Durst La 1200, CLS450 head, too bright!

**jeroldharter** · 9-Feb-2010, 19:19

I have the same problem with my Beseler Dichro 45S light source being too bright at small enlargements. I solved it in the end buy purchasing some Heliopan ND filters, 8x and 2x, for use below the lens (no discernible problems with that). I can easily remove the filter for higher magnification enlargements.

Although I did not think of it at the time, I should have purchased step up rings to my largest enlarging lens size so that the filters would be interchangeable amongst all my lenses.

**ChrisN** · 9-Feb-2010, 23:34

Thanks Jerold; that is another interesting thought. I do have a 10-stop ND filter in 77mm - I wonder what filter ring my enlarger lens is? I'll go and check!

Today I've visited the plastic supplier again and obtained another piece of frosted perspex to put under the top plate. I'll try that tonight and see if it makes any difference. If nothing else the light will be well and truly diffused!

**ChrisN** · 10-Feb-2010, 00:27

Test completed: I'm now out to 45s @ f/22. That's more usable for me (as a novice I need plenty of time for dodging and burning), but I gather f/22 is not ideal.

I suppose another option hinted at above is to change the lens to move the head further from the paper for the same image size. I've currently got a 135mm lens - should I try a 150mm? That will make it a little more difficult to focus (to reach the focus knob at the same time as squinting into a focus-scope).

**ic-racer** · 11-Feb-2010, 19:33

Originally Posted by ChrisN

I suppose another option hinted at above is to change the lens to move the head further from the paper for the same image size. I've currently got a 135mm lens - should I try a 150mm? That will make it a little more difficult to focus (to reach the focus knob at the same time as squinting into a focus-scope).

Exposure will be the same. (conservation of matter and energy etc..

)

Sounds like you are on the right track with the diffuser though.

**ChrisN** · 12-Feb-2010, 04:14

Another thought: would it be useful to try to drop the voltage? I've read that will extend the life of the bulb, too. What voltage drop would I need to halve the brightness, and what would be a reasonable way to reduce the voltage by that amount? The standard bulb is 24 volts and 250 watts. I have the TRA450 power supply.

**ic-racer** · 12-Feb-2010, 17:12

In theory lower voltage would do it but I'd be very very careful with what I did to any working Durst power supply.
I don't know if all TRA450s are the same, but the schematic I have shows that it uses a transformer, and provides a fixed voltage (unlike some of the other 'switching' power supplies that have a voltage trimmer potentiometer)