contrast filters

[CMoore]

It is very possible i misunderstood, but..... are there enlargers that use a Green and Blue filter rather than a Yellow and Magenta filter.?
Thank You

 

[AgX]

Additive working enlargers use blue, green, red lighting+

But then these are not used as contrast filters, but just as colour correction filters.


However in making prints from a colour negative on panchromatic paper one can use contrast filters, similar as in taking with camera.

 

[MattKing]

It is very possible i misunderstood, but..... are there enlargers that use a Green and Blue filter rather than a Yellow and Magenta filter.?
Thank You

Yes - the later Ilford Multigrade 500 and all the Ilford Multigrade 600 light sources are good examples. With them, when you look at the image on the easel, it is blue-green.
The reason is that variable contrast paper works because you can adjust the contrast by varying the amounts of green light and blue light.
By comparison, in a system that relies on magenta and yellow filters:
1) Magenta filters subtract green light from a light source (like a tungsten or halogen bulb) that emits a continuous spectrum - increase the magenta filtration, and you decrease the relative amount of green in the light, and as a result increase the contrast of the print; and
2) Yellow filters subtract blue light from a light source (like a tungsten or halogen bulb) that emits a continuous spectrum - increase the yellow filtration, and you decrease the relative amount of blue in the light, and as a result decrease the contrast of the print; and
3) In both cases, if you increase the filtration you will also increase the relative amount of red in the light, but paper doesn't respond to that red light.
If your original source is tungsten or halogen, it was probably at one time both cheaper and easier to use magenta and yellow filtration than to attempt to filter out all but the relatively pure green and blue. In addition, I find it slightly more difficult to focus and compose on the easel with a blue-green source - I wish that the Ilford heads added some red when in "Focus" mode.

 

[CMoore]

Sorry if i am being dense, but....... with the Ilford 500-600.
Was the light source only of the Blue/Green spectrum, or did the filtration system filter out all (including Red) but either Blue or Green.?
Thanks Again

 

[MattKing]

Sorry if i am being dense, but....... with the Ilