Thomas Duplex Issues

[Ken Nadvornick]

A quick caveat regarding the possibility of using Rubylith as a Duplex filter replacement. The Rosco filter sheets are made of a rugged heat-resistant polyester material as they are intended to filter theatrical lighting. Using them in a Duplex should be right up their design alley.

But Rubylith I'm not so sure about. I don't know what it's made of. Or the coloring agent that is used. Or how those may stand up to the prolonged heat from close proximity to an LPS lamp. I've never tried using Rubylith for a six or eight hour darkroom session, let alone a dozen of those in a row over time.

Remember also, the Rubylith cuts out a lot of light because it's absorbing that energy. It is not a dichroic medium. And absorbing energy means it will get hot. So at a minimum it may fade somewhat quickly. Or at the other end of the scale it may fail catastrophically. Or it may be just fine. I don't know for sure.

Just something to keep in mind...

When I receive the other filter samples that Greg is kindly offering I intend to continue testing to try and get to the bottom of this. Unfortunately I don't often have large blocks of free time, so it may take awhile. I can post frequently to APUG because I sit in front of computers writing software all day. But I don't always have big chunks of disposable time otherwise.

Ken

 

[Sundowner]

A quick caveat regarding the possibility of using Rubylith as a Duplex filter replacement. The Rosco filter sheets are made of a rugged heat-resistant polyester material as they are intended to filter theatrical lighting. Using them in a Duplex should be right up their design alley.

But Rubylith I'm not so sure about. I don't know what it's made of. Or the coloring agent that is used. Or how those may stand up to the prolonged heat from close proximity to an LPS lamp. I've never tried using Rubylith for a six or eight hour darkroom session, let alone a dozen of those in a row over time.

Remember also, the Rubylith cuts out a lot of light because it's absorbing that energy. It is not a dichroic medium. And absorbing energy means it will get hot. So at a minimum it may fade somewhat quickly. Or at the other end of the scale it may fail catastrophically. Or it may be just fine. I don't know for sure.

Just something to keep in mind...

When I receive the other filter samples that Greg is kindly offering I intend to continue testing to try and get to the bottom of this. Unfortunately I don't often have large blocks of free time, so it may take awhile. I can post frequently to APUG because I sit in front of computers writing software all day. But I don't always have big chunks of disposable time otherwise.

Ken

I haven't found that the housing seems to get very hot in a couple hours' time, but I'll certainly keep this in mind; hopefully, rubylith wouldn't fade over a three- to six-month period or fail in catastrophic fashion. As far as the light-cutting is concerned, the amount that passes the filter is enough to keep the room REALLY BRIGHT; I'm going to have to cut it down further to see anything on the easel. I'll be really interested in seeing your results from Greg's filters; thus far I think we've had a lot of good information in this thread and I'm hoping that there will be more coming. :munch:

 

[George Nova Scotia]

I've been following this thread and must say that I've run into a similar problem with the Thomas Duplex and Ilford Warmtone paper using Rosco 19 Fire & even adding some layers of a Rosco Red. MGIV is fine, just the WT (FB in my case). I also have two of the Kodak "beehive" style lamps with Kodak OC filters & 15w bulbs - this setup is clean up to 20 minutes - I got bored after that. I wasn't ready to use the WT paper & with the OC filters that's about as far as I went.

Keep up the good work.

 

[Sundowner]

I've been following this thread and must say that I've run into a similar problem with the Thomas Duplex and Ilford Warmtone paper using Rosco 19 Fire & even adding some layers of a Rosco Red. MGIV is fine, just the WT (FB in my case). I also have two of the Kodak "beehive" style lamps with Kodak OC filters & 15w bulbs - this setup is clean up to 20 minutes - I got bored after that. I wasn't ready to use the WT paper & with the OC filters that's about as far as I went.

Keep up the good work.

