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  #21  
Old 2nd May 2021, 01:04 PM
John King John King is online now
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Quote:
Originally Posted by Mike O'Pray View Post
A bit of a follow-up on my part. I tried to do a test for the DUKA using what I recall to be the previous setting I had used for RA4 which was 10. This is amazingly bright and probably accords with Dave's "read newsprint" level although that might be stretching things a bit but certainly a very comfortable level.

I hadn't seen any fogging previously even when I used to cut 10x8 to make 2x 5x8s then place in easel and finally into the drum or none that I recognised. However I now recall that all my prints were borderless and it is just possible that any fogging was disguised. No white borders to check.

I tried a crude test last night at a level of 10 and cyan fog was apparent in a matter of a very short time less than one minute. Either I need to be lightning fast at paper removal, placing in easel, exposing and placing in Nova slot or I need to reduce the level to what I think will be just about a manageable but not comfortable level.

Dave, what test did you apply to get to your 5 mins level? Based on last night, I'd give my right arm for 5 mins safety. 2 mins or even one might do.

It kind of suggests that cutting down 10x8 to say 5x7( two cuts needed) is now a no-no unless done in total darkness and these days 5x7 RA4 cut paper is unobtainable.

Thanks

Mike - somewhat demoralised
Mike it will also be affected depending on the distance from the paper and the fitting of the safelight. I also work between the diffused light source and the paper on the enlarging easel.
You could also try knocking the setting down a couple of notches. I use Kodak paper from the roll, so it has 2 exposures to the light from the Duka. However having used both Kodak and Fuji paper, I estimate the Kodak paper is at least 1 stop slower than Fuji which will help of course.
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  #22  
Old 4th May 2021, 08:19 PM
JOReynolds JOReynolds is offline
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Default Colour paper safelighting

In the 1980s I visited the darkrooms in the basement of the Centre Georges Pompidou in the Beaubourg, Paris. After a few minutes of dark-adaptation the level of safelighting, from sodium vapour lamps, appeared startlingly high - they needed it! I have clear memories of the staff hanging 52" wide rolls of colour paper onto a steel wall with magnets and stepladders. The enlarger was, of course, horizontal, on rails.
The sodium lamps emit narrow spectral lines between the green- and red-sensitive emulsion sensitivities. Filters over the lamps hold back the UV.
The accompaniment was weird electronic noises from Pierre Boulez' IRCAM school of music down the corridor (he had been conductor of the BBC Symphony Orchestra in the previous decade). Does anyone remember the stacked ball loudspeakers of the era?
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  #23  
Old 4th May 2021, 08:31 PM
JOReynolds JOReynolds is offline
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Originally Posted by Terry S View Post
Reading the specs on the page link above, the colour tube is stated as being ' 590nm'.

Typing this into ebay UK, it came up with a number of items, but one was a standard light bulb, in an E12 base, that says that it is in the 590nm spectrum.
It would be worth asking your colour paper supplier what is the response spectrum of the emulsion. The problem with LEDs is that, although the emission peaks at a specified wavelength, they usually have a bell-shaped curve with a pronounced 'skirt', which may not be what you are looking for.
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Old 5th May 2021, 03:17 PM
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I had a (very) brief flirtation with colour printing a few years back and tried 590nm LEDs but as I recall, the level had to be so low to avoid fogging, they were of very limited use.

It is possible my LEDs were not very good and were emitting away from their nominal wavelength. They have a narrow bandwidth, but as JO observes, it is not infinitely short and they will emit either side to some degree. The better the quality, the lower those off-centre emissions will be, but will never be as sharp as a discharge lamp like the Duka.

Perhaps putting them behind a colour safelight filter will allow brighter light than would be possible with just the filter and a normal lamp, so I would not take my limited experience as gospel. An LED is cheap enough to try - just make sure you get good quality ones and do not over-drive them.

Last edited by Bob; 6th May 2021 at 12:31 AM.
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