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Lensrentals: MTF 25mm Prime Lens Comparison
#1
Very interesting comparison.

The copy to copy variation is not pretty, especially regarding the Pany 25mm.

 

https://www.lensrentals.com/blog/2018/01...omparison/

 

Brandon Dube (working at lensrentals) seems to be very knowledgeable as far as lens design goes.

 

From the comments section:

 

Phillip Reeve:

Question to Brandon: How can it be that the OM 1.2/25 is so much less sharp than the FE 1.8/55 (in relative terms comparing 10 LP/mm (FE55) to 20 LP/mm (OM25) and 20 LP/mm to 40 LP/mm) at their widest aperture? The OM should have all the advantages: It is massively more complex (19 with lots of fancy glass vs 10 elements), more expensive, heavier and it has a smaller aperture. Yet the Sony has a much higher contrast in that comparison. Thanks Smile

 

Brandon Dube:
Better and easier optical design -- f/1.8 is a lot easier than f/1.2, but the olympus lens also has a very complicated design. The light is squeezed down towards the middle (elements 1-5), pushed back up (6-8), slowly made to be converging again (9-15), and finally focused (16-19). This is the technique used by photolithography lenses to flatten the field (get rid of field curvature and astigmatism). The requirements of those lenses are sub-nanometer field flatness, so they really need it. For a camera lens? Well, not even the Masterprimes or Summilux-C lenses do that (at $40,000/ea). You can see Olympus leveraged it here to produce a very flat field, pretty high resolution (in absolute terms...) design at the expense of making the lens very complicated and expensive to produce.

The Sony lens also has 3 aspheres (maybe 4 aspheric surfaces) vs 1 in the olympus. If they had opted for 3-4 aspheres and 6 fewer lenses in Olympus' design, without this field curvature correcting technique, they probably could have produced a superior design.

So I would say that the Sony lens, whoever designed it, was done more cleverly and the result is better. The Olympus lens, whoever designed it, is probably a good optical designer (the product is pretty good and utilizes some advanced design techniques) but didn't stop to ask ask "should I" before betting on "can I."

As an aside, the A7rIII has 4.5 micron pixels and can "see" up to 110 lp/mm. None of the spatial frequencies shown on these plots really show "pixel level" detail. We show down to more like 2-4 pixel level of detail, which is probably about how close you want to look at your pictures unless you're posting 100% crops online or using them to measure things.

--Florent

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Lensrentals: MTF 25mm Prime Lens Comparison - by thxbb12 - 01-15-2018, 05:11 PM

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