The Humans Are Dead

As discussed in the previous post, an important part of shooting TtV is building a usable contraption. The crucial purpose is simply to block the light (and thus any unwanted glare or reflections) when shooting between top and bottom cameras. There are many fine box or tube style contraptions out there for connecting to unmodified bottom cameras. To put one together you just have to find some kind of tube like material of approximately the right diameter to work with. I scrounged around for a while and came up with the idea to use cardboard postal shipping tubes. After trying out various ways for cutting and notching the tube to fit over my bottom camera I opted to go a completely different route (influenced by what people were doing over at the sPiNoFF! Group). Instead of keeping the bottom camera intact, I decided to remove the glass elements completely from the bottom camera, in this case a Kodak Duaflex IV and build a homebrew cannon style “lens” to hold them.

The idea was to get two different size postal tubes that would fit inside of each other, a 2 1/2″ and a 3″ diameter tube would do the trick. Then cut holes to mount the glass elements from the Duaflex in the plastic end caps that fit the tubes, so I could switch glass as easy as popping in a new end cap. The back element (bubble) pops into an end of the 2 1/2″ tube, the other end of this tube jams snugly into the lens hood that fits the pentax kit lens. Then the front element (objective lens) mounts into the 3″ tube, which slides over the 2 1/2″ tube. There would be a consistent 1/8″ gap between the tubes which I figured I would fill by wrapping black felt around the end of the inner tube to block light and tighten up the telescoping action.

But before we can get to all that, we have to dig the glass out of the Duaflex

Cracking open the Duaflex proved to be pretty easy, four screws per element and you’re in business. But before you actually start tearing the thing apart you need to measure to find the ideal focal distance for your camera. So throw down a ruler and position the face of your back camera’s lens at one end. Position the viewfinder of the bottom camera at the other end of the ruler. Move the viewfinder forward until your camera will no longer find focus, then step it back until it does again. This should give you the minimum distance which should also mean that the viewfinder is as big as possible in the frame.

Now it’s operation time. To get at the bubble, you undo the two screws that hold the flip-up viewfinder cover in place. Then there are two screws that hold the latch that the film door hooks into. Once those are out the top pulls off and the bubble is free.

Access to the front objective lenses is even more straight forward, just four screws at the corners of the faceplate.

There you have it, both glass elements from the Duaflex IV ready for a new life.

Now that the materials have been gathered, it’s time to cut the tubes to size. I have the size for the inner tube from the process of measuring the minimum focal distance. To figure the length of the outer tube I took a bit of a guess. I read in one of the posts for the sPiNoFF! pool that the ideal distance between bubble and objective is usually someplace around 2 1/2″. My design for this cannon is going to allow that distance to be manipulated by sliding the outer tube in or out over the inner tube. So what I needed was a range. I decided to go with a minimum distance (when the cannon is fully closed) of 2″ between the bubble and objective. The outer edge of my lens hood would act as a minimum position stop. From that I now had a length for the outer tube. Cutting the tubes to length was an easy task for a chop saw.

Once I had the tubes cut I thought it might be wise to test my measurements. So I put the end cap into the inner tube and attached it to my camera for a test focus.

Now to cut openings in the end caps to mount the elements. I traced the outline of the bubble on to one of the end caps. The corners of the bubble are rounded so I found a drill bit with roughly the same diameter. Then I drilled holes at the four corners. Once the corner points were drilled I simply cut along the lines between the hole to remove the rest of the plastic. That process worked pretty well so I did the same thing with the round hole for the objective lens I used a larger drill bit to remove most of the material then cleaned up the hole with a utility knife.

The glass then snaps into the cut holes. For now I’m just using tape to secure them into the holes in the end caps.

Now the end caps can be put into their respective tubes, the inner tube is wedged into the lens hood and I have the two parts completed.

Now for a bit of clever (?) engineering. The two tubes fit inside each other but not snugly. There is still about an 1/8″ gap which I had planned to fill in with bands of black felt or something, that is until I dug around and found something else. I had a spool of wire with a thick rubber shielding. The wire was exactly 1/8″ in diameter, I pulled the actual wire out of the shielding so it could compress a bit. Then I cut a length long enough to wrap around the inner tube 4 times to create a kind of primitive roller bearing for the tube to slide on.

When you pull the outer tube to extend the lens it rolls across the wire. The idea strikes me as kind of like using trees as rollers to move giant blocks of stone… so this guy has been official dubbed the Rapa Nui Cannon.

Now, with all the work done it’s time to see the results.

Check out the rest in my “through the homebrew lens” set on Flickr. I’ll be adding more as I take them

This entry was posted on Tuesday, January 9th, 2007 at 10:51 pm and is filed under Photography. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.