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Comparison Canon FD 35mm f/2 concave vs Rokkor MD 35mm f/2.8
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PostPosted: Tue Dec 27, 2022 2:09 pm    Post subject: Comparison Canon FD 35mm f/2 concave vs Rokkor MD 35mm f/2.8 Reply with quote
Comparison between the Canon FD 35mm f/2 chrome nose (last concave version) versus the Minolta MD 35mm f/2.8.

Center comparison:
centercomparison by devoscasper, on Flickr

Both lenses show excellent center resolution and contrast. Contrast a bit lower from the Canon wide open, but still very good resolution. The yellowing of the thoriated glass is visible.

Corner comparison:
cornercomparison by devoscasper, on Flickr

The Minolta, which has an excellent reputation, is clearly better in resolving the extreme corners up until f/8. At f/8, the difference is negligible. The corners of the Canon improve a bit further at f/11, and become slightly better than the Minolta's.

Then, a bokeh test:
bokehcomparison by devoscasper, on Flickr

Of course subjective, but I like the Canon's bokeh slightly more. Not tested here, but in the department of flare resistance the Minolta is better.


PostPosted: Tue Dec 27, 2022 5:01 pm    Post subject: Reply with quote
It would be interesting to know if Thorium lenses, once aged, also affects CA (the Canon seems to have more than the Minolta). From memory I have once read that Thorium glass not only colours with age (yellow/amber), but that other optical properties are also affected.

The yellowing can be partially cured by exposure to UV light, but I don't know if that also fixes any other possible age-related optical issues of Thorium glass.

What is sure is that depending on the destination it won't always make it past all customs-checks when shipping internationally, on account of the very detectable radiation (not too harmful in occasional use, but very detectable above background levels when checked for).


PostPosted: Tue Dec 27, 2022 5:32 pm    Post subject: Reply with quote
RokkorDoctor wrote:
It would be interesting to know if Thorium lenses, once aged, also affects CA (the Canon seems to have more than the Minolta). From memory I have once read that Thorium glass not only colours with age (yellow/amber), but that other optical properties are also affected.

The yellowing can be partially cured by exposure to UV light, but I don't know if that also fixes any other possible age-related optical issues of Thorium glass.

What is sure is that depending on the destination it won't always make it past all customs-checks when shipping internationally, on account of the very detectable radiation (not too harmful in occasional use, but very detectable above background levels when checked for).


Apart from browning, I do not believe that there are any other optical effects from radiation in thoriated lenses. If anyone knows otherwise please post a link.


PostPosted: Tue Dec 27, 2022 8:07 pm    Post subject: Reply with quote
Thanks for that comparison!

It confirms for the concave FD 2/35mm what we have seen before for the convex FD 2/35mm: That the Minolta MD 2.8/35mm (and the MC/MD 1.8/35 as well, BTW) are better suited for landscape purposes than the Canon FD and nFD 2/35mm lenses.

http://www.artaphot.ch/systemuebergreifend/objektive/610-35mm-1-2-1-1-8-1-1-4-lenses

S


PostPosted: Wed Dec 28, 2022 7:02 am    Post subject: Reply with quote
stevemark wrote:
Thanks for that comparison!

It confirms for the concave FD 2/35mm what we have seen before for the convex FD 2/35mm: That the Minolta MD 2.8/35mm (and the MC/MD 1.8/35 as well, BTW) are better suited for landscape purposes than the Canon FD and nFD 2/35mm lenses.

http://www.artaphot.ch/systemuebergreifend/objektive/610-35mm-1-2-1-1-8-1-1-4-lenses

S


Yeah, it’s a great lens. And cheap.


PostPosted: Wed Dec 28, 2022 8:39 am    Post subject: Reply with quote
kymarto wrote:
RokkorDoctor wrote:
It would be interesting to know if Thorium lenses, once aged, also affects CA (the Canon seems to have more than the Minolta). From memory I have once read that Thorium glass not only colours with age (yellow/amber), but that other optical properties are also affected.

