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  1. #1

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    Thomas Duplex Issues

    Someone help me troubleshoot what's going on here, because I'm stumped; I inherited a literally-brand-new-except-for-the-box Thomas Duplex, and after going over the thing with a fine-toothed comb I'm still having issues with it burning the paper during a very basic eight-minute coin test.

    I'm not kidding when I say that the safelight is new; it doesn't have a single scratch on it. In fact, the only thing that needed replacement/rebuilding were the old gelatin filters that were crinkled and thoroughly useless, which is expected with these lights. I rebuilt the inner filters by using the factory glass on the outside and a piece of 50% transmission diffusion plastic on the inside, with the suggested #19 Fire gel sandwiched between the two. For the outer filters, I used a #27 Medium Red between two pieces of factory glass. I used a black vinyl tape to secure the glass and plastic plates together; it works pretty well.

    After rebuilding the filters I tested the safelight and got a light burning of the paper in less than a minute's time with the outer vanes slightly open; I used a CD as a poor man's prism and found that there was a faint band of green light making its way either through or around the #19 inner filter. This green band was also present without the filter in place, although it was much stronger and joined by some blue/purple stuff; with the outer vanes closed there was nothing except the yellow/orange/red spectrum to be seen. So, I tried a second test with the vanes fully closed and got exactly the same results.

    At this point I was confused because there should be no way that any paper-exposing light could be making it's way through the filters, so I chalked it up to light leakage in he housing and went over all of the safelight's seams with black tape. After that, I taped the inner filters in place - I found a couple of spots where light could easily leak around the filter - and tried a third test with the outer vanes slightly open again. Same results; the one-minute coin silhouette was easily visible.

    In a slight bit of desperation I taped the outer vanes down to prevent any and all chances of light leakage, and I ran a fourth test...and got the same results again. I've got no light leaks, no light skipping around the filters, so it seems that the only thing that could be happening is that the filters themselves are...well, not filtering. I find this hard to believe because people have a lot of success with rebuilding Thomas filters with the #19 and #27 gels, but I don't know what else it could be.

    Anyone got any thoughts that might help me out, here? Am I doing something wrong that I don't know about?

  2. #2
    Ken Nadvornick's Avatar
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    Which paper are you using for testing? I know some of them (Slavich, for example) specifically state that only red light is safe. For those I use a DIY 635nm red LED safelight.

    Your description sounds thorough and correct to me. Is your tape lifting up from the heat perhaps? Is it truly opaque?

    I suppose you could try temporarily covering the outside of the outer filters with some taped down red Rubylith. What you need to find is some level of baseline configuration that works so you can then work backwards from that to isolate the problem.

    Ken
    "They are the proof that something was there and no longer is. Like a stain. And the stillness of them is boggling. You can turn away but when you come back they’ll still be there looking at you."

    — Diane Arbus, March 15, 1971, in response to a request for a brief statement about photographs

  3. #3
    zsas's Avatar
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    Ken's right, something sounds outta whack.

    Sorry to be mr obvious, but, any reason to not buy this? Sorry if you're aware of this, but if not...
    http://www.freestylephoto.biz/42135-...lter-Set-(FBD)
    Andy

  4. #4

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    Dear Sundowner,

    Probably a stupid suggestion on my part but are you sure the fogging is from the safelight rather than another source?

    Neal Wydra

  5. #5
    Greg Davis's Avatar
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    The filters are wrong. The pair on the moveable vanes should be two sheets of the Rosco #19 with diffusion, but the bottom pair should be a sheet of Rosco #3406 and #3407 with diffusion. This matches the filters that are sold commercially for this safelight.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

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  6. #6
    Ken Nadvornick's Avatar
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    I dunno' Greg. For b&w all I use is a single layer of Roscoe #19 Fire between glass sheets without any diffusion. The Roscoe spectral transmission chart says this should be sufficient. And for both my CD and pre-flashed fogging tests of Ilford MGIV, it is.

    This filter is located in the lower filter position. The vanes contain only sheets of black mount board. That allows me to adjust down to total darkness for easel framing and focusing.

    Ken
    Last edited by Ken Nadvornick; 09-04-2013 at 09:20 AM. Click to view previous post history. Reason: Clarity..
    "They are the proof that something was there and no longer is. Like a stain. And the stillness of them is boggling. You can turn away but when you come back they’ll still be there looking at you."

    — Diane Arbus, March 15, 1971, in response to a request for a brief statement about photographs

  7. #7

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    Some thoughts -

    1) Test Neal's thought that the fogging may be coming from something other than the Thomas Duplex - try a fog test with the light off, to make sure that your darkroom is dark when the lights are off.

    2) I use an Agfa Sodium Vapour light - which is similar, but smaller than the Thomas Duplex. My lights take a long time to warm up, and until they are warmed up, will fog paper - I turn the safelight on 20 minutes before I start printing to allow it to stabilize - are you doing your test immediately after turning the light on?

    3) Are there flourescent lights in the room (even if they are turned off). It may be that the light from the safelight is exciting the phosphors in the flourescent lights and they are emitting light which is fogging your paper.

