Help on focus.

I seem to have a focus problem, me or camera. When I have a subject at a distance let’s say full body in frame using a low aperture such as 1.8 or 2 in aperture priority outside light, single point and single servo with a 35mm lens and I move the focus square to the face of subject and take the shot many times or most times the focus point seems random. It may be to the right of left, front or behind the subject. I thought it was to be where you move the square to. I have done this with two different lens is why I think it’s the camera. Camera is a d7100. Lens are 35mm Nikon and a 50-150 sigma 2.8.
Just to add when I take a shot close up it seems to work OK but it seems the focus has never been perfect on camera but i thought it was just me.
Think I am doing something wrong or send the camera back?
Thanks Rich.

At 1.8 or 2 f-stop your depth of field will be very small. If you are shooting AF-S, it locks focus at the moment you half-press the shutter button (or the back button focus button, if you do that).

In my experience doing this, I discovered that I would move a little right before firing the shot. In other words, shooting handheld (no tripod), I was locking focus but then rocking forward or back just a tad when firing the actual shot. That moved the focus point. With such a narrow depth of field, the results will be evident.

At the distance you are describing, there is little to be gained by shooting so wide open, unless you are in very low light. Bump that aperture to f 5.6 and see what happens, or change to AF-C so the camera keeps adjusting focus right to the moment you fire.

Also, you might check the fine-tuning of your lens. There are many threads on this, but basically there is a menu setting that lets you calibrate each lens independently for your body. The most common way is to set up a ruler at an angle, focus on a precise point (say the 6 inch mark), then see what part of the ruler is in best focus. You then change the focus calibration in the menu so that the camera learns to move the focus forward or backward so that the spot you want is the spot that's in focus.

I plan on doing the fine tune soon. Thanks for the reply I think you are right on i need to bump it up some and be more still lol getting older and not as steady the wife likes the blur to the background but it seems to also soften things to much. After looking at the photos more I also feel that i need to learn to adjust for light and shadows better and make some adjustments in the camera some shots just look washed out or pale.

A few things to mention.

Make sure you are in actual single point focus mode and not just seeing a single point in the viewfinder. That's on my mind because somebody asked about that recently. They were concerned because they only saw a single point even though they were in 9 point mode. Sounds like you got it right, but worth mentioning just in case.

In your playback menu, you can set the camera to show your focus point highlighted when you playback your image. That might help you figure out the problem.

Also make sure your af-s servo mode is set for focus priority. That is the default for af-s, so if you haven't messed with it, it should fine. If it was in release priority, you could get random focus since the shutter could fire before the focus settles.

As for washed out pictures, make sure you are in matrix metering mode. You still might need to adjust things for conditions, but if you accidentally left the camera in spot or center weighted metering, you can get unexpected results.

Definitely look into AF fine tune. I was not enjoying my Tamron 70-200mm at f2.8 but once I did the tune, that lens now looks amazing wide open, the way I expected it to look. I've tried FoCal but hated it and it didn't really help. I bought a $5 AF target on Amazon and just set it up with my tripod and did it manually which really didn't take long.

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