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

[Frode]

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.

Thank you, Ilkka :-)

Yes, it might be that I need to send it in (recalibrate and re- adjust the AF points?). Still like to hope that there's "a way out"....

I dont expect the D850 to have the same performance as the D5 regarding AF, but hoped it would be as good as the D4s (don't feel I can "trust" the camera yet).

Usually I use my gear in good lighting conditions (fast shutter speed and low iso), but worst case scenario would be like indoor (dark outside), tungsten light, portraits of people (almost static) and exposures like 1/250, f/1.8- 2 and iso 6400- 12800. Not often though. In such conditions I don't have to high expectations, but would like to feel a bit more secure on how the camera works (AF).

I like to use my 20mm relatively close up to my main subjects (in order to get a view of the environment also, though often isolated using a large aperture like f/1.8- 2.. Main subject is often a person or animal/bird. Distance often between 1- 3 meters.

The way I've used my Nikons so far: if cross sensor af points are being used then I aim the af- sensor at area where there's vertical lines of contrast. When using the other af- sensors I go for horizontal lines of contrast.

With my former D4s I found that the coverage of the af sensors was 1/3 outside of the visible af point, at all four directions. With the D850 (so far...), it looks like it covers a lot more space outside the af sensor, making it hard to know what to expect to be in focus. I feel like I have to check every photo in order to see if it`s in focus or not. I felt I could trust my D4s a LOT more.

Looking forward to hopefully "trust" the camera again, it`s a great camera in many ways!

[Frode]

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.

Hmmm, I've got to get my hands on a better AF target and do a new test, because so far my impression is that the fields are MUCH bigger with my D850 compared to my former D4s.

[Ilkka Nissilä]

Hmmm, I've got to get my hands on a better AF target and do a new test, because so far my impression is that the fields are MUCH bigger with my D850 compared to my former D4s.

This doesn't sound right. I've found with the D810 and earlier cameras that when pointing a single sensor at a face in whole body portrait, that the camera would often focus on the backlit hair instead of the eye that I pointed the sensor at. This doesn't happen with the D5; I get very precise focusing on the face and the sensitivity of the AF sensor doesn't extend to the hair. In fact I can focus on the cheek's imperfections and it just locks on and holds focus. The D850 is a bit of a mystery as it doesn't do quite as well in tracking an approaching subject though it seems the AF sensor has similar sensitivity and characteristics. It's a bit like the camera lacked the power to do as fast tracking of a moving subject as effectively.

But the sensitive field of the individual sensors in the D850 in single point mode should be much narrower than on a D4s or D810.

What could be causing the impression that you're getting is the fact that the camera can see detail even in white surface if it has any structure to it, it doesn't need the line to focus based on, just some low-contrast structure (surface imperfections) can be enough. Of course high contrast detail is better but it can focus on relatively low contrast details also.

I generally point the single sensor on an eye but if I use D9, I often just point the primary point on the cheek, and it can hold focus very well without being attracted to the hair around the face.

Edit: I am just reviewing photos made with the 105/1.4 and D850 and I find that almost perfect focus when I was using 3D Tracking (with face priority) and this is really a positive surprise. So, 3D tracking and moving subjects, and single point or D9 on static subjects works extremely well, but for some reason I get inconsistent results with single point and D9 on faster approaching subjects. I should probably stop complaining and learn to use the camera. :-)

(Sorry for getting off-track. I will investigate the 20/1.8 this coming weekend.)

[Frode]

The way I see it my D850 does seem to have about the same "problem" as the D810 (focusing on the face = sharp on backlit hair). Though, I must do some further testing in order to be certain. Suspect user error (af point to big compared to the contrast area it was pointed towards).

Regarding tracking compared to D5 (or any one digit bodies) other bodies do seem to lack some "juice". That be cameras like D700 (vs D3) and D810 (vs D4/s). In my opinion.

I tried to focus on the white area on the target used earlier (white paper with a black line), but it didn't lock until it got closer to the line. Non variable in structure/contrast in the white as far as I can see. Against a black cover (notebook) with some fine structure it locked though.

As far as I can remember the size of the af sensor in the viewfinder was bigger with my D4s compared to the D850 (?). In that regard the sensitive field might be narrower?

Hmm, regarding focus on relatively low contrast detail, I wonder if I have to high expectations? Can you describe what what you consider low contrast detail?

I`ve had good experience with D9 (blocked shot AF response set to 2) when photographing kids playing football (soccer) with my AFS 85 1.8 (yes, not far from the field :-).

Yesterday evening (low light) I found that the two columns at both sides, which according to Nikon are cross sensors, are clearly more precise when pointed at horizontal lines of contrast compared to vertical. Yes, they do react at vertical lines, but compared to the three center columns with cross sensors, they clearly hunted where as the center sensors didn't hunt at all (4EV vs 3EV?). The outer points locked focus when pointed at horizontal lines. Same with the other four columns with "standard" focus points (black ones - which didn't lock focus at all when pointed at vertical lines of contrast).

Please dont be sorry for getting off- track, always interesting to read about others experiences  .

I should probably be the one who should stop complaining and learn to use the camera  . Working on it..... 

[Frode]

Doing some more testing today (using my last summer vacation days.....) and I'm leaning toward the assumption that the camera needs to be calibrated (phase detect sensor alignment problem). Will send it in.