  8. #8
    Greg Davis's Avatar
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    Quote Originally Posted by Ken Nadvornick View Post
    I dunno' Greg. For b&w all I use is a single layer of Roscoe #19 Fire between glass sheets without any diffusion. The Roscoe spectral transmission chart says this should be sufficient. And for both my CD and pre-flashed fogging tests of Ilford MGIV, it is.

    This filter is located in the lower filter position. The vanes contain only sheets of black mount board. That allows me to adjust down to total darkness for easel framing and focusing.

    Ken
    I tried that after your posts in the other thread. I had fog after very short times. I test using Kodak's method of using safelight exposure before a medium gray exposure, and again after a medium gray exposure on separate pieces of paper. Using the filters I mentioned gave me safe times after exposure of up to three minutes with the vanes fully open, and well past seven minutes with them fully closed. With just the #19 filter in place I had safe times of less than one minute fully closed after the paper received printing exposure. Just my experience.

    I should note that I was using Ilford MGWT paper. Regular MG gave slightly longer safelight times, though I don't know why since printing times are shorter with MG than MGWT.

    And, yes, I was meticulous about other sources of light being an influence. Even the glow from my watch face was eliminated from the darkroom first.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  9. #9

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    Wow! All kinds of responses! Thank you, everyone!

    Quote Originally Posted by Ken Nadvornick View Post
    Which paper are you using for testing? I know some of them (Slavich, for example) specifically state that only red light is safe. For those I use a DIY 635nm red LED safelight.
    I'm currently printing on Oriental, and it's OC-safe for over an hour with my Kodak D safelights.

    Quote Originally Posted by Ken Nadvornick View Post
    Your description sounds thorough and correct to me. Is your tape lifting up from the heat perhaps? Is it truly opaque? I suppose you could try temporarily covering the outside of the outer filters with some taped down red Rubylith. What you need to find is some level of baseline configuration that works so you can then work backwards from that to isolate the problem.
    The tape isn't lifting and it's opaque; I just checked to see whether or not either could be a factor. I ordered some rubylith to see if that helps, but I don't have it on-hand yet.

    Quote Originally Posted by zsas View Post
    Ken's right, something sounds outta whack. Sorry to be mr obvious, but, any reason to not buy this? Sorry if you're aware of this, but if not...
    http://www.freestylephoto.biz/42135-...lter-Set-(FBD)
    I have seen those filters; I already had the gels on-hand and the diffusion plastic, so I was hoping to use them. Also, the rubylith I ordered only cost $10 for a rather large sheet.

    Quote Originally Posted by Neal View Post
    Dear Sundowner,

    Probably a stupid suggestion on my part but are you sure the fogging is from the safelight rather than another source?

    Neal Wydra
    I'm pretty sure, Neal; I've had no issues with this paper in the exact same conditions, with the exception of the safelight change. That tells me that something, as we've discovered, is indeed in need of re-wacking.

    Quote Originally Posted by Greg Davis View Post
    The filters are wrong. The pair on the moveable vanes should be two sheets of the Rosco #19 with diffusion, but the bottom pair should be a sheet of Rosco #3406 and #3407 with diffusion. This matches the filters that are sold commercially for this safelight.
    That's different than what I've seen so far. Hmm.

    Quote Originally Posted by Ken Nadvornick View Post
    I dunno' Greg. For b&w all I use is a single layer of Roscoe #19 Fire between glass sheets without any diffusion. The Roscoe spectral transmission chart says this should be sufficient. And for both my CD and pre-flashed fogging tests of Ilford MGIV, it is.

    This filter is located in the lower filter position. The vanes contain only sheets of black mount board. That allows me to adjust down to total darkness for easel framing and focusing.

    Ken
    This is more in-line with what I'd been reading; I was hoping to use the outer vanes to control the overall light level but I haven't made it that far, yet.

    Quote Originally Posted by Mark_S View Post
    Some thoughts -

    1) Test Neal's thought that the fogging may be coming from something other than the Thomas Duplex - try a fog test with the light off, to make sure that your darkroom is dark when the lights are off.

    2) I use an Agfa Sodium Vapour light - which is similar, but smaller than the Thomas Duplex. My lights take a long time to warm up, and until they are warmed up, will fog paper - I turn the safelight on 20 minutes before I start printing to allow it to stabilize - are you doing your test immediately after turning the light on?

    3) Are there flourescent lights in the room (even if they are turned off). It may be that the light from the safelight is exciting the phosphors in the flourescent lights and they are emitting light which is fogging your paper.
    1) Just now I tried one strip that was left out in the dark for eight minutes, and another directly from the paper safe; both printed perfect, unexposed white.
    2) I let the light warm up for about ten minutes or so; I can try it after a longer time, though. That won't be a problem.
    3) No fluorescent stuff anywhere near the darkroom, for exactly the reason you mentioned.

  10. #10
    Greg Davis's Avatar
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    I don't know what you have been reading, but I purchased a set of filters from Thomas Duplex and cut them open to find the Rosco gel numbers still printed on them.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

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