Thomas Duplex Issues

[Sundowner]

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? :confused:

 

[Ken Nadvornick]

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

 

[zsas]

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-Thomas-Bandamp-W-Safelight-Filter-Set-(FBD)

 

[Neal]

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

 

[Ken Nadvornick]

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

 

[Mark_S]

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.

 

[Sundowner]

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

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.

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.

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-Thomas-Bandamp-W-Safelight-Filter-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.

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.

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.

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.

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.

 

[Sundowner]

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.

Wow...that's odd. I just looked up those filters and the wavelengths they allow to pass are not what I would have expected at all. The factory filters that came with mine were horrendously cracked/crinkled gelatin with no printed numbers to be found, and I looked pretty hard to find one just in case I had to cross-reference something. That's very interesting info; thank you!

 

[Ken Nadvornick]

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.

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.

Hi Greg,

This is the first chance I've had to look into this further. I went and checked my set of original FBD filters for my Duplex. I purchased my unit new before they were discontinued so I know they were OEM pieces. They showed no indication of Roscoe product or serial numbers. Could it be that the construction of the filters changed over the product lifetime of these safelights? Mine was purchased quite a few years ago.

I then had a look at the spectral transmission graphs made available online by Roscoe. There are two very slightly different versions of the #19 Fire filter listed. I've referenced the version I purchased. Here are the three in question for others who may not have seen them:

Rosco E-Colour+ #019 Fire

Rosco Roscolux #3406 Sun85

Roscoe Roscolux #3407 Sun CTO

And here again is that LPS line spectrum from Brian Niece, Associate Professor of Chemistry at Assumption College in Massachusetts (fourth item down the page):

Low Pressure Sodium Line Spectrum

From the generated line spectrum of an LPS lamp the extra blues and greens caused by the inclusion of the argon/neon Penning mixture are readily apparent. And a look at the #19 Fire filter chart shows that it should be almost perfectly opaque to those wavelengths all by itself. For standard OC-rated b&w materials this filter should work fine. And in practice, at least for me, it does.

On the other hand, I'm not sure what additional safeness the other two filters would add, given their respective charts. Especially in the green regions for VC papers. Filter #3407 in particular allows a substantial percentage of blue-greens and greens to pass. This should be an obvious risk factor for VC papers if the #19 were not present.

Might these second two filters be intended for different materials? I'm really curious regarding your observed results.

Ken

 

[frobozz]

Might these second two filters be intended for different materials? I'm really curious regarding your observed results.

Well, we need a cross-reference between Thomas' "edge tape color" based ID scheme, and the various gel colors, but as a clue, here are the official instructions from Thomas (I scanned the sheets that came with mine):

http://backglass.org/duncan/darkroom/thomas_duplex_super_safelight_instr.pdf

Duncan

 

[Sundowner]

From the generated line spectrum of an LPS lamp the extra blues and greens caused by the inclusion of the argon/neon Penning mixture are readily apparent. And a look at the #19 Fire filter chart shows that it should be almost perfectly opaque to those wavelengths all by itself. For standard OC-rated b&w materials this filter should work fine. And in practice, at least for me, it does.

On the other hand, I'm not sure what additional safeness the other two filters would add, given their respective charts. Especially in the green regions for VC papers. Filter #3407 in particular allows a substantial percentage of blue-greens and greens to pass. This should be an obvious risk factor for VC papers if the #19 were not present.

This is the part that confuses me. The 19 filter is only supposed to allow the passage of a slight percentage of green-ish wavelengths, and this was very evident in my not-at-all scientific test; there was a definite green band right where one would expect it, were they looking at the chart for the 19 filter. I was under the impression that this wouldn't be an issue when I ordered the 19 and 27 filters, because I'd read so many reports of them being great cutoff filters for the sodium lamp...but somehow I still got a definite graying of the paper after less than a minute's time. With that said, I can't figure out how the other two filter numbers would help, because they seem to be letting in a lot of blue/green wavelengths.

Well, we need a cross-reference between Thomas' "edge tape color" based ID scheme, and the various gel colors, but as a clue, here are the official instructions from Thomas (I scanned the sheets that came with mine):

I just found that online not too long ago; thanks for posting it!

