Durst La 1200, CLS450 head, too bright!

[ChrisN]

Today I've finally got my darkroom finished to the point where I can start to use it, and I fired up the Durst Lab 1200 for the first time since acquiring it some time ago. It has a CLS 450 head with Femobox 450. I'm using it to print 4x5 B&W negs, at 8x10 on Ilford RC multigrade paper. My problem is that even with filtration dialed in for grade 3 1/2 and the lens closed down to f/22 my exposure time is only 10 seconds. I'd prefer to use an exposure in the 20 to 30 second range and at f/8.

I suspect I might be missing a diffuser in the Femobox. There is a diffuser in the base of the head, and one in the base of the Femobox, but none in the top of the Femobox. Any ideas? Thanks! :)

[Tony Lakin]

Today I've finally got my darkroom finished to the point where I can start to use it, and I fired up the Durst Lab 1200 for the first time since acquiring it some time ago. It has a CLS 450 head with Femobox 450. I'm using it to print 4x5 B&W negs, at 8x10 on Ilford RC multigrade paper. My problem is that even with filtration dialed in for grade 3 1/2 and the lens closed down to f/22 my exposure time is only 10 seconds. I'd prefer to use an exposure in the 20 to 30 second range and at f/8.

I suspect I might be missing a diffuser in the Femobox. There is a diffuser in the base of the head, and one in the base of the Femobox, but none in the top of the Femobox. Any ideas? Thanks! :)

Hi
I have a Laborator 1000CE with a CLS450 head and Taunobox 450 5X4 mixing chamber, the Taunobox has a Diffuser on top as well as on the bottom I suspect your Femobox should have a top diffuser also, it should be a simple matter for you to place a piece of diffusing material on top ie opal acryllic, ground glass or even a piece of 5x4 film processed to a suitable density.

Ihope this helps.
Good luck.

[Roger Thoms]

Here is a listing on the auction site for a Durst diffusion panel. item # 150411616679

Roger

[ic-racer]

Here is a listing on the auction site for a Durst diffusion panel. item # 150411616679

Roger

That is the thin bottom one. Maybe that is what the OP has and he needs to find the thicker one.

[Tony Lakin]

Today I've finally got my darkroom finished to the point where I can start to use it, and I fired up the Durst Lab 1200 for the first time since acquiring it some time ago. It has a CLS 450 head with Femobox 450. I'm using it to print 4x5 B&W negs, at 8x10 on Ilford RC multigrade paper. My problem is that even with filtration dialed in for grade 3 1/2 and the lens closed down to f/22 my exposure time is only 10 seconds. I'd prefer to use an exposure in the 20 to 30 second range and at f/8.

I suspect I might be missing a diffuser in the Femobox. There is a diffuser in the base of the head, and one in the base of the Femobox, but none in the top of the Femobox. Any ideas? Thanks! :)

Hi again
Had another thought, if you are happy with the evenness of the illumination and only using the L1200 for Multigrade printing you can use the Cyan filter to create neutral density this would not affect the contrast, if you used graded papers you could use any of the filters as neutral density.

[athens01]

I'm not familiar with that enlarger, but many have a high and a low light setting. Like the above post, (and if it has a color head), dialing in equal parts of cyan magenta and yellow will add neutral filtration, so 25 cyan, 75 yellow and 40 magenta is the same filtration as 0 cyan, 50 yellow and 20 magenta. When I print color, I try and print at the same f/stop and exposure time and just adjust color and maintain the same exposure by changing filtration.

[athens01]

Apologies for my math: 25c, 75y, 40m = 0c, 50y, and 15m. Or for that matter 100c, 175y , 140m in filtration. You could also use actual ND filters but...


Maybe my math explains so of those inconsistent prints.

[ic-racer]

Cyan has no effect. It cuts light that the paper can't 'see.'

If you need more 'neutral density' add extra Y and M together.

[Tony Lakin]

Cyan has no effect. It cuts light that the paper can't 'see.'

If you need more 'neutral density' add extra Y and M together.

I stand to be corrected but I am sure that adding cyan filtration must reduce the amount of light reaching the negative regardless of the sensitivity of the paper.

[athens01]

Like I said, I've only used cyan to manage exposure time in color printing, try it an let us know if adding 100 points (for example) of cyan doesn't change exposure time. I'm also surprised there's no variable output on the enlarger.
I guess having a stack of standard ND filters on hand is the easiest unless, of course, the paper doesn't want to see the red/cyan filtered by those either.

