Lighting choices for Durst L138

[Pere Casals]

if I understand you right you can adjust the bulb color with the green and blue buttons on the wireless remote?

Yes, no cable. For VC paper Green and Yellow is the same because yellow is green plus irrelevant red. Also blue is the same than purple. You always throw the red to see better while burning/dodging.

So in split grade you use only Yellow and Purple, you make a Yellow exposure followed by a Purple exposure, balancing both times you adjust grade. You may dodge/burn more or less a print area when you make the yellow or the green exposure, so you may adjust local contrast in any area of the print.

Do you have the specific light temperature values that match the Ilford / Foma / Kodak specs?

I guess it's 3200K , the tungsten one. Enlargers equiped with cold cathode illuminators had a shift in the contrast compared tungsten ones, so another filter grade had to be used for the same result.

See "EXPOSING LIGHT SOURCES" section in page 3.
https://www.ilfordphoto.com/wp/wp-co...Multigrade.pdf
https://web.archive.org/web/20190318...Multigrade.pdf

How do you measure it under the enlarger? Do you have a RGB meter?

For Split grade you usually make a control strip for the shadows with Purple light and another one for the highlights with yellow light. Then you make the print by combining both exposure times with both colors. The Purple exposure won't modify highlights and the Yellows exposure won't modify shadows. This is the starting point.

So you don't really need to measure anything, you just make two control strips that combined would adjust grade an exposure.

https://www.ilfordphoto.com/split-grade-printing/
http://www.darkroomdave.com/tutorial...rade-printing/
https://web.archive.org/web/20180317...rade-printing/

Me, I meter light with a cheap ($20) lux meter. I calibrate paper and I try to realize what density I'll obtain in any area of the print. I'm still learning and refining my methods.

[ic-racer]

A ground glass may be placed in the filter drawer (also mentioned in the manual) and in that situation perfect uniformity is obtained. In that case even clear bulbs showing the filament can be used.

I don't own a condenser 138, but if it did, this is what I'd do.

[Larry Gebhardt]

I've used bare LEDs behind both a sheet of opal glass and diffusion plexiglass like like Makrolon in place of the heat diffuser. It works well. A halogen reflector bulb should be fine as well since you have the horizontal socket option. Makrolon gives a very even diffusion, but may not take the heat from a high wattage halogen bulb.

I never documented using the reflector bulb, but i imagine you can picture it. My current setup is here: http://www.trippingthroughthedark.co...8s-condensers/ and shows the diffusion glass in place.

[Larry Gebhardt]

One other issue to worry about is many LED bulbs use phosphors. These continue to glow after power is removed. I'd avoid this type of bulb as it will make test strips with short steps inaccurate.

[Pere Casals]

this type of bulb as it will make test strips with short steps inaccurate.

In my experience, this has may have an effect with film calibrations if we want accurate absolute units in the graphs. For paper it would have (perhaps) the effect of a second's fraction, if we find the amount then we may always substract it in the timer.

I guess that RGB bulbs don't contain phosphors... IMHO best is to use an RGB bulb because it allows easy split grade, with the advantage that the header is not touched at all, preventing vibrations.

... Thanks for sharing the 138 manual in your web site.

[Larry Gebhardt]

In my experience, this has may have an effect with film calibrations if we want accurate absolute units in the graphs. For paper it would have (perhaps) the effect of a second's fraction, if we find the amount then we may always substract it in the timer.

I guess that RGB bulbs don't contain phosphors... IMHO best is to use an RGB bulb because it allows easy split grade, with the advantage that the header is not touched at all, preventing vibrations.

... Thanks for sharing the 138 manual in your web site.

The RBG LEDs I've seen do not use phosphors. But most high CRI bulbs seem to use them based on the glow after turning them off. Glad you found the manuals helpful.

What are your exposure times like with that RGBW bulb and 5x7 film? Older bulbs like that weren't bright enough for large prints when I tried them, but a lot has changed since then.

[Pere Casals]

What are your exposure times like with that RGBW bulb and 5x7 film?

Larry, as it is a condenser setup, I guess that achievable exposure depends mostly on the print size, not on negative size. Because with 5x7 we use the right condensers to have the similar yield than with 4x5.

I use around 20 seconds exposures for 4x5, stopping some two stops, with some 30cm prints.

With a 18W LED bulb with the two 240 condensers, a plain Rodagon 210mm @ f/5.6, a 4x5 negative and print size 42cm high (portrait orientation) I get some 8 Lux on the easel. In the circle boundary I have some 15% fall-off in Lux, may be 1/6 stop, from the lens, I guess.

Still I lack a 150mm, so I make 4x5 with the 210, a 138 allows for such kind of things...






I have some 100W rgb leds that I will install for big prints.

This is $20:



It is IR but it has the remote receiver connected to the power supply with a cable, so the receiver is placed outside of the head. This led requires some refrigeration in its back, better with a tinny fan.

Problem is that R, G and B are in three strips and not inter-mixed, so I'm planing a sort of small mixing box with some mirrors and a 110mm difusser to match the 138 bulb. The 18w bulb does not reheat, but the 100w led requires some refrigeration.

The 100W led is similar effect than a 1kw tungsten... and IMHO we can go further with some refrigeration in the box. Such a power amount looks weird, but I'm considering to print on big glass coated with DIY emulsion.

Also (beyond 810 contact copies) I've to say that I discovered what's a sharp enlarged print with the 138 and 4x5 negatives... it's impressive to inspect the print with a x8 magnifier, realizing that detail is way, way beyond what naked eye may see. Impressive...

[ic-racer]

Problem is that R, G and B are in three strips and not inter-mixed, so I'm planing a sort of small mixing box with some mirrors and a 110mm difusser to match the 138 bulb.

I don't know if you have see how Philips addresses the issue of mixing colors with a condenser setup. In this case 3 colored beams converge behind the diffusion disk. The disk and colored lamp assembly takes the place of the dome of the opal lamp from the B&W version of the head. 90 degree mirror is not shown.

[Pere Casals]

Philips

Yes... I find this is a nice way.

But the LED has instead 3 emiting surfaces... perhaps a tinny box made of (first surface kind) mirrors, with two frosted barriers in the light path... the multipe reflection should deliver uniformity.

[swmcl]

OK. Sorry I've been away.

My bulb was purchased at a local hardware store. There is nothing special about it.

I can't see where to place a ground glass in the 'filter drawer'. To be more precise, I can't see a filter drawer !!

Maybe an alternative would be to get another mirror cut to size and then grind that. That would make it a 'ground-mirror' ...

I do see a ledge inside where the mirror is just above the top condenser where a sheet of glass might sit. This might also be a site for a ground-glass (perhaps ground on both sides ...).

Perhaps a combination of both the ground-mirror and ground-glass might make for a very evenly lit result ...

edit: I think the handle on the right hand side is the filter drawer - it is vertical behind the heatshield glass ... ?