Silverbased

Welcome to Part Two of our project converting a cheap focus-free 35mm “trashcam” into a pinhole camera.

Part One covered choosing the right trashy plastic camera to use, then taking it apart. The crucial point to remember is that your camera must have a little lens-cover flap, which will become the new shutter after the pinhole mod.

Trashing and Hacking

With the camera’s lensboard removed, we expose the original spring-operated shutter blade (see the final photo in Part One).

Pull out the original shutter blade and spring, and throw them away. If you had already removed the lens, throw it away too. But keep its retaining ring—we will need this later.

If the lens was glued into place from the back of the lensboard, you may need to shatter it by tapping a nail through it; then pick out the fragments.

Now you need to decide the best location within the camera’s innards to place a thin metal wafer for your pinhole. The deeper back into the camera body you choose, the wider the angle of view you’ll get in your photos. But if you go too wide, the edges of the opening in the front shell of the camera can creep into the field of view.

With this model I decided to take a chance, and glue the pinhole behind the lensboard. For cameras having only a small opening through the front shell, a pinhole mounted in the front of the lensboard is better.

The original shutter blade pivoted between some molded ridges, both on the main body piece shown here and on the back of the lensboard. With a sharp blade, shave these away, so that there will be clearance for your pinhole’s sheet metal.

The aperture stop in the lensboard also needs to be trimmed away, to insure it doesn’t obstruct the pinhole’s view. But keep the raised collar around the opening intact.

Finally, enlarge the front opening of the retaining ring. This image shows the ring after widening its hole as far as possible.

Remember that our shutter flap will slide against this ring; so its front face needs to remain flat and without rough edges.

(If your lens was glued in from behind so you don’t have a retainer ring, the same consideration applies to the raised collar on the lensboard.)

Pinhole Time

Next we need to choose the right pinhole size, and make the actual pinhole.

The distance from the pinhole to the film plane determines the right diameter for the hole, so find a way to roughly measure this distance on your camera. On my particular model it’s 25mm. This functions like the “focal length” of your pinhole. And whooeee—25mm is a real wide-angle!

You might imagine that the smaller you made your pinhole, the sharper the image would be. But it’s not quite that simple. Light waves grazing the edge of the hole diffract in unwanted directions. So there are formulas for calculating the hole diameter which yields the best sharpness, given a particular focal length.

Actually, using 0.2mm is close enough for most plastic trashcams; but you can get more precise using an online calculator like the one at Mr. Pinhole’s site.

That calculator also tells you the equivalent f/stop of the pinhole, which in my case is f/119. That’s near enough that I’ll round it off to f/128, exactly 6 stops smaller than f/16 (helpful to know when it comes time to determine exposures).

Fabricating a Pinhole

There are several schools of thought on the best method for making a pinhole, so I’ll keep things brief in describing my method.

I tap a small bump into thin sheet metal (pop-can sidewall will work); then sand the bump against 320-grit sandpaper until the metal is paper-thin. I press the bump against something firm like a phone book, and with the very tip of a sewing needle, pierce the tiniest hole I can. The shaft of the needle mustn’t go through.

I use squares of metal 50mm x 50mm—the same size as a 35mm slide mount. This lets you use the slide holder of a film scanner (or, a slide projector) to get an enlarged view of the pinhole. The hole needs to be nicely round, and not ragged; and by knowing the scan resolution (or magnification of a projected slide) you can calculate the diameter.

By gently twirling the needle tip in the hole, and lightly sanding after, you can nudge the diameter larger until you reach your target size. (Blow out any dust before checking it.) You’ll probably need to make a few pinholes to get a good one; but even if the diameter is off by 20%, that’s only a fraction of an f/stop in exposure error.

Place the Pinhole

Trim the edges of the pinhole metal until it fits into the location you chose. If the pinhole is going behind the lensboard (as here), test-fit that there are no remaining ridges or nubs which would keep the lensboard from snapping back into place.

