canon - Can I set a button to a particular focus distance on 5DIII (and ML)?

Can I, by simply pressing a button, set the autofocus to a precise, pre-registered distance value ? ( and then, I guess, lock AF ).

The goal is simple: Hyperfocal - On my zoom lens, there are no steps between 1m and infinity and it is impossible to judge to focus distance this way.

The only way I actually have is to keep a piece of string with the wanted precalulated hyperfocal focus distance and autofocus on the end of that string. But in practice, in the situations I will be in, that will be impossible.

Friend of mine said he can actually do that with his old Pentax.

I looked everywhere in canon menus, everywhere in Magic Lantern menus, but couldn't find anything like that.

Is that possible ?

Answer

With the Canon system pre-set focus distances are registered in the lens, rather than the body. The only lenses of which I am aware that offer this feature are the Super Telephoto series. But even those lenses wouldn't really help you very much for what you say you want to do.

There is no single hyperfocal distance for a given lens at a given focal length. Changing any one of several parameters will also change the calculated hyperfocal distance. These parameters include: aperture, sensor size, intended display size, intended viewing distance, etc. Change any one of them and the hyperfocal distance also changes.

For example, I can figure the hyperfocal distance for my 100m lens set at f/8 mounted on my Canon FF camera and based on and intended display size of an 8x12" print viewed from 12 inches the hyperfocal distance calculates to 155 feet. If I shoot the photo with the focus point aimed at 155 feet and make an 8x12" print everything from about 77 feet to infinity will look like it is in focus.

But what happens if I decide to make a 16x24" print from the same image file? Using the larger print size and assuming the same viewing distance, the same DoF calculator says the depth of field now only extends from between 103 feet and 312 feet when the camera was focused at 155 feet! To get the hyperfocal distance for a 16x20 print using the same camera and lens set at f/8 I should have focused at 308 feet.

Why is this so? Because depth of field is an illusion.