# Pentax 67 pinhole size

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• 06-19-2013, 05:49 AM
markbau
Pentax 67 pinhole size
I have a spare body cap for my 67 and would like to play around with making some pinhole images. What size hole would I have to drill into a metal plate embedded into the body cap to get a workable aperture?

Thanks for any help.

Mark
• 06-19-2013, 07:46 AM
Jim Jones
For best results it depends on the distance between the pinhole and the film. A good free program for determining the pinhole diameter is www.pinhole.cz/en/pinholedesigner/www.pinhole.cz/en/pinholedesigner/. Much information on pinhole photography and camera improvising is at http://www.f295.org/main/forum/ and http://home.online.no/~gjon/pinhole.htmhttp://home.online.no/~gjon/pinhole.htm. Drills small enough for this application are scarce and fragile. Pinholes are often made by slightly penetrating very thin material (usually brass or aluminum) with a needle, sanding off the burr that this produces, and repeating the process until the desired size is reached. It isn't difficult.
• 06-19-2013, 10:19 AM
Jeff Searust
Use several formulas for determining pinhole size. They will all be slightly different--- See Eric Renner's book also.

I had a drill bit for doing pinholes at one pint, and I dropped it on a linoleum floor from about 3 feet and the bit broke into 3 pieces.... that's how tiny and fragile they are. Go for the needle method and measure with a scanner.
• 06-19-2013, 11:07 AM
Loris Medici
A nice formula is: SQRT(2.44 x .00053 x focal length in mm)

For instance, the optimum pinhole size for (say ...) 60mm focal length would be:
SQRT(2.44 x .00053 x 60) ~= .2786mm ~= 280um

Note: .00053 is the median wavelength (in mm) of green light.

Hope this helps,
Loris.
• 06-19-2013, 12:25 PM
Quote:

Originally Posted by Jim Jones
For best results it depends on the distance between the pinhole and the film. A good free program for determining the pinhole diameter is www.pinhole.cz/en/pinholedesigner/www.pinhole.cz/en/pinholedesigner/.

+1
• 06-19-2013, 10:00 PM
markbau
Thanks for the replies. Unfortunately I am 100% Mac so the program wont run on my computer. I should have no problem drilling small holes as I've been doing it since I was 15 building scale models out of brass, the smallest hole I regularly drill in 30 thou brass for my model work is 0.34mm (.0135") As best I can measure the pinhole to film distance on my 67 is 55mm (approx 2 1/4 inches)
• 06-19-2013, 11:51 PM
SMBooth
if the film to hole distance is about 55mm then a pinhole diameter of .3mm is fine, your .34 will work fine to just adjust the f stop. That's f183 for the .3mm and f161 for your .34mm
• 06-20-2013, 12:09 AM
Poisson Du Jour
Quote:

Originally Posted by SMBooth
if the film to hole distance is about 55mm then a pinhole diameter of .3mm is fine, your .34 will work fine to just adjust the f stop. That's f183 for the .3mm and f161 for your .34mm

The film plane to inner flange distance would be 55mm, yes. But a body cap adds about 8mm (the Pentax one I have), placing the pinhole further away? I noticed this when I put the body cap on the 67 earlier. Just a thought. I have been mulling a pinhole for the 67 for a few weeks now. Most interesting.
• 06-20-2013, 05:35 AM
markbau
I was allowing for the lens cap. My measurement wasn't exact as I couldn't get the mirror up as I have a roll of film in it. I never have figured out how to fire the shutter without film in the camera even though I've owned it for 20 years, just never needed to!

Quote:

Originally Posted by Poisson Du Jour
The film plane to inner flange distance would be 55mm, yes. But a body cap adds about 8mm (the Pentax one I have), placing the pinhole further away? I noticed this when I put the body cap on the 67 earlier. Just a thought. I have been mulling a pinhole for the 67 for a few weeks now. Most interesting.

• 06-20-2013, 05:44 AM
markbau
Is there any reason not to make a bigger hole so that the exposures are shorter or am I missing something? f161, according to the sunny 16 rule, would be approx 2 second exposure meaning I'm in reciprocity land even on a sunny day!
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