AFS 20 1.8G and optical performance (w/ D850)

[Erik Lund]

Are these crops? if not, you must be almost at closest distance, with what follows of implications,,,
Where was the AF-focus points in the images? I get its left and right, but where exactly,,,

Do you notice the field curvature and vignetting?

[Ilkka Nissilä]

No, not normal. I get very consistent AF with this lens.

[Frode]

Are these crops? if not, you must be almost at closest distance, with what follows of implications,,,
Where was the AF-focus points in the images? I get its left and right, but where exactly,,,

Do you notice the field curvature and vignetting?

No crops, not at THE closest distance, but not far from either.

Colored the area where I focused - good point, Erik  .

I dont know what I notice anymore, must say I'm a bit frustrated regarding the D850 and its AF combined with MY lenses. It`s hit and miss. Can't say that I trust these combinations, would NEVER do a wedding the way things are right now.

Thank you for your response.

[Frode]

No, not normal. I get very consistent AF with this lens.

Hmm, not what I wanted to hear....
 
Raptor- season closing in, but the way tings are right now, I'm considering trading in my Nikon- stuff. I really love to photograph, especially when out in the nature, but I'm so fed up spending time with gear (expensive - for me any way) that doesn't work as it should. I'm absolutely NOT impressed with D850 and its AF (with my lenses :-).

Thank you for your response :-).

[Frode]

D850 + AFS 20 1.8G, AF- S, single AF mode:

Looks like the AF coverage of a single AF point is MUCH larger than it appears in the viewfinder. Pictures shows where I got AF- lock.

About the same result with the other AF points.

Other D850 users, do you have the same "performance"?!

[Erik Lund]

You need to us better AF targets for such a test, and not that close up.
And yes the sensors are wider/larger than indicated in the viewfinder.
They are also different kinds, cross and straight.
A single black line is also a very bad target for AF Sensors,,,

[Frode]

You need to us better AF targets for such a test, and not that close up.
And yes the sensors are wider/larger than indicated in the viewfinder.
They are also different kinds, cross and straight.
A single black line is also a very bad target for AF Sensors,,,

Thank you again, Erik.

Regarding AF targets, I looked up Nikon and found that such "easy" targets was ok to use (?). Se links below. For the record, I focused through the viewfinder :-).

https://nps.nikonimaging.com/technical_solutions/d4s_tips/af_fine-tuning/
https://nps.nikonimaging.com/technical_solutions/d850_tips/useful/auto_af_fine-tuning/

The AF sensors were a bit bigger than they appear in the viewfinder with my former D4s also, but not THAT big.

Yes, with my lenses (1.8 and 2.8 lenses) the three middle rows and last two in both ends (left/right) are cross sensors, reading vertical AND horizontal lines. Other just horizontal lines. Took it into account when performing the "test"  .

Also, got the same result when focusing further away from the target.

[Erik Lund]

The sensors don't "read" lines, they see contrast.
I don't think that your thin lines are equal to the broad fat lines of Nikons sugessted.
Didn't you use AF? You state: "focused through the viewfinder" ?

[Nikfuson]

Remember the "invisible" af sensors:

[Frode]

The sensors don't "read" lines, they see contrast.
I don't think that your thin lines are equal to the broad fat lines of Nikons sugessted.
Didn't you use AF? You state: "focused through the viewfinder" ?

You’re probably right about my target, Erik.

Yes, it’s the contrast the sensors see.

My bad, yes I used AF (not via liveview  .

Went to my local store today; my copy of the 20mm was soft at the edges compared to a sample they had. Bought a new one. Much better.

[Frode]

Remember the "invisible" af sensors:

Thank you  ,

Yes, it might be the «invisible» AF sensors that makes the «active» AF area somewhat bigger (?).

Wish I could turn them of when needed, though.

[Ilkka Nissilä]

I dont know what I notice anymore, must say I'm a bit frustrated regarding the D850 and its AF combined with MY lenses. It`s hit and miss. Can't say that I trust these combinations, would NEVER do a wedding the way things are right now.

I don't suppose it would be possible to have Nikon service take a look at your camera and lens?

Regarding the D850, the AF on moving subjects is slightly disappointing with my fast primes (compared to D5) but very good on stationary subjects such as portraits. With the D5 the AF results make me speechless in many cases.  The D850 is very sensitive and good in focusing but somehow with moving subjects I tend to get less consistent results than with the D5.

AF tends to be better with longer focal lengths than shorter ones. But I've been very pleased with the 20/1.8 AF-S's autofocus in general (using on D810, D5 and D850). It's fast and consistent in focusing, and much much better than the 14-24/2.8 or 24/1.4. Aesthetically I prefer the 24mm f/1.4's "look" but the 20mm for AF consistency.

I can do some further experimentation with the 20mm f/1.8 and D850. How low lighting conditions are you expecting to use yours in? In very low light there can be additional variation in AF results. I can try in similar conditions.

I think for formal AF tests I would preferably use the kind of distance range where your normal shots are in. E.g. with 20mm I would use a 2m distance to target, maybe 3m.

[Ilkka Nissilä]

If you use single point, the system uses a single point, the invisible points are only used when a larger area is selected. The in between points are displayed in the viewfinder as dots if you select 9-point dynamic area, for example.

In practice the AF receptive fields in multi-cam 20k are much smaller than in the multi-cam 3500.

[Bent Hjarbo]

The sensors don't "read" lines, they see contrast.
I don't think that your thin lines are equal to the broad fat lines of Nikons sugessted.
Didn't you use AF? You state: "focused through the viewfinder" ?

Phase detection in normal mode and contrast in live view.

[Erik Lund]

Yes they have nice names for it