brainwagon "There is much pleasure in useless knowledge." — Bertrand Russell

2Jul/140

An Experimental 4×5 Camera with a ridiculous lens… and a ridiculous selfie

Over the years that I've been interested in computer graphics and telescopes, I've managed to pick up a bit of knowledge about optics in general, and specifically about camera lens design. In the past, I've been particularly interested in old cameras and photography, and in a kind of photographic minimalism. But it has remained mostly an academic interest, with no real practical results.

Until recently.

I was recently asked to provide a little bit of background on camera lenses and lens design at an informal workshop. The purpose of the workshop was for each participant to build and use a camera of their own construction. I've taken similar courses before where we did pinhole photography. Here's the apex of that experiment, a picture of my desktop:

pinhole3-pos

Taken with this camera. Note the curved back, which results in the odd panoramic distortion of the previous picture.

pinhole

But this time class was a bit more ambitious. We were going to make cameras that would shoot on 4x5 film, and use a real lens (or lenses) to give us faster focal ratios and interesting distortions and other effects. We ordered some lenses with focal lengths of around 150mm from Surplus Shed for a few bucks apiece (favoring some positive meniscus lenses, as well as some with about 300mm that we thought we'd experiment with some symmetrical lens arrangements, got some 4x5 sheet film holders, and a pile of black foamcore and gaffer tape. Each person's camera was a bit different. Here's mine:

It's a pair of boxes about 7" across which telescope together. To create a bit of a light trap, there is both an inner and an outer box in the back, and the section which holds the lens slips in between those two, and also provides a rough focussing mechanism. The lens is a meniscus with about 150mm focal length, and about 50mm in diameter. It's not an achromat, just a simple lens, configured as a Wollaston landscape lens. 220px-WollastonMeniscus-text.svgI constructed a small box to hold it about 1 inch behind the front of the camera, and then punched a 1/4" hole in some black paper to serve as a stop. Instead of a true shutter, I decided to just make a little trap door. For our first tests, we were going to image directly onto photographic paper, which had an ASA rating of around 3 or 4. With the 1/4" stop in place, my camera operates at around f/24. To make my first "selfie" in room light, I guestimated an exposure time of 30 seconds. The first exposure was far too light. I then caved and used a smartphone app to give a better estimate, and it suggested a three minute exposure time. I shot this on ASA 3 positive paper. I triggered the shutter myself, then sat down and tried to be as still as possible. When the time was up I got back up and closed the shutter. Into the darkroom... and bathing in the rinse!

photo 1

I cropped the picture and scanned it, cropped it, did a very tiny exposure tweak to darken it a bit (probably should have left it in the developer a touch longer), and here's my selfie:

portrait

I'll try to get some new shots next week. But it's a fun project, I urge anyone to give it a try. These simple lenses are more effective than you would think.

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