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Old 1st February 2024, 02:14 PM
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Martin Aislabie Martin Aislabie is offline
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Quote:
Originally Posted by Terry S View Post
I'd have to double check, but I think that the majority of my different enlarging easels (in fact how many of these easels does one person need / require?) have a white coating to them, with black blades and side and top.

As for your second bit Martin, I'm not sure if I understand what you mean. If the paper is opaque, I'm not sure what difference it makes as to the colour and any light reflected - to where?

Terry S
Back in to the paper.

So you get a form of double exposure - particularly when you have deep shadows next to very pale highlights.

It is the same reason films have an anti-halation backing to them.

Martin
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Old 2nd February 2024, 01:00 AM
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Just did a simple back-of-envelope test. Light box, two layers of MGIV-WT fibre paper and a spotmeter. Two layers of paper were used to simulate the light going from the enlarger lens through the paper to the base of the easel, and bouncing back up to the emulsion side.

I read the light-box surface by placing the meter lens on the diffused surface of the light-box and took a reading.

I read the simulated reflected light by placing the two layers of paper on the light-box and took a reading from the blank margin in the same way from the same location on the light-box surface.

Result: the two layers of paper gave a 4.5 stop reduction in light transmission. I did not think of an easy way to allow for the easel base light absorption, but I expect it will be at least half a stop (possibly more) so for a white base you are looking at something in the order of 5+ stops reduction in the light reflected back to the underside of the paper emulsion using MGIV-WT fibre paper.

It would seem that an orange base colour would be a good option to reduce the reflection of image-forming light further. Yellow will also reduce emulsion-affecting light bouncing back up, but it is closer to green in wavelength, and MG emulsions are sensitive to green. But if one is going down that route, you may as well use matt black...

The question then being: can you see a minus-5 stop blurry echo of the image in practice? I suspect not, but I've never tried it - my two main easels have yellow and black bases respectively. The yellow easel is a Saunders 4-blade, but I can't think of any way to describe the colour that would be helpful in selecting a matching paint colour (and being colour-blind does not help)...

Last edited by Bob; 2nd February 2024 at 02:55 AM.
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Old 3rd February 2024, 12:36 AM
MattKing MattKing is offline
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As I understand the theory, the issue isn't necessarily with the bounce back light visibly fogging the paper, but rather affecting the paper's response in a way that is similar to a low level pre-flash.
In particular, in theory, the affect that such a pre-flash can have on the paper's contrast behavior.
The yellow colour reduces the amount of bounce back while still helping users see an image when focusing and composing.
Don't forget that the easels were intended for colour printing as well.
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