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John Jarosz
14-Mar-2016, 13:29
I've been working to build an LED lightsource for contact printing ULF size negs. I've wanted to address the need for the ability to do VC silver papers. I've found these 3 color LEDs that are strip mounted. They can be cut into lengths as needed for whatever format you need (but the lengths must be in multiples of 3 LEDs). I found these on Amazon but their origin is China, and the documentation is poor/non-existent. So I've invented a lot as I go. It works for me. The materials are cheap enough that if you screw it all up it's not a huge loss. Price of an education. Do not get the waterproof versions as it's really difficult to get at the electrical contacts on the strip. The connections to the strips are made with clamp-on connectors also sold thru Amazon.

The circuitry is quite simple. 12 VDC go to all the strips. Each color has a separate path back to the controller. I won't draw the circuit, but if you think it thru you should get where you need to be. I'm a mechanical guy by trade and I won't wade into drawing circuits on the internet to be picked apart by 'experts'. (I also won't discuss mathematical expressions, tires, oil, religion or politics online. :-) )

My ULF size is 8x20. I made the lightsource about 10"x23". Originally I planned to have the light and the printing frame in close proximity but I have way too much light. The photos show how it's built right now. There are twice as many LEDs shown as I'm actually using. You only need about half as many LEDs as in the photo. Even with the smaller number of LEDs there is surprising uniformity of illumination without a diffuser (measured with a spot meter on a thin sheet of paper in the vacuum frame). The frame can get quite close to the LEDs before you start to see the light pattern on the paper.

The LEDs are controlled by a little remote control. Red Blue and Green (or white) can be individually controlled. You vary the mix of Green and Blue in one exposure (and intensity). The power source is a switch mode power supply (like a laptop). The LED's do not turn on and off instantly because this type power supply needs to charge and discharge when powered on/off. I fixed this by adding a 120vac relay with dry contacts that turns the 12VDC output on/off thru my darkroom timer. Now the LEDs come on/off instantly. The controller remembers what you did last even if the power is disconnected. For something that was designed as a decoration element, these LEDs are quite nice.

I'm only using the Blue and Green portions of the LED's. Exposures are on the order of 5-10 seconds right now even though the lightsource is 60 inches from the negative. Still a little short. I could add a diffuser but that seems like a waste. The darn LEDs are so bright you could use this panel for portrait work. I can see that the real use of these are for an 8x10 head.

John Jarosz
14-Mar-2016, 13:30
Here are scans of a Blue and Green exposure on Ilford VC paper. Now the experimenting really begins with the actual printing. But I think this shows I can control the response of the two emulsions of the VC paper.

bob carnie
14-Mar-2016, 13:36
Wow very promising John- I am looking for this system for 30 x30 film to silver paper contacts that I want to do.

I am also looking to do UV exposure the same way for 30 x40 pt and tri colours over pt

Have you seen the Nuarc LED version for plate burners??

Tim Parkin is working on a unit for Pt Pd and I was asking him if there was a way that would do both wavelengths of light so one could use the same unit for Silver - very fast and Pt Pd and Bum - very slow

bob carnie
14-Mar-2016, 13:38
together I think you can get whatever you want in all areas...


How even is the edge to edge... Ie would you put a control strip on all four corners and middle and balance all to working tolerences?


Here are scans of a Blue and Green exposure on Ilford VC paper. Now the experimenting really begins with the actual printing. But I think this shows I can control the response of the two emulsions of the VC paper.

John Jarosz
14-Mar-2016, 13:54
Hi Bob,

Funny you should mention UV. I'm also working on a UV source for Carbon Transfer. I finally decided my old UV source was too dangerous. These strips should be much more even

http://www.amazon.com/Wit-Lighting-16-4ft-395nm-405nm-Purple-Non-Waterproof/dp/B00MR4ZKRU/ref=pd_sim_sbs_60_2?ie=UTF8&dpID=51ltBjb91cL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=1Q63SHGPFC0FWAQ77276

Edit: I used the wrong link for the UV LED's. The other source is too expensive. This link is 1/3 the price.
Edit #2: the first edit was wrong. This one is correct. Sorry

I just received these from China. Much closer spacing of the individual LEDs so that is probably how they achieve the higher output.

