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  #21  
Old 29th July 2009, 01:33 PM
Mike O'Pray Mike O'Pray is offline
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Quote:
Originally Posted by Trevor Crone View Post
This may be of interest to those asking/thinking about projection printing on Lodima:

http://www.michaelandpaula.com/mp/Az...D=11743&CID=13
Trevor Thanks for that link which I think answers the question I was going to ask about why a 100W enlarger couldn't expose a neg onto say 8x10 Lodima in quite a bit less time than a 60W bulb contact print at 8 feet instead of the 4 mins quoted in the link for a projected print. It's a bigger bulb and at a much smaller distance, say, 2 feet.

It has answered the question by making me think and I come up with the inverse square law answer. The neg in the enlarger is a long way from the print(2 feet) instead of right next to it in the contact prints so the light travel is vastly greater.

On the other hand in a contact print of 36 x 35mm negs, my contact exposure time is not much different from one neg in the carrier which is projected onto paper 2 feet away as opposed to be sandwiched against the 36 negs. So maybe it all down to the speed of the Lodima paper?

I am confused. What's the explanation? Thanks

Mike
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  #22  
Old 29th July 2009, 04:13 PM
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Trevor Crone Trevor Crone is offline
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Mike, silver chloride contact papers like Lodima are incredibly slow compared to papers designed for enlarging.
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  #23  
Old 29th July 2009, 05:51 PM
Mike O'Pray Mike O'Pray is offline
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Thanks Trevor. Can you also help me to improve my reading of posts as well?. I have just realised that your 60W lamp is 8 inches( two apostrophies there, not one) away NOT 8 feet which might have lead me to the slowness of the paper as the real reason :

Mike
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  #24  
Old 29th July 2009, 08:14 PM
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Mike, I over looked your mention of 8 feet instead of 8 inches otherwise I would have pointed that out.
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  #25  
Old 29th July 2009, 10:40 PM
Martin Reed Martin Reed is offline
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It's not impossible to projection print onto contact speed paper - back in the 70's when there was a lot of cheap document & technical material around and I had no money I tried all of these, expect maybe a 20 minute exposure with full aperture. But then you will also probably run into reciprocity failure effects, with an exposure this long, so you'll have to burn in for another stop in the corners...it's not what the material is made for.
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  #26  
Old 11th August 2009, 06:40 PM
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Quote:
Originally Posted by Trevor Crone View Post
Rob, I did try my MG enlarger head as a light source (300W) for contact printing (8x10) and an image was just noticable after a 1 minute exposure time. I thought this method would end up being too long and would cause my enlarger head to over heat. So I think to enlarge on this paper times would be very long indeed.

For contact printing I use an oversize 60 watt lamp at a distance of 8" and the exposure times are on average between 20, 25 seconds.
Trevor, I have placed an order for 100 sheets of 8x10 grade 2 Lodima. Which lamp is it you are using and do you hold or move this above the negative and paper?
Also, does the Lodima manufacturer provide any specific instructions about how to process this particular paper?
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  #27  
Old 11th August 2009, 08:01 PM
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Keith, I find these lamps (also with ES fitting and other wattage) very good in providing a very even illumination. Especially as my set up places the lamp just 8" from the paper. The further the lamp is from the paper the more even the illumination will be (within reason). You have to balance this with reasonable exposure times. With this lamp and distance my negatives give me an average exposure of 20-25 seconds.

The pre-production paper I got didn't have any information whatsoever, but there is a fair bit here. Look under 'writings'. And here

PS. The lamp is fixed above the neg+paper.
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Last edited by Trevor Crone; 11th August 2009 at 08:11 PM. Reason: additional info.
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  #28  
Old 11th August 2009, 08:17 PM
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Question Table-lamp for holding the bulb?

Quote:
Originally Posted by Trevor Crone View Post
Keith, I find these lamps (also with ES fitting and other wattage) very good in providing a very even illumination. Especially as my set up places the lamp just 8" from the paper. The further the lamp is from the paper the more even the illumination will be (within reason). You have to balance this with reasonable exposure times. With this lamp and distance my negatives give me an average exposure of 20-25 seconds.

The pre-production paper I got didn't have any information whatsoever, but there is a fair bit here. Look under 'writings'.

PS. The lamp is fixed above the neg+paper.
Thanks for the link Trevor. I also have a contact-printing frame on the way. Is the bulb in a desk/table-lamp or similar and do you simply time it using the on/off switch?
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  #29  
Old 11th August 2009, 11:05 PM
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Keith, the lamp is in a purpose built light box which I originally built for Pt/Pd printing using UV lamps. I remove the UV lamps and add the bulb I linked to. It is just in an ordinary bayonet cap lamp holder which is screwed to the top of the cupboard. I've connected it to an enlarger timer made by Viponel which I bought on Ebay. That way I'm assured of accurate and repeatable timing.

It is best to have the lamp suspended/fixed above the contact printing frame to ensure the lamp is central and illumination is as even as possible. If you have a spot meter this is easy to check. Or do a 'grey flash', that is expose a sheet of paper until you just get a light to mid-grey tone, any uneveness of illumination is very appparent. Knowing where any uneveness is, usually the corners, is just a case of 'burning in' to even out the tones.

Some people place a piece of opal glass/plastic between the lamp and printing frame, which is said to help even out the illumination. I've not tried this so can't say from personal experience.
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  #30  
Old 12th August 2009, 05:36 PM
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I know where there is a Marrutt CP450 Contact-Printer for sale as mentioned in ILFORD MONOCHROME DARKROOM PRACTICE by Jack H Coote on page 151, but I don`t know much about them.
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