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ND filters would certainly be easily replaced, but still, how would one go about calculating how much ND needs to be used for say 400 speed film? Is there a method? Or just trial and error?
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 Originally Posted by Greg Davis
ND filters would certainly be easily replaced, but still, how would one go about calculating how much ND needs to be used for say 400 speed film? Is there a method? Or just trial and error?
Just trial and error. In the EG&G manual there is a chart because they know roughly how bright the thing was when new.
With respect to the Wejex, or any of the x-ray type sensitometers, or a home-made sensitometer you just have to adjust the intensity by trial and error so you can get the whole film curve.
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I guess that's all I need to know. Building the thing shouldn't be a problem. Thanks for answering my questions.
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Originally Posted by Greg Davis
ND filters would certainly be easily replaced, but still, how would one go about calculating how much ND needs to be used for say 400 speed film? Is there a method? Or just trial and error?
It does not have to be merely trial and error. One you know the ND filtration that is needed for an ASA 100 film you should be able to adjust for an ASA 400 film by adding two stops more of ND filtration. One stop is the equivalent of log 0.30 of ND filtration.
Sandy King
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Originally Posted by ic-racer
Yes, mine came with that handy little filter slot.
You also mentioned a 2 second exposure with yours.
In mine, the lamp is indeed on for about 2 seconds, and it buzzes for about 2 seconds but the rotating shutter covers the lamp for half that time, resulting in a one second exposure. Are you sure your shutter is working OK?
You also mentioned you use ND filters. Does yours look like mine on the bottom? If it does, you can pop off that little cover plug an get access to the rheostat for adjusting lamp intensity.
I have not opened the Wejex in a long while but as best I remember there was no rotary shutter, only a bulb that turned on for 2.5 seconds. I know that it is possible to adjust the rheostat for intensity but I am ok with it as is since I dedicate the Wejex to testing film for long exposures. For most testing I use the EG&G.
Sandy King
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Originally Posted by sanking
I have not opened the Wejex in a long while but as best I remember there was no rotary shutter, only a bulb that turned on for 2.5 seconds.
Very interesting. So there may be quite some variability between Wejex units. I'll have to post some pictures of the inside of mine. The rotating shutter assembly is pretty cool.
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Last edited by ic-racer; 04-04-2010 at 11:52 AM. Click to view previous post history.
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I was actually thinking of using an enlarger diffusion box as the basis with just a plywood box exterior. This would give me a nice even light with minimal modification, but I did consider one of these printers.
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I recently purchased a Wejex I-W sensitometer. Everything seems to work, but the glass next to the step wedge was broken. I had to remove it completely to get at the wedge in order to measure the step densities, so now I have to replace the glass. It is extremely thin. On the order of a 1/4 millimeter thin. The only glass I can find online that thin is microscope slide cover glass. Microscope slides are too thick, but the cover glass is thinner, however, it is very small. I have to find a piece that is 1 3/8 inches wide by 5 1/4 inches long. I found some slightly larger so I could cut it down, but I would have to buy a package of 36, which is in the cost range of $220. Does anybody know of a source for glass this thin and large, or use it at work that can send a single piece?
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I'd seriously consider converting it over to a system like the EG&G posted in picture #55 above with just a plain piece of thicker glass. The EG&G, being a more advanced unit, allows freedom to use any type of step wedge. You are instructed to tape your favorite step wedge in place over the glass. The Wejex with the 'built-in' step wedge is more for an 'unskilled labor' setting where the intention was to be goof-proof.
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