Lighting choices for Durst L138 [Archive] - Large Format Photography Forum

swmcl

17-Mar-2019, 20:52

Daniel Casper Lohenstein

17-Mar-2019, 21:30

Hi all,

I'll try to upload a picture of my simple and untested attempt to get the L138 into the modern age. Why ? Because the original lamps are almost impossible to keep replacing. This one is a 27W daylight LED lamp with the edison screw that is part of the original equipment. I would not need the infrared heatshield glass to be left in place (it is shown in the photo).

My question:

Is this going to work ? I don't yet have a darkroom. I live in a rental and have only the enlarger.

Cheers,
Steve
Hello,
I tried a LED globe with a diameter of 125mm and a power of 75W (7W) yesterday. you have to use at least 95mm to achieve an even and constant illumination in mf and 110mm in lf.

I made some prints in 30x40cm. They are constantly illuminated without vignetting. But I needed longer exposure times and a larger aperture to get faces grey (f8 instead of f11) and another 100-200% to darken the corners (some kind of children portraits in the Nadar inspired glamourous style of the golden twenties, taken with Rollei Ortho 25 ...)

What I want to say: it works, but it isn' t that bright. You have to use larger apertures and you have to expose longer. Perhaps you need another developer, I am sure you come into the dead zone of the Schwarzschild empire. Especially with old vintage paper that has lost already its power you will have to live with lower contrast.

regards

andreios

17-Mar-2019, 21:46

Where did you get led bulb this size? I am still using regular bulbs in my 138, but I only have time smaller ones and for even illumination of a 13x18 neg I have to put in a diffuser which also prolongs exposure times. I'd be keen to try your solution...

Daniel Casper Lohenstein

17-Mar-2019, 22:21

noser.ch in Switzerland. I mentioned the link in the othe L138 thread ... But: I continue looking for a more powerful globe. regards

PS: https://www.ses-shop.ch/led-leuchtmittel/e27-led-birnen/led-birne-ufo-24w-neutralweiss-2-610lm-120-ip20_2708_2582/ - The next LED I will try, already equivalent to 160 W. Neutral white. 200mm diameter. Should be enough ...

andreios

18-Mar-2019, 02:48

Thanks for the UFO hint... Found the 200mm diameter 24W locally. They even have in stock a 36W unit with 250mm diameter - will have to check first if it would fit inside the head though...

Pere Casals

18-Mar-2019, 03:42

Is this going to work ?

I made the same in a 138S, it works perfectl IMHO. The bulb should be of the warm light type and better if it is high CRI, (say CRI 95), it that way color filters for variable contrast papers will work mostly as intended.

You may refine that by placing an RGB bulb controlled with a radio wireless remote (rather an IR remote). In that way you may press R button for safe light, and Yellow (or Green) and Purple (or Blue) to conveniently print with the split grade method. This is a VC head in practice.

188902

Daniel Casper Lohenstein

18-Mar-2019, 05:03

I made the same in a 138S, it works perfectl IMHO. The bulb should be of the warm light type and better if it is high CRI, (say CRI 95), it that way color filters for variable contrast papers will work mostly as intended.

You may refine that by placing an RGB bulb controlled with a radio wireless remote (rather an IR remote). In that way you may press R button for safe light, and Yellow (or Green) and Purple (or Blue) to conveniently print with the split grade method. This is a VC head in practice.

188902

Hi Pere Casals,

if I understand you right you can adjust the bulb color with the green and blue buttons on the wireless remote? This is great! Do you have the specific light temperature values that match the Ilford / Foma / Kodak specs? How do you measure it under the enlarger? Do you have a RGB meter?

Regards

Daniel Casper Lohenstein

18-Mar-2019, 05:25

Thanks for the UFO hint... Found the 200mm diameter 24W locally. They even have in stock a 36W unit with 250mm diameter - will have to check first if it would fit inside the head though...

