Re: Building pinhole cameras
Albert Strauss (a.strauss@worldnet.att.net)
Thu, 8 Aug 1996 23:43:03 +0000
At 01:53 AM 8/7/96 +0000, you wrote:
>Someone asked me for clarification on how I made my "pseudo-pinhole"
>diaphragm:
>
>> The solution I came up with was the use of a Waterhouse stop with a very
>> small aperture to replace the iris diaphragm in a conventional lens. I
>made
>> a 1 mm Waterhouse stop using the usual pinhole technique with sewing
>needles,
>> sandpaper, etc. as has been recently described on this list. The brass
>shim
>> stock was too flimsy to use without some sort of reinforcement; so, I glued
>> it to a piece of wood veneer 1/28" thick as a support. I painted the
>entire structure
>> black.
>
>The Waterhouse stop is simply a disk which has a hole in the center of it--in
>this case, a pinhole. These date from the mid-19th century, before the
>invention of the iris diaphragm. Many lenses from that period were supplied
>with a series of disks with apertures of varying size. A disk with the
>desired aperture was inserted through a slot in the lens barrel into the
>optical center of the lens and functioned just as a modern adjustable iris
>diaphragm does.
>
>The lens I use for the pseudo-pinhole is a modern view camera lens (135mm
>Symmar in a #0 Compur shutter); any lens mounted in a shutter should do just
>as well. If you screw off either the front or the back element, the
>diaphragm and shutter are exposed. I made my pinhole diaphragm as a disk
>just the right size to fit into this space. It may require a bit of
>engineering with sandpaper and files etc. to get it to fit properly; this
>should be no problem, as brass and wood veneer (or cardboard, very thin
>plastic, or whatever support material you want to use) are soft and easy to
>sand. You obviously don't want it to fit **too** tightly, as it could be
>difficult to remove if it gets lodged in the shutter.
>
>So, after composing on the ground glass, I screw off the front half of the
>lens, open the diaphragm completely, drop in the Waterhouse stop, and screw
>the front element back on (not tightly, in order to avoid damaging the
>shutter and diaphragm). The effective f stop is easy to figure: with a 1 mm
>aperture, measure the distance from the film plane to the center of the lens
>in mm, and that is your f stop (f = focal length / aperture).
>
>I have used this only for macro work. But, I see no reason why it shouldn't
>have the same effect with the subject at a more conventional distance from
>the camera.
>
If you removed just the front element of the lens, the rear element acts as
lens of greater focal length and smaller aperture. If you focused the camera
before you unscrewed the front element then the rear element by itself is
out of focus. add to that the diffraction limited aperture and you have a
similar effect, but it is not a true pinhole. Is this not so ??
Al