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Sony 20G on Nikon bodies - soft edges

snapsy
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p.1 #1 · p.1 #1 · Sony 20G on Nikon bodies - soft edges

Cross-posting on both Nikon and Sony boards...

I own a sharp and well-centered copy of a Sony 20G f/1.8. I shoot it on an A7rIV but purchased the lens to use on my Z7 as well with a Megadap ETZ21.

The 20G is sharp to the edges wide-open on the A7rIV but is very soft on both edges on the Z7, at least until around f/5.6. I've tried it with two different Megadap adapters and on two different Z7 bodies, so it doesn't appear to be a tilted adapter or camera mount. I've also eliminated Sony lens corrections as the difference by stripping out the Sony correction profile and not observing any difference in the edges (this lens have very little distortion).

I also tried it on a Z6 and see similar softness, although it's less noticeable due to the lower MP.

I don't see this on narrower focal lengths, for example on the 50GM f/1.2

Sony 20mm @ f/1.8, Center of Frame, A7rIV vs Z7, 100% Crops
Sony 20mm @ f/1.8, Left Horizontal Edge of Frame, A7rIV vs Z7, 100% Crops

Any ideas? My only guesses are the adapter design, or that the the Sony has offset microlenses to account for the periphery of this lens design but I don't recall ever reading that to be the case.

Edited on Feb 09, 2024 at 11:49 AM · View previous versions

Feb 08, 2024 at 11:26 AM

Kasper6188
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p.1 #2 · p.1 #2 · Sony 20G on Nikon bodies - soft edges

Maybe the sony bodies have a baked in corner fix applying behind the scenes? Just a thought

Feb 08, 2024 at 11:35 AM

RoamingScott
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p.1 #3 · p.1 #3 · Sony 20G on Nikon bodies - soft edges

Kasper6188 wrote:
Maybe the sony bodies have a baked in corner fix applying behind the scenes? Just a thought

That's absolutely correct for many of the smaller recent Sony lenses, and the 20G is no exception. I was always shocked at how much correction it needed. Sony "cheats" optically but "fixes" it to serviceable levels via software corrections.

Now whether that's the case with this particular situation, who knows.

Feb 08, 2024 at 11:42 AM

snapsy
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p.1 #4 · p.1 #4 · Sony 20G on Nikon bodies - soft edges

RoamingScott wrote:
That's absolutely correct for many of the smaller recent Sony lenses, and the 20G is no exception. I was always shocked at how much correction it needed. Sony "cheats" optically but "fixes" it to serviceable levels via software corrections.

Sony bakes in vignetting correction into the raw (at least they used to - haven't checked recently) but I've never seen evidence that they bake in distortion correction as well. The raws produced on my A7rIV with this lens have a distortion correction profile attached, which I stripped off during my investigation to exclude that as a cause.

Feb 08, 2024 at 11:45 AM

nhmorgan
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p.1 #5 · p.1 #5 · Sony 20G on Nikon bodies - soft edges

Shooting a lot of astro, I've noticed that adapters tend to not play well. I think it is often an issue of back focus not being quite right. I owned a 14mm 1.4 Sigma that was fine on Sony, but soft in the edges on Nikon with the megadap. Like you, I also found the 20mm wasn't as good on Nikon as it was on Sony. Even with Nikon's own FTZ adapter, I've found that the corners are more problematic on Z bodies than F bodies with the sigma 40mm. The one exception this this as the Sony 14mm GM, which played very nicely with my z7.

Feb 08, 2024 at 11:54 AM

Kasper6188
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p.1 #6 · p.1 #6 · Sony 20G on Nikon bodies - soft edges

Another thought. Sony uses a thicker filter stack. In my experience with Leica glass and adapting to various other systems, the wider the lens the more the stack thickness matters in the corners.

Feb 08, 2024 at 11:55 AM

Creative Edge
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p.1 #7 · p.1 #7 · Sony 20G on Nikon bodies - soft edges

I use Canon glass adapted on my Z9 and I have found the glass I use to work just as well as the F mount glass.
I have never not seen any soft edges even on the wide angle glass (16-35 2.8III)
I think it has more to do with something going on on the Sony side and not with adapting glass to Nikon as a whole.