Oups, I see now that I was wrong: the diameter of the bulb is not 120 but 200mm. This is great, but perhaps it is larger than the L138 head. I will try it. It's a pity that the windows that lets the light through into the mirror housing is so small. I am afraid that there will be not enough light coming through that window. But the UFO lamp is flat - perhaps I can adjust it in a greater distance to the heat protection glass.

If the UFO bulb is too large, I will try to build a light box that fits into the condenser slots, containing the UFO bulb ...

One of the advantages of the L138 is that it is quite huge. So you can make a lot DIY.

ic-racer

18-Mar-2019, 06:27

The smaller the lamp, the smaller you maximum negative size for enlargement. Keep testing lamps until you have even baseboard illumination for your intended format. Be sure to stop down the lens to appropriate aperture when testing for light falloff. Unless you have an f12 process lens, most enlarging lenses have a pronounced hot-spot in the middle when used at 'focusing' aperture. Also, magnification affects light falloff (different lens to negative distances for the same negative/lens combination). So take that into account when testing.

Make sure you globe is large enough.

188909

Sample test results. My enlarger came to me with the output pattern on the top right. Center bottom after tweaking. (Grade 5 prints).
188910

Pere Casals

18-Mar-2019, 07:18

Make sure you globe is large enough.

138 manual says that a 110mm diameter bulb is recommended for 5x7, for 4x5 IMHO a regular bulb is ok is we adjust to the right front-back position of the bulb.

https://www.trippingthroughthedark.com/files/durst138/Durst%20Laborator%20138%20Instructions.pdf, page 3, 4.
https://web.archive.org/web/20190318144940/https://www.trippingthroughthedark.com/files/durst138/Durst%20Laborator%20138%20Instructions.pdf

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.

To me this is a great choice because it delivers best of diffuser and condenser enlargers. It is a matter of taste if we use a glass that is more or less "grounded". While masking enough dust, scratches and grain the illumination it's still contrasty and powerful. To me it's the way a 138 performs the best.

Pere Casals

18-Mar-2019, 07:41

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-content/uploads/2017/03/Contrast-control-for-Ilford-Multigrade.pdf
https://web.archive.org/web/20190318144750/https://www.ilfordphoto.com/wp/wp-content/uploads/2017/03/Contrast-control-for-Ilford-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/split-grade-printing/
https://web.archive.org/web/20180317063554/http://www.darkroomdave.com/tutorial/split-grade-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

18-Mar-2019, 07:55

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

18-Mar-2019, 08:14

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.com/variable-contrast-led-head-for-durst-138s-condensers/ and shows the diffusion glass in place.

Larry Gebhardt

18-Mar-2019, 08:17

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

18-Mar-2019, 09:10

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

18-Mar-2019, 10:26

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

18-Mar-2019, 11:17

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...

188911

188912

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

This is $20:

188916

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

18-Mar-2019, 12:32

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.

188919
188922

Pere Casals

18-Mar-2019, 12:44

Philips

http://www.jollinger.com/photo/enlargers/images/enlargers/philips/philips_pcs2000(1982).jpg

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

18-Mar-2019, 18:14

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 ... ?

swmcl

18-Mar-2019, 18:49

Pere Casals

18-Mar-2019, 19:38

Yes, it is the vert. handle...

188931

At least the 138S variant has a filter drawer.

With the bulb you have, adjust the position of the bulb to have an even illumination.

I purchased the rgb bulb at Amazon

Daniel Casper Lohenstein

18-Mar-2019, 23:54

OK.

My bulb says 16W (did the packet say 27W ??) and I think it is an E27 socket with 230V and is only 72mm in diameter. I'm in Australia and I think that some of you may not understand how few options we have here. The Swiss flat bulb looks quite good. I can't see any supplier of LED bulbs with a remote control anywhere in Australia.

