Author Topic: AFS 20 1.8G and optical performance (w/ D850)  (Read 6266 times)

Frode

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AFS 20 1.8G and optical performance (w/ D850)
« on: August 14, 2018, 21:03:24 »
My sample is tack sharp when using the center AF- point. No need for fine- tuning there.

However, when using any of the outer AF points (other than the 15 crossensors in the senter), I get soft focus (no matter what side). Need about -15 when using theese in order to get OK sharpness.

Been told that this is normal due to the strong vignetting.

Experience/thoughts?

Roland Vink

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #1 on: August 14, 2018, 22:16:58 »
Vignetting should affect image brightness, not sharpness. Field curvature and/or focus shift on stopping down maybe?

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #2 on: August 14, 2018, 23:13:09 »
Vignetting should affect image brightness, not sharpness. Field curvature and/or focus shift on stopping down maybe?

I have no idea, Roland, but field curvature sounds logic...? Used the lens wide open only.

Hmm, I miss the opportunity to compose in the viewfinder instead of cropping afterwards.

With the AFS 50 1.8G and AFS 85 1.8G, all focus points works just fine. With AFS 400 2.8 VR all but the last row at both ends works fine. Last rows are a bit soft.

Erik Lund

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #3 on: August 15, 2018, 08:03:34 »
Post a couple of images, then it's maybe possible to tell what is going on ;)
Erik Lund

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #4 on: August 15, 2018, 13:06:50 »
Did at non- scientific test of both my AFS 50 1.8G and AFS 20 1.8G. First out, the 50mm.

AFS 50 1.8G:
4927, AF center, 1.8

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #5 on: August 15, 2018, 13:07:25 »
AFS 50 1.8G
4928, AF left, 1.8

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #6 on: August 15, 2018, 13:08:02 »
AFS 50 1.8G
4929, AF right, 1.8

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #7 on: August 15, 2018, 13:08:48 »
AFS 50 1.8G
4930, AF right, 2.5

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #8 on: August 15, 2018, 13:09:26 »
AFS 50 1.8G
4931, AF left, 2.5

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #9 on: August 15, 2018, 13:10:07 »
AFS 20 1.8G
4974, AF center, 1.8

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #10 on: August 15, 2018, 13:10:46 »
AFS 20 1.8G
4975, AF left, 1.8

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #11 on: August 15, 2018, 13:11:22 »
AFS 20 1.8G
4976, AF right, 1.8

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #12 on: August 15, 2018, 13:12:28 »
AFS 20 1.8G
4979, AF left, 5.6

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #13 on: August 15, 2018, 13:13:00 »
AFS 20 1.8G
4981, AF right, 5.6

Frode

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Re: AFS 20 1.8G and optical performance (w/ D850)
« Reply #14 on: August 15, 2018, 13:13:57 »
Had to stop down the 20mm to 5.6 in order to get ok sharpens, f/4 was not sharp enough.