What are the actual Multigrade colors?

[1kgcoffee]

I'm interested in using a programmable LED color bulb for advanced multigrade B&W printing. But before I can do this, I need to know/find the color of light that comes out of 00-5? 00 looks kind of amber, 5 looks to be towards magenta. Does anyone have specific numbers?

My plan is to used timed sliders or a curve to automatically set the exposure colors in the bulb. For example a few seconds on grade one, then burn on the shadows to a certain point on the curve by stepping the color up gradually over a few seconds. Currently not possible. But I can't do this unless I know what colors are tied to each grade.

(Hue and saturation if you know them...)

Thanks in advance,
1kgcoffee

 

[MattKing]

Are you referring to the individual filters? If so, they are designed to filter out varying amounts of green and blue light from an incandescent or halogen source.
They aren't designed to transmit just a single colour.

 

[jeffreyg]

this site might be helpful. https://www.energyearth.com/general/categories/lighting/learn-more

http://www.jeffreyglasser.com/

 

[voceumana]

You could measure each filter with a color densitometer to determine this.

The real problem, as I see it, is that LED wavelengths are pretty much fixed or at least very narrow bandwidth, so you really can't build an LED light source that would have the exact same color as any given filter. You won't get a perfect match to the filter steps.

That said, a proportional mix of blue and green LED light via percentage of exposure (time or amount of light) should be able to achieve the same contract results as the filters, but won't have the neutral density effect of the filters which provides matched exposure speed..

 

[flavio81]

I'm interested in using a programmable LED color bulb

I'd be careful. IIRC, LED bulbs can produce a lot of light outside the visible spectrum. Papers are sensitive also to these part of the spectrum and will be focused different by the enlarging lens (unless you have a perfect ultra-apochromatic lens). This might rob sharpness.

Unless, of course, you filter the light so no UV and IR residues are there.

As for the colors themselves, search ILFORD PDFs for multigrade printing. They tell you what is the equivalent of each filter to color correction for Durst (and others) color heads. This could help.

 

[David Brown]

You would be better off using blue and green light sources and doing additive rather than subtractive (magenta and yellow). You could set up your prototype and do tests to find the combinations of blue and green exposures to give you the grades you wanted.

 

[MattKing]

Why do you need grades at all?
Using a step wedge, do lots of tests (on the same sheet would work). Start at full green and then subtract green and add blue as you go. You will end up with a range of contrasts. Pick several that form together a reasonably linear progression. That will give you a plot of results that you can use thereafter.
Take a look at the Model 2 Data on Modern Enlargers' website to see what I mean about using a step wedge: http://www.modernenlargerlamps.com/Modern_Enlarger_Lamps/Welcome.html
His model 3 did what you are trying to do, but his non-IOS version is still at the prototype stage.

 

[wiltw]

Not a simple answer...

https://www.photrio.com/forum/threa...h-a-color-enlarger.107847/page-3#post-2048636

 

[ic-racer]

The Ilford 500 head is additive and uses Blue and Green light.

The latest Ilford Multigrade individual filters are subtractive. The #5 does not appear to be simply a magenta filter to my eye. A while back, a forum member posted that he had access to spectrophogogrammetric equipment. I suggested he test the Ilford #5 filter to see what its spectrum looks like. The request fell on deaf ears.

 

[RauschenOderKorn]

I'm interested in using a programmable LED color bulb for advanced multigrade B&W printing. But before I can do this, I need to know/find the color of light that comes out of 00-5? 00 looks kind of amber, 5 looks to be towards magenta. Does anyone have specific numbers?

That would require you to know the exact spectrum the LED emits to produce a certain colour, too, not just the colour of the multigrade filter. In most cases, suppliers won´t provide that in a data-sheet.

There have been some projects with RGB-LEDs shown on this forum. If you use a programmable controler, you can build the light source first and figure out adjustment of the green and blue exposure according to test strips later. Alternatively, you can have a look at the datasheet of the Heiland LED modules for instance, that´s a good starting point.

 

[DREW WILEY]

Not all VC papers are exactly the same. But all can be printed using either blue versus green, or alternately magenta (=minus green) versus yellow (=minus blue).

 

[1kgcoffee]

Thanks for all the responses.. I didn't even think of the effect of IR light, but my test prints are very sharp so far so hoping it's not an issue. Step wedge testing is also a great idea, but I'm time poor right now.