Feb 08, 2024 at 12:31 PM

j4nu
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p.1 #8 · p.1 #8 · Sony 20G on Nikon bodies - soft edges

Kasper6188 wrote:
Another thought. Sony uses a thicker filter stack. In my experience with Leica glass and adapting to various other systems, the wider the lens the more the stack thickness matters in the corners.

I also think that's it. Distortion correction can be disabled in LR or other RAW processor, so it's not the matter of Sony baking the RAW in this case (that's easy to check by taping the contacts too).

Feb 08, 2024 at 01:17 PM

tsdevine
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p.1 #9 · p.1 #9 · Sony 20G on Nikon bodies - soft edges

Sony can’t magically make a lens sharp on Sony. It’s either flange distance tolerance related on the adapter side, or cover glass thickness difference, or both.

Feb 08, 2024 at 01:49 PM

Kasper6188
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p.1 #10 · p.1 #10 · Sony 20G on Nikon bodies - soft edges

tsdevine wrote:
Sony can’t magically make a lens sharp on Sony. It’s either flange distance tolerance related on the adapter side, or cover glass thickness difference, or both.

With modern processing power I don't see why any company couldn't write some sort of algorithm into the camera to complete the formula. FW updates add lens compatibility all the time, who really knows what's going on behind closed doors

Feb 08, 2024 at 02:20 PM

tsdevine
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p.1 #11 · p.1 #11 · Sony 20G on Nikon bodies - soft edges

I can show you a RAW from the 20-70 G that has black corners. All the corrections are done in Lightroom to make it look good.

If Sony can make any lens sharp corner to corner at any aperture via firmware, then great, I’d love that. But they’re not doing it with a lens that is even newer than the 20G..

Sony a7R V + Sony 20-70 f/4 G RAW file processed in Lightroom with distortion correction off.

Same corrected in Lightroom.

The OP should be able to pick the 20 G profile in Lightroom (other RAW converters I can't say exactly how you would do it, but other than DxO I would think it generally should be possible).

I do think the cover glass thickness and/or flange distance fluff that is added for tolerence purposes with the adapter are probably the most likely culprits.

Kasper6188 wrote:
With modern processing power I don't see why any company couldn't write some sort of algorithm into the camera to complete the formula. FW updates add lens compatibility all the time, who really knows what's going on behind closed doors

Edited on Feb 08, 2024 at 02:50 PM · View previous versions

Feb 08, 2024 at 02:25 PM

snapsy
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p.1 #12 · p.1 #12 · Sony 20G on Nikon bodies - soft edges

Kasper6188 wrote:
Another thought. Sony uses a thicker filter stack. In my experience with Leica glass and adapting to various other systems, the wider the lens the more the stack thickness matters in the corners.

I always assumed the issue was limited to going to a thicker stack rather than thinner but perhaps that's not the case, esp if the optical formula is highly tailored to a specific distance.

Feb 08, 2024 at 02:48 PM

tsdevine
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p.1 #13 · p.1 #13 · Sony 20G on Nikon bodies - soft edges

If you modify the Sony stack, like with Kolari, it can hurt the performance of some native lenses. Full disclosure I don't have first hand experience, but I don't think I'm going out on a limb there.

snapsy wrote:
I always assumed the issue was limited to going to a thicker stack rather than thinner but perhaps that's not the case, esp if the optical formula is highly tailored to a specific distance.

Feb 08, 2024 at 02:52 PM

snapsy
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p.1 #14 · p.1 #14 · Sony 20G on Nikon bodies - soft edges

tsdevine wrote:
If you modify the Sony stack, like with Kolari, it can hurt the performance of some native lenses. Full disclosure I don't have first hand experience, but I don't think I'm going out on a limb there.

Thanks. When I read your post I did a search for Kolari and found this:

https://phillipreeve.net/blog/review-kolari-ultra-thin-sensor-stack-modification/

Feb 08, 2024 at 02:56 PM

tsdevine
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p.1 #15 · p.1 #15 · Sony 20G on Nikon bodies - soft edges

Great resource there. Notice the following in the summary.