Hi,

after reading Pere Casals thoughts about RGB LEDs, I looked for RGB LED strips from China, they cost about 15 USD, 1 cm wide, 5 m long, with controller and remote control. You can cut them down to 3 LEDs on a strip of 5 cm. You can connect the strips as you want, with 4 cables, that are bundled into RGB cable strings.

imagine you cut 18 strips with 15 cm length each. They are self-adhesive. You row them on a 18 x 15 cm board and connect them, then you will have a bright light board with changeable light, that you can insert into the upper condenser slot. The lower condenser slot will be a lightbox with walls made of styrofoam.

If you use some potentiometers you will be able to build a controller box on the front of your lightboard. https://www.youtube.com/watch?v=wns8xrxTYhU You could meter exactly the color temperature. You could build some scales.

Would it be realistic?

Regards

Pere Casals

19-Mar-2019, 02:27

If you use some potentiometers

Daniel, the potentiometers may reheat a lot, better if using a DC/DC voltage converter for each color channel, with vol/amp displays, all very cheap. The readings will provide reference points.

Something like this, $10 each:

188937

If displays had an internal illuminator we may place red gelain filter on it. Those can be nicely integrated in a panel, the panel would also have switches por the individual channels.

A refinement would be placing two relays in the Blue and Green independent wires (going to the led from the converter) that would be activated by the darkroom timer. This makes sense because for BW we may want to cut Green and Blue while allowing Red.

So the circuit is, AC mains to the DC power supply, the PS feeds the 3 DC/DC converters. From that we have 4 wires to the LEDS, common+rgb, we place a switch in each wire(4 switches). Then the G and B wires would have each a 230/110V AC relay that would be activated by the timer.

This would be optimal for BW work, allowing split grade with timer, as G and B have individual switches we can use the timer for both exposures. Red would be always ON, because it has no effect. Of course with Red ON, when we activate G or B then we have Yellow or Purple, basicly the 00 and 5 filter grades.

Of course we may "calibrate" our setup to know the dimmer settings (displayed voltage/intensity) in the G and B channels than produce any of the Ilford grades and equivalent exposures...

If wanting to print RA-4 then a 3rd relay could be installed for R channel. That relay can be bypassed with an additional switch, for BW convenience.

_____________

The strips are suitable to retrofit the illuminator of a diffuser enlarger, if it's condenser type then better a discrete powerful led.

swmcl

19-Mar-2019, 13:40

So I need a Heiland LED Cold Light made in China for a reasonable cost. The Heilands themselves are ridiculously priced (CatLabs) - a complete joke for what is involved with the technology. All they are is a specialist application of some very mundane technology nowadays.

I could perhaps adapt a continuous light source of the photographic kind ?? Something from B&H ??

Pere Casals

19-Mar-2019, 14:03

Heiland is a reputed and a serious gear maker. A pro working all day long with an enlarger would be happy to pay a lot for high quality solutions, it's not my case.

But you have it solved, just place a 110mm dome or disc in front of the bulb you have and you can start working, or place a piece of frosted glass in the drawer. The important thing is starting, later you may refine your setup, but anyway you depart from a privileged situation, a 138 is a war machine... Problem I've with the 138 is deserving such a privilege !

Daniel Casper Lohenstein

20-Mar-2019, 02:30

I could perhaps adapt a continuous light source of the photographic kind ?? Something from B&H ??

Well, this thread shows you a few options:

the LED globe > 110 mm
the UFO bulb < 200 mm
the RGB bulb with wireless controller
the RGB strips with wireless controller and lightbox
the RGB strips with DC-DC 5A step-down buck thing
the Heiland cold light

You don't need B&H, just get your stuff from e.g. Ebay, Aliexpress or elsewhere

Keep in mind that bulbs should be >110 and >200mm and that you need an equivalent of ~75-150 Watt.

Regards

Drew Wiley

20-Mar-2019, 20:30

I'm a bit skeptical about getting clean color prints from any kind of current RGB LED system. You'll get something usable, but it might still leave a bit of "mud" in the print. You'd get better color from one of the later Durst halogen Colorheads made for the 138 chassis, provided the dichroic filters are still in good condition. But bagging one affordably requires some luck, especially where you live.

