DOF and range finders

The biggest problem I have with DOF charts is estimating distance such as 171.45 feet of 97.34 feet. I have never been very good at that stuff. Wide angle lens es are not a problem. It the longer lenses that are hard to estimate DOF. Whil e looking at a sporting good catalog I noticed that they have some very good ran ge finders that can also function as binoculars (sp). Nikon makes one which wei ghs 10 oz and can provide measurements form 30' to 2400'.

Is this a silly thing to consider? Has anyone every resorted to using such a to ol in the field? Or perhaps using Polaroid type 55 film and louping the negativ e to check for sharpness is sufficient (which is what I currently do now with va ring degrees of success).

I think golf shops sell rangefinders, too, though they might read in yards. A friend of mine uses a laser rangefinder to measure distances. We've used it along w/ self-computed DOF tables to determine what point to focus on and exactly what aperture to use to obtain the proper (albeit theoretical) DOF. I wish Pentax could incorporate a rangefinder into their digital spotmeter. :-)

Stephen: 30 feet to 2400 feet is almost all at the infinity setting of most lenses. It wouldn't help you at the closer depth of field ranges. There used to be, and maybe still is, rangefinders built specifically for photography that were hand-held. You brought the rangefinder into alignment and read the feet on a scale. You may still be able to get them new or used. A better method with a view camera is to mark the distance at five feet on the camera bed and again at infinity. See how much distance the lens moves to focus on each distance. You can also mark it for 10, 15, and 25 feet. Use tape if you don't want to mark on the rail or bed of the camera. This is much faster. The other option is to get familiar with those distances and what they look like. Hope this helps.

Instead of using a DOF chart and a rangefinder, you might try a Rodenstock DOF calculator. With this device, you focus on the near and far points you want sharp and measure the distance the standard moves between the two. The calculator (which is something like a round slide rule) tells you the aperture you need to keep everything sharp. You don't have to know the distance from camera to near and far points. The calculator is small, flat, and costs about $30, which seems like a lot for what it is, but much less than a rangefinder. Once you figure it out, it's easy to use.

Why don't you use hyperfocal distance focusing? I have them worked for 101mm,135mm,240mm,300mm, let me know if you want them.Pat

This web site offers interactive DOF calculations for various film sizes:

http://www10.geocities.com/SiliconValley/7116/jv_dofc.html

Stephen: Save $30. Focus on the near, then the far and note the distance the focusing standard moves in mm. Multiply by 5 if you are tolerant, or 6 if you are conservative to get the minimum fstop you need to carry the DOF. This assumes 4x5.

Glen is right, of course. If you are using 8x10, you can multiply by 2.5 or 3. However, be aware that this calculation assumes that the focusing rail is level (if it's tilted down, the effective distance is less, so you don't need to be stopped down as far) and that the magnification ratio is low (ie., landscapes instead of macro--if the magnification ratio is higher, you also don't have to stop down as much). The Rodenstock calculator does allow you to factor angle and magnification ratio in to the calculation, but this might not be worth $30 to you.