This is little harder to to figure out than I hoped but from my success printing ra-4 I'm guessing (HOPING) that the lifx bulb gives near continuous spectrum of visible lights. They do produce very pure whites with accurate color temperatures, which tells me that as long as saturation is not too high you get a good variety of spectrum. Awaiting official confirmation. The phillips hue bulb definitely does not provide such a wide spectrum. These bulbs really are amazing and supposed to output 16million colors.

Most papers are sensitive from 630-590nm (green to blue). I'm guessing the blue end is the softer grade? Ilford sheets say 120y (00) to around 200magenta (5). Not sure how to translate that to hue. Other problem is that the grades do not seem to be evenly spaced over this spectrum. I may need to get in contact with this 'modern enlarger' person.

 

[MattKing]

I'm guessing the blue end is the softer grade?

Actually, the various (2 or 3) emulsions all have the same contrast.
What they have is different sensitivities, or "speeds". The faster emulsions have, relatively speaking, more blue sensitivity than green sensitivity. The faster emulsions build density faster, and thus add contrast.
With variable contrast papers, you adjust the contrast by adjusting the ratio of blue and green light. As it switches toward blue, the contrast goes up. If the ratio switches toward green, the contrast goes down.
The blue sensitive emulsion is very responsive. In most cases, if you print with just green, the result looks close to okay. The amount of extra density you need to add (by exposing the blue sensitive emulsion) to make it look best is surprisingly small.

 

[RauschenOderKorn]

Most papers are sensitive from 630-590nm (green to blue).

If i remeber correctly, they are also quite sensitive to UV. But the green and the blue light are used to control contrast.

 

[RauschenOderKorn]

Thanks for all the responses.. I didn't even think of the effect of IR light, but my test prints are very sharp so far so hoping it's not an issue.

IR is much less significant with LED than with old-school bulbs, no need to worry about that.

 

[DREW WILEY]

Blue-sensitive is the high-contrast emulsion; green-sensitive, the low contrast one.

 

[RauschenOderKorn]

The blue sensitive emulsion is very responsive. In most cases, if you print with just green, the result looks close to okay. The amount of extra density you need to add (by exposing the blue sensitive emulsion) to make it look best is surprisingly small.

I have worked with a calibrated LED-Lightsource (by Heiland electronics, unfortunately not mine) and cannot confirm this as a general rule. Using only green light should produce an extremly low contrast picture. So either you have high contrast negatives (above1,3 logD) or your light source might also emit some UV or something similar.

 

[MattKing]

I have worked with a calibrated LED-Lightsource (by Heiland electronics, unfortunately not mine) and cannot confirm this as a general rule. Using only green light should produce an extremly low contrast picture. So either you have high contrast negatives (above1,3 logD) or your light source might also emit some UV or something similar.

The green only exposure is certainly low in contrast. What I was trying to indicate is that the visual effect of adding even small amounts of blue exposure is quite dramatic.
Try the experiment. Prepare a satisfying print from a "normal" negative using split grade techniques involving a "0" filter and a "5" filter (and no burning or dodging).
Now do separate prints from the same negative - one using the same amount of "0" exposure only, and the other one using the same amount of "5" exposure only.
I think you might find the results interesting.

 

[RauschenOderKorn]

Other problem is that the grades do not seem to be evenly spaced over this spectrum.

Evenly spaced is a tricky word when you are working on a log-scale and you have to adjust for the intensity of green and blue light source and the particular curve of your paper (i.e. each paper has a different curve, so you have to adjust for each paper individually). The easiest way to find out ist using a Stoufer greyscale and trial-and-error until you got it figured out.

Theoretically, the paper grades should translate into the following copying ranges (taken from: Wilhelm Heiland - Tonwerte Perfekt):

Grade - Copying Range
0 - 1,4 lodD (usually green light only)
1 - 1,2 logD

2 - 1,0 logD
3 - 0,8 logD
4 - 0,65 logD
5 - 0,5 logD (usually blue light only)​

I´d start by testing if the hardest and softest values are somewhere in the range, to eliminate possible problems form the beginning. These problems can include unfresh paper, spent developer, general processing problems and an unsuitable light source (LEDs can emit UV or create the visible colours by addition of other wavelenths). If you can achieve the grades 0 and >3.5 , that would be a good result. Then I´d start testing for the exposure time combinations of the intermediate grades.

Please let us know your results!

