What happens when you use a 45MP camera with a 500mm F4? Any lapse in your technique shows up as slightly soft images! Honestly, this is user error more than anything. My 500mm F4 is razor sharp, and the D850 continues to amaze me on many levels including resolution. But one way to improve performance is to use Auto AF Fine Tuning.
Wait a second, am I saying the lens and/or camera are having sharpness issues. No, both items work perfectly fine. But what happens is when you pair a new camera with a new lens (meaning you haven’t used this combo before), you might have to fine tune where the lens focuses…it might just focus a little in front or back of your subject. All cameras and lenses have this issue, but we generally don’t see it as depth of field covers it up, and it is very slight. Most of my soft images using long glass are because I was shaky and didn’t shoot at a fast enough shutter speed.
But new Nikon cameras like the D5, D500 and D850 have an auto AF fine tuning feature that is very simple to use. The basic steps are
1. Set up a focus target like a magazine cover at the distance you normally use the lens. For my 500mm that was about 40 feet. Make sure you are on a stable tripod.
2. Next, use Live View and and focus on your target. Press and hold the AF-mode and movie-record buttons at the same time. This prompts a screen that asks if you would like to proceed and things are sharp. Hit Yes.
3. The next screen shows you the saved value. You can fine tune many different lenses, and these values are all stored for future use.
Do I really need to do this? If you find you have tack sharp images, then don’t worry about it. I noticed with 500mm that a few frames seemed slightly soft due to where the camera/lens focused. After determining that -7 was the right calibration, my sharp image ratio increased.