The yellowing can be partially cured by exposure to UV light, but I don't know if that also fixes any other possible age-related optical issues of Thorium glass.

What is sure is that depending on the destination it won't always make it past all customs-checks when shipping internationally, on account of the very detectable radiation (not too harmful in occasional use, but very detectable above background levels when checked for).


Apart from browning, I do not believe that there are any other optical effects from radiation in thoriated lenses. If anyone knows otherwise please post a link.


https://www.dpreview.com/forums/post/61218888


PostPosted: Wed Dec 28, 2022 10:17 am    Post subject: Reply with quote
Ernst Dinkla wrote:
kymarto wrote:
RokkorDoctor wrote:
It would be interesting to know if Thorium lenses, once aged, also affects CA (the Canon seems to have more than the Minolta). From memory I have once read that Thorium glass not only colours with age (yellow/amber), but that other optical properties are also affected.

The yellowing can be partially cured by exposure to UV light, but I don't know if that also fixes any other possible age-related optical issues of Thorium glass.

What is sure is that depending on the destination it won't always make it past all customs-checks when shipping internationally, on account of the very detectable radiation (not too harmful in occasional use, but very detectable above background levels when checked for).


Apart from browning, I do not believe that there are any other optical effects from radiation in thoriated lenses. If anyone knows otherwise please post a link.


https://www.dpreview.com/forums/post/61218888


Anything other than a single unattributed comment in a thread. I've studied this quite extensively and never seen a mention of anything remotely similar. Only coloration

https://en.wikipedia.org/wiki/F-centers


PostPosted: Wed Dec 28, 2022 4:43 pm    Post subject: Reply with quote
kymarto wrote:
Ernst Dinkla wrote:
kymarto wrote:
RokkorDoctor wrote:
It would be interesting to know if Thorium lenses, once aged, also affects CA (the Canon seems to have more than the Minolta). From memory I have once read that Thorium glass not only colours with age (yellow/amber), but that other optical properties are also affected.

The yellowing can be partially cured by exposure to UV light, but I don't know if that also fixes any other possible age-related optical issues of Thorium glass.

What is sure is that depending on the destination it won't always make it past all customs-checks when shipping internationally, on account of the very detectable radiation (not too harmful in occasional use, but very detectable above background levels when checked for).


Apart from browning, I do not believe that there are any other optical effects from radiation in thoriated lenses. If anyone knows otherwise please post a link.


https://www.dpreview.com/forums/post/61218888


Anything other than a single unattributed comment in a thread. I've studied this quite extensively and never seen a mention of anything remotely similar. Only coloration

https://en.wikipedia.org/wiki/F-centers


Maybe we should ask him to give some comments on his statements.

I doubt for what the glass is known for; a high refractive index with relative low dispersion, will be kept at the same level with what goes on in that glass over 50 years. Maybe it can hardly be optically tested but I would be surprised if it did not have any effect on resolution / CAs.

Ignoring these aspects there still is the lower light transmission and the heavier blue light blocking which has to be compensated. For me reason enough to give lenses like that a UV light treatment.

One article mentioned a low level of extra sensor noise due to the radioactivity of a lens. Not something to worry about in practice as I understand it. I guess it would have been worse with an unused film in some vintage camera models.


PostPosted: Wed Dec 28, 2022 5:53 pm    Post subject: Reply with quote
The composition of the glass does not change, nor the curvature, and so neither will the index of refraction nor the dispersion.


PostPosted: Wed Dec 28, 2022 6:27 pm    Post subject: Reply with quote
Corrected link: https://en.wikipedia.org/wiki/F-center

Quote:
An F center or Farbe center (from the original German Farbzentrum, where Farbe means color and zentrum means center) is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more unpaired electrons. Electrons in such a vacancy in a crystal lattice tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored. The greater the number of F centers, the more intense the color of the compound. F centers are a type of color center.