 

[RauschenOderKorn]

Try the experiment. Prepare a satisfying print from a "normal" negative using split grade techniques involving a "0" filter and a "5" filter (and no burning or dodging).
Now do separate prints from the same negative - one using the same amount of "0" exposure only, and the other one using the same amount of "5" exposure only.

I have not tried this, but assuming that a "normal" negative prints about the same time (more or less) of green and blue, taking into account that all emulsions in MG-paper are blue sensitive,that

we only have one green sensitive emulsion,​

that blue light has more energie than green light, and that the scales are logarithmic, I´d guess that the blue exposure will show more than 90% of the final picture with too much local contrast and the green will show only barely recognizable shades. Dmax should be almost complete in the "blue" print, while the "green" print will be barely visible.

Right?

 

[MattKing]

I have not tried this, but assuming that a "normal" negative prints about the same time (more or less) of green and blue, taking into account that all emulsions in MG-paper are blue sensitive,that

we only have one green sensitive emulsion,​

that blue light has more energie than green light, and that the scales are logarithmic, I´d guess that the blue exposure will show more than 90% of the final picture with too much local contrast and the green will show only barely recognizable shades. Dmax should be almost complete in the "blue" print, while the "green" print will be barely visible.

Right?

As I understand it, all the emulsions have some green sensitivity, whereas the two or three emulsions that contribute to higher contrast have more blue sensitivity in the mix.
I think you will find that it is the "blue" print that is barely visible.
That has been my experience with Ilford materials, and IIRC, also with older Kodak and current Oriental materials.

 

[RauschenOderKorn]

As I understand it, all the emulsions have some green sensitivity, whereas the two or three emulsions that contribute to higher contrast have more blue sensitivity in the mix.

All chloro-bromide emulsion are blue sensitive, the green sensitivity has to be added.

 

[RauschenOderKorn]

I think you will find that it is the "blue" print that is barely visible.
That has been my experience with Ilford materials, and IIRC, also with older Kodak and current Oriental materials.

Very interesting, opposite of what I expected.
I will make a few test and show the results here, I hope I will have time next weekend.

 

[DREW WILEY]

Back when papers were generally marketed in separate grades rather than VC, the parameters and spacing of those grades tended to differ from brand to brand. And I'm skeptical that anyone can quantify this adopted grade terminology without sacrificing options to experiment with more than one brand of personally standardized paper, developer, temp, time, etc. With VC paper you have a continuum between high and low contrast potential, not something segmented like a centipede. A simple test strip can replace hundreds of hours of futzing around with hypothetical numbers.

 

[Kilgallb]

I got this reply from Ilford a few months ago.

Good afternoon Bill,
For split grade printing, most people use grade 00 (or 0) and 5 filters. ie the extreme filters in our kits. 00 (or 0) being what will give softest contrast - and 5 giving the hardest contrast.
Filter 00 (or 0) is yellow. Grade 5 is a strong magenta.
Inbetween these, the other filters are a variety of less magenta as the filters back off from 5, to stronger yellow/orange colourations as the filters move up from 00.

So - referring back to your other comments re how the paper responds etc, you likely know most of the below - but hopefully it can still be a helpful recap for you.....
Multigrade is coated using 3 separate emulsions. Each emulsion is a basic blue emulsion - to which we add different amounts of sensitising dyes.
The emulsions are blue sensitive with a slight sensitivity to green light - such that part of the emulsion is sensitive mainly to blue light, part to blue with some sensitivity to green light, and part to both blue and green light.

All 3 parts of the emulsion have the same contrast. They also all have the same speed to blue light, but the part of the emulsion with only a small amount of green sensitising dye has a low speed and is thus less sensitive to green light.

When the paper is exposed to blue light, all parts of the emulsion react and contribute to the final image. This image is high contrast - because of the additive effect produced by the 3 emulsions with the same speed and contrast.

When the paper is exposed to green light, only the parts of the emulsion with the larger amounts of green sensitising dye react initially. This is because the 3 emulsions have very different sensitivities to green light.

By varying the proportions of blue to green light, a contrast range between these 2 extremes can be obtained. The simplest way to control the colour of the light reaching the emulsion -during exposure is by the use of filters.
A magenta filter absorbs green light and transmits blue.
A yellow filter absorbs blue light and transmits green.
So in this way - by using the full range of filters in kits - high, normal and low contrast images can be made.