LED enlarger head for B&W -- question in passing

[Duolab123]

For 4x5 and smaller films I use a Beseler 45 Universal head. Closed loop, 3 halogen lamps on the VC version, green and blue dichro filters, and a clear filter. Blue and green are for VC paper, clear for graded papers. The computer controller figures out "grades".

For larger negatives I was lucky to have found a 5x7 and 8x10 Zone VI enlarger. Both have the last version of the green tube/blue tube cold light head. These are closed loop through a Metrolux II compensating timer.

The Zone VI heads were somewhat intimidating at first. The box that controls the ratio of blue and green, has 2 dimmers, one for each tube, instead of contrast grades it has letters, ABC etc. I of course, found it necessary to mark the combination of settings that produced "grades".
I usually don't do much fancy, but I have done split printing using separate blue and green exposures.

[koraks]

@Ulophot, I understand about the typo and the fact someone else is building this for you, ok! The blue/green ratio still seems way off to me for a mid-range (ca 2.) contrast. You might want to look into this and have a chat with your designer to see what's up. However, it's not an issue as long as you can hit grade 0 and grade 5 with the head.

As to calibration: you can actually create a calibration curve for the light source that approximates equal exposure times across most grade settings. In my experience not all grades because you run out of green light at some point, but it's usually possible to keep exposure constant across grades 1 through 4 or so. As far as I recall from working with Ilford filters that's similar to those.

Calibrating your led grades to ilford grades is also possible. It's a little additional work and math, but certainly doable. I didn't find it important enough to go there, but I did do the equal exposure calibration thing on both led heads I built. It sure is convenient.

Don't fuss about what people are saying about continuous spectrum etc. It's inconsequential. Calibration is needed anyway, and it still would be if the led source would have been continuous. Anyway, it's something you work around "automatically" if you calibrate your leds to match ilford grades.

Regarding the use of red led for focusing etc: yes, that can be done (in fact, I do it as well), but be careful using only red as a focusing tool used when the paper is already on the easel. It WILL fog. The question is by how much and if it'll turn up as fog or as a subtle contrast reduction. You don't want either. If you want to use pure red for focusing on the paper itself, be sure to add a good red filter.

[Ulophot]

Thanks to all.

Duolab, what I am attempting to create is something about which I had started a thread or two some time ago (2020?), which I have since “shopped” around to various photo gadget makers to see if they had any interest: a plain vanilla, budget-model, white light diffusion LED head to replace our aging coldlight heads. There are DIY models for those who can build, and then there’s the “Rolls”, the Heiland, for those who can afford it. Nothing in-between, to my knowledge.
The one my friend is building is already more complex than I had suggested. I had envisioned white-only LEDs; he opted for the RBG panel. I had offered a blue &green LED alternative, but he may well have gulped hard when I sent him this link:

http://www.jbhphoto.com/wp-content/u...Printing03.pdf

I am paying for materials, he is doing the work, based loosely on Marco’s (elgatosuizo’s) design, with a 3D-printed a head enclosure of his own invention that takes my suggestions into account. As indicated, we’re still ironing out issues. The photo realm is new to him, and it’s taking much longer than he expected, due to various problems encountered along the way. There may eventually be wider benefits for others.

The Gr. 2 calibration, again, is just to provide a useful standard. If the other contrast grades don’t space evenly, due to the differences between incandescent and LED with its spikey nature, testing will at least show that. If needed, I will at some point create a new exposure chart, based on some tone -- possibly a Zone VI, maybe VIII -- for maintaining that value when switching between filters. My preliminary tests suggest that I won’t need one. I’m not a great printer, but I am a good one and experienced.

Doremus, I’ll keep in mind adding the red back in and see if it makes a difference. At this point, I am not having difficulty with the projected image, but my testing has just gotten started with a couple of negs.

[Duolab123]

If I outlive my dichro/cold light heads I will take up golf

Anything else that requires computer etc. I'm running away. Always can make contact prints

I hope this works out as the beautiful Heiland made heads look confusing.

[Ulophot]

I'm happy to report that testing with a borrowed Stouffer 21-step wedge put my Gr. 2 just about on the mark at ISO(R) 112 with Ilford WTF (my standard paper), and that both #1 and #5 filters produced their proper contrast levels as well.

My old contrast issue with Foma Classic remains; the #5, even after eliminating Green entirely, gives only a Gr. 3. I have tested for safelight fogging exhaustively and eliminated that as a factor. Whether or not I just got a box that sat in a hot delivery truck or something, or the paper just doesn't produce that contrast (as at least one person here reported), or the blue of my LED is just not blue enough (added spikes or whatever that the paper is reacting to) will have to wait till I run out. Meanwhile, 3 is not so bad most of the time, and it still gives me an alternative of color and surface for the great majority of negatives.

[interneg]

Blue filtration tends to max out around G4.25 - at least that's Ilford's verdict both on their MG500 head & the Heiland LED. The magenta G5 seems to pass deeper into the blue than the narrow bandpass LED.

[Michael R]

Blue filtration tends to max out around G4.25 - at least that's Ilford's verdict both on their MG500 head & the Heiland LED. The magenta G5 seems to pass deeper into the blue than the narrow bandpass LED.

This makes sense. Despite the assertion by some, getting max contrast likely requires some blue and/or violet beyond what is normally sent to the paper through certain blue filters or by blue light sources such as commonly used LEDs.

[interneg]

This makes sense. Despite the assertion by some, getting max contrast likely requires some blue and/or violet beyond what is normally sent to the paper through certain blue filters or by blue light sources such as commonly used LEDs.

I think that comparing the bandpasses of #47/#47B/#98 (a fair assumption would probably be that both the dichroic & the LED run about the same or narrower than the #47) vis-a-vis the various low #30's magenta Wrattens (#32?) & the CC Magenta bandpasses - and even the old polycontrast filters (I found some data for the early 70s series - where the max filter value was 'PC4') can be quite enlightening regarding the shortcomings of additive blue filtration for getting max contrast out of papers. The problem may be that a 'bluer' LED might run risks of making the Heiland head less good for colour (I suspect it's been aimed to deliver somewhere in the region of a #25/#29, #47/98, #61/#99 effective range).

On the other hand, I think that with something like the Omega dichroic, a #47 likely would deliver a higher contrast because the max magenta value seems not to be as good as De Vere (for example) - or white light plus multigrade filters.

[koraks]

In the first version of my led enlarger I tested a deeper color of blue. That is, for the final version I went with the universally recommended royal blue, which is around 450nm. Most/all led strips will have blue leds of a significantly longer wavelength. However, my testing with 430nm leds didn't yield much difference as I recall vis a vis royal blue for black & white. It DID produce massive problems with color printing though, so I very quickly moved away to royal blue which more closely matches Kodak additive color printing filters.
Can't really comment on max contrast differences between a color dichroic head and led as I never systematically compared them. I did not notice any problems with lack of "oomph" when migrating to LED, but admittedly I did all/most of my b&w printing with an Ilford 500 head before, so I was already a lost cause apparently.