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.
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
Quote Originally Posted by Greg Davis View Post
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