Pinhole doodads and reciproci-whatsamagitzits

[christopher walrath]

Hi all. I'm always one to be difficult so I'm trolling this one in all the forums I frequent, including here, BP, APUG and here. So here goes.

I have been on the periphary of pinhole photography for sometime but, now that I am finally able to develop my own B&W I'm going for it. I took an old folder (6x6 Wirgin) and removed the bellows/lens assembly to make a 35mm perspective control lens and I was trying to come up with another fate for the folder body than the trash receptical. Then it dawned on me. Medium format pinhole. I reassembled the innards (roll film brackets, film tensioners) and then set about to building the front of the camera. I cut cardboard from the back of a Steno pad about 10mm larger than the old lens window and cut a hole in the center of that and then covered it with black electrical tape. I then cut a 5cm square piece of aluminum foil, rubbed it flat and taped it to the inside of the pinhole board. Then I mounted that to the front of the body and marked the center on the inside. Took a regular sewing needle and applied very light pressure while rolling it slightly in my fingers until the needle tip just pierced the foil. Then I cut out another square of cardboard, smaller this time and covered it, taped a hinge onto it and mounted it over the pinhole. I also fix a couple loops of thread so that I could more easily open the cover. Put a piece of tape over the tripod hole inside the camera body, loaded film, tied the lid closed with a thin black shoe string and christened it the Walra-Lux 2008.

Now I have made a couple of exposures. But I need to test this camera a little bit. I have TMX-120 loaded and the aperture is around f/256 (needle tip miked at about .2mm and the focal length is about 27mm). This would require any meter reading calling for an exposure at EV16 about one second exposure. Which means EV 10 would need a little over a minute mathematically. How would I figure reciprocity adjustments? Since Kodak publishes an additional 5 seconds if a meter reading requires ten seconds, I'm figuring that you should add about four seconds to a reading that would call for an 8 second exposure. And since that same publication says to adjust a 100 second required exposure by doubling it so probably about the same for a two minute exposure, expose for four minutes. But waht about in between? Do I do what Kodak did and just bracket it until I get the matching exposure and publish it or has anyone here already done pinhole and reciprocity with TMX and can shed some light on the subject (no pun intended)? Any comments would be greatly appreciated.

 

[compur]

I think you're gonna have to do some trial and error but I would start by
doubling your mathematically figured exposure time.

 

[windrivermaiden]

somewhere in this forum I swear that there was a link to a page that explained all this in great detail.

How I would do it...trial and error. most of the fun of pinhole is to see whatcha get.

 

[JamesD]

Generally, I make a few test exposures under the conditions I'm planning to shoot, recording the meter readings from my 35mm camera. Then, selecting the best exposures, I make a chart based on the meter readings. Then, I work from that, metering with my camera if I'm not sure about the lighting conditions. I also always work out a sunny/16 exposure and label the camera or pinhole mounting.

 

[christopher walrath]

I came up with these general numbers. As f/256 at one second is EV16, here is what I have.

EV - recommended time - adjusted for reciprocity
EV16 - 1 sec - 1 sec
EV15 - 2 sec - 2.5 sec
EV14 - 4 sec - 5.5 sec
EV13 - 8 sec - 12 sec
EV12 - 15 sec - 25 sec
EV11 - 30 sec - 50 sec
EV10 - 60 sec - 110 sec
EV9 - 120 sec - 240 sec
EV8 - 240 sec - 510 sec

This fits Kodak's recommendations for TMX in their literature which states 'expose TMX for 15 seconds when exposure calls for 10 and expose for 200 seconds when exposure calls for 100'. Works so far.