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fotoshark
01-11-2006, 03:14 PM
Hello everyone; I am very new to this (online forums) and hope I am doing it properly. I want to build a pinhole camera to accomodate 4X5 film holders. I have several questions. 1- What is the ideal hole size to use? If using a material like brass, how do you drill the small hole (do bits come as small as needed?) and lastly how far does the pinhole need to be from the film plan to cover the 4X5 film area (focal length?) I've looked online for 4X5 plans but most design are fairly primitive and dont touch on specifics. I want to build my camera out of wood and have a brass plate for the pinhole. Any help or info is greatly appreciated. Thanks

Tom Persinger
01-11-2006, 04:55 PM
here you go!
http://www.popularwoodworking.com/features/fea.asp?id=1048

should cover everything you need on your first wooden camera!

knut
01-11-2006, 05:29 PM
Hi and welcome! Online forums may be a bit unfamiliar in the beginning, but you can get a lot of useful information, and it can be somewhat addictive :)

Your questions about hole size and focal length are correlated. The optimum holesize (given that you want maximum sharpness and resolution) is normally given as a function of focal length and the wavelength of the light. A lot of formulas exist, but a simple and quite usefull one is:

dh = sqrt(f)/25

where dh is hole diameter and f is focal length, both given in millimeters. In Other words; take the square root of the focal length and divide by 25.

As for the required focal length, there's no definite limit. As the focal length gets shorter, the light falloff towards the corners (vignetting) gets more significant. With extreme wide angles you will also probably notice reduced sharpness towards the corners. A rule of thumb may be that the image diagonal should be no more than 3 to 3.5 times the focal length. The diagonal of a 4x5 negative is about 155mm, giving a minimum focal length of some 45 - 52mm, or somewhere around 50mm. Even shorter focal lengths work; in the gallery you can see several examples of 4x5s with a 25mm focal length. So far I have experimented with 50 and 75mm. 50mm works quite well, and is a lot of fun, but the light falloff is quite noticable but still acceptable in most cases (depends what effect you want in images though).

So your procedure should probably be:
a) decide what angle of view you want, this dermines the focal length. A "normal" length would be about 150mm (ie. the image diagonal). If you want a wide angle, then maybe something like 75 - 100mm might be a good start?
b) Calculate the hole size based on the focal length.

The pinhole designer program may be useful: http://www.pinhole.cz/en/pinholedesigner/

Let's say you want 90mm focal length. The formule given above gives you a hole diamter of 0.38mm and the pinhole designer gives 0.42mm, in other words you probably want about 0.4mm. Drill bits of that size exits, but I would guess they are pretty fragile... A very common method is to use a sewing needle to pierce a hole in a piece of thin sheet metal, and then sand down rough edges with eg. #500 paper. The piece of metal in which you pierce the hole should be as thin as possible in order to achieve the best quality of your images. It's also possible to buy readily made pinholes.