Pere Casals

21-Mar-2019, 02:22

I'm a bit skeptical about getting clean color prints from any kind of current RGB LED system.

Drew, IMHO your remark has sense, I've also explored this concern. Mostly we have a good deal of control by adjusting RGB channels, but we may have a channel crossover that it would be different than with tungsten illumination. Probably most RGB bulbs have a non optimal CRI having valleys between the main colors.

IMHO the crossover can be adjusted if we place also some adjustable Orange and Cyan leds in the illumination that would adjust in those mentioned spectral valleys. The RGB illumination sure will deliver a lower channel crossover than tugnsten, but with additional Orange and Cyan leds we would adjust crossover like we want, sporting and amazing control in the color output.

So IMHO a LED color head may not deliver exactly the same color crossover than with tungsten, and installing 5 channels is a drawback, but this would deliver a total control. I plan to install also orange/cyan leds in a color head, not knowing it that would be necessary/useful, just to have the resource if it turns necessary.

Anyway today RA-4 has a drawback. Papers are very saturated, this is not a problem with digital processing as we may digitally lower saturation, so most of the market wants saturated papers to be laser exposed that will perfom for any job, while portraiture papers for optical printing are a bit hidden, at least to me.

swmcl

24-Mar-2019, 14:12

OK. I've ordered something to play with ...

What I want you guys to tell me is the lumens I need. How many lumens of white light is required at the baseboard ? I can't see a lumens figure on the Heiland webpage. Most of the devices I see are quoting lumens.

What have I done ?? Well ... its a NiceFoto TC-668 RGB 40W LED video light Dimmable Panel LED Video Light , 3200k-6500k, CRI 95+,TLCI 97+ for photography and video from Alibaba

https://www.alibaba.com/product-detail/NiceFoto-TC-668-RGB-40W-LED_60838662659.html?spm=a2700.galleryofferlist.normalList.356.2d1a1855IRBlf9

This device boasts 4600 of those Mr. Lumens.

-------------

I'll need to make up a housing for it of course but I figure it will lay horizontally on top of a custom housing bolted to the frame of the L138. It is also big enough for an L184 ... So that would be two enlargers in one. This panel thingy is a big big for the L138 so it is a bit wasted. It will be an optimum size for any L184 ...

Just gotta hope the lumens is enough.

Please tell me I'm in with a fighting chance !

Cheers,
Steve

interneg

25-Mar-2019, 12:52

I'm a bit skeptical about getting clean color prints from any kind of current RGB LED system.

As long as they hit the spectral transmission peaks of #70, #98 & #99 filters with good hard cut-offs (something LED's are very, very good at), you should get very accurate colour if the rest of the system is sensibly designed. That said, it might also show up deficiencies elsewhere in the imaging chain - for example, one of things that's popping up as a result of the emergence of laser projection of digital cinema is that it's super demanding of good colour calibration throughout the grading process - if you're off by 2nm from where you should be, it'll show, badly.

I also suspect that 475nm LEDs might not be a bad place to start if looking for a BW only system for Multigrade filters.

Anyway today RA-4 has a drawback. Papers are very saturated, ...while portraiture papers for optical printing are a bit hidden, at least to me.

Actually, they're pretty controllable - have you seen any recent top-notch optical RA-4 prints? Contrast & saturation can be controlled by flashing, masking etc very well indeed. Always easier to reduce contrast & saturation than add it.