Yes I have more testing to do. I can tell you that by measurement with both the Pentax spotmeter and my iphone the readings all over the illuminated print areas even, very close. I did those measurements by looking at a paper surface using the transmitted light thru the paper.

angusparker
14-Mar-2016, 13:59
Somebody needs to start making a UV contact box with these LEDs for sale. Seems like a no brainer and a lot cheaper (and safer) to produce than what we have with tubes at the moment.

Peter De Smidt
14-Mar-2016, 14:41
Daniel and I used similar strips from Lee Valley for the light sources for our dslr scanners. They really do put out an incredible amount of light.

ic-racer
14-Mar-2016, 15:39
Nice. Thanks for sharing.

Randy Moe
14-Mar-2016, 16:39
Good to know it's too powerful.

Looks like you used 2 rolls, to make 15 rows 24" long.

I want what you made but add switchable UV strips in between so I can use one set for silver and by switching also Salt printing.

John Jarosz
14-Mar-2016, 17:06
Yes, I used 2 rolls. Trouble is, the little controllers they make can only handle 1 roll. So I have 2 controllers (infrared remote handset in the pic that controls both controllers).

As of right now I have no idea how strong are the UV LEDs. For carbon transfer, more UV is always better. Don't know if that's true for Salt or anything else. One RBG roll is enough for contact printing silver enlarging paper (I don't know about stuff like Lodima) at a 60" printing distance. It should be no problem to put in a UV strip. Since it has it's own controller you'd be ready to go.

Also - There are quite a few different LEDs strips out there. I was surprised. All made in China with no tech support that I know of. Even the instructions that come with the goods are pitifully written, almost unintelligible. I'm sure in Chinese they make perfect sense. Some of the strips are resold by US companies - I have not tried to get any info from them. The prices from the US companies are 3x in some cases. I've had no problems getting this stuff direct from China by mail. Keep in mind these strips are made as decorative items, I'm sure they have no anticipation of the LEDs being repurposed as shown here.

Peter De Smidt
14-Mar-2016, 17:24
We had good luck with our strips. The USA company even answered some technical questions for us. http://www.leevalley.com/us/wood/Page.aspx?p=70326&cat=1,43349,70322

Randy Moe
14-Mar-2016, 18:41
We had good luck with our strips. The USA company even answered some technical questions for us. http://www.leevalley.com/us/wood/Page.aspx?p=70326&cat=1,43349,70322

Are you sure that's not Ken Lee Valley? Just kidding Ken Lee, in a couple images on the Lee Valley site there are vases looking kinda like something you may have imaged....

I think we need to source and use power supplies carefully. I really worry about all the stuff we keep plugging in.

barnacle
15-Mar-2016, 01:54
Make sure your power supplies are CE (for Europe) or UL (for the States) marked - and genuinely so. That should ensure that the safety and electronic emissions from the power supply are OK.
Fuse your output *at the power supply end* and use fused mains supplies (I don't think you have fused plugs in the States?) because the purpose of the fuse is not to protect the equipment, it's to protect the lines from overheating and causing fires.

Neil

ic-racer
15-Mar-2016, 06:29
On the "LED Wholesalers" website I found that controller to find more info but no instructions. Could you elaborate on why you chose that controller over the others and if you would choose that one again. I'm curious if you can save green and blue settings. Or maybe you are not using that function and doing separate green and blue exposures controlling the time.

I'm just guessing but does each click of the 'green arrow' or 'blue arrow' change the level the same amount. So could one use say "three clicks of green and 4 clicks of blue" to get repeatable mixed color results?

John Jarosz
15-Mar-2016, 06:57
It appears that the controller remembers the last operation used by each function. I can't find any specific 'save' function. I scanned the entire User manual. Since I bought two units I got two user manuals but one was so poorly printed it was unreadable. The printed size is 3"x4" (75mmx100mm)

John Jarosz
15-Mar-2016, 07:03
So could one use say "three clicks of green and 4 clicks of blue" to get repeatable mixed color results?

Yes. I think this works. But I haven't done enough serious printing with it yet to know for sure. Each click probably does increase/descrease something a constant increment but who knows if that relates to the light output (especially considering the color difference). Because then you start talking about energy which may not be the same in terms of light.

I didn't really choose that controller. It's what came with the package I bought.

Peter De Smidt
15-Mar-2016, 09:07
More controllers, including one with a knob for each channel: http://www.leevalley.com/us/hardware/page.aspx?cat=3,70322&p=70327