"Ter McDonagh" <[EMAIL PROTECTED]> wrote: > I think I'm settling on the sliding box design with the front box slightly > larger (maybe 7"x7") and having tripod mounts and a lensboard holder. The > smaller rear box will provide my focusing. Being an engineer I'm angry I > didn't come up with the rear focus idea myself. > > New questions are: > [1] With the double wall construction, I guess the inner walls can be a > much lighter material? Maybe a heavy cardstock?
Apart from it's function as a light trap for the focusing box, the inner wall should also act as a trap for stray light to reduce flare. I'd suggest that you use something like balsa wood or foam core painted with Krylon Ultra Flat Black spray. Before assembling the sides, consider adding baffles to the innermost "box". You could hot-glue strips of black balsa or mount board across each side tilting toward the lens at a 45 degree angle. Any stray light from outside the framed portion would reflect from the baffle to the black box wall. The height and number of strips should be chosen so that they block your view of the inner box sides when you look through the back. The strips may be staggered on adjoining walls so you don't have to miter them. > [2] How do you guys get the two boxes to slide smoothly? I'm thinking > maybe some teflon runner angles or teflon tape. It'll make it slide easier, > but introduce more of a gap for light. I don't have faith in myself to make > the two boxes so closely aligned as to slide easily without some "help". You'd be best served by a close fit - with a 16" lens ease of fine focusing isn't that critical. You could leave a 1/16" between the outer and focusing boxes, and wrap the focusing box with glued strips of black velvet to act as a light trap. A couple of thumbtacks near the end of the outer and focusing box can be used to reduce friction. They are placed at weight bearing points - at the bottom rear of the outer box and top front edge of the focusing box. I'd make the box as long as possible. After the camera is constructed and lens attached, you can determine balance points for tripod attachments to permit horizontal and vertical framing. Alternatively, the lens could be mounted on a board hinged at the bottom and backed by a short bellows to permit front tilt. That would be a useful feature for landscape photography. To keep things simple, the focusing back can be pulled out and rotated 90 degrees to change orientation. Rise and fall aren't that important for a long lens. > [3] For the interior I was planning to hit it with flat black primer and > blow in some flocking while it's still wet, let it dry, and then hit it with > another coat of primer. Is this satisfactory? It would work, but it isn't as effective as the baffles. Black velvet or paper velour glued to the interior before assembly traps light better. > [4] Since I'm planning on exposures of a couple seconds I was going to go > without a proper shutter at first. Does a flap of black felt thrown over > the lens provide less chance of a blurred exposure than trying to put on the > lens cap? The cap is more secure, and when it's held over the center of the lens, light to the film should be blocked. However, I wouldn't use the cap since exposures should be on the order of a fraction of a second. Since the lens which is long for the format and the on-film view angle is small, you probably can front mount a shutter to the lens without vignetting even if the opening is smaller. than the lens diameter. I checked a 19" lens by projecting a backlit 4x5 ground glass back onto a distant wall. When stopped down, there wasn't any vignetting with a Compur 1 shutter at the front of the lens. With tilt, that might not be the case. Other "features" might include a thumbscrew to lock focus and to prevent the back from sliding out, a carrying handle, a pop-up wire frame finder to check framing possibilities while holding the camera, a top or side mounted worm drive between the sections for fine focusing, etc... When used Speed Graphics were cheap (~$50), the bellows, bed, etc. could be removed and the body used on the back of a box camera to provide a shutter and GG focusing. LF teles, better MF and 35 mm systems, and improved films replaced the homemade setups and Big Berthas. ________________________________________________________________ Sign Up for Juno Platinum Internet Access Today Only $9.95 per month! Visit www.juno.com _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
