Rubylith Safelight.

[BobUK]

How many layers of Rubylith should I use when making a darkroom safelight filter for ortho ?

Or is it trial and error for ones own circumstances ?

Thanks.

 

[koraks]

Trial and error, yeah. It depends on too many factors. However, if two layers doesn't cut it, I'd look for other solutions - less power, indirect/bounced light.

 

[Mick Fagan]

I just measured my Kodak red safelight glass in my darkroom. This is/was designed for orthochromatic film and in fact was used by me for close to 15 years exposing lithographic film in my vertical A3 camera.

At approximately 300mm distance from the safelight and centred, I had my Sekonic L-308X light meter set to 100 ASA, with the dome covering the sensor.

60 seconds at f/16.5 give or take was the consistent reading. Or 8 seconds at f/5.6 if your light meter cannot go that long.

This should give you a starting figure at the very least.

In general, and after decades of using orthochromatic lithographic film, there is a reasonably big fudge factor, but the amount of time you have your film under a safelight and the distance away from the safelight also come into play.

Let us know how you go.

 

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[BobUK]

I just measured my Kodak red safelight glass in my darkroom. This is/was designed for orthochromatic film and in fact was used by me for close to 15 years exposing lithographic film in my vertical A3 camera.

At approximately 300mm distance from the safelight and centred, I had my Sekonic L-308X light meter set to 100 ASA, with the dome covering the sensor.

60 seconds at f/16.5 give or take was the consistent reading. Or 8 seconds at f/5.6 if your light meter cannot go that long.

This should give you a starting figure at the very least.

In general, and after decades of using orthochromatic lithographic film, there is a reasonably big fudge factor, but the amount of time you have your film under a safelight and the distance away from the safelight also come into play.

Let us know how you go.

Hello Mick
Thank you for the details.

In a Kodak Beehive lamp with a 25watt tungsten bulb on 240 v ac I have very similar results.


Two sheets of Rubylith plus a diffusing sheet bought separately from Lee Filters.

I also have an L-308X meter and my readings at 300mm, 100asa are as follows.

60 seconds f 20

8 seconds f 6.3

Too close to worry about. That's a good enough match for me.



A small tip for the L-308 meter.
After dropping the flash co-ax socket cover in quite short grass, I spent about a quarter of an hour trying to find it, even after seeing it hit the ground.
Now a short length of stout thread holds the cover to the bar that the lanyard connects to.

Thanks again.

 

[Mick Fagan]

Bob, well that is good news, I suppose the icing on the cake will be if everything works once you start using the safelight.


With regard to the flash co-ax socket cover, I had completely forgotten about it; I don't use flash these days, but you never know.

I went and had a look at my meter, yep, that cover is a sturdy little thing, with a surprising amount of force required to pull it out. No doubt with regular use it may slide in and out more easily than it did a few moments ago, so maybe I'll have a think about something; perhaps some fishing line as the retaining hole looks to be about 2mm. That was the first time I have pulled that cover off, although it is just possible that when I first received the meter, I may have pulled that cover off for a look.

One of the surprises with the L308-X light meter, was/is the carry case. I attach my carry case to my belt on my left front side, and with the long lanyard around my neck, I place the meter upside down into the case. I simply pull on the lanyard and I have my meter right to go in seconds, then when finished I simply slide it back into the case top first; so ridiculously easy and my light meter is always ready to be used.

As virtually all of my photography these days encompasses me working under a dark cloth, and using a hand held meter, having this carry case and lanyard arrangement, is the bees knees.