DOF and laser optical range finders.

[stevewillard]

I am investigating using a laser optical range finder and a DOF calculator for measuring

DOF in the field. The application is primarily for my 500mm and 720mm lenses. DOF can

be in the hundreds to thousands of feet with these lenses and tilts do not add much for

these big guys.

 

In particular, I am looking at the Nikon Monarch Laser 800 which boasts new technology

enabling an accuracy +/- 1/2 yard and can measure distances from 30' to 2400'.

 

Has anybody had any experince with this approcah?

[leonard_evens]

Might I suggest another approach.

 

All the information you need is available on your camera. The lens itself can be used as a rangefinder. Of course, it is not very accurate, but the point is that it is just as accurate as it needs to be since the image is formed on the film side of the lens, and only distances on that side need to be measured. Using expensive laser rangefinding equipment won't give you better ways to determine depth of field.

 

Look at the discussion of focusing and focus spread at www.largeformatphotography.info, which explains this in detail. If you can take the math, see also my essay

www.math.northwestern.edu/~len/photos/pages/dof_essay.pdf

 

To make accurate use of these methods you need to be able to measure distances along the rail or bed fairly accurately. That can be done with a scale on the focusing knob. Some cameras come equipped with such a scale. The large format website has a page showing how to do that for other cameras with the scale calibrated directly in f-stops. My essay shows how I did it with a mm scale for my Toho FC-45X.

[roger krueger]

I just bought a Leica Disto for focusing--my intended use is a little different than yours,

scale focusing a Mamiya Press in conditions dark enough to make both the camera

rangefinder and ground glass problematic--but it seems like a valid approach for what

you want too.

 

While Leonard's approach is perfectly valid for what you want, it seems like a lot of extra

work. Quick kids, which is easier, pushing a button on a rangefinder, or focusing a view

camera several extra times for each shot?

 

For what you're doing the Nikon seems like a reasonable choice. The Leica is much more

accurate (1/8"), but only goes 600 feet.

[roger krueger]

One caveat--with a lens with a reasonably flat field, it's the distance to the CENTER of a

given plane of focus that matters, not the actual distance to an off-center subject.

Measurements of an off-center subect will be increasingly inaccurate as the angular

separation from the center of the field increases.

 

Put another way, if you have a plane of focus 100 feet away, the straight-line distance to a

corner may well be 110 feet or more, but from a focus-math point of view it's still at 100

feet.