Drew Wiley

25-Mar-2019, 13:54

Pere - RA4 contrast and hue punch can be tweaked slightly via specific paper choice, and more significantly by relatively simple masking techniques. ... And swmcl - LED light panels claiming to have CRI 95 have gotten pretty good, but are probably not truly in that range of quality; and even if they were, that means that five out of every hundred representative hues is going to be a mismatch. No toy video light like that Alibaba thing is going to do a decent job color printing. And the specs are unquestionably misleading because they are based on the hypothetical rated color temperature of certain LED's without factoring in the offset of diffusion plastics etc. Same can be said for camera store light boxes. It's not just about lumens or even averaged out color temperature. You need the ability to get fairly precise control on specific color dye spikes, which modern colorheads are designed to do, generally using halogen bulbs and subtractive CMY dichroic filters. Yes, you have a fighting chance. Every boxer who enters the ring and wakes up in the middle of the first round with a busted lip, black eye, and dizzy head learns something useful. ... Now for Interneg - Do you have any idea of how very little light actually gets through 70, 98, and 99 filters? - or how very few were ever used for actual color printing? That's not how it's done. For my additive colorheads I use a trimmer
system, which achieves narrow-band cutoff not via absurd density, but by providing a dichroic sandwich the light can pass between, trimming off what lies on either side. That's not feasible with banks of tiny little LED's. I'm not discounting the eventual possibilities. LED technology is still a bit adolescent for precise color work. VC black and white printing is more realistic. I'm now using LED panels for copystand work, including color.

swmcl

25-Mar-2019, 15:17

Thanks Drew,

I've always appreciated your thoughts.

I'm not going to be colour printing anytime soon. A 'fighting chance' is worth the cost of the journey. I appreciate that if manufacturers of LEDs were to listen to the concerns and wishes of the colour and B&W film photographic community they could make products that would very much make our lives better. We are a very small market segment and so this is not going to happen. What this panel is trying to do is approach the Arri panels in performance - we all know the cost of Arri panels at B&H. The Chinese want a slice of that market (I've seen adverts boasting 'Arri-like performance' but they spelt Arri wrong !!). My hope is that an offshoot of this direction is a suitable-enough light source that can do a reasonable and cost-effective job in B&W printing. It is silly to think we could keep finding bulbs and other parts for enlargers that are already 50 years old. I hope this kind of thing might get us out of a bind. It won't be perfect but it could do a 90 - 95 % job (to the photographer) and if the end viewer (common man) can't tell the difference, it is effectively a 100% job.

Drew Wiley

25-Mar-2019, 15:46

You're not risking much money, and if it doesn't work out, the light panel will still be good for something else. And after a few good brawls in the ring, the technology will have improved, and you'll have a much better idea how to make it win. Arri is pro stuff. I like their focussing fresnel lighting. Have fun with your project! Durst enlargers are wonderful once you've got them all tuned up.

interneg

25-Mar-2019, 17:17

Do you have any idea of how very little light actually gets through 70, 98, and 99 filters? - or how very few were ever used for actual color printing?

Yes, I am very much aware of both the low transmission & limited circulation outside of R&D labs, however it is the gold-standard of colour separation - which is why I pointed out that LED technology can deliver the same narrow bandpasses with much more light output relative to power.

That's not how it's done. For my additive colorheads I use a trimmer
system, which achieves narrow-band cutoff not via absurd density, but by providing a dichroic sandwich the light can pass between, trimming off what lies on either side. That's not feasible with banks of tiny little LED's. I'm not discounting the eventual possibilities. LED technology is still a bit adolescent for precise color work.

Again, I'm aware of these systems - are you adding dichroics with cut-offs at 390 & 520nm on blue & green respectively? Are you using MOSFETs to control the bulbs?

I think the biggest problem with additive LED heads has often been poor system design, rather than the competence of the components when appropriately chosen - we're probably rapidly approaching the point where it's likely to be at best a dead heat between the technologies.

