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Lens design. Specifically 35/1.4 and 24/1.4.

  
 
RustyBug
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p.2 #1 · p.2 #1 · Lens design. Specifically 35/1.4 and 24/1.4.


wolfloid wrote:
The only thing that surprises me is that the 24mm GM is smaller and lighter than the newer 35mm GM, whereas in the Summiluxes it is so markedly the other way around.



If you take a look at the Summicron 50, 40 and 35 ... the 40 is smaller than the other two (despite being 50 years old), despite having the same aperture designation of f/2.0. The lens design approach, and the corresponding differences in optical properties, of the 50 and 35 are probably closer to the similar design, whereas the 40 is likely different design choices to make it physically smaller, yet with the same f/2 rating.

Optical design is always a series of compromises / tradeoffs. For me, the size difference of the Sony doesn't strike me peculiar ... it just suggests that either the 24 GM traded off some properties for its size, or the 35 gained some properties for its size. I just don't have the needed info to explain what those quid pro quo's might be ... vignetting and mustache distortion are two that I'd look at to see how much more / less the 24 vs. 35 incur. Multiple other properties too ... but, that point is that they likely aren' "apples to apples", just because they are f/1.4 to f/1.4. That's kind like saying a Washington apple should be similar to a Fuji apple because they are both red. They have different characteristics that extend far beyond the maximum aperture to assume they should be similar. Again ... back to needing lens design and performance info.




Nov 22, 2023 at 11:26 AM
Nushi
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p.2 #2 · p.2 #2 · Lens design. Specifically 35/1.4 and 24/1.4.


Those interested in optical analysis of the 24 and 35 Sony GM lenses can have a look here:
https://lensreview.xyz/sony-fe-24-1-4-gm-analyze/
https://lensreview.xyz/sony-35-1-4-gm-analyze/

Ray tracing diagrams from the above articles below:













The 35 has a translated article: https://lensreview-en.xyz/sony-fe-35mm-f1-4-gm/ the 24 has to go through you favourite translator software. The diagrams need no explanation.

Edit: Oh and the above diagrams show that both lenses start with a retrofocus group despite the short back focus of the lenses. The red lines, those converging in the centre of the sensor, "flare" outward before the aperture which is what retrofocus is. This was usually used to enable longer back fous but is here used for different purposes,



Nov 22, 2023 at 11:54 AM
Nushi
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p.2 #3 · p.2 #3 · Lens design. Specifically 35/1.4 and 24/1.4.


https://opticexplorer.sharedigm.com had lux 35 asph v1 which is pretty close to the current one.







I'm no expert but that seems like it's not actually a retrofocus design, it's flaring a bit though I think but I'm not sure where the line is drawn. So there we have a possible answer as already suggested. Lecia decided to keep the non retrofocal design of the 35 probably to keep size down. With the 24 they have no such option.

Some other Leica 35's for comparison

non asph lux (absolutely not retrofocal, the rays converge as normal)






apo cron









Nov 22, 2023 at 02:19 PM
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