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# Thread: Pentax 67 pinhole size

1. ## 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

2. 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.

3. 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.

4. 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.

5. 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

6. 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)

7. 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

8. 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.

9. 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!

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.

10. 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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