D800 left - center - right AF tolerance + green LCD

Started Jan 29, 2013 | Discussions thread
Leonard Shepherd
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Re: now some guidance used by some advanced photographers
In reply to Marc Heijligers, Jan 31, 2013

Marc Heijligers wrote:

Leonard Shepherd wrote:

As a guide the lines on the target should extend just beyond the top and bottom boundaries of your D800 viewfinder rectangle when using single point autofocus.

What a nonsense, what is the source of this type of information?

Maybe the Nikon D800 manual page 100 as usually. (just joking)

That page doesn't say anything about centring objects or fill viewfinder rectangles, so I'm curious what the source of Leonard's info is.

Suggested check one - stick a half an inch by half an inch piece of dark tape on a white wall, camera focused to give a 3' x 2' subject area. With the tape well outside the viewfinder press and hold the shutter release, slowly move the viewfinder rectangle toward the tape and see at what what position relative to the rectangle centre autofocus kicks in. This is how to find out where the autofocus lines can detect detail

The length of the detection lines varies from camera to camera; between single point and dynamic autofocus, and with extreme outer autofocus points. A minor detail - some older cameras need a one inch piece of tape for this check to work.

Suggested check two - place a fine detail reference subject well outside the focus area. This is your autofocus accuracy check. Then place a single narrow black line type target under the viewfinder rectangle and see how much focus variation there is when the single line is at the centre and then (starting from the same manually set focus distance) above and below the centre by checking when the reference target sharpness indicates correct focus may not have been achieved. This check helps learn which types of subject are best precisely centred.

Suggested check three - select auto area autofocus and try it indoors in low light with subjects at different distances. Note which red viewfinder marks illuminate, and which do not. You are likely to find some subjects you expect autofocus to detect do not illuminate.

Check two needs only to be done once. Checks one and three are the best way I know off of finding out whether the autofocus characteristics have changed each time you get a new camera body

Nikon give general guidance and, if you care to look for it on page 100, acknowledge sometimes when AF is not accurate MF can get better results. Nikon repeat this guidance on page 413.

I was giving specific guidance to a user who was having problems with a very specific and uncommon autofocus target.

Most learn early on that autofocus can focus on the background when there is a less than ideal target at the centre of the viewfinder mark, though Nikon do not specifically mention this on page 100. This type of "learning experience" helps clarify what and where something is placed in the viewfinder does have an influence in where autofocus chooses to focus with a few targets.

It is my experience the OP's target is one which has to be precisely centred covering a specific part of the viewfinder area to be sure it is giving a reliable result. This is probably why, repeating a previous detail, Nikon appear to use a test rig and a focus distance accurate do better than 2 inches

Most I think would agree becoming a proficient photographer involves more than just reading the instruction book. In much the same way, buying a music score is only one step in a less experienced musician becoming a proficient.

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Leonard Shepherd
Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.

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