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Nikon 20mm Falloff Comparison (on FX)
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February 2008

This compares the falloff of every 20mm SLR lens ever made by Nikon for film or FX digital. Most of you may not care about FX today, but when Nikon brings out an affordable full-frame digital, you will.

I could have shown this for DX digital, but didn't bother because it's not particularly relevant (NPR). It's silly to use these big 20mm ultrawide FX lenses on DX because there are so many better ways to get 20mm in DX, like the 12-24mm DX or the 18-55mm AFS kit lens.

If you care about DX, the falloff doesn't matter for these lenses, since DX only uses the central area. Look at the images below, and you'll see any significant falloff happens outside the DX area (see FX vs DX for the relative sizes).

 
f/4
f/5.6
f/8

UD
       

 

 

*The 14-24mm can't take a flat front filter so I couldn't use an expodisc for this test. I have to go buy more hardware to test this sort of lens.

Analysis

No big deal, stop down two stops and they're all the same over the past 40 years. Don't confuse a third of a stop here or there of exposure variation for differences in falloff. For instance, the 20mm f/2.8 AF looks like it's worse than the optically identical 20mm f/2.8 AI-s wide open, but in fact, it's just a small difference in exposure. I could have re-shot this to make that go away, but that's cheating (actually I would have, but I'm too lazy).

The f/4 and f/3.5 lenses look a little worse at f/5.6, but that's because that's only one stop stopped down for an f/3.5 lens, but two stops stopped down for the faster f/2.8 lenses.

 

Maximum Apertures

20mm UD: f/3.5.

20mm f/4 AI: f/4.

20mm f/3.5 AI: f/3.5.

20mm f/2.8 AI-s: f/2.8.

20mm AF: f/2.8.

20-35mm: f/2.8.

17-35mm: f/2.8.

18-35mm: f/3.5.

14-24mm: f/2.8.

 

PLUG

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Thanks for reading!

Ken

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