I purchased a set from Freestyle while Thomas was still in business. I bought a yellow tape, a red tape, and a black tape. I took them apart a few years later to see if they were filters I could replace myself for less money. In the yellow tape filter I found two sheets of gel filter material. One had the number 3407, the other 3406. I recognized them as Rosco filters from my sample book. The red tape had "ROSCO 19" printed on the edge of the filter. The black tape did not have any markings, but were the same colors as the yellow tape, but used more layers of filter material inside. All of them used the tissue paper that comes with Rosco filters as the diffusion material.

The numbers were not present in both filters of a pair. I don't think they were intended to be left on the filter material when cut and put in place. I had a very old set of Thomas Duplex filters, and they were different material. It was far too old and faded to tell what they once were. It is possible that the filters sold for these safelights now and just before Thomas Duplex stopped selling their lights are made by someone else and they just use what they think may work, but if you buy a set of filters from Freestyle or KHB Photographix, these are what you get.

You could always buy a set, open them, and tell us what is in them. If they are different than what I have, then I was sold the wrong filters. But I doubt it.

I think the filters I had in mine when I got it were the older style, as well...and they were desiccated beyond recognition. I'm almost tempted to buy the inner set and see what comes in them...but that may have to wait until I have some extra cash. For now, I'm hoping that the rubylith I ordered will come in soon and hopefully allow me to actually use the safelight, rather than just look at it.

 

[Ken Nadvornick]

This is the part that confuses me...

And it's confusing me as well. The #19 filter should cut off virtually ALL of the blues and greens. In other words, when in place you should see no blue and/or green bands at all.

Before my successful (pre-fogged) safelight tests I fired up the Duplex, let it warm for ~30 minutes, then looked at the CD reflections unfiltered. In addition to the massive yellow sodium doublet, I saw the much, much fainter blue and green spikes. I also saw the extra deep red spike.

Then while looking directly at those spikes I interposed a single layer of #19 filter. The blue and green spikes disappeared. When I removed the #19, they returned. Back and forth.

Later, when I performed the safelight test I was able to leave a sheet of Kentmere Bromide #3 graded paper out for ~30 minutes with no hint of fogging.* As you may know, bromide papers are very fast. It should have responded to any blue light present. But it didn't. It remained pure white. (Even checked with a reflection densitometer to factor out my subjective eyes.)

So as I said, I too am confused.

Also keep in mind that if you use a cover sheet of Rubylith you will likely be filtering out all of the yellow sodium light as well. At least in a perfect world. I've never tried it myself, so I don't know how much will pass. Maybe only that secondary red spike I mentioned above?

Ken

* Apologies, as I earlier identified the test paper as Ilford MGIV. It was actually the Kentmere Bromide. The Ilford was used for my red LED safelight testing.

 

[Ken Nadvornick]

Yes, I did. That's what I meant when I said "pre-fogged." Perhaps not the best choice of words by me. Probably should have said "threshold fogged."

A test was first made to determine threshold exposure for the Bromide #3 paper. Then the test sheet was pre-exposed to just below that threshold level. Any additional safelight fogging exposure should have therefore been immediately visible after development. Either to my eye, or to the far more sensitive reflection densitometer. Comparisons were made against a similarly pre-exposed control sheet that was not subjected to the safelight.

It should also be noted that 30 minutes was an arbitrary cutoff by me. Because there was no detectable fogging, the actual safe time limit was therefore an unknown time beyond 30 minutes.

When I later performed similar testing for a DIY red LED safelight under Rubylith, I extended the test out to 60 minutes without any apparent fogging on MGIV. That's where my earlier incorrect reference to MGIV came from.

Ken

 

[Sundowner]

And it's confusing me as well. The #19 filter should cut off virtually ALL of the blues and greens. In other words, when in place you should see no blue and/or green bands at all.

Before my successful (pre-fogged) safelight tests I fired up the Duplex, let it warm for ~30 minutes, then looked at the CD reflections unfiltered. In addition to the massive yellow sodium doublet, I saw the much, much fainter blue and green spikes. I also saw the extra deep red spike.

