It really does work. Of the four pictures I took in Pololu Valley, this one worked the best. But it's not without its flaws.
The good news is at 2400 DPI, this is a 12,000 x 9,600 pixel image, or the rough equivalent of a 110 megapixel camera. So there's a clear advantage to using the thing. I'm not just doing it to be "retro".
The bad news is at the full 2400 DPI scan, the image starts to go a little soft. And so the planning starts:
- Item #1 - Test my lens against a USAF resolution target to find out what aperture setting gets me the most resolution. What's my lens's sweet spot?
Also, the negative was slightly over-exposed. I've tested this camera for light leaks, and because it's uniformly over-exposed, I don't think this is from fogging of the film from a leak. I know this shutter tends to run long, but I've never stuck it on a chronograph. Time to do so.
- Item #2 - Chronograph my shutter, make a new label for the lens board with the real open/close times for each setting, laminate it, and stick it on.
Ok, the obvious one: It's tilted. The Picavet suspension on this camera uses eyebolts rather than pulleys. The suspension lines have a fair bit of drag on them where they pass through the eyebolts, and it appears it's enough to let the camera hang at some oddball angles. The angle with respect to the horizon is 13.6 degrees, give or take. Not cool.
- Item #3 - Replace the eyebolts on the Picavet with ball-bearing pulleys. I have sheaves and bearings in-hand, so this is a matter of making blocks.
Also, I'm beginning to see the advantage of the smaller Picavet, not just for reasons of portability. Smaller Picavet crosses exert more of a righting force on the rig for less friction on the lines. James Gentles has done the most extensive testing on Picavet geometry of anyone I know, so I have a roadmap to follow.
- Item #4 - Re-build the Picavet to use the Gent-X geometry developed by James Gentles, and put into production by Brooks Leffler.
Next, my mechanics for aiming the camera aren't what I'd like them to be. I'd like to re-design the pivots to be hard axles with separate brake mechanisms for each. This will allow for more clamping force without necessarily ripping threads out.
- Item #5 - Re-design all the rig's pivots to have positive braking mechanisms, and to have rigid axles.
Finally, the last time I took this picture it was a vertical panorama using my digital rig. I think of this angle of Pololu Valley as a vertical. Shame I didn't design in any provision for rotating the film 90 degrees so I could do verticals! Luckily the fix is pretty easy.
- Item #6 - Add a second set of bracket holes so the entire camera box can be rotated 90 degrees for vertical shots.
There is one left-over from the initial design that I never dealt with: When you pull the dark slide out of a 4x5 film holder, felt light traps are supposed to keep light from leaking into the camera through the dark slide slot. But felt wears out, light gets in, film gets fogged. So it's only prudent when using a 4x5 camera to hold your hat, your hand, or the dark slide itself over the slot in the film holder to keep direct sunlight off of it. You can't do this when your camera is three hundred feet in the air over your head!
- Item #7 - Install Velcro strips on the camera body, and make a dark cloth that can be tacked over the exposed edge of the film holder prior to flight. This is a ten minute job on a sewing machine.
In any case the camera is good enough to be used as-is. But I'm pretty driven to get all these items taken care of as quickly as possible. In the meanwhile it's time to go through all my KAP trips, and to see what subjects really lend themselves to a large format picture. Right now I only have Tmax 100 film available, so all my 4x5 KAP shots will necessarily be black and white. But Fuji Velvia and Kodak Portra VC are two outstanding color films available in 4x5 format, so once the bugs are worked out with Tmax and the camera is flying clean and steady, I will start shooting color as well.
Tom
No comments:
Post a Comment