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Pete Watkins
8-Nov-2010, 06:44
I've recently aquired an old De Vere 45a with cold cathode head. It seems O.K. at the moment but has anybody here made up a do it yourself LED lighthead? The "bulb" isn't going to last for ever.
Pete.

R Mann
8-Nov-2010, 07:33
You should take a look at this -

http://www.reefcentral.com/forums/showthread.php?t=1826521

Dave Grenet
8-Nov-2010, 07:53
Check out http://huws.org.uk/

I'm working on my own Graflarger LED head at the moment but I have a little way to go and it isn't really a priority...

Do you have any electronics experience?

jon.oman
8-Nov-2010, 08:22
http://www.ledtronics.com/products/ProductsDetails.aspx?WP=C349K594

http://www.deadbread.com/crumbs/23c.html

Take a look at the above links. This guy made his own from simple plug-in LEDs. No electronics work to do.

Pete Watkins
8-Nov-2010, 09:33
Many thanks for your help. I have a "tame" electrician on hand if I feel that I need one. I'm a total coward with electrics so I'll get him to check everything that I do anyway.
Thanks again,
Pete.

Eric Woodbury
8-Nov-2010, 10:17
Nothing wrong with cold cathode and it will last a very long time. If it worries you, consider getting a spare tube.

Jerry Bodine
8-Nov-2010, 12:38
[QUOTE=jon.oman;646953
http://www.deadbread.com/crumbs/23c.htmlQUOTE]

To quote from near the end of this article:

"The light spectrum of the white LEDs could be a problem for some people using variable contrast paper. I use VC paper, and VC paper does work with my enlarger -- however the maximum paper grade I've been able to obtain is about 3 1/2 - 4. The problem is how VC paper is designed. The hard paper grades -- about grade 4 and up -- in variable contrast paper are triggered by ultraviolet light. Tungsten and fluorescent "cold" lights produce small amounts of UV, but white (and blue) LEDs don't."

Can anyone confirm that blue LEDs don't generate UV and that UV is necessary to reach Grade 5?

Jack Dahlgren
8-Nov-2010, 13:13
[QUOTE=jon.oman;646953
http://www.deadbread.com/crumbs/23c.htmlQUOTE]

To quote from near the end of this article:

"The light spectrum of the white LEDs could be a problem for some people using variable contrast paper. I use VC paper, and VC paper does work with my enlarger -- however the maximum paper grade I've been able to obtain is about 3 1/2 - 4. The problem is how VC paper is designed. The hard paper grades -- about grade 4 and up -- in variable contrast paper are triggered by ultraviolet light. Tungsten and fluorescent "cold" lights produce small amounts of UV, but white (and blue) LEDs don't."

Can anyone confirm that blue LEDs don't generate UV and that UV is necessary to reach Grade 5?

UV LED's are available for less than a buck. If you wanted to build a light source with a couple of different colors you could avoid the whole idea of filters and just dial in different amounts of each spectrum to control contrast. This works for B&W - Color would be a different problem altogether.

Robert Hall
8-Nov-2010, 13:57
[QUOTE=jon.oman;646953
http://www.deadbread.com/crumbs/23c.htmlQUOTE]

To quote from near the end of this article:


Can anyone confirm that blue LEDs don't generate UV and that UV is necessary to reach Grade 5?


LED's have a vary narrow spectrum. They are like the flutes (musical instrument) of the lighting world.

If VC papers need UV, then that might be a problem. Of course they make UV and IR LED's too. :)

3e8
8-Nov-2010, 14:18
[QUOTE=Jerry Bodine;647053]
If VC papers need UV, then that might be a problem. Of course they make UV and IR LED's too. :)

Based on the last post here (http://photo.net/black-and-white-photo-printing-finishing-forum/00ShfN), the peak sensitivity for high contrast is 450-460 nm, which corresponds to most "royal blue" LED's, not just "blue" LED's.

Bryan

konakoa
8-Nov-2010, 18:11
www.deadbread.com/crumbs/23c.html Hey, that's my website!

I've just built a second LED head to improve on the original. It's white LEDs + UV LEDs combined. The head is finished and on a new enlarger. I'm currently testing the new head and until I've done some extensive printing I won't have anything concrete, but so far the UV LEDs did the trick. It's an excellent match for a 5+ filter on my condenser and cold light enlargers.

As part of the testing process I test printed with blue only (470nm) LEDs. They didn't have near the contrast of UV (405nm) LEDs on variable contrast paper.

jon.oman
8-Nov-2010, 18:49
Danny,

We passed a couple of emails back and fourth last year when I was thinking of making an 8x10 inch version. I never really found the time! I do think it was a neat setup. Are you going to publish an article with your latest findings?

Wade D
8-Nov-2010, 22:30
Heiland in Germany makes a very nice split grade VC head: http://www.heilandelectronic.de/.
It uses 100's of blue, green and red LED's and they have sizes for many enlargers. Looks pretty good but I didn't see any prices on the page I visited.

Arne Croell
8-Nov-2010, 23:24
www.deadbread.com/crumbs/23c.html Hey, that's my website!

I've just built a second LED head to improve on the original. It's white LEDs + UV LEDs combined. The head is finished and on a new enlarger. I'm currently testing the new head and until I've done some extensive printing I won't have anything concrete, but so far the UV LEDs did the trick. It's an excellent match for a 5+ filter on my condenser and cold light enlargers.

As part of the testing process I test printed with blue only (470nm) LEDs. They didn't have near the contrast of UV (405nm) LEDs on variable contrast paper.
You might want to check whether you're prints are fully in focus. Years ago there were reports that since enlarger lenses are not corrected for UV and VC papers were more UV sensitive one could get a significant focus shift for that part. The test and the numbers can be found in Ctein's book "Post exposure". Actually some of the "Apo"-designated lenses were worse than some others if I remember it correctly.

Henry Ambrose
9-Nov-2010, 05:53
Pete, I have an LED head that Huw built. It uses blue and green LEDs and is variable contrast/constant exposure. It works great. If you are serious send Huw an email as he knows exactly how to do this.

konakoa
9-Nov-2010, 11:47
Jon, yep!

Arne, I've read it cover to cover several times. It's a great technical book without being overly nerdy. Ctein's work with VC paper and UV sensitivity was my influence for the new LED head. The focus shift is a twofold problem: VC papers are now UV sensitive and enlarger lenses just can't be made to correctly focus UV at the same time as visible light.

I've got two ways to deal with possible focus shifts: I have a built in switch to turn the UV LEDs on or off when not needed. Second, I'm not having to deal with much of an enlargement factor with 4x5. Ctein's work was with enlarged 35mm; about an 8X enlargement to 8x10 prints. I'll be using the head for 4x5 enlarged to 8x10 and 11x14. Not as much of an enlargement, so the focus shift may not be as much of an issue.