate the point on the aperture ring that will provide you with twice the speed,
surprisingly physically close from the f2,8 stop.

So now you have true f2,0 on the MD 1,7 and you can compare with the famous 50 2,0 MDIII considered the best full open. Same results.

So the 1,7 is not the lesser lens, it just provides you with a weaker wider aperture you are free to use.

H


The MD 1.7/50mm variants (MD-I, MD-II, and MD-III) all have a bit more astigmatism than the MD-III 2/50mm, at corresponding
f-stops (just tested wide open, at f3.5 and at f5.6). In addition the MD-III has virtually zero distortion (in the 0.1% range).

On 43 MP FF sensors, using f5.6, the MD-III 2/50mm images are perfect, even in the corners: No astigmatism, no lateral CA,
no distortion Wink

S


Agreed on all your points regarding the qualities of the MDIII 50 2,0.

To my eyes the 1,7 is slightly behind regarding CA and distortion but at such a high level that it is not really a problem. And, the bokeh of the 1,7 is closer to the one of the 1,4 7/6 which is more noticeable than the above slight disadvantages.

So all in all two interesting lenses.


PostPosted: Sun Apr 02, 2023 10:39 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
lumens pixel wrote:

Agreed on all your points regarding the qualities of the MDIII 50 2,0.

To my eyes the 1,7 is slightly behind regarding CA and distortion but at such a high level that it is not really a problem. And, the bokeh
of the 1,7 is closer to the one of the 1,4 7/6 which is more noticeable than the above slight disadvantages.

So all in all two interesting lenses.


Yeah, we are pixel peeping for sure...! I certainly would not be able to see whether an image was made using the MD 1.7/50 or the MD 2/50.
But when I have to choose a MF 50mm, I usually take the MD-III 2/50 nevertheless (for landscape/architecture) ...

And if it has to be a fast "character lens"? Sometimes MC-X 1.2/58, sometimes Nikkor Ai 1.2/55, sometimes MD 1.2/50. And on the A900
(which I still use regularly) it's the SAL/MinAF 1.4/50mm.

S


PostPosted: Mon Apr 03, 2023 1:20 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
stevemark wrote:
lumens pixel wrote:

Agreed on all your points regarding the qualities of the MDIII 50 2,0.

To my eyes the 1,7 is slightly behind regarding CA and distortion but at such a high level that it is not really a problem. And, the bokeh
of the 1,7 is closer to the one of the 1,4 7/6 which is more noticeable than the above slight disadvantages.

So all in all two interesting lenses.


Yeah, we are pixel peeping for sure...! I certainly would not be able to see whether an image was made using the MD 1.7/50 or the MD 2/50.
But when I have to choose a MF 50mm, I usually take the MD-III 2/50 nevertheless (for landscape/architecture) ...

And if it has to be a fast "character lens"? Sometimes MC-X 1.2/58, sometimes Nikkor Ai 1.2/55, sometimes MD 1.2/50. And on the A900
(which I still use regularly) it's the SAL/MinAF 1.4/50mm.

S


Now if you consider the situation on the side of the advantages of the 1,7 you could state that it has less field curvature and CA than the 1,4 while retaining its bokeh.

So the 1,4 rules at 1,4 and the 2,0 in the corners at wide apertures ( not by much if you have a good copy). There is still a lot of room for the 1,7 that is belittled.

Perhaps this is the reason why it has been sold for so a long time. An engineering rather than a marketing decision.
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