Monday, March 5, 2018

Pinhole Lab Camera Accessories: Pinhole Distance Reducer and Extension


How far the image-forming objective is from the film plane is one of the fundamental descriptors of a camera system.  Along with film size and aperture, it determines most of the visual and technical attributes of the image.

With lenses this is known as focal length. Determining it with lenses is complicated.  With my Canon FD 20mm f2.8 lens, the nearest piece of glass is 50mm from the film plane.  It takes a whole article in Wikipedia to explain it.  With pinhole, you can just measure with a ruler, or in my current case, cut the right size piece of cardboard.

One of the prime characteristics of the Pinhole Lab Camera is having two separate pinhole distances to experiment with -  2.5 and 4 inches.  That's a bit of a limited selection, and stays pretty well in the moderately wide angle segment of the range.


Two fairly simple accessories can expand the options available, and of course, impact the image.

A Pinhole Distance Reducer can be easily made by cutting 4 x 4 inch squares of another widely available material, corrugated cardboard, and gluing them together.  With the box I used, it took five layers to make a half inch.

Placing that against the back of the camera front (of course stuck on with a loop of tape), you can then place the paper at a 2 inch distance from the pinhole giving a 64 x 90 degree angle of view at f102 (with our .5mm pinholes), a 35mm equivalent of 18mm.



Adding a second reducer brings you to 1.5 inches, 76 x 106 degrees at f76, a 35mm equivalent of 14mm.


Making an extension to move the film away from the pinhole requires a part made from glueing a template to cardboard and folding and glueing as with the camera.  It's basically a two inch band the size of the camera back which fits into the camera front. It is then stepped down to the size of the front, with a light trap around the joint which the back then fits into.  It's sort of as if you cut off the front of a camera. The template is on-line, and I will be doing a separate step-by-step post on building it, including notes on a few new materials.


One of these extensions makes the camera 6 inches long,  23 x 36 degrees at f305, which brings us all the way out to the range often referred to as - drum roll - normal! A 35mm equivalent of 55mm.  Also we've finally gotten to where those .5mm pinholes are optimal according to Lord Rayleigh.


Finally a second extension (make two at once and save on glue-drying time!) will bring you out to moderate telephoto portrait range, 18 x 28 degrees at f406, a 35mm equivalent of 70mm. That f ratio is getting to be a whopper, with a sunny day exposure of two minutes with paper.  If we're just considering the width of the image, this is the same as the Moderately Telephoto Pinhole Camera in a Plain Brown Wrapper.



Here's a table describing the entire range.



Depicted graphically.

And where the photons hit the film plane.

At one and a half inches


Two inches


Two and a half inches


Four inches


At six inches


and at eight inches.


Here's one of those documentation shots that shows the relationship of things from the side.


Here's another sequence of the full range in a more confined setting.  The camera is up against the headrest on the rear passenger-side seat of a Mustang.

One and half inches


Two inches


Two and a half.


Four inches


Six inches


And all the way out at eight.


If Mazda wasn't already using it, maybe the motto of the Pinhole Lab Camera should be "Zoom, Zoom"



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