Hello! I've taken my first test pictures of a hyperfocal 16x20 Cardboard ULF camera. The lens is the 28 inch element of a Gundlach triple convertible, and it covers fine. The glass is only OK. Since I'll be using this at f128 (maybe f64), I bought an inexpensive shutter and glued it to the back of the lens. No turning back now, but for $50 total, it's worth a try.
I debated using foamcore and Styrofoam, then I figured why not just use cardboard since I don't need focusing. It's a one shot design. I'll load it in the dark and then develop so I don't need film holders. The back is 24x24 inches and the front 10x10 inches. The conical shape gives it a fair amount of rigidity.
When I measured the focal length of the lens using a telescope eyepiece at infinity, I got 26 1/2 inches from the center of the elements instead of 28. Using a CoC of 0.3mm, I obtained a hyperfocal distance of 38.2 feet and this was 28 inches from the center of the elements when I used a telescope eyepiece focused to 38.2 feet.
For this test, I taped 4x5 TMax 400 to the center of the back. It was dusk, so the exposure was 75 seconds at f128. For comparison, I moved up and shot 4x5 TMax400with a 90mm SuperAngulon at f64 at 5 seconds. This was taken 45 minutes before the hyperfocal camera, so its exposure was shorter. I focused the 90mm at 38 feet.
Unfortunately, I missed the fence I was aiming for with the hyperfocal camera, but the foot of the fence at 35 feet is visible as are several leaves at 22 feet. The leaves are 14 feet from the 90mm.
I scanned the hyperfocal negative at 300 spi and the 90mm negative at 1200spi, though I had to crop about 1:5 or 6 instead of 1:4 in order to obtain similar distances between the leaves.
Interestingly, to my eye, the leaves look sharper in the 90mm negative on the right, but the fence post looks sharper in the hyperfocal negative on the left when I enlarged them for easier viewing.
The next step is to try a 16x20 paper negative. Best regards.
Mike
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