Bruce Barrett (Personal)

Using Negative Material to Create Pinholes

One or the perenial problems with pinhole photography is creating clean, round pinholes of known diameter. In rec.photography David Roberts proposed taking a picture of a black dot on a white background and using the resulting negative as the pinhole.

I have implimented a slightly different version of David Roberts idea. At first I thought I'd do it David's way but was woried about trying to determine the hole size accurately. (Creating a black dot, photographing it so it would scale correctly on the film, etc.) I later learned that what he did was create the dot and a line of known length which he then used as a scale.

Here's what I did (instead)...

  1. Created a PostScript program that will generate small dots,
       of varrying sizes on a page. My current pin hole sizes range
       from 0.03mm to 0.5mm in 0.01mm steps. (48 to a page)
  2. Distribute the dots on the page such that they can later
       be cut into strips 35mm wide and stored in a standard 35mm
       negative carrier. (6 holes per strip, 8 strips)
  3. Included the size of each dot and its f-stop for the 4 focal 
       lengths I have available to me.
  4. Ran the whole thing out to "lino", a 4064 dpi postscript engine,
       asking for a negative. You'll need to find a well equiped copy center
       or service bureau for this step. Cost: about $18 US, could be as low
       as $9 US for 2400 dpi, especially "in quantity."
  5. Cut the resulting sheet into "negative strips".
  6. Took the "same" photo with several different "pin holes" to
       determine the optimum size for each "focal length".

    (Photo's are taken, for now, by sliding the pinhole over a hole in a
     body cap on my 35mm SLR. Add extension tubes for longer "focal" 
     lengths.)

Each row of six pinholes on the page looks something like this:


Where:
	V is the distance from film to pinhole.
	f if the f-stop number at that length
	0.41 (in this example) is the diameter of the "hole" in mm.
	The dot in the center of the circle is the pin hole. Having the
	circle there makes it eaiser to find the (sometimes) very small holes.

The camera set up to take a picture looks like this:

There's a 5/32" hole drilled in the body cap, centered. There's a 1/4" hole punched (just used a paper punch) in a negative carrier strip. The negative carrier strip should be 1 frame shorter than your pin hole strips so you can manipulate it easily in any position. The carrier strip is hot glued to a piece of card stock for a bit of stability and the card stock hot glued to the body cap.

The pin hole strip (lino) of your choice simply goes into the negative carrier.

I haven't yet tried 2 pinholes or elongated holes.

I'm using an SLR because

that's what I have available to me
I don't have to create a "shutter" for the pinhole
it's easy to take multiple shots.
the camera is light-tight

I'm using black and white film so I don't have to worry as much about reciprocity failure.

I'll be glad to make the postscript code available to those who would like to try this out.
In fact, it's right here!

(c) Copyright 1995, 1996, Bruce Barrett, all rights reserved.

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