Then while looking directly at those spikes I interposed a single layer of #19 filter. The blue and green spikes disappeared. When I removed the #19, they returned. Back and forth.

Later, when I performed the safelight test I was able to leave a sheet of Kentmere Bromide #3 graded paper out for ~30 minutes with no hint of fogging.* As you may know, bromide papers are very fast. It should have responded to any blue light present. But it didn't. It remained pure white. (Even checked with a reflection densitometer to factor out my subjective eyes.)

So as I said, I too am confused.

Also keep in mind that if you use a cover sheet of Rubylith you will likely be filtering out all of the yellow sodium light as well. At least in a perfect world. I've never tried it myself, so I don't know how much will pass. Maybe only that secondary red spike I mentioned above?

Ken

* Apologies, as I earlier identified the test paper as Ilford MGIV. It was actually the Kentmere Bromide. The Ilford was used for my red LED safelight testing.

Well, allow me to make it even more confusing: I did the exact same thing that you did with filtered and unfiltered reflections on the CD. Unfiltered, I saw the blue and green bands, and also the massive yellow sodium band and the deep red...exactly as expected. With the #19 filter in place, the yellow and red were unaffected and the blue was entirely cut out...but the green band was still dimly present. I actually managed to do a side-by-side comparison with the #19 filter halfway covering the sodium lamp, and although the green band was attenuated it was, as aforementioned, present. So, I don't know what to make of that, because there should be very, very little green coming through the #19 filter...but it was most assuredly there, and likely - in my opinion - burning the paper.

 

[Jim Noel]

I simplified the solution in my 10x10' darkroom. I use the supplied yellow/tan filter over the tube. I inserted black foam core in the vanes to attenuate the light. I have never had a problem with fogging in the 20+ years I have used this light.

 

[Sundowner]

I simplified the solution in my 10x10' darkroom. I use the supplied yellow/tan filter over the tube. I inserted black foam core in the vanes to attenuate the light. I have never had a problem with fogging in the 20+ years I have used this light.

That's basically the point that I wanted to get to, down the road...but I haven't gotten to "never had a problem with fogging" yet.

 

[Ronald Moravec]

Go with the filter sold by manufacturer. Rosco gels come in large sheets and the code number is printed only in one corner. Depending on where the cuts are made, it may or may not show up.

I use the gels in green and blue as VC filters for Aristo cold light head using all the grades of each, 1/8 to full. The man who made Aristo heads put me on to it.

 

[Ken Nadvornick]

Hmm...

If the set of filters you are using, regardless of where they came from or what material they are made of, are successfully removing all of the extraneous higher wavelengths above the sodium D-lines doublet at ~589nm, then the only other immediate explanation is that the paper emulsion sensitivity is bleeding over to some degree into that wavelength. Either because it was designed to do that, or it has aged to do that.

Or something else silly is going on. Like, say, a leaky paper safe. When I did my testing I did take new sheets of fresh paper directly from the box it came in while in total darkness, then held them in a clamshell safe that I also occasionally use to store loaded film hangers, while the Duplex warmed up. I don't really think this is it, but it is a very slight possibility.

I am now looking for some time here to go down to my darkroom and also repeat the CD wavelength check. Maybe tonight.

Perhaps my color vision is slightly different than his and I missed the very faint residual green line that 'Sundowner' observed. Since I tested on Kentmere Bromide, which should be blue-sensitive only, I would still have seen no fogging if, as he observed, all of the blue was removed.

Tests on VC paper (which I haven't done under the Duplex) would be a different story however, if there was some minor residual green remaining. And I do note that if one looks at the Rosco transmission chart for the #19 filter, there IS a very slight transmission of greens. It looks to maybe only be 2-3%. But it's definitely there, if the chart is accurate.

For the record, of late I've been using only the red LEDs because I got into working with some Slavich graded bromide, and that paper is marked as red-only safe. Then when using MGIV I've just continued with those LEDs.

Ken

 

[Roger Cole]

Defective #19 filter?