Maybe there's something different in the emulsion, perchance? I'm not using a warm tone paper but from what I can tell, Oriental VCFB is pretty sensitive to green...so maybe you're in the same situation as me. :confused:

Another follow-up. I conducted the test again with Ilford MGWT, but with the vanes fully closed. As before, I am using the yellow tape filter in the bottom, which contains 3407 and 3406 Rosco filters, and a red tape filter in the vanes containing a sheet of #19 Fire.

No fogging after 7 minutes. With the vanes open I had fogging at the 3 minute mark.

I extended the test to 3, 9, and 21 minutes, 3x the original test. Vanes still fully closed.

No fogging at all.

Okay, well that partially explains the confusion I had on how the 3406 and 3407 filters were blocking the correct wavelengths; somehow, I missed you having a 19 filter in the vanes. That makes more sense, now; it sort of makes me even more confused about the WT paper, but right now I'll accept partial confusion as a form of progress.

I'm going to try a longer test tonight and see where I get.

 

[Sundowner]

Well, these are designed to have the yellow tape filter in place for all safelight purposes, and only the filter in the vanes are changed to suit the specific material being handled. The 3406 filter is very similar to an Wratten 85B filter for excess blue, and the 3407 is a Wratten 85B with 3 stop ND. This filter may just attenuate the spectrum a small amount, but mostly knock down the intensity of the bulb. The filter in the vanes would shift the spectrum for the appropriate light sensitive material, whether it is orthochromatic, VC paper, RA4, x-ray, etc.

I don't know, I am just thinking out loud.

Actually, that makes a lot of sense. Nice thought process!

 

[clayne]

So was the original scenario that the light was being used with only half the filters? Yeah that would definitely do it - you need the filters no matter what.

 

[Sundowner]

So was the original scenario that the light was being used with only half the filters? Yeah that would definitely do it - you need the filters no matter what.

Well, my original scenario was the #19 filter in the lower position and the #27 filter in the vanes, but I got fogging even with the vanes completely closed; Greg's setup isn't the same as the one I had.

 

[Ken Nadvornick]

And to make things worse, my original scenario was single sheets of #19 in the lower position, and black mount board in the vanes to allow for controlling intensity. Pre-threshold-exposure testing with (presumably blue-only sensitive) Kentmere Bromide showed no fogging out to at least 30 minutes.

The problem may be that #19 alone works well to block the two residual blue bands present, but only partially blocks the two green bands also present. These bands, along with an additional deep red one, likely arise from the Penning Mixture gases (argon and neon) also present in the lamp to assist with initial striking.

In other words, Bromide is OK, but Ilford VC is not, depending on exposure times.

Ken

 

[Sundowner]

And to make things worse, my original scenario was single sheets of #19 in the lower position, and black mount board in the vanes to allow for controlling intensity. Pre-threshold-exposure testing with (presumably blue-only sensitive) Kentmere Bromide showed no fogging out to at least 30 minutes.

The problem may be that #19 alone works well to block the two residual blue bands present, but only partially blocks the two green bands also present. These bands, along with an additional deep red one, likely arise from the Penning Mixture gases (argon and neon) also present in the lamp to assist with initial striking.

In other words, Bromide is OK, but Ilford VC is not, depending on exposure times.

Ken

That's exactly my line of thinking at current; #19 has been reported to be a successful replacement in too many instances for me to think that it just doesn't work, but I think that - like most things - it only works well in certain situations. From the information here and my own observations it seems to be a great option for those using blue-sensitive papers, and not very effective at all for anything that's green-sensitive. However, rubylith seems to be doing well in that latter capacity and from a few discussions I've had with people that know the material far better than me, I'm not worried about failure/fade at this point in time; it seems to have a good track record as an effective safelight filter for the sodium spectrum.

I still haven't managed a better safelight test than my makeshift eight-minute coin check, but I did leave the light on for several hours straight last night in order to see how warm it got; the result was that the filter area was only lukewarm, but the lower part of the housing near the ballast was radiating a good deal of heat...so it appears that the ballast is the warm part on the light. I'm not sure if that's normal or not, but it was noticeably hot so I might consider putting a finned heat sink on the thing just to keep it cooled down a bit. Anyone else have any sort of significant heat from the ballast area?