[athens01]

Sorry to keep harping on it, but were talking about amounts of light not wave length or color of light. If adding equal part magenta and yellow are "neutral" why would paper companies list suggested filtration for specific filters for color head enlargers be a combination of yellow and magenta? If adding equal parts yellow and magenta were neutral then a print at 10 yellow, 50 magenta would be the same as a print at 40 magenta. Or 100 yellow and 50 magenta would be a 50 yellow. Obviously having filter combinations of magenta and yellow is what makes the filter, not what cancels
it.

[Renato Tonelli]

Maybe the head on your L1200 is different from mine. In addition to the YMC filters, mine also has a Neutral Density filter setting. Maybe the earlier color heads don't have this feature? The lamphouse is is so bright that without the ND setting, my exposures would be 10 scs. or less.

Adding equal parts Y & M or Cyan seems counter intuitive to me but it's late and I may not be thinking straight.

[ChrisN]

Thanks for the ideas, everyone. Yes, the diffuser I am missing is the one in the top of the mixing box - that ebay listing is for one in the bottom. But that does raise the possibility that the one I have in the bottom might be the optional less-dense one.

I visited a local plastics supplier today who was able to supply me with a 90mm x 90mm x 3mm piece of frosted perspex at nil cost. I've fitted that, and installed a 200w bulb to replace the usual 250w. Between the two I've now got a 30 second exposure at the same other settings. That's usable, but I still need to dial it back a few stops. I might be able to fit a second layer of frosted perspex beneath the first.

[ic-racer]

I stand to be corrected but I am sure that adding cyan filtration must reduce the amount of light reaching the negative regardless of the sensitivity of the paper.

Think of it (cyan) as using a dimmer safelight bulb. You can tell the difference but your paper can't :)

[athens01]

Adding equal parts cyan magenta and yellow is subtracting "white" light from the source, but the color of the light is still "white" You can see it when you dial it in. Start with equal amounts of yellow and magenta and dial in the same amount of cyan. The color goes back to that without any filtration, but it's not as bright. The paper may not "see" red, but in equal parts the light is white as if the bulb had no filtration at all, but it is dimmer. I'll explain more when I'm not
using a freakin' phone to reply.

[ChrisN]

Still playing with this. I substituted a 2-stop ND filter for the top diffuser, and it was worse - very short exposure needed again. I'll try for another layer of the diffuser perspex under the top piece.

The discussion about the colour filtering is very interesting, but I'd rather not play with the filtration settings at this stage as I'm trying to use the suggested settings I found somewhere on the 'net, per the attached snapshot. Once I've settled in a bit with the enlarger I'll feel more confident.

[ic-racer]

Yes that scale looks like the one from the Ilford paper insert. I use that one with my CLS2000 and it works perfect.

? Why did you replace the diffuser with the ND filter? Can't you use both together?

[ChrisN]

Yes that scale looks like the one from the Ilford paper insert. I use that one with my CLS2000 and it works perfect.

? Why did you replace the diffuser with the ND filter? Can't you use both together?

To see if it would work! And no, the two combine to too great a thickness. But there is room to add another layer under the top plate if the piece is cut to the correct size.

[Tony Lakin]

Think of it (cyan) as using a dimmer safelight bulb. You can tell the difference but your paper can't :)

"By balancing the yellow and magenta dichroic filtration with a color enlarger head, you can achieve a full range of evenly spaced contrast grades and incremental grades with VC papers. With a careful balance of yellow and magenta, it is possible to speed-match the filtration. Cyan can also be used as ND filtration to help speed-match filtration".

From "The variable contrast printing manual" by Steve Anchell.

[ic-racer]

"By balancing the yellow and magenta dichroic filtration with a color enlarger head, you can achieve a full range of evenly spaced contrast grades and incremental grades with VC papers. With a careful balance of yellow and magenta, it is possible to speed-match the filtration. Cyan can also be used as ND filtration to help speed-match filtration".

From "The variable contrast printing manual" by Steve Anchell.

Ilford MG paper is sensitive to bright red light. So technically that is correct. But in general, any 'anti-cyan' light is not going to have much effect (if any) on the paper's exposure.

I use "primary Red" Rosco for my 'safe filter' under the enlarger lens. When I dial in cyan with that 'safe filter' in place the image, expectedly goes black. But, technically that Rosco filter is not perfectly safe (as Ilford's data indicate and as I have found out from trials).
Ten minutes and a step wedge and one can see if it (cyan) does anything to a print under your own conditions.

[jeroldharter]

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]

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]

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]

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]

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]

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)