 

[Sundowner]

Go with the filter sold by manufacturer. Rosco gels come in large sheets and the code number is printed only in one corner. Depending on where the cuts are made, it may or may not show up.

I use the gels in green and blue as VC filters for Aristo cold light head using all the grades of each, 1/8 to full. The man who made Aristo heads put me on to it.

I'm about at the point of trying a fresh filter from Freestyle (or whomsoever retails them) just to see what happens. The sheet of rubylith came in today, though, so I'm going to test that out tonight...and if I still get fogging then I'll know something silly is going on, somewhere, although I don't know what it could be. I've developed an unexposed strip and gotten pristine white, so I know the emulsion isn't just graying over time.

Also, I never thought of using blue/green gels as cold light filters...that's pretty innovative!

I did another safelight test this morning. First, I used a CD as Ken spells out to check for other colors of light. With the vanes wide open, and the Yellow tape filter in place in the bottom, the Red tape filter in the vanes, I saw no color except yellow. Still with the vanes wide open, I exposed two pieces of paper to the safelight, one was flashed before the safelight exposure, the other afterwards. Both showed signs of fog after 3 minutes in the flashed area, none in the borders. Both showed fogging at 7 minutes in the flashed area, none in the borders. My previous test was done in a different darkroom and I cannot guarantee there wasn't a light leak.

I expect better performance with the vanes fully or partially closed.

I didn't even make it to three minutes; based on what I saw on my very-inelegant coin test, I had near-immediate, sub-1-minute fogging...but I halfway expected that with the green band that I saw. I wish I could get a picture of it; the best I can say is that it looked like a fuzzier version of the sodium spectrum that was linked-to earlier in this thread, excerpting the blue band. I know I don't have light leaks, because nothing has changed in my darkroom except this safelight and heretofore I could leave Oriental out for an hour without a trace of fogging...and that was a long, boring hour, let me tell you.

Hmm...

If the set of filters you are using, regardless of where they came from or what material they are made of, are successfully removing all of the extraneous higher wavelengths above the sodium D-lines doublet at ~589nm, then the only other immediate explanation is that the paper emulsion sensitivity is bleeding over to some degree into that wavelength. Either because it was designed to do that, or it has aged to do that.

Or something else silly is going on. Like, say, a leaky paper safe. When I did my testing I did take new sheets of fresh paper directly from the box it came in while in total darkness, then held them in a clamshell safe that I also occasionally use to store loaded film hangers, while the Duplex warmed up. I don't really think this is it, but it is a very slight possibility.

I am now looking for some time here to go down to my darkroom and also repeat the CD wavelength check. Maybe tonight.

Perhaps my color vision is slightly different than his and I missed the very faint residual green line that 'Sundowner' observed. Since I tested on Kentmere Bromide, which should be blue-sensitive only, I would still have seen no fogging if, as he observed, all of the blue was removed.

Tests on VC paper (which I haven't done under the Duplex) would be a different story however, if there was some minor residual green remaining. And I do note that if one looks at the Rosco transmission chart for the #19 filter, there IS a very slight transmission of greens. It looks to maybe only be 2-3%. But it's definitely there, if the chart is accurate.

For the record, of late I've been using only the red LEDs because I got into working with some Slavich graded bromide, and that paper is marked as red-only safe. Then when using MGIV I've just continued with those LEDs.

Ken

Maybe it's the VC paper I'm using, then; I don't know how green-sensitive Oriental's Seagull VCFB really is, but now that I think about it my splint-print soft/hard exposures - I use Ilford's MG 00 and then the 5 - are actually pretty close to each other, time-wise. Heretofore, the hard exposures were always longer because of the one-stop light loss, and when I printed on Ilford MG-IV the exposures were usually in a 1:2 ratio. Perhaps, then, Seagull is more green sensitive and I have a compound problem. Thoughts?

My paper is a brand new box of MGWT, the paper is taken from the box, not a safe. PM me your address and I will send you some of the filter material I am using, which is the same stuff in the filters sold by Freestyle and others for these safelights. You can try it out yourself.