 

[Sundowner]

Pictured: Approximate color with a rubylith filter.




Apologies for the horrid cell-phone pictures; I had to play with the settings to get it to record something that approximates the real-life view and it generated a lot of noise in the image. Those problems aside, it's easy to see that this is a MASSIVE amount of light; one can easily read labels and see across the room.

Pictured: Pay no attention to the clutter in the background.




Snapping these two images was kind of entertaining because I could see WAY better than my phone's camera could see; the room is actually a lot brighter than the image implies and the printing on the Sprint bottle isn't nearly that blotchy. Ahh, the wonders of high-ISO digital photography...

 

[Sundowner]

Quick Update: I had a marathon printing session today that started with a couple of long paper tests; the long story made short is that I didn't have fogging or issues with highlights in any way, even after 30+ minutes under the safelight. The rubylith seems to cut the over-bright sodium lamp down to a very nice level and I printed all night with the vanes wide open. Seems that I've gotten this particular issue solved! Thanks to everyone for all their help and suggestions!

 

[Ken Nadvornick]

That's great to hear.

Given that APUG is such a valuable database for searching, perhaps when you get a chance you could expand on your comments just a bit and give an explicit full description of your solution?

For example, did you use only Rubylith filtration? Or was Rubylith in addition to other filters? If so, which ones? What positions? How many layers of Rubylith? Sandwiched between glass? Pre-threshold fog testing? Paper brands that did not fog? Distance of test papers from safelight? Etc., etc.?

It's virtually certain that someone else down the road will find this thread and read those explicit answers and want to give it a try themselves...

I'm still planning on more testing myself once I get my hands on some of those alternative filter materials. Unfortunately right now I'm planning for a cross-state large format photo vacation for October before the weather turns ugly again for ten months. So for the moment this is on hold.

Ken

 

[Sundowner]

Given that APUG is such a valuable database for searching, perhaps when you get a chance you could expand on your comments just a bit and give an explicit full description of your solution?

That's a good idea. I'll spell it out very clearly, then: There are two issues at play with the Thomas; light leaks and improper filtration...and to get good performance out of the light, both issues need to be resolved.

One must first realize that due to the manner in which the Thomas is built - folded sheet metal that's riveted together - the gaps and seams in the safelight housing itself are a likely source for the unintentional escape of unfiltered sodium light; one must also realize that even a small amount of this light can be problematic because of the sheer intensity of the lamp. With that in mind, my advice is very simple: tape over every seam on the housing right out of the gate and thus negate the possibility of errant light escaping. A cleaner solution would be to take the housing apart and install some light-blocking foam or baffling of some sort wherever it's needed (which is almost everywhere) or to caulk over the seams with black silicone, but an effective on-the-cheap fix is any sort of opaque black tape. In addition to all of the seams on the housing, the interior corners of the lower filter "trays" - and if you have one of these lights you know exactly what I'm talking about - need to be taped/blocked, and the lower filters themselves won't be hurt by being taped into place, either. I'll restate it again for emphasis: TAPE OVER EVERY SEAM OR GAP.

The second issue is filtration, and without re-hashing everything we've covered so far, I'll simply give you my final filter construction: one (1) sheet of rubylith sandwiched between the stock filter glass panels, with the edges taped as per a factory filter. There are no additional filters employed, and no diffusion material of any sort. There are no additional filters in the vanes; instead, a matte black board can be installed in order to dim the light as needed (such as when composing on the easel). The rubylith filter cuts the light output of the sodium lamp down quite a bit, but it's still quite formidable; thus, those that use faster papers or whom prefer less overall illumination may find that installing a black panel in the vanes greatly aids in controlling the ambient light level. I have found that I prefer the wide-open setting, but that's personal preference.

