I <3 Thomas Duplex

[frobozz]

Here's a scan I made a few years ago of the instructions (such as they are) that came with my Thomas Duplex safelight:

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

Duncan

[Greg Davis]

To continue this thread, I took apart my filters and looked inside to see what gels are used. They are as follows:

Yellow tape:
White vellum diffusion
Roscosun CTO #3406
Roscosun 85 N.6 #3407

Red tape:
White vellum diffusion
Rosco Fire #19 (two sheets)

Black tape:
White vellum diffusion
Roscosun CTO #3407
Roscosun 85 N.6 #3406 (four sheets)
Roscosun CTO #3407 (again)
White vellum diffusion

The manufacturer cut the sheets in such a way that the gel numbers were still on the edges.

I also have an old filter from Thomas Duplex that I am unsure of its purpose since the tape has been replaced, but it had an amber filter like a 3407 and 3406 combined, a dark green filter like a Wratten #58 with two diffusion sheets between them.

[scheimfluger_77]

I bought a used $40 Thomas Duplex safelight today. The filters were kind of beat, so I replaced them with Rosco #19 "Fire" which has the right type of wavelength cut off:
...

How many layers of the Rosco filter do you use?

Steve

[scheimfluger_77]

Rubylith is red. It will dramatically reduce the brightness of the monochromatic yellow sodium vapor lamp used in the Thomas Duplex.

Not a good choice IM[-H]O.

- Leigh

Leigh, you've mentioned using the #19 filters in other posts. Do you actually open the glass sandwich and replace the existing filter or leave the old one in?

Steve

Oops! Never mind, I read the later posts. Thanks. :-)

[Greg Davis]

If you replace them, open the glass sandwich and replace the filter and vellum, then retape it together.

[Ken Nadvornick]

I've been recommending the Roscoe #19 Fire filter for years. It's a complete replacement for the black-and-white set of OEM filters that originally came with the unit. Meaning you can completely replace them with a single thickness of the Roscoe material. When you do this replacement the Roscoe filter will completely block the additional blue and green wavelength spikes coming from the low-pressure sodium vapor tube.

While the LPS tube is nominally a sodium-only device which should produce only light from the well-known sodium emission doublet at ~589nm, it also includes small amounts of argon and neon. These gases (called a Penning mixture) are required to assist in the inital striking of the lamp. They are also the source of the additional blue and green spikes in the output spectrum.

These spikes are the true source of the long-standing complaints that the Duplex is "too bright and fogs paper." Remove these spikes and the sodium-only light will not fog your paper, if it's Kodak OC filter safe in the first place. I have pre-flash tested my #19-filtered Duplex out to 30 minutes with Kentmere Bromide grade #3 (a fast bromide emulsion) without any hint of fog.

My standard advice is to go find a CD or DVD disc from your collection, then hold it up to an unfiltered Duplex lamp and look at the reflected light. You will easily see the blues and greens separated out. Then look at the same lamp through a #19 filter and will see the blues and greens have vanished, with only the sodium yellow remaining. This visual test works on any safelight. It's especially recommended for red LED lamps, as they too will often emit small blue or green spikes.

The Roscoe filter will also reduce the intensity of the sodium light down to about 35% of its unfiltered intensity. This is actually very useful in smaller darkrooms. Although safe, the intensity can get in the way during image focusing on the easel.

Ken

[Edit: For those who may wish to purchase a new low-pressure sodium safelight, but thought they missed the boat when the Thomas Instrument Company went out of business, check out this LPS-based OC-1012 Safelight from the Sebastian Darkroom Products division of California Stainless Manufacturing. California Stainless is the OEM manufacturer for many of the Arkay lines of stainless steel products. Email them and ask for a paper catalog. It's pretty cool.]

[Edit2: My current (January 2012) price list shows the OC-1012 Safelight (model #72882) at $370.00, and the LPS replacement tubes at $135.00.]

[RalphLambrecht]

Aw, c'mon, Ralph. What's not to love? It's bright and safe. What more do you need?

subduedeven illumination and not something in the middle of the room. i'm always in my own shadow with the thomas. i prefer more smaller lights even ly distributed through out the room.

[Greg Davis]

To come back to this thread, does anyone know what kind of tape is used? The colored tape I have found so far is just vinyl electrical tape, which is too thick and stretchy.

[Ken Nadvornick]

An option I tried were those inexpensive small stainless steel binder clips available from any stationary store. Held the glass sheets together snuggly and were unaffected by the lamp heat.

Ken

[ChristopherCoy]

Hey thanks for the link! I got one free because the university I was working at tossed it. I've been using it for years and the replacement bulbs cost $100. The place you recommend is a 1/3 of that.

Just for those who may be reading this later, bulbman.com has SOX35 bulbs for $34 as well.