And as I said, I get some fogging when the vanes are wide open after three minutes, but closed down, I get much longer times while still bright enough to work easily.

I should note that I am using these Kodak instructions to perform the test.

I was going to move on to that exact Kodak test after successfully completing my ad-hoc coin test; haven't made it that far, yet. :munch:

Defective #19 filter?

I've wondered that, actually, simply because I found a LOT of information on rebuilding the Thomas with the #19 filter and when I did so I got results that seemed very atypical. Either that, or I'm really much more incompetent in the darkroom than I suspect...and that's an accomplishment!

I'm going to go in and try a test with the rubylith right now, and see where I get. I'll post some results in a bit... :munch:

 

[Sundowner]

Do you have both the top and bottom filters? If you are only using the top filters, that may be the source of the problem.

I did have both, yes; I had the red-tape and yellow-tape varieties, with yellow on the inner filters and red in the vanes, if I remember correctly. The inner filter was replaced with the problematic #19 filter and the outer vane filter was replaced with the #27 medium red. I didn't notice much of a difference in the amount of fog/burn with the vanes in any given position, which implies - to my limited understanding - that the #19 filter didn't work very well, and that the #27 filter didn't change much of what the paper saw, even though it certainly made an impact on what I could see.

I didn't have time to get the paper test done, but I did manage to get the rubylith cut and installed, and I also snapped a couple of quick cell-phone images that didn't distort the colors too much. As it turns out, the light that the rubylith allows through isn't red at all; it's really about as orange as it looks in the following photo.

Pictured: And I'm not sure what that means.




In that image, the rubylith is actually sandwiched between two sheets of glass and taped into place so that there are no light leaks; it doesn't look very sealed, but I promise you that it is. The light is surprisingly orange; I figured that it would be much redder...so either I was 100% wrong or I got some non-kosher rubylith. Regardless, it seems to be working because I also managed to catch a very non-scientific CD reflection that shows the sodium bands.

Pictured: Absence of green and/or blue.




Since I managed to catch the color bands, I'll try and replace the #19 filter and see if I can show the green band that I've been seeing...and I'll also try the paper test and see if I can make it to eight minutes this time. If not...well, it's back to Square One.

 

[Ken Nadvornick]

Finally made it down to my darkroom this evening for some visual sodium safelight testing.

Here's what I did...

Removed the Duplex from it's correctly configured hanging mount.
Placed it on a table in a darkened basement at night.
Turned off all other light sources in the house.
Removed all filters so only the bare bulb was showing.
Closed the empty vanes.
Let bulb warm and stabilize for 60 minutes.
This bulb is a relatively low mileage sample.
Made an observation on the bare bulb itself as a baseline.

Here's what I saw...

DVDs showed better color bands than CDs.
DVD movie Mama Mia! hardly showed any colors.
DVD movie My Big Fat Greek Wedding was much better.
DVD movie Four Weddings and a Funeral showed excellent color bands.
Using FWAAF I saw 2 faint blue bands, 2 green bands, and 1 red band.
The sodium yellow intensity was blinding.

Here's what I did...

Covered both slots with a single layer of filter material.
Filter material was Rosco #19 Fire polyester.
Filter material was not sandwiched between glass sheets.

Here's what I saw...

Both blue bands gone.
A single reduced green band still visible, the 1 red band still visible.
The sodium yellow intensity was moderately reduced.

Here's what I did...

Covered both slots with a double layer of #19 filter material.

Here's what I saw...

Both blue bands gone.
Both green bands gone.
One red band still visible.
The sodium yellow intensity was severely reduced.

And here's what I think...

All my original observations were made using the DVD for the movie The Hunt for Red October.* I now see that different discs have very different reflection characteristics. My original observations showed no residual blues or greens through a single layer of #19. Using the FWAAF disc I now see a definite residual green band.

My original paper fogging tests were made using only pre-threshold-exposed Kentmere Bromide #3 sheets. This should be a blue-sensitive only paper. It showed no fogging even after 30+ minutes.