At this point, the longest paper test I've conducted is 32 minutes on Oriental Seagull VC-FBII, and I noticed no fogging or burning on either pre-flashed or virgin paper; needless to say, this is FAR longer than is required for...well, almost anything. The approximate distance at which the test was conducted was 4 feet, with the vanes at their maximum opening. I can't speak for papers other than Seagull, but since this has been my most problematic paper in relation to safelights - it tends to fog/burn the quickest - I can only assume that most other papers would be safe under the rubylith filtration as well.

That's all I can come up with, for now, but as I recall other important details - and I'm sure that I will - I'll add/edit as needed.

 

[jstraw]

"one (1) sheet of rubylith sandwiched between the stock filter glass panels"

It's still unclear to me whether you removed the original filtration material from the glass sandwich or added the rubylith to the original material.

 

[Sundowner]

It's still unclear to me whether you removed the original filtration material from the glass sandwich or added the rubylith to the original material.

Yes, the original filters were removed. I had stated that early in the thread, and in the sentence after the one you quoted I said that no additional filters were used... but I can see how that might not have been clear. So, to restate: the only filter used was a single sheet of rubylith between the stock glass panels.

 

[jstraw]

Yes, the original filters were removed. I had stated that early in the thread, and in the sentence after the one you quoted I said that no additional filters were used... but I can see how that might not have been clear. So, to restate: the only filter used was a single sheet of rubylith between the stock glass panels.

Thanks. I may start taping up my Thomas this weekend. I have some rubylith on the way.

 

[Sundowner]

Thanks. I may start taping up my Thomas this weekend. I have some rubylith on the way.

Don't skimp on the tape; I had light leaks galore on mine and it caused me no end of frustration. A $3 roll of electrical tape will go a long way, even if it's not the perfect solution. Pay particular attention to the inside corners of the lower filter trays; I had 1/16" gaps in the sheet metal in those areas.

 

[KennyMark]

My goal is to be able to refurbish my safelights to as near OEM condition as possible. After reading every web page, PDF, scrap of paper, blog, and forum post that I could find pertaining to Thomas Duplex Safelight filtration and filter replacement, I've compiled the following information in the hopes that sharing it may further the cause. I've not created a bibliography here, but if you desire to know the source of any portion of this, just ask and I'll share. I've gone out of my way to eliminate conjecture, opinion, and wishes from this information. Obviously if we could talk to whomever worked in purchasing for Thomas or had their account at the supplier of gels, we could learn much more. For now and perhaps evermore, we lack this and must pursue other avenues.
Cheers,
Kenny

Manufacturer's information
Thomas Duplex Safelights were sold in three configurations of four different filter packs.

The filter packs were identified by the color of tape used to bind all four edges of a sandwich of filters, diffusion material, and glass. The colors were Yellow, Black, Red, and Green. Each safelight had a pair of each colored filter pack that it shipped with.

The filter packs were made in two different dimensions, the larger size for the lower stationary position and the smaller size for the operable vane which when elevated revealed the lower filter pack.

By operating the moveable vanes each model could potentially protect two different photographic materials. There was not any marking on the case of the safelight indicating which model it was.

Model DUG was sold for use with color paper and black and white paper. DUG models were shipped with a yellow taped filter pack in the lower stationary positions, and a black taped filter pack in the moveable vanes.

Model DUB was sold for use with orthographic materials and black and white paper. DUB models were shipped with a yellow taped filter pack in the lower stationary position, and a red taped filter pack in the moveable vanes.

Model DUX was sold for use with X-RAY film. DUX models were shipped with a green taped filter pack in the lower stationary position, and a red taped filter pack in the moveable vanes. (Note: I found no reference to model DUX being used neither with vanes elevated nor for use with orthographic materials.)

Thomas also offered to make custom version of filtration packs for specific needs of their customers. This means that there may be some of these custom units in the wild that might not have any markings designating their special use.

