Have RF lenses had their day ?

Started Jan 5, 2014 | Discussions thread
Jay Ell Regular Member • Posts: 256
Large ***focusing errors*** and misconceptions

harold1968 wrote:

Leica lenses, as Karbe admitted in a recent interview, follow the same design pattern they always did. This is an uncorrected rear element structure, where correction was not required due to the thickness of film emulsion.

This is a bit confusing use of terminology.

Correction is only needed is aberrations are introduced in the first place. The simpler near symmetric designs cause little aberrations but that does not mean that the design somehow ignores minimizing them. It is much easier to minimize them in such lens than with a complex retrofocus.

The reason why the modern mirrorless lenses tend not to have simple designs in the wide end is indeed due to silicon based sensors. Even with advanced microlenses a modern sensor can not capture non-perpendicular light efficiently, leading to issues like colour vignette and detail smearing.

this has meant that the digital Leica's have to have an extreme combination of angled micro lenses and software fringing correction.

What is "angled micro lens"? The microlenses outside of the center are shifted to guide the light more efficienty to the proper photodiode, and in the case of the most recent Leica M, the microlens design itself also seems quite radical. Also that camera has no AA-filter to cause edge issues and the pixels are very large also to reduce edge issues.

With a fully corrected rear element, as Sony aptly demonstrated in the RX1, corner issues can be eliminated for a flat sensor.

What is a "fully corrected rear element"? I have to ask this because such things do not exist. All elements cause aberrations. To remove aberratiions you need to counter the aberrations created by elements by adding new elements with different aberrations. A good example is a simple close-up lens - a single element close-up lens will always cause pretty significant aberrations no matter how expensive, while a simple doublet (two elements glued) can reduce the total aberrations to very small amount.

And sensor flatness has nothing to do with the issue. The issue is about exit pupil. If the exiit pupil of the objective is close to the sensor, aberrations in the edges are likely. This is mainly an issue with wide angle lenses, thus the wide angles for digital tend to has exit pupil far from the sensor, them being retrofocus.

although the A7(r) does have a combination of software and micro lens adjustment(in the case of the A7R) it seems that correctly designed lenses, like the 55mm, deliver spectacular results.

What is a "correctly designed lens"?

it greatly surprised me to see the Sony Zeiss 55mm easily eclipsing the Leica 50mm Summilux in all aspects:

And if you see such result, you should wonder if the test was done well. It wasn't and it doesn't.


Massive focus errors. If the focus is 15 cm in front of the eye, the eye is soft. And looking at the full sized images, he seems to have focused manually lots to the front (to the front shoulder).

This is the real advantage of modern lenses - autofocus. While they are not perfect, they're better every year and special things like focusing to the eyes can be achieved very accurately if the firmware allows (assuming contrast detection is used instead of phase detection).

Also the performance of the Otis 55. Not only does this indicate that the modern "digitally designed" lenses are superior, that Zeiss appears to leading he pack of current lens design.

This tests indicates nothing like that. Having to design for digital is a handicap, not an advantage.

given the cost of Leica lenses, the nasty field curvature seems not worth it, especially with FF digital cameras.

There is no such nasty field curvature. Instead the optical stack in front of the digital sensor changes the length of the optical path differently depending on the angle light hits it. This causes slight defocusing in areas. Add the "normal" aberrations of the light hitting the lens non-perpedicular manner and no wonder the performance is reduced when the sensor and it's toppings (the optical stack above it, ie. microlenses, colour filter array and ofen, though not in this case, AA-filters) can't hadle light that is non-perpendicular well. This is where film has a big advantage.

In the future, hopefully, we will be seeing organic image detectors and this issue will go away (or be reduced lots, depending on the colour separation method).

i understand people with collections, and seeing the clarity of these lenses with smaller sensors, like the OM-D , Nex and Fuji series, but I am struggling why I should keep my 50mm Summilux asph ?

If you don't like it, sell it. Or better yet, donate it to me or some other good cause.

Summary: it is the limits of current sensor (and toppings) technology and lack of autofocus which are the issues, not the lens design.

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Copyright © Jay Ell

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