Drew Wiley

25-Mar-2019, 19:05

Each of the three colors involves a PAIR of dichroic filters, cutting each off both directions, rather than a narrow single filter. Too narrow an nm width is counterproductive. The spectral sensitivity of dichroic filters shifts if they overheat, not to mention the complication of reciprocity failure getting longer and longer. I designed all this relative to make big prints from heavily-masked Ciba printing. Can't get into too much detail here, except that it's simultaneous additive, feedback-based upon pulsed halogens, which means a lot of headache triacs susceptible to cross-talk interference issues. The whole machine is exceptionally heavy, about 14 ft tall, and built like a tank (earthquake country!). The color output and panel control is superb. I designed it to run dramatically cooler than the Durst commercial additive option, which never made it to public market but did get employed by the NSA for aerial recon photos - those colorheads run extremely hot and need the filters replaced every six months ($$$). Since then sine-wave lighting control has become an option, but one dependent upon software, which is always a risk for becoming prematurely obsolete, so I bypassed it. I'd have the same worry about current LED's - the mere fact the technology is evolving so fast means that specific replacement components might become unavailable quickly too, while a drawer full of halogen bulbs might keep one going another fifty years. I built my colorheads using special aerospace gaskets and sealants, so they should last quite a few more years than me! But I also have a Durst L184 with a subtractive colorhead set up if the bigger fancier machine happens to throw a triac tantrum. My biggest problem at the moment is just finding the time to print color. I've been heavily involved in black and white printing lately.

Pere Casals

26-Mar-2019, 09:48

Actually, they're pretty controllable - have you seen any recent top-notch optical RA-4 prints? Contrast & saturation can be controlled by flashing, masking etc very well indeed. Always easier to reduce contrast & saturation than add it.

My ignorance is deep, I've never printed RA-4, but I think that I will...

I guess a way would be preflashig with a mask. A general pre-flash would lower a lot saturation in the highlights, but with little effect in the shadows, so the desaturation would not be uniform...

Pere - RA4 contrast and hue punch can be tweaked slightly via specific paper choice, and more significantly by relatively simple masking techniques. ... And swmcl - LED light panels claiming to have CRI 95 have gotten pretty good, but are probably not truly in that range of quality; and even if they were, that means that five out of every hundred representative hues is going to be a mismatch. No toy video light like that Alibaba thing is going to do a decent job color printing. And the specs are unquestionably misleading because they are based on the hypothetical rated color temperature of certain LED's without factoring in the offset of diffusion plastics etc. Same can be said for camera store light boxes. It's not just about lumens or even averaged out color temperature. You need the ability to get fairly precise control on specific color dye spikes, which modern colorheads are designed to do, generally using halogen bulbs and subtractive CMY dichroic filters.

Drew, I see two possibilities to retrofit a color head, one is using a white LED sporting CRI 98, this would match a tugnsten, but as Larry noted we shoud the see if we have an after-glow because of the phosphor.

The other way is an R-G-B LED, my guess is that by adjusting the spectrum with also Cyan and a Orange LEDs this would deliver enough control, just a guess, it should be tested in practice...

Drew Wiley

26-Mar-2019, 10:10

I'm sure LED will be the solution of the future, Pere, though use of enlargers for color printing will no doubt continue to diminish. But LED's just aren't really there yet, when it comes to taking a step to seriously improve color printing per se. Let me briefly state why. Assuming those who do continue to gravitate toward optical printing will do so to achieve a level of print quality difficult otherwise, that should take into account a strong enough light source to punch through supplementary mask density as well as the original neg. And even though RA4 papers themselves print fairly fast, achieving precise composition in big enlargements as seen through a dense orange dye mask, on color neg film, itself requires quite a bit of extra light. For example, I compose with adjustable masking blades on a big precision easel, so my white borders will act of the final frame. Even with a huge fairly high-aperture lens (a 360/5.6 El Nikkor) and 1700 watts of halogen, it's a bit of a headache when punching large prints. But don't be fooled by advertised CRI ratings. It's not that simple, nor can you always trust marketing hype. The color accuracy has to correspond to three specific wavelengths, and do so narrowly, in order to be ideal. But when that day arrives, separately controllable RGB would be preferable.

Pere Casals

26-Mar-2019, 10:46

Even with a huge fairly high-aperture lens (a 360/5.6 El Nikkor) and 1700 watts of halogen, it's a bit of a headache when punching large prints.

The equivalent LED power would be 170W...

But we have another source for the efficiency: Condenser !

