Focus points - sizes and ways to focus?

JJ_SO

Two years ago I bought a D5100 after being switched to Nikon with a D7000. The sensor sizes are identical, the sizes of the focus points - or should I say "focus areas"? - are not.


100% view of both "focus point" marks shown in Aperture. Height of D5100 focus area is 1/7, width 1/3 of the D7000 area.

After 2 years using these cameras I still don't have a certain feeling about "what happens in these areas"? The small areas of the D5100 are sometimes great, when too much elements in different distances can be seen around the important focus target, so i can precisely aim at. And hope, I didn't move too much before pushing the shutter button. It's difficult to aim with tiny points.

On the other hand, although it's easier not to miss the focus target with the big areas of a D7x00 / D800, sometimes I really would like to know how I can help the AF doing the best it can do? What to do with targets which are smaller than the focus area? Which spot in this area is really deciding about sharp or second best sharp? I was looking in the manual and in a book about D7000, but this information is somehow hard to get.

PB_PM

The focus areas aren't a box or square, so that comparison is meaningless. Focus points have two shapes ( "+" cross type, or "|" vertical). The boxes are there to give you an approximate idea of where the point are.

JJ_SO

Thank you, PB_PM.

An approximate idea is not helping me much to be certain when I autofocus. In earlier days, with microprism ring and split-image indicator it was clearly visible what happens and in which direction the "line in question" has to be orientated. I found that helpful. The "blackboxes" of AF-points are not very helpful. "Here's something doing action for AF". Does somebody knows a link where I can find better information than the manuals provide? Even a book with the promising subtitle "what you don't find in the manual" marks the 9 AF points in the middle of D7000's finder as cross sensors. And two pages later it adds the surrounding 12 AF-points as well as cross sensors. Can't be, there are only 9 of them in technical data. If these cross types have a "+" shape, it's pointless to focus with hem on a horizontal or vertical line which is passing exactly the center of the plus - it better is a diagonal, right?

DJBee49

JJSO. Thom Hogan publishes a guide to your camera and will I am sure clarify the situation for you within it. His guides are excellent - easy to understand and highly informative. There is a link for you below.

/www.bythom.com/nikond5100guide.htm

spraynpray

Maybe you are over thinking this JJ. I find that if my focus locks solidly on the item I have it on then I'm good to go. If it is a subject where time is less important and I am uncertain about focus, I have the camera on a tripod and I use live view to zoom in to the exact spot so I can override with manual focus. You mention the old fresnel ring and split prism focusing screens - we all wish they were still around!

Shooting from the hip is always hit and miss to a small extent so I guess that is what instant manual override is for.

Then there is chimping...

JJ_SO

Thanks, DJBee49, I'll have a look into it.

Thanks spnp as well. "If it is a subject where time is less important and I am uncertain about focus" - then the tripod solution is a good one, but most of the time I am in such a situation, not doable because I need to stay mobile. I'm asking for the moments I see too much elements in the squarish boxes called AF-"point"