Originally Posted by sanking
Thanks for the info. Can you post a picture of your unit? I wonder how else it is different from the one I have. Mine buzzes for about 2 seconds but the shutter is only open for one second. I know the current model they show on the Tobias web site is smaller than mine, and I suspect the inner workings may not be the same (http://ourworld.compuserve.com/homep.../prodother.htm)
I really like the Wejex design and in fact was looking into parts availablility to do a little article about making a sensitometer based on some of the existing designs.
Timing with the Wejex is very consistent because it uses a Synchronous motor in which the speed is dependent on the Hertz of the energy source, not the voltage. So it runs at the same speed at 117V and 121V etc. As long as the Hertz is the same (60Hz in the USA).
I found a source for a 60 RPM synchronous motor. With a shutter shaped like a semicircle (180 degrees) it would produce an exposure time of 1/2 second. Then all you would need would be a microswitch, bulb and box, diffusor, stepwedge, etc.
The other way to go would be to use LEDS and something like the 555 IC timing chip and battery power and base it on the X-rite style (though, with 'white' LEDs).
The third way would be to copy the EG&G and just get a used standard photoflash with a Manual setting, and put this into a box.
For those with EG&G sensitometers that may be following this thread, I found a source for the FT-118 tube. http://www.electronicpartsupply.com/
The Radio Shack tube was nice because I was able to get it in a moment, and able to verify the sensitometer was in working condition quickly. Now that I know I will keep the sensitometer, having the original tube for less than $10 will be great.
Hi Guys !
For a long time now, I was considering buying an sensitometer. But the price tag is astronomical, even on Ebay.
I was wondering if one could make good use for B&W material testing of dual color sensitometers used in X-Ray material testing like the X-Rite 383 which shows up from time to time ?
I have been trying to get an x-rite on e-bay for about 25-30 USD to use for testing, but two just got away. I want to compare it with the Wejex and the EG&G.
Originally Posted by GeorgesGiralt
I can't just put a green or blue filter in the Wejex because, I think the x-rite uses LEDS which will have a discontinuous spectrum that cannot be duplicated with a simple blue or green filter. I DO actually keep a BLUE 80A filter in the Wejex, but since the common light bulb in my Wejex is a continuous spectrum device, some red does get through.
I really think that for 'process control' use (that is checking development times) the x-rite devices will work fine, but I want to test it first so I am not posting nonesense.
Just a follow up post on the flash bulb that I got from http://www.electronicpartsupply.com/
. It IS a 1.5 loop tube, like the original, but the overall dimensions are slightly smaller. Otherwise it looks like a good replacement.
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After reading the EG&G manual I now understand the special light filters that are missing for my unit. Since the light output for the three flash speeds is so different, they had the equivelant of Neutral Density filters to make the 10-2 and 10-3 speeds the same intensity as the 10-4 speed.
Rather than relying on gelatin or acetate filters that may fade with time, or rather than the expense of pure carbon filters they used a very simple solution.
The filters are just sheets of plexiglass that are black or painted black and they have a series of lines on them to controll the light intensity.
One filter has 3 slits and the other has 19 slits.
Last night I cut 2 pieces of plexiglass to the appropriate size and then painted one side of each with semigloss black paint.
Today I will mark out where I want the slits to be and just scrape the paint away using the blade of a fine screwdriver. I can then fine tune them by adding or removing more paint as directed by flashmeter measurements.
I made my 'filters' the other day. I was not shure how large the lines were to be. My first filter used lines about 2mm wide. I made 3 lines and it was too bright for the 10-3 setting. I tried it on the 10-2 setting and it seemed to be just right.
For the next filter I used 0.5 mm lines. I started with just one line and it was too dark. Then I added a second line and it was just right for the 10-3 setting.
I also replaced the Radio shack flash tube with the new FT-118 replacement. The replacement is not an exact replica. It is a little smaller than the original. I suspect either the Radio Shack tube or the replacement FT-118 will work fine.
Now I am ready to start to do some testing. I am probably just going to test the Wejex and EG&G as I have been unable to get an X-rite on ebay for $25. I guess I need to put out some posts about how they are totally unsuited for panchromatic film so people stop bidding them up
I did some research and it seems that the resolution of conventional film radiography is a little better than the 'film-less' radiography and this makes conventional film somewhat better for mammography. In mammography, one needs good film resolution to detect microcalcifications and subltle spiculated lesions that might be masked by the surrounding breast parenchyma. I suspect that as digital gets better this will all change. But this continued use of conventional film for mammography is, I believe, the reason that there are still high prices on the x-rite sensitometers. As 'film-less' imaging takes over the field of mammography I suspect these x-rite sensitometers will really come down in price.
Amazing Eye for Brightness
Did my first H&D curves with the EG&G.
I exposed a strip of film to each setting on the EG&G. The first segment was 10-2 with my filter with 3 wide slits. Next was 10-3 with the filter with 2 narrow slits and finally 10-4 with no filter.
Now, I don't have a flash meter. So I use my eye to match the intensity of the 10-4 flash to the others and kept scratching lines in the black paint on the filters until the intensity matched up to my eye. I thought I could get to 1 to 2 stops.
Well, I plotted the three H&D curves and they almost superimpose exactly! WOW!
Here is some of the raw data:
[Step #] [10-4 (no filter)] [10-3 (3 wide slits)] [10-2 (2 narrow slits)]
18 1.32 1.31 1.31
17 1.38 1.38 1.38
16 1.47 1.46 1.45
15 1.56 1.54 1.54
14 1.65 1.62 1.62
13 1.74 1.70 1.71
EG&G on e-bay
I have no affiliation with this item, nor can I vouch for its quality, however, if someone is looking for an EG&G sensitometer, this looks like a working example of a mark VII.