Color condenser heads were also there: http://www.khbphotografix.com/omega/Condenser/D2Type2.htm

Condensers for 8x10 are king size, but now we have new resources that were not as available in the past.

Let me guess a 8x10 color solution:

> Condenser type.

> Condensers made from solar energy frenels

> R-G-B LEDs with also Orange and Cyan illuminators to control the channel crosstalk, my guess is that this would solve any color need.

> Perhaps some (more or less) frosted glass in the path to lower collimation.

With only 200W of LEDs a condenser (or "semi" condenser) configuration would deliver an impressive yield, even for mural prints.

Pere Casals

26-Mar-2019, 16:46

How many lumens of white light is required at the baseboard ?

In the baseboard you need Lux, not Lumens, Lumens are for the emiting source.

Basicly you may substitute the specified tungsten light source by a LED source sporting 10% of the power, because LEDs deliver a much higher yield.

As LEDs do reheat less you may overpower the head, to some x3 the equivalent power. In such a case you may want to have an electronic dimmer to decrease power for small prints, if not you will have to stop too much the lens to have long enough exposures.

I've a 18W LED bulb in the (condenser) 138S, this ends in some 8 Lux on the easel with lens wide open at f/5.6 for 40cm prints. This ends in around 20 seconds exposures at f/11, which is a suitable aperture for LF enlarging lenses.

A diffuser head requieres more power, but your starting point it is 10% to 15% of the original tungsten power. Use warm color bulbs similar to tungsten in Kelvin, or RGB bulbs for direct split grade.

Drew Wiley

26-Mar-2019, 17:05

I work in actual log density units at the baseboard, Pere. Yes, I have a lux meter; but my easel densitometer is simply way way more accurate; and will even read down into ranges a lux meter is blind to. All this reinventing of the colorhead concept is pretty interesting; but I've gotten enough battle scars doing that kind of thing already a number of times that I know not to underestimate the potential difficulties in actual execution of any such idea. For instance, claiming 170 W of LED is equivalent to 1700 watts of halogen is sheer nonsense. Look directly into the exposure light of a halogen enlarger that powerful, and it will probably blind you, at least temporarily. It's like looking at the sun. And this is in reference to tightly controlled RGB band width. It remains to be seen if LED's are even capable of that task yet. You can't realistically install tiny little trimmer filters on each one of them to get the precise color realistically necessary for high-quality applications. Even big laser printers have trouble keeping up with halogen light output. That's because there's no such thing as a true green diode. What they do is filter out the tiny bit of green present in a red diode and utilize that. Yes, there are industrial lasers that cut through an inch of solid steel - but they can't print color paper! That's why many RA4 papers have been re-balanced for greater green sensitivity. I once had a Durst color mural enlarger that would punch a 30X40 inch Cibachromes from 4x5 with a .90 density supplementary mask in about 12 seconds!, which means it would have done a comparably sized RA4 print in a fraction of a second. It had four cooling hoses made of pure silicone, and a cooling fan that drew more 240V wattage than the average shop table saw. Leave a chrome image in the carrier for 90 seconds and the dye would be all faded. Got rid of that thing and designed my own colorhead. So yes, you are guessing, Pere, and it shows. Not a crime. It's fun to surmise the possible, even if it's impossible.

Pere Casals

26-Mar-2019, 17:36

For instance, claiming 170 W of LED is equivalent to 1700 watts of halogen is sheer nonsense.

Some 200W of LED is equivalent to 1700 watts of regular incandescence tungsten bulbs, hallogen has around x2 the efficiency so 400w of LED are equivalent to to 1700 watts hallogen.

The 138 power is referenced to regular incandescence, not to hallogen...

I work in actual log density units at the baseboard

Me also. But for calibrations I want to know absolute Lux, later I apply Log.

Yes, I have a lux meter; but my easel densitometer is simply way way more accurate; and will even read down into ranges a lux meter is blind to.

My cheap one reads 0.01Lux, very precise. Problem it that has a big dome, so it is not metering small spots, but it's what I have.

