Re: [Cameramakers] x-synched 4x5 slr
This looks interesting, Please keep us posted. Gene Johnson [EMAIL PROTECTED] wrote: > > Hah! Glad to see there are some other crazies out there. As I see it, it's > all got to happen in one smooth, fairly simutaneous motion, or you might as > well use a view camera. That means mirror up, aperture stopped, and exposure > with flash, all in less than a second or so. > > I, too, thought about using a speed graphic for the back end, till I found a > series D on ebay cheap eonugh. But it's basically the same back there, so it > will be relevant. > > First problem is flash synch, and that should be easy enough. Enlarge the > curtain aperture to full frame, and add a contact. Thought about using an > electic eye (infrared) and even a magnetic tape head, but I think the > contact is still the best. Worked 50 yrs ago Sure, the synched speed > will be slowww, but maybe we can deal with that later. Motorize it? > > Next is mirror slam. On RB's, a spring launches the mirror up with a deciced > thwack. I'ts a 10 minute operation to reverse that spring to hold the mirror > down, intead, which means the shutter release actuator (what ever that turns > out to be) must force the mirror up to release the shutter (that part is > automatic with RB's). This also cures one of the RB's weaknessesa tendency > to develop light leaks around the mirror as the release trigger wears or > loosens. > > Auto aperture: Oh boy. Super D's are outrageously expensive in 4x5, and the > 3x4's are too tight inside to allow use with long lenses. You'd have to add > an ungainly extension onto the back. And, as far as I know, you're limited > to the 4.5 152mm and 5.6 190 Ektars. Nice lenses, but still too short. I > wanna use nice long barrel lenses I can maybe afford. > > Nuff for now. But the rest involves springs, thin wire cables, and sleeved > piano wire ala model airplane control linkage. I'll keep you posted. > > Roger Stevens > ___ > Cameramakers mailing list > [EMAIL PROTECTED] > http://rmp.opusis.com/mailman/listinfo/cameramakers ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
Re: [Cameramakers] pinhole measurement
At 07:06 PM 8/17/01 -0300, you wrote: >Does anyone have an efficient way to measure the size of pinholes without >using specialized equipment? On the Bender website the pinhole camera >kit includes: > >"Pinhole Measuring Device -- Use it with your enlarger to view and accurately >measure your pinholes, for the optimum in sharpness and controllability." > >Anyone have it? Suggestions? I can probably figure something out, but >if you know how to do this it will save me a lot of "circling" around the most >efficient way to do it. This might be useful: http://www.pinholevisions.org/resources/articles/poke.html >My first approximation would be to create a negative that has a line on it >that is, say, one inch long, and then set my enlarger so that the image of >the line on the baseboard is ten inches long (or twenty if I can go that >high). >Once that is done the pinhole sheet can be put in the place of the negative >and the size (and shape) of the hole measured on the baseboard. Even with >only a magnification of ten, a 0.3mm hole (for a "75mm" pinhole) would be >3mm on the baseboard (or 6mm if I can go up to 20x). > >Thanks. > >Myron > > >___ >Cameramakers mailing list >[EMAIL PROTECTED] >http://rmp.opusis.com/mailman/listinfo/cameramakers ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
[Cameramakers] Pinhole Measurement
How about measuring the light transmission of the pinhole with a light meter? Shine a strong lamp on the pinhole at a known distance between the lamp and pinhole and pinhole and a screen. Measure the spot on the screen with a normal lightmeter of adequate sensitivity.Then calibrate by using a "pinhole" of a calibrated size, say 1 mm. I believe a machinists #60 drill makes a hole quite near 1 mm. Of course, the distances are kept the same in both measurements. Don't forget the light intensity goes as diameter squared, as does the aperture scale of the light meter. Instead of a screen, you could just put the lightmeter behind the pinhole (maybe with or maybe without an incident light option). This would offer more sensitivity but you must be a little careful to correctly hit the sensor and you should keep in mind that if the sensor is a photoresistor it may give quite different readings if the same amount of light falls as a concentrated spot on the sensor as compared to falling fairly well uniformly over the sensor. The incident light option gets around this and a photo diode based meter is unlikely to exhibit the problem. A suitable source can reduce this problem greatly. Bob PS How about avoiding the whole issue by making the hole the correct size by construction. If you push a tapered needle into whatever is receiving the hole and you know the needle diameter at the largest diameter of the needle which entered the hole, don't you more or less know the pinhole diameter. You can measure a needle with a workshop micrometer. You could also puch the needle into an existing hole until it stops and measure in the same way. I once made a gauge for small holes working this way, following a design known for decades if not centuries! Dr. Robert Mueller Institut für Festkörperforschung, FZ-Juelich D-52425 Juelich, Germany phone: + 49 2461 61 4550 FAX: + 49 2461 61 2610 email: [EMAIL PROTECTED] ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