Glue the pinhole in position. I like to use black silicone sealant for this (it’s sold as automotive gasket material), since it blocks light from leaking through any small gaps. Check through the back of the camera that the pinhole is centered, sliding from side to side if needed. Don’t get glue in the hole!

Too Smart For Its Own Good

Next we can start putting the camera back together—with one important final modification.

You may have noticed that your camera originally had a nifty interlock between its lens cover and its shutter button. If the cover flap was closed, the button could not be pressed down.

Once we gutted the original shutter mechanism, the button atop the camera no longer does anything to start exposures (the lens-cover slider will do that instead). But we still need to click the top button each time we want to advance the film to the next frame.

In our finished camera, the cover flap will be closed any time we aren’t exposing film. Hence we need to disable the interlock, so you can click and wind between exposures with the flap still closed. My illustration shows where an arm on the lens-cover slider originally blocked the shutter plunger. Remove the slider, and cut this arm away, and the release button can be clicked even with the flap closed.

Finally, we can put all the parts back together: Snap the lensboard in place, and add the retaining ring. (With the lens missing, the ring may fit loosely, requiring some dots of glue to hold its ears in place.)

Replace the cover flap and its slider, and check that it works smoothly to cap and uncap the pinhole opening.

Time for a Sanity Check

Next, put the front shell of the camera back in place again. (It can take a few attempts to put the front on without dislodging the cover-flap/slider mechanism.) Do not replace the four screws yet—we need to make one important check.

Open the shutter flap; and with the back of the camera open, hold up the pinhole towards a bright light. Sight through the film gate towards the pinhole, rocking the camera back and forth. The pinhole should remain brightly lit from anywhere in the frame—all the way around the perimeter, into all four corners.

Uh Oh!

Trying this test on the camera shown here, I discovered trouble. I realized I’d been too ambitious at trying to get the shortest possible focal length and the widest angle of view. The front shell’s opening blocked the corners of the image!

Remember that a pinhole has effectively infinite depth of field. So the round edges of of the opening would appear sharp in the photos—the pictures would look like they’d been taken through a port-hole. While it might be interesting to play around with that effect, I preferred an unobstructed view.

I solved the problem by taking a file to the edges of the front opening—shaping a bevel with the same rectangular proportions as the 35mm frame. I checked my progress by sighting along the edges of the film gate, and eventually removed enough material: The pinhole had an unobstructed view all the way into the corners. Whew!

With that crisis averted, finally we’re ready to put all the camera parts back together. Replace the latch spring (if yours fell out); the rewind crank (if you removed it); the wrist-strap (if you want it); and the four screws that hold the front shell in place. Make one last check that your shutter flap is opening correctly, and your camera is ready to shoot!

Finishing touches

Because pinhole exposures can be quite long—with indoor light, even many minutes—holding the camera steady during that time becomes a problem.

I suggest adding a flat piece of wood as a base—much easier than the camera’s rounded body to steady against a table, a bench, a door frame etc.

If you have a tripod available, a 1/4″-20 nut epoxied into the base serves perfectly as a tripod socket.

Note that the base needs to be cut short, so it does not cover up the rewind release. (Or if you prefer, drill a large finger-hole lined up with the release button.)

Once you’re certain you won’t need to open up the camera again, glue the base in place (hot-melt glue works great). Just watch out to make sure that the back can still open freely.

Shooting with the Pinhole

This wide-angle style of pinhole camera gives interesting stretched-out, dreamlike images. Both near and far are equally in focus (or equally defocused?); yet anything that moves during the exposure disappears in a ghostly blur. A pinhole camera’s potential for intriguing, expressive images is something I’ll leave it to you to explore.

But if you’re a beginner who would like some basic tips on operating the camera, exposure suggestions, etc., I’ve put them into a PDF file which you can print out and take along when you go out shooting with your new little plastic pal.

Happy pinholing!

[Return to Part One.]