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Thread: New LED Diffusion Lamp House for Omega D Enlargers

  1. #11

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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    Quote Originally Posted by cardiomac View Post
    By universal do you mean like what I have now but without the vertical arms attaching it to the enlarger? You would have to lift it with your hands.
    Yes, a 5x7 box unit like the Aristogrid units would be easy to fit into most 5x7 enlargers. Leave the lifting details to the buyer if the enlarger design doesn't take a boxed light source. What you have for the D2 scaled up to 5x7 or 8x10 would fill a hole in the market, as Aristogrid seems to be only making replacement light sources on special orders. Even the Beseler 8x10 conversion used a box light unit that just sits on the adapter. I think you might find there are a lot of us who would be interested in larger units.

  2. #12

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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    Quote Originally Posted by Roger Cole View Post
    Would a 5x7 model fit on a 4x5 chassis? That would be a great incentive to look into a 5x7 camera. Even better if you could come up with an 8x10 model like the old Bessler head that fit on their 4x5 chassis. The difficulty of optically enlarging these are the biggest thing that keeps me from becoming seriously interested in either. Zone VI 5x7s come up occasionally but are much more expensive than a 4x5 Omega chassis and one of your heads, even including the likely price change for a larger model.

    I have a Zone VI type 2 but also have a D5 which I started converting to a 5x7..Aristo was unable to supply a head so I quit working on it. A simple riser is all that's needed to make the negative stage work for 5x7 and this LED head would be awesome..Evan Clarke

  3. #13
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    BTW I have his LED lamphouse for my D2V condenser head and it's a very well made piece of gear that works great. Not sure if I posted the scans here of the comparison I did for evenness with the incandescent lamphouse but I know I posted them on APUG.
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  4. #14

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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    Quote Originally Posted by Bob Mann View Post
    Yes, a 5x7 box unit like the Aristogrid units would be easy to fit into most 5x7 enlargers. Leave the lifting details to the buyer if the enlarger design doesn't take a boxed light source. What you have for the D2 scaled up to 5x7 or 8x10 would fill a hole in the market, as Aristogrid seems to be only making replacement light sources on special orders. Even the Beseler 8x10 conversion used a box light unit that just sits on the adapter. I think you might find there are a lot of us who would be interested in larger units.
    I couldn't have said it much better than that. A 5x7 box unit now and an 8x10 unit after that, or just the 8x10.

    Most people looking for one of these units I suspect would be fabricating their own adapters. An adapter isn't what I'm looking for, just the light source boxed head unit. "Universal" light source.

    I started and ended the Aristo project too. Now I'm finishing a three halogen bulb with dichroic filter diffused light head for a Durst 5x7. if I knew an LED head was available I would buy one instead.

    Curt

  5. #15

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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    Quote Originally Posted by Curt View Post
    I couldn't have said it much better than that. A 5x7 box unit now and an 8x10 unit after that, or just the 8x10.

    Most people looking for one of these units I suspect would be fabricating their own adapters. An adapter isn't what I'm looking for, just the light source boxed head unit. "Universal" light source.

    I started and ended the Aristo project too. Now I'm finishing a three halogen bulb with dichroic filter diffused light head for a Durst 5x7. if I knew an LED head was available I would buy one instead.

    Curt
    Thanks for all the feedback. I will definitely put the larger format project on my list of things to do. Right now I'm working at perfecting a variable contrast model that uses blue and green LED's. One thing I'm struggling with is whether to have individual brightness controls for the two colors or to have a contrast (blend) control and global brightness control. Another issue is whether to put the controls on the head itself or in a separate bench top box. My preference is to put it on the head. Any ideas?

  6. #16
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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    On my beseler cb7, I can't easily read the numbers on the contrast dial when it's higher than 8x10 print size. It's up high! If you can put it on the head, aiming the controls down a little would be better than straight ahead. Having the control in a separate box is more clutter on the work area and one more thing to keep paper away from if it's got illumination.

    I'm fine with individual brightness controls, but either arrangement is workable. A simple chart could be made afterwards to show what combinations to use as actual contrast could vary depending on the spectral sensitivity of the paper choices.

    What I'd really want (and would pay extra for) would be a serial (perhaps via 1wire) or USB input where I could computer control it by sending a simple command (such as 3 floating numbers) over the wire like x% green intensity, x%blue intensity, 14 second, and it would do that. Sort of bring it into the 21st century. our own Apps that operate the enlarger would also log settings so we don't have to, perhaps use a webcam for an exposure meter, etc...

  7. #17
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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    Quote Originally Posted by cardiomac View Post
    Right now I'm working at perfecting a variable contrast model that uses blue and green LED's.
    Cardiomac, this is a subject I'm keen on as I've built a few LED enlarger heads (www.deadbread.com/crumbs/23c.html) and I'd like to share some observations from my own testing of blue and green LEDs last year:

    Despite appearances blue LEDs aren't a "pure" blue. To the eye they are strong vibrant blue color, but they're actually a combination of blue and green. I observed this with a homemade spectrometer and with VC paper printing tests. This is important as blue LEDs (with the inherent slight green bias) by themselves just won't allow for the maximum hard contrast grades. For the best results you'll need to use a blue LED without any green hidden in its spectrum.