All this reinventing of the colorhead concept is pretty interesting; ....... Not a crime. It's fun to surmise the possible, even if it's impossible.

For sure that a RGB LED retrofit for BW printing will work amazingly well, it's what I'm using and my calibrations work pretty fine:

189255

(From left, grades 0, 1, 2, 3, then the compressed grades 4 and 5 (upsidedown) because not exposed double time, and at right full power white light)

So for BW LEDs are perfect...

Of course printing RA-4 would require some refinements, I guess I would be able to also get perfect results, but first I've lo learn RA-4 printing

Luis-F-S

27-Mar-2019, 10:55

There have been a number of threads on this subject. The one that comes to mind is:

https://www.largeformatphotography.info/forum/showthread.php?74895-Durst-138S-Replacement-Bubs

https://www.largeformatphotography.info/forum/showthread.php?116320-durst-laborator-138s-questions

Not necessarily for color, but for B&W printing. For color work, Durst made several CLS heads, the 600 watt CLS-301 which used halogen bulbs (ELH) like the DeVere heads do & the 2000 watt CLS-300 and the later CLS 1000 head which I believe used a specialized Durst 1000 watt halogen bulb, the Colamp 1840 which it shared with the 8x10 color head. The bulb may have been the EIKO 031293032409?

Drew Wiley

27-Mar-2019, 14:14

They made several more heads Durst made in addition to those, some very expensive; and there were numerous aftermarkets heads from other companies for Durst chassis, some of which were pretty lousy, some pretty good. None of them used proprietary bulbs. Any serious scientific bulb supplier has the right ones; no need to pay obscene Durst bulb prices. Opal lamps are more an antique concept, so involve scrounging around. And the parabolic reflectors for the CLS300 could be hell to find replacements for. It was possible to recoat them; but most people simple replaced the lights with lower wattage ones having built-in reflectors.

interneg

29-Mar-2019, 17:28

Each of the three colors involves a PAIR of dichroic filters, cutting each off both directions, rather than a narrow single filter. Too narrow an nm width is counterproductive.

I probably didn't make my question clear enough - was quite aware that was probably how you were doing things on the blue & green, wasn't sure what was happening on the red filter.

BTDT with both overheated dichroics & triac fun & games on various systems - which is why the lower heat from LED & a system with a sensible degree of future upgradeability (mainly a question of sensible circuit design & connector placement within that circuit) are attractive.

Drew Wiley

29-Mar-2019, 18:05

The biggest problem with at least big powerful colorheads and triacs etc is EMI (electomagnetic interference). Too much going on a once is just like throwing rocks into a pool at the same time. The more you throw in, the more the ripples are likely intersect in an unpredictable way. When you use more than three or four lamps at a time, this has to be factored. Sine wave control can handle up to 16 to 20 circuits at once, but wasn't available quite yet when I began my colorhead project, and is also computer and software dependent, which introduces a whole new layer of complication. My 5X7 RGB colorhead uses only 3 lamps, so doesn't have the same issue. With the bigger 8x10 head, efficient cooling was achieved by splitting it into a V-head, then combining the light below. But that makes the head quite heavy. No problem, since I build the chassis like a boulder too; but it's not a marketable concept. I'm getting itchy to start color printing again, but the weather is still temperamental. I'm allergic to RA4 chemistry, so do the actually processing outdoors in mild weather on a portable cart equipped capable of handling up to 30X40 inch drums. It will be interesting to see where all this new LED technology goes.

ac12

3-May-2019, 23:12

Larry Gebhardt

5-May-2019, 06:49

Test the G30 bulbs with an empty negative holder. The coatings on bulbs are not always even and the condensers will show up those spots. This was much more likely to be a problem on bulbs not meant for photo use, though maybe modern manufacturing has minimized the issue. The nice thing is you can turn the bulb and find the best side. I found an odd issue that took a bit to track down to the bulb. I kept trying to see it on the negative, then the condensers and finally figured out it was a small imperfection in the bulb.