I was not able to find any information regarding the specific gels originally sold with the Duplex safelights nor their transmission or attenuation characteristics.

One black taped filter pack that I have opened included six sheets of what appeared to my eyes as the same material. There was a sheet of translucent paper tissue on each side of the pack between the gel and the glass. I believe that this was an OEM pack as the gelatin material and the diffusion material were affixed together with a pair of smaller than office equipment staples along one of the short edges. My belief that this is OEM is also based in part on the difference between it and the contents of a black taped filter pack that Greg Davis reported opening that contained a different set of filters (continue reading below for a summary of Greg's findings). It is also noteworthy that one of the filters located in the outermost position of the sandwich shows fading of the area not covered by the tape. I assume that this would have been the one facing the lamp, but have no to way to confirm this as it also could have been the outward facing position and could have been exposed to another strong source of light.

Aftermarket filter replacements

At least two retailers offer replacement filter packs for sale. KBH in Canada, and Freestyle in California. Greg Davis has reported earlier in this thread that upon purchasing a pair of each of the Yellow, Red, and Black filter packs from Freestyle, he cut them open and discovered that some of them had identification numbers on the gels from the manufacturer. Here is a summary of his findings:

Yellow taped - one sheet of Rosco Roscolux #3406 Sun85 and one sheet of Rosco Roscolux #3407 SunCTO with diffusion material on each side of the gel pack between the gel and the glass.

Black taped - two sheets of each of unmarked gelatin filters that to his eye looked identical to the Rosco Roscolux #3406 Sun85 and Rosco Roscolux #3407 SunCTO with diffusion material on each side of the gel pack between the gel and the glass.

Red taped - two sheets of Rosco E-Colour+ #019 Fire with diffusion material on each side of the gel pack between the gel and the glass.

Below is space for additional information as reported to me or in this thread.

Reports from users on contents of filter packs they have opened up:

Known OEM filters (reported by original purchaser that can confirm provenance and original tape colors):

Yellow tape: None yet

Black tape: None yet

Red tape: None yet

Green tape: None yet

Suspected OEM filters (reported by owners unable to confirm provenance nor original tape colors)

Yellow tape: None yet

Black tape: KennyMark - six sheets of identical unmarked gelatin with diffusion, stapled. One sheet showing masked fading.

Red tape: None yet

Green tape: None yet

Known aftermarket filters (reported by users having purchased replacement filter packs from retailers)

Yellow tape: Greg Davis - one sheet each of Rosco Roscolux #3406 Sun85 and #3407 SunCTO with diffusion.

Black tape: Greg Davis - two sheets each of unmarked filters identical to his aftermarket yellow tape packs above (#3406 and #3407).

Red tape: Greg Davis - two sheets of Rosco E-Colour+ #019 Fire with diffusion.

Green tape: None yet

Other filters (reported by users purchasing used safelights, replacements from auction sites, DIY packs, and completely unknown)

Yellow tape: None yet

Black tape: None yet

Red tape: None yet

Green tape: None yet

Masking tape: KennyMark - obvious DIY, single sheet of unmarked filter, badly deteriorated with wrinkles and cracks without diffusion.

 

[David A. Goldfarb]

Thanks for the info! That's very useful. I hadn't even realized there were different filters available, but I'm glad I got the one I need.

 

[KennyMark]

Thanks for the info! That's very useful. I hadn't even realized there were different filters available, but I'm glad I got the one I need.

If you care to help, we would love to know what you find inside your filters!

 

[David A. Goldfarb]

Since I recently set up a new darkroom, smaller than the last, I've got the Thomas Safelight packed in storage, but maybe at some point I can get it out and look.

 

[mgb74]

All the discussion lately about the Thomas Duplex made me want to get mine out of storage and check it out. It was purchased used and I never used (instead using a couple of Kodak 10x12 lights). Here's what I found.