    Second, the sensitivity of VC paper changes drastically with the color of the light. Green takes a a fair amount time to expose paper fully. Blue takes but fractions of a second. Variable contrast paper does not have an even response to the two colors of light. Adjusting the amount of blue and green will also have the added headache of simultaneously changing the basic print exposure time.

    Ilford (and once upon a time, Kodak) solved this for variable contrast paper with their VC printing filters by building in varying amounts of neutral density into each filter. Every filter has slightly different amounts of neutral density so in use when a #2 is replaced with a #3, the underlying basic exposure for the paper is still the same.

    Food for thought.

  8. #18

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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    Just my random thoughts -

    Didn't Calumet try to market an LED head a few years ago with built in VC controls? As I recall it was very expensive and didn't sell very well. My input would be to keep it simple and let the old VC filter system do the hard work, while you just work on changing the light source to retrofit into enlargers - at a reasonable price. I think a fairly large number of current users would be interested in upgrading.

  9. #19

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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    Quote Originally Posted by konakoa View Post
    Cardiomac, this is a subject I'm keen on as I've built a few LED enlarger heads (www.deadbread.com/crumbs/23c.html) and I'd like to share some observations from my own testing of blue and green LEDs last year:
    Thanks for adding your thoughts. I've read your website maybe a dozen times trying to glean as much from it as I can. It's very strong work and greatly appreciated by me and I'm sure many others.

    Quote Originally Posted by konakoa View Post
    Despite appearances blue LEDs aren't a "pure" blue. To the eye they are strong vibrant blue color, but they're actually a combination of blue and green. I observed this with a homemade spectrometer and with VC paper printing tests. This is important as blue LEDs (with the inherent slight green bias) by themselves just won't allow for the maximum hard contrast grades. For the best results you'll need to use a blue LED without any green hidden in its spectrum.
    I'm with you here. I tried to build a VC head about 5 years ago using some blue and green LED arrays (see picture) and had the same problem - couldn't get more than about a grade 2 contrast. Those LED's peaked at about 480nm or so, like the ones you used. Since then however, Cree has come out with high brightness royal blue LED's that peak at 450nm (graph). They should give a pretty hard contrast. The spectral sensitivity of Ilford paper is shown in the other graph. The curves begin to diverge at about 470nm so, again, I'm hoping 450nm will be sufficiently blue. If not, I've seen some violet (not ultraviolet) LED's on the market that may work.

    Quote Originally Posted by konakoa View Post
    Second, the sensitivity of VC paper changes drastically with the color of the light. Green takes a a fair amount time to expose paper fully. Blue takes but fractions of a second. Variable contrast paper does not have an even response to the two colors of light. Adjusting the amount of blue and green will also have the added headache of simultaneously changing the basic print exposure time.

    Ilford (and once upon a time, Kodak) solved this for variable contrast paper with their VC printing filters by building in varying amounts of neutral density into each filter. Every filter has slightly different amounts of neutral density so in use when a #2 is replaced with a #3, the underlying basic exposure for the paper is still the same.
    I saw this too and it has been one of the reasons I haven't been keen to pursue the simple blue/green brightness control approach but I think I've now got it figured out ... finally. Instead of using simple individual brightness controls, I plan to use an Arduino microcomputer to control the brightness of the two colors. You will be able to dial in the contrast you want and the Arduino will adjust the brightness of the two colors to maintain a constant mid tone exposure using an algorithm calibrated for a common paper (like Ilford MGIV). Not all manufacturer's papers have the same spectral sensitivity, however, so a global brightness adjustment will also be included to fine-tune the brightness for any particular paper. Eventually I hope to allow the user to develop their own contrast algorithms based on their preferred paper/developer. Using a microcomputer has the additional advantage of making it easy to add additional features like timing or metronome capability. It may even be possible to script a complicated dodge-and-burn routine into the computer complete with changes in contrast during the exposure as audible cues are sounded to guide the printer.

    Exciting stuff, wouldn't you agree?
    Attached Thumbnails Attached Thumbnails VC Head.jpg   Royal Blue Spectrum.jpg   Ilford Paper Sensitivity.png  

  10. #20

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    Re: New LED Diffusion Lamp House for Omega D Enlargers

    This is a follow-up to my last post. I ran some test prints tonight using my Omega diffusion housing with four Cree XP-E Royal Blue (450nM) LED's driven at 900 mA. Scans of the prints are attached. The first print is just pure blue light with no filtration. Exposure was 10 seconds at f11 on 8x10 Ilford MGIV paper developed in Dektol for 2 minutes. About five steps are needed to go from black to white with the 21 step tablet. This is about a contrast grade 4 to 4 1/2. Brightness is excellent and about 2 full stops brighter than a 150W incandescent bulb in a condenser housing.

    The second print was exposed the same as the first but a #5 Ilford filter was placed below the lens. About 4 steps are counted in this print, or about contrast Grade 5. The filter cuts the brightness by at least a full stop.

    By way of comparison, white LED's with a Grade 5 filter yield about 3 1/2 steps.

    So the conclusion is that the Cree Royal Blue LED's are capable of producing fairly high contrast but not the maximum contrast the paper is capable of. The addition of a Grade 5 VC filter improves the contrast slightly but at the expense of significant printing speed.

    In practice, I think a maximum native contrast of Grade 4 is sufficient for most purposes. For those rare occasions when a grade 5 is absolutely necessary, a #5 under-the-lens filter can be added with appropriate exposure compensation.


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