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Other lens use on A7R (II)


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And a lot of other cameras (including top of the line Canon and Nikon cameras) use the same Sony sensors. So a lens that performs well on a Sony performs equally well on those.

All digital cameras have a cover glass on the sensor, typically 2 mm thick (m43's cover glass is twice that).

 

The Sony company that makes sensors, by the way, is not the same Sony company that makes cameras.

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I believe the 'thick' glass was intended by Sony to ease the telecentricity issue, as well as absorb colour-distorting IR. When acute oblique rays pass through the glass they're deviated inwards a little. Effectively moving the exit pupil of the lens forward slightly.

 

That short back-focus lenses and microlens arrays don't play nicely together is a well known phenomenon, and Leica had to offset their microlens and Bayer array from the sensor photosites to make the IQ of their existing wide angle lenses acceptable.

 

That's why there are very few non-retrofocus wide angle lenses produced today for mirrorless digital cameras. The short flange distance makes their use possible, but not necessarily desirable.

 

Film, OTOH, just covers up a multitude of optical sins.

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Thick glass is also (only?) used to create distance between dust and the sensor. That makes dust appear more diffuse.

 

The shift in focus due to glass between lens and sensor is about 1/3 of the thickness of the glass. But with plane glass, the shift depends on how oblique the rays are, so plane glass introduced spherical aberrations.

The degree of that depends, indeed, on the exit pupil position. So it not only changes between lenses, but also with focus.

 

Having said all that: the difference between cameras, or sensors rather, in this regard is small. Yes, some (m43) have much thicker covers.

Not all Sony sensors (to name but one) are equal, and a lens made to perform well on one sensor has to deal with the different thickness of covers on other Sony sensors. But there is not that much to worry about. Yes, the difference between a slightly sub 2 mm glass and a more than 4 mm cover is quite big. But if you try an old lens, not made for sensors with covers on a m43 and a A7 (whichever one), the difference in performance you will see is not due to the lens.

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The Leica M8 had a cover glass 0.8 mm thick, and suffered from excessive IR sensitivity. I owned a Nikon D2H, which had a similar problem. In both cases, an IR absorbing filter improved the images. This was corrected in the M9 to about 1.3 mm. IR sensitivity was reduced, at the expense of corner sharpness with lenses 50 mm or shorter, and noticeable vignetting and color shifts at the corners. While vignetting and color shifts can be corrected in the camera, focal distortions cannot.

 

Here are results of a test I conducted with a Sony A7ii and various lenses.

 

201372828_NikonAIS50mmTest.thumb.jpg.06720f3c0857455cf9f7fd5902a70d48.jpg 819100584_Loxia50mmTest.thumb.jpg.3c27bf9882d8a84dd7ee4be1a0f19864.jpg 1023624441_Summicronv250mmTest.thumb.jpg.f2dbfc156eb4f86e5a2e9dc1d932739b.jpg

 

1299950985_Loxia50mmTest.thumb.jpg.6112043d71e8a952b98289c24bf5b9e0.jpg

 

741763185_Summicronv250mmTest.thumb.jpg.31b6a31a2a1efa738e21235cdd538b88.jpg

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Gee, that Summicron really is a bit poor!

 

I just bought a 50mm f/1.8 YongNuo in Nikon mount out of curiosity (it was so cheap my arm was virtually twisted to take it). A quick test showed why it was so cheap, but it performs about as well as that Summicron by the look of it.

 

P. S. Is the duplication of Loxia and Summicron results an error Ed? Or were there supposed to be more and different tests?

And I hope the inability to remove excess pictures in an edit has been corrected in the new format of PN.

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I tested a Nikon 50/1.4 AIS at the same time. In reflection, I did have a 55/2.8 Micro, but didn't think to test it. The Nikon did pretty well, probably because it has a long back focus distance, which reduces the angle of incidence at the sensor, hence the distortion caused by the cover glass.

 

784017546_NikonAIS50mmTest.thumb.jpg.e2b16987743961e231ed85245e665bd0.jpg

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it has a long back focus distance, which reduces the angle of incidence at the sensor, hence the distortion caused by the cover glass.

Hmmm. Not totally convinced that Sony's sensor is completely at fault here.

 

I just ran a quick comparison of how my collection of 50mm lenses perform on Nikon bodies and on the A7r4. In my estimation - not much differently. The wide open SA 'halo' on the f/1.4 AIS, f/1.8 AF and AF-D, and that of the YongNuo f/1.8 are almost identical on a D800 and D7200 too. As is the Loca that's visible on all those 50mms until about f/4.

 

An old pre-Ai 50mm f/2 Nikkor is only slightly better wide-open and performs much the same across Nikon and Sony platforms. Showing its slightly lesser faults on an equal-opportunity basis.

 

In fact all the Nikon lenses that I tried on the Sony, via an adapter, revealed their inherent optical aberrations very similarly. Nothing novel or exaggerated appeared on the Sony, apart from a little additional flare in a few cases.

 

OTOH, those lenses that performed well on the Nikon bodies also performed well on the Sony. No additional colour fringing or other artefacts revealed themselves. Except that a 60 megapixel sensor shows optical faults a lot easier than does a 36 megapixel one. But the similar pixel density of the DX D7200 is pretty revealing too, obviously only over the centre of the image circle though.

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My results are consistent with the effect of a thick (2 mm) cover glass. Zeiss Loxia lenses are designed as though the Sony cover glass were part of the lens. LensRentals inserts a clear glass filter in order to evaluate this lens, and similar dedicated lenses. The back focus distance of the Leica lens increases the angle of inch toward the edges of the field. The Nikon lens has a long back focus distance to clear the mirror of an SLR. While the 50/1.4 is not a stellar lens, it outperforms the Summicron in this case.

 

I compared a Leica Summaron 35/2.8 lens with a Loxia 35/2, with even more pronounced differences. On the other hand, a Summicron 90/2 had no signs of edge deterioration, nor did a Loxia 85/2.8, Sony 90/2.8 Macro, or Zeiss Basis 85/1.8.

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LensRentals inserts a clear glass filter in order to evaluate this lens, and similar dedicated lenses.

Where, and on what?

Surely they should just be using a Sony camera.

 

Thing is, that those short flange-distance Leica wideangle lenses were never designed to be used with any digital sensor, just with film.

 

I'm pretty sure that if they could somehow be stuffed close enough to focus on a Nikon or Canon sensor, then the result would be little different from those on a Sony. I don't have a Nikon MILC so I can't test that.

 

There are a few native Sony lenses that have a rear element close to the lens mount, but mostly this appears to be a negative element or group designed to increase the effective distance of the rear node. It's all about telecentricity, or getting as close to it as possible. Which is why all the hoo-hah about Nikon's 'large diameter/short flange-distance' Z mount is mostly hype and flim-flam. Those pesky sensor microlenses just don't play nicely with a short back-focus. No matter who makes the sensor.

 

Pity the Foveon design seems to be a dead duck.

Edited by rodeo_joe|1
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