Based on what I saw tonight, I now need to try Ilford MGIV VC blue/green paper to see if that residual green band makes a difference. Based on Sundowner's results, I would expect it to fog on the low contrast end to some detectable level when using my single sheet of #19 material. Then I need to try doubling up the sheets.

For grins I did a Web search for a narrow-width bandpass filter material centered on the two sodium D-lines at ~589nm. Turns out you can get precisely that spec material. But it's ~$200-$350 per 2x2-inch glass squares for scientific usage. Yikes. But if we were rich that would do the trick perfectly...

Greg, I'm PMing my mailing address as you suggested. If you'd be willing to loan me enough of those other two Rosco filters to cover the upper vanes of the Duplex for a visual check, I'd be glad to return them.

Ken

* You know... Red... October... Safelight testing... <Groan..>

 

[clayne]

When the thread has taken it to the point of which type of cinematic material is on each DVD used for spectral comparison then I know we've hit gold; I'm not surprised Ken has taken us there too.

FWIW: I also have a Thomas Duplex, used it with vanes just about fully closed and never experienced fogging with either MCC110 or Emaks graded papers. However, I didn't use it 100% of the time because it was just too bright for my 10 by 16 by 12' (ceilings) garage darkroom at the time. When I did use it I used it in addition to 2 ceiling banked red LED safelights. I did not remember seeing any kind of fogging as a result of this safelight.

I did use the included filters (they're translucent red) at all times - just that the vanes were sometimes slightly open. I never used it without filters.

 

[Sundowner]

Here's what I did...

Covered both slots with a single layer of filter material.
Filter material was Rosco #19 Fire polyester.
Filter material was not sandwiched between glass sheets.

Here's what I saw...

Both blue bands gone.
A single reduced green band still visible, the 1 red band still visible.
The sodium yellow intensity was moderately reduced.

That's basically what I got. Faint green, huge yellow, moderate red.

Here's what I did...

Covered both slots with a double layer of #19 filter material.

Here's what I saw...

Both blue bands gone.
Both green bands gone.
One red band still visible.
The sodium yellow intensity was severely reduced.

I haven't tried doubling the filter, yet, but I think I'll give it a shot.

And here's what I think...

All my original observations were made using the DVD for the movie The Hunt for Red October.* I now see that different discs have very different reflection characteristics. My original observations showed no residual blues or greens through a single layer of #19. Using the FWAAF disc I now see a definite residual green band.

My original paper fogging tests were made using only pre-threshold-exposed Kentmere Bromide #3 sheets. This should be a blue-sensitive only paper. It showed no fogging even after 30+ minutes.

Based on what I saw tonight, I now need to try Ilford MGIV VC blue/green paper to see if that residual green band makes a difference. Based on Sundowner's results, I would expect it to fog on the low contrast end to some detectable level when using my single sheet of #19 material. Then I need to try doubling up the sheets.

I hadn't really thought that different discs would show different bands, but I guess that could easily be true; I only used the one disc and I got the blue/green/yellow/red pattern you described...but I'm still confused as to why I got so much fogging when I threw the #27 filter over top of the #19, because that should have been a total cutoff of anything that could hurt the paper, regardless of sensitivity...unless something silly was happening: porous filter, paper emulsion acting screwy, etc. That's why I'm going to try the rubylith; it should be paper-safe, and if I still get fogging then something completely odd is happening.

 

[Sundowner]

Okay, quick update with some results: I tried the non-scientific eight-minute coin test again, just now. I used a single layer of rubylith between two sheets of glass in the lower filter position and sealed up all possible light leaks on the safelight; the safelight itself was allowed to warm up for about 20 minutes or so. After developing the test strip in complete darkness I can't see any traces of fogging or coin silhouettes...so in addition to being ecstatic at having made progress, we now know two things:

1) The rubylith layer effectively cuts the blue-green bands out and acts as an effective filter.
2) The paper emulsion is more than likely intact, which makes sense because it's being stored properly.

At this point, I think my next step is to flash the paper to its threshold and do a more accurate test, and to try installing some opaque panels in the vanes; the rubylith cuts a lot of the overall light, but it's still ridiculously bright in the darkroom and a bit less light would be appreciated when working over an enlarger easel.