


Building a Pinhole Camera
After reading Cus's pinhole camera thread, I decided that I wanted to build a pinhole camera (or at least design one on paper and give up after the math required to design one kicked my butt).
I printed out an article on Geocities that gave the pinhole diameter formulas, f/stop formula (which I already knew), and other calculations. This article gives aperture diameter formulas in inches and millimeters. I decided to use millimeters because I'm more familiar with the metric system. The formula for pinhole diameter in millimeters is.
"Pinhole Diameter=0.0366(square root of focal length)"
Since I'm not a fan of math, I decided to use a nice, even number. I stupidly picked 1mm as my diameter, not thinking of how big that would make the camera. I ended up with a camera 15.8 feet long :\
If anyone is interested in how I (correctly ir incorrectly) came up with that, I'll type out my process.
Pinhole Diameter=0.0366(square root of focal length) with a 1mm pinhole diameter
1=0.0366(square root of x)
1^2=(0.0366^2)(x)
1=0.00133956x
1/0.00133956=x
x=746.5137806
I rounded 746.5137806 to 746.5mm
To get 15.8 feet, I multiplied 746.5 by 10 to get 74.65cm. I then divided 74.65 by 2.54 to get 29.38in.
This is actually a lot more practical than the calculation I had before. It's amazing how one mistake can throw a measuremoent off that much
Last edited by WGibsonPhotography; 06242009 at 02:09 PM. Click to view previous post history.

Your Metric to English conversion is off, to go from cm to inches you divide. 74.65 cm is 29.38 inches (74.65/2.54). Still pretty long but not so bad as 15 feet (4572 mm).
If you have access to, or buy a machinist's caliper, you can just measure the needle, then using the formulas figure out what the FL would be. Cheap ones are around for 20 USD, or so.
Last edited by bdial; 06242009 at 12:19 PM. Click to view previous post history.

I'm afraid the math is incorrect. You shouldn't multiply your cm to get inches, you should divide. A quick look shows that 746mm is less than 1 meter, so it's got to be under 3 feet. Notwithstanding this, it would still be a big camera.

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Mike your needle and multiply by 300 (edit) to get your focal length () and you should have a great aperture.
Last edited by Christopher Walrath; 06242009 at 04:37 PM. Click to view previous post history.
Thank you.
CW
"Wubba, wubba, wubba. Bing, bang, bong. Yuck, yuck, yuck and a fiddledeedee."  The Yeti

I think you mean focal length.

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As long as the needle has a good sharp point, the dimpleandsand method can produce a pinhole smaller than the needle diameter. You don't push the needle through, you just raise a bump and use fine sandpaper to remove enough material to expose a hole. (I use #600 wetordry wet.) That process also gives the hole some approximation of a knife edge. Then you can work your way up to the desired diameter. The trick is being able to measure where you are. Purely by accident, I have a little 50x handheld microscope with a direct measuring reticle built in, which works for me, but I know some folks are pretty successful using a [whisper] scanner [/whisper] to come up with a measurement.
I would be inclined to pick the "focal" length and then work up the pinhole size. But that's partly because my efforts to date have involved making adapters to fit existing camera gear.
DaveT


I have one more question: Would balsa wood be an appropriate material to make a pinhole camera out of (painted, of course)? I think I can get sheets of it at a local crafts store.

Take a highpowered flashlight and hold it right up against the material, and hold it right next to your eye while sheilding it with your hand. If you can't see the light at all when you turn it off and on, it should be good. I doubt balsa wood will be lighttight enough.

Originally Posted by BetterSense
Take a highpowered flashlight and hold it right up against the material, and hold it right next to your eye while sheilding it with your hand. If you can't see the light at all when you turn it off and on, it should be good. I doubt balsa wood will be lighttight enough.
that's a good idea. Balsa wood is pretty thin, and I doubt it'll be good enough unless I paint it. Even then, the paint might be good enough. I should be able to find something at Hobby Lobby that'll work, even if it isnt balsa wood

