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Adapting a Durst Laborator 1000 condenser head to work with LEDs

lungovw

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Jun 4, 2007
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Sao Paulo - Brazil
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I have just finished an adaptation in a Durst Laborator 1000, condenser head, and changed it to a diffuser head using LEDs. I am very much surprised with the results. Highlights:
1) It is incredibly fast, that means, a lot of light output compared with the former lightbulb I was using. A few seconds with lens stopped down to f/32 is enough for a 2x magnification from 4x5.
2) It uses a micro-controller (Arduino family) to mix green and blue light in order to get contrast control. That makes very easy to use different contrast in different areas of the same print (more troublesome with filters).

I made a video showing one print made with it:


More technical details about the project can be found at https://apenasimagens.com/en/enlarger-head-using-leds/

For those of you who have thought or considered LEDs, I would like to say: go for it, it is really a step change.
 
Oh, one more Brazilian here! Great first post!

I would say "welcome to APUG" or, better yet, "welcome to Photrio", but I see you're a member for a long time!
 
Wow, great video, very instructional! Thank you for sharing!

One question: due to the high light output of the LEDs you need to stop down the lens to f/22 or more. I personally would be wary of using such a small aperture, as it is not the optimal f/stop of the lens. Did you see any change in lens performance compared to, say, f/8 or so?
Can possibly the light output be reduced, for instance by reducing the current going through the LEDs? (not sure whether the color will remain the same, though - maybe the info is in the spec of the LED)
Or using a neutral density filter perhaps?

Using an Arduino is a great idea! The next step in your project is to connect a phototransistor to the Arduino to measure exposure times, similar to what the Analyser Pro does
(http://www.rhdesigns.co.uk/darkroom/html/analyser_pro.html)

Just a few 2-cent ideas which came out of my engineer's mind

Etienne
 
Etienne, I was also concerned about using such low apertures that I have never used before. But the result was OK, I did not notice any problem. The lens was a 105 mm so the entrance pupil for f22 is about 5mm, maybe that is still too big to produce any significant diffraction that would compromise the final image. But anyway I will for sure introduce means to reduce light output and cut it by a factor between zero and 1. That is in order to allow more time to work on the image if burning and dodging is needed. I don't think this will change LED color because they can only emit in the wavelength the material they are made of is by nature set to emit. The dimmer effect is based on a modulation in time, very quickly the LED is turned on and off and in this way they output less light. The Arduinos have a built-in capability of sending this PWM signals that modulate the power in this way, so it can be done via software with no need of any hardware change or adaptation. Thanks for the link, I will check it out. It is a good idea to integrate a light meter and I still have some free pins on the Arduino to which I could connect a light-sensor.
 
Thank you, and very interesting. When my Aristo 2-tube VCL-4500 gets frail in its old age I will have a go at following your model. I might have resort to simple analog current reducing (switching resistors etc) for the two circuits to control brightness and contrast rather than try to master the Arduino programming though. I think my learning curve could be a bit too long!
 
John, I think you can't change the tension/current on an LED in order to get sufficient control on light output. Above its operational voltage it gets brighter but easily melts down. Below that voltage it just does not turn on. To control intensity you have to apply an intermittent tension of the same value. That can be done with electronics (capacitors/ transistors/ resistors) but I think that is far more complicated than using micro-controllers like Arduino with less custom made circuitry.
 

I had assumed that the method for which I can control the power of my safelight LEDs would work. Just a potentiometer wired as a simple variable resistor. It does go fairly dim, and I thought a higher R value would make it even dimmer, but they are a fairly ordinary LED and perhaps the very high power ones that you've used don't offer that range. I do understand the problem of overcurrent! Anyway, with a set of spare tubes and my advanced age I might get away with just using the VCL4500. It's great to know that there's an alternative though. And thanks for sharing your expertise.
 
Wow, I'm impressed!
 

In addition to the lost power and the heat, this kind of regulation would have the big inconvenience of not properly driving the LEDs. The LEDs need to be driven with a constant current, not a constant voltage, in order to have a controllable output. DC current regulators do exist, but then temperature has an influence on the response of the LED too. You have a far better control, as well as a better efficiency, with a PWM controller. In this case you want to control the balance between two LED banks in order to adjust the contrast, which makes things even more difficult.

Note that making a PWM regulator with an Arduino is not all that difficult, you just need to know (or learn) some electronics, programming, and sensitometry (to calibrate your system). It can be time-consuming, but also a fun project if you have the time.
 
Just an observation which hasn't much to do with this LED project. My Aristo VCL4500 head has a green tube and a blue tube. This model has the green tube on full all the time for the usual range of contrasts, and the adjustment of contrast is done by varying the blue tube. (The green tube can be turned off if you're wanting max contrast). I found it very curious that turning up the contrast required very little exposure adjustment, often none. Maybe this could also be the case with this LED project, which might allow a simpler controller.
 
Wouldn't a ND filter between the light source and the negative be simpler?
 
Fujicaman1957 said:
Wouldn't a ND filter between the light source and the negative be simpler?
Click to expand...

Heck, you don't even need a filter, stick a scrap of ND lighting gel in the filter slot. I keep them cut in 1 and 2 stop sheets, I just keep them clean and store them in the multicontrast filter box. A sheet of gel is about six bucks, and you can stack them to your heart's content. Sometimes I rest one in the red filter holder when I need to burn something for a couple seconds, just to give me a little more control.
 
Very well thought out.
I love your solution to regulate the power of each color by pulsing the LEDs much like how fuel injectors work in your car.

thanks for sharing.


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