Mark, A hot shot engineering dept can do a lot. I was a tech in one. I used 100's of rolls of 12" Fuji Film.
It wasn't light sensitive but self developing pressure sensitive.
Never found a good artistic usage...
Mark, A hot shot engineering dept can do a lot. I was a tech in one. I used 100's of rolls of 12" Fuji Film.
It wasn't light sensitive but self developing pressure sensitive.
Never found a good artistic usage...
Tin Can
This is a great thread! My 138 has been used largely for its easel, i.e., a flat surface in a darkroom that accumulates junk that won't go elsewhere, but I am now inspired to take another run at it. Bulbs have arrived, and now I have a PH212 and a G40 ready to go for testing the 5x7 format. I also have a piece of diffusing glass, if necessary. I will be using an Ilford EM-10 to measure the light. I would like to set it up so that I can print up to 16x20. I am assuming that if I get the bulb in position to do 16x20 evenly, it will be ok for any smaller enlargements.
I hope to have this done within a few days.
Before I even got the chance to plug in bulbs to test, a friend showed up with an LED light source he has been working on (partly inspired by Larry Gephardt). It is just a test version with 6 LED's but so far, the results are encouraging. He arranged the LED's in a circle at first but there was too much drop off so we put them in two rows of three. We also used opal glass instead of the heat absorption glass. We had to put the LED's as close to the glass as possible to get even illumination. The was still a drop off at the edges of about 1/3 of a stop or slightly more, so we want to experiment a little more. We are going to use two rows of LED "stars" (three LEDs mounted together) for a total of 18 LED's which we hope will allow us to get farther back from the glass and even out the illumination.
I sure hope this works. If it does, it will be a very inexpensive solution to a real PITA problem.
Did you see this link in another thread? I plan to copy or improve this design. http://jbhphoto.com/blog/2016/07/02/leds-vc-printing/Originally Posted by docw
Tin Can
Randy, thanks for this! This is very exciting.
I think so also.
Last night I recovered a recycled Saltzman head part which will work for me as enclosure and heat sink.
We should move this conversation to a new DIY thread. Please do the honors as I won't have anything for some time.
Tin Can
docw asked in a PM about equipment for measuring light fall off. My response went over the 2000-character limit, so I'll put the bulk of it here for posterity:
I used a Welch Densichron for my tests. There are currently a few of these listed on the evil auction site at various prices. One listing looks like it has a probe with a diffuser tip that one could use to replicate my measurements. Another listing looks like it has calibration targets for the reflection head, so you might get a reflection densitometer thrown in as well. Note that that these are vacuum-tube technology from the 1950's, so you'll be taking a risk WRT whether it's in good working order.
The Densichrons have markings in .02 density units, and you can use the space in between them to get .01 precision. More importantly, once calibrated, they actually seem to be _accurate_ to +/- .01 density based on my readings from a calibrated Stouffer step wedge. You can even use it as a transmission densitometer with a separate (but bulky and more rare) "transmission unit".
The probes normally come with a set of apertures that let you tune the sensitivity, but I found that if you let the light hit the photo tube directly, it is very sensitive to the orientation of the probe. This is fine if the probe is in a fixed position, but bad if you want to move it to the corners like I did. So, you will want to have some kind of diffuser in place if you go this route.
I would think that the Ilford EM10 would be usable for this, but the markings aren't linear, so you would need to calibrate your own scale. e.g., go through all of the click stops on a given enlarging lens and see where they fall on the EM10 dial. It should be reasonably accurate to use linear interpolation between measured click stops. Also, don't change direction when changing click stops.
Some alternatives to the Densichron that come to mind:
Lektra also made a photometer, but I haven't seen them on eBay. Markings in 1/3 stop, IIRC.
Some higher-end color analyzers (e.g., Beseler 3 series?) have readings in density units. I can't vouch for their accuracy.
The old Gossen Luna Pro has a baseboard photometer attachment and markings in 1/3 stop. You should be able to interpolate between these to get 1/6 stop accuracy (= 0.05 density). These are quite inexpensive now because they're calibrated for mercury batteries. However, the battery issue shouldn't matter for this application because you'd be taking relative readings.
I would think that any of these would be fine for determining whether or not a given bulb is "good enough" for day-to-day use, but maybe less useful for determining which bulb is the best of a given bunch.
Also, if anyone ends up buying (or has bought) a Densichron, I would greatly appreciate a PDF scan of any manuals, instructions, or other paperwork that comes with it -- information is scarce on these!
Thanks for this, quine. The Luna Pro attachment might be the way to go. I also have an Omega Simtron color analyzer but I would have to get a manual for it. I have no idea how it works. It was given to me ages ago.
For now, I am simply using a Pentax spotmeter to get readings off the baseboard. It isn't very subtle and I doubt it will help in getting "perfect" illumination but at least for now, it is helping me to centre the LED's for even illumination.
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