## Need 5x7 hyperfocal distance mathematicsgreenspun.com : LUSENET : Large format photography : One Thread |

I plan to use a 135mm and 150 mm lens on a 4x5 camera. A friend of mine has a 5x7 camera -- he plans to use the lenses also. Questions--- What are the hyperfocal mathematics so that one can plot out a chart for 5x7? I have a hyperfocal distance chart for the 4x5 format. Can I use my 4x5 chart for 5x7 as well? If not--- Why? as stated above the same lenses will be used. For those who are not familiar with hyperfocal distance-- After the mathematics are done all you do is use your result chart--Simply set your camera to focus on a given hyperfocal distance with lens set on a selected f stop.The shutter should reference metered speeds for the f stop you select. Your chart calculations will reference you exactly where the nearest sharp distance is with infinity being sharp as well. This can be done for all f stops on your lens or lenses. Now after all the explanation -- who can answer the three questions I asked? Thanks, Tom talltandj@aol.com

-- Thomas Ferko (talltandj@aol.com), February 11, 1998

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-- WFPA (wfpa@johndesq.com), February 11, 1998.

According to the Kodak publication on optical formulas, the formula for hyperfocal distance is H=F^2/(f x d), where F is the focal length of the lens, f is the f-stop, and d is the diameter of the acceptable circle of confusion on the film. The film format does not directly enter into this calculation. However, since a larger film format will require a lower degree of enlargement to produce any given size print, the circle of confusion (as measured on the film) can be larger to produce the same size circle of confusion on the print.

-- Rob Rothman (rrothman@riag.com), February 16, 1998.

Along with the helpfull response that I recieved on depth of field and hyperfocal distance I recently located an on line computer that will solve these problems for all film formats. It will chart out f stops on any camera with any lens desired. Just select the film format you are using and plug in what is known to you. The unknowns will appear. Its very simple to use. You might want to bookmark it. Please check out: http://www.worldphoto.com/depthof.htm Thanks, Tom

-- Thomas Ferko (talltandj@aol.com), February 16, 1998.

DV = distance bed moves between sharp focus of "near" object and sharp focus of "far" object- focus on exact midpoint between near and far focus extremes - Optimum f:stop = square root of (375 * dv) - works for any lens - all you really need is a little metric ruler and a chart or calculator - method does not work where the focus extremes have very different magnifications (where one is close to 1), as in extreme close ups

The Mar/Apr. Photo Techniques has two great articles on focussing the view camera using this method.

Cheers,

-- windsor (windsor@netrover.com), February 16, 1998.

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