Doesn't sound like the crystal dimension is changed with yellowing; therefore no change in refraction, yes?


PostPosted: Wed Dec 28, 2022 7:11 pm    Post subject: Reply with quote
I consider the coloration as a build-in yellow/orange filter. Wink


PostPosted: Wed Dec 28, 2022 10:10 pm    Post subject: Reply with quote
visualopsins wrote:
Corrected link: https://en.wikipedia.org/wiki/F-center

Quote:
An F center or Farbe center (from the original German Farbzentrum, where Farbe means color and zentrum means center) is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more unpaired electrons. Electrons in such a vacancy in a crystal lattice tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored. The greater the number of F centers, the more intense the color of the compound. F centers are a type of color center.


Doesn't sound like the crystal dimension is changed with yellowing; therefore no change in refraction, yes?


Exactly


PostPosted: Thu Dec 29, 2022 10:33 am    Post subject: Reply with quote
kymarto wrote:
visualopsins wrote:
Corrected link: https://en.wikipedia.org/wiki/F-center

Quote:
An F center or Farbe center (from the original German Farbzentrum, where Farbe means color and zentrum means center) is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more unpaired electrons. Electrons in such a vacancy in a crystal lattice tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored. The greater the number of F centers, the more intense the color of the compound. F centers are a type of color center.


Doesn't sound like the crystal dimension is changed with yellowing; therefore no change in refraction, yes?


Exactly


Surely it is inevitable that over time the optical properties will change?

What starts off as thorium, eventually will end up as lead due to the radioactive decay. Glass with ~30% thorium will surely have different optical properties than glass with ~30% lead? During this decay more and more thorium will change into a host of other daughter elements.

Near "full" decay will take hundreds of billions of years if not longer in the case of thorium, but since the decay clearly already introduces colour centres in our lifetime (yellowing), is it not inconceivable that the slow but gradual build-up of other daughter elements are slowly going to change the glass structure? (this is a genuine question; I'm not an optical materials expert)


PostPosted: Thu Dec 29, 2022 10:52 am    Post subject: Reply with quote
There might be imperceptible changes, but so small as to be completely insignificant. Th-232 has a half life of 14 billion years. These lenses are 50 years old, so 0.000000018% has decayed so far. I can guarantee that that is not what is causing the exhibited chromatic aberration.


PostPosted: Thu Dec 29, 2022 11:08 am    Post subject: Reply with quote
CA is still pretty well controlled by the Canon considering its age, note that this is a 100% crop on a 42+ mp sensor. And the Minolta is a more modern lens.


PostPosted: Thu Dec 29, 2022 3:41 pm    Post subject: Reply with quote
Nice test and I am not surprised by the result.

A quick and dirty comparison of a nFD 35 2,8 and of the concave Canon did not evidence a significant difference at shared apertures.

The Minolta 5/5 35 2,8 is outstanding and the test renders justice to this lens.

I have not tested the MC HH 35 1,8 but the more recent MD 1,8 is certainly inferior to the modern 2,8.

So unless you are stucked needing f 2,0 I see no need to pay for the big glass.


PostPosted: Thu Dec 29, 2022 3:48 pm    Post subject: Reply with quote
lumens pixel wrote:
Nice test and I am not surprised by the result.

A quick and dirty comparison of a nFD 35 2,8 and of the concave Canon did not evidence a significant difference at shared apertures.

The Minolta 5/5 35 2,8 is outstanding and the test renders justice to this lens.

I have not tested the MC HH 35 1,8 but the more recent MD 1,8 is certainly inferior to the modern 2,8.

So unless you are stucked needing f 2,0 I see no need to pay for the big glass.


True. I have tested the MC HH 35/1.8. It’s a nice lens with classic rendering. It’s not on par with the MD 35/2.8 though.
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