There were 2 on each side of the lower stationary area. All had yellow tape. On each side, 1 appeared to be original and 1 clearly not. I say appeared to be original based on the quality of the tape job. All appeared to have an OC colored gel and a diffusion sheet. I took apart the 2 that I didn't think are original. They had 1 layer of the OC colored gel and one diffusion sheet and had some gaps between the gel and the edge of the glass (again supporting my "non-original" thinking).

The yellow tape on the "non-original" filters appeared to be common vinyl electrical tape. The possibly original filters had a tape that seemed more paper based (like masking tape) and had some texture to it.

I don't know why the prior owner had 2 filters on each side. I.E. whether to moderate the light or to provide additional filtration.

The filters in the moveable vanes have black tape. They appear to have an OC colored gel (or gels) in between 2 sheets of diffusion material. Much less light transmission than the filters in the stationary area. I did not take these apart.

I hope to test the light this weekend with the current filters. I built a set of filters for the moveable vanes that are just 1 layer of matte acetate (no gel). They seem to work well when left closed. Also, I plan to build up a set of filters for the stationary area using some rubylith I have and test that as well.

 

[StoneNYC]

All the discussion lately about the Thomas Duplex made me want to get mine out of storage and check it out. It was purchased used and I never used (instead using a couple of Kodak 10x12 lights). Here's what I found.

There were 2 on each side of the lower stationary area. All had yellow tape. On each side, 1 appeared to be original and 1 clearly not. I say appeared to be original based on the quality of the tape job. All appeared to have an OC colored gel and a diffusion sheet. I took apart the 2 that I didn't think are original. They had 1 layer of the OC colored gel and one diffusion sheet and had some gaps between the gel and the edge of the glass (again supporting my "non-original" thinking).

The yellow tape on the "non-original" filters appeared to be common vinyl electrical tape. The possibly original filters had a tape that seemed more paper based (like masking tape) and had some texture to it.

I don't know why the prior owner had 2 filters on each side. I.E. whether to moderate the light or to provide additional filtration.

The filters in the moveable vanes have black tape. They appear to have an OC colored gel (or gels) in between 2 sheets of diffusion material. Much less light transmission than the filters in the stationary area. I did not take these apart.

I hope to test the light this weekend with the current filters. I built a set of filters for the moveable vanes that are just 1 layer of matte acetate (no gel). They seem to work well when left closed. Also, I plan to build up a set of filters for the stationary area using some rubylith I have and test that as well.

If you don't want it I'll take one please

 

[mgb74]

...One must first realize that due to the manner in which the Thomas is built - folded sheet metal that's riveted together - the gaps and seams in the safelight housing itself are a likely source for the unintentional escape of unfiltered sodium light; one must also realize that even a small amount of this light can be problematic because of the sheer intensity of the lamp. With that in mind, my advice is very simple: tape over every seam on the housing right out of the gate and thus negate the possibility of errant light escaping. A cleaner solution would be to take the housing apart and install some light-blocking foam or baffling of some sort wherever it's needed (which is almost everywhere) or to caulk over the seams with black silicone, but an effective on-the-cheap fix is any sort of opaque black tape. In addition to all of the seams on the housing, the interior corners of the lower filter "trays" - and if you have one of these lights you know exactly what I'm talking about - need to be taped/blocked, and the lower filters themselves won't be hurt by being taped into place, either. I'll restate it again for emphasis: TAPE OVER EVERY SEAM OR GAP...

Mine has vents on the bottom which "leak" light. Is there some internal light baffling I might be missing? The "leak" did not seem to have an effect during my 8 minute test.

 

[mgb74]

...I hope to test the light this weekend with the current filters. I built a set of filters for the moveable vanes that are just 1 layer of matte acetate (no gel). They seem to work well when left closed. Also, I plan to build up a set of filters for the stationary area using some rubylith I have and test that as well.

I did a quick test of the rubylith filters with exposure for 0, 2, 4, 6, and 8 minutes. I don't see any evidence of paper fogging.