"Decreases performance of some native lenses"

So if moving from a stock Sony sensor to a Kolari modded sensor with thinner cover glass can decrease the performance of some native lenses.....then I think it's logical it could do the same when adapting to Nikon which has thinner cover glass than the Sony stock sensor.

snapsy wrote:
Thanks. When I read your post I did a search for Kolari and found this:

https://phillipreeve.net/blog/review-kolari-ultra-thin-sensor-stack-modification/

Feb 08, 2024 at 03:00 PM

snapsy
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p.1 #16 · p.1 #16 · Sony 20G on Nikon bodies - soft edges

tsdevine wrote:
Great resource there. Notice the following in the summary.

"Decreases performance of some native lenses"

So if moving from a stock Sony sensor to a Kolari modded sensor with thinner cover glass can decrease the performance of some native lenses.....then I think it's logical it could do the same when adapting to Nikon which has thinner cover glass than the Sony stock sensor.

Yep, read that. They also mention it affects wide and fast glass more. The widest native lens that article tested was 35mm

This is interesting because I've never seen any online posts comparing or warning about the cover glass differences affecting FE lens performance on Z bodies (with an adapter). Or perhaps I missed it. Makes sense. If there were no previous posts on this issue then this thread can serve as the first.

Feb 08, 2024 at 03:05 PM

Aztatlan
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p.1 #17 · p.1 #17 · Sony 20G on Nikon bodies - soft edges

This is without a doubt related to adapter thickness or cover glass thickness or both. I've seen the same issue adapting some F mount lenses to E back in the early days. In that case, the adapter was slightly too thin, which is often by design as it allows the tolerances needed to reach infinity focus (if adapter is too thick, you can't.)

Feb 08, 2024 at 05:25 PM

Alistair1
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p.1 #18 · p.1 #18 · Sony 20G on Nikon bodies - soft edges

Is the field of view wider than 20mm by any chance?

Feb 08, 2024 at 08:08 PM

snapsy
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p.1 #19 · p.1 #19 · Sony 20G on Nikon bodies - soft edges

Here's a comparison with the Sony 20-70 f/4 @ 20mm f/4. This lens doesn't exhibit the edge softness of the 20mm f/1.8, which even at f/4 shows edge softness on the Z7 vs A7rIV.

Sony 20-70mm @ 20mm f/4, Center of Frame, A7rIV vs Z7, 100% Crops
Sony 20-70mm @ 20mm f/4, Right Horizontal Edge of Frame, A7rIV vs Z7, 100% Crops

Feb 09, 2024 at 11:26 AM

tsdevine
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p.1 #20 · p.1 #20 · Sony 20G on Nikon bodies - soft edges

Incident angle can aggravate the difference in stack thickness. So it is possible that you see different degradation between the 20 G and 20-70 G. If the light is directed at a steeper angle on the 20 G towards the edges and corners, compared to the 20-70 G @ 20......there can be a larger impact to a thinner stack when you compare the two lenses. Again, what I said above though could make sense, if the lens design of each lens has a different incident angle as the image is being projected onto the sensor.

That's part of the reason that "some" lenses can have degradation that was noted in that article you linked to. The wider the lens, often the steeper the incident angle. But even within wide angles there can be variations in the design, it can be worse on some than others. And faster lenses need larger front elements, so they often have higher incident angles as a result. The longer the focal length, the incident angle may not be as high just by the nature of it being a telephoto.

I believe what I described is a plausible reason for what you are seeing, but I have no way to prove it. I would assume the degredation on the 20 G is worst wide open and slowly gets better as you stop down. How much worse is the 20 G (vs stock Sony) vs the 20-70 G @ 20mm (vs stock Sony) when both lenses are at f/4? If the 20 G seems to degrade more, it may just be a higher incident angle.

snapsy wrote:
Here's a comparison with the Sony 20-70 f/4 @ 20mm f/4. This lens doesn't exhibit the edge softness of the 20mm f/1.8, which even at f/4 shows edge softness on the Z7 vs A7rIV.

Sony 20-70mm @ 20mm f/4, Center of Frame, A7rIV vs Z7, 100% Crops
Sony 20-70mm @ 20mm f/4, Right Horizontal Edge of Frame, A7rIV vs Z7, 100% Crops

Edited on Feb 09, 2024 at 12:39 PM · View previous versions

Feb 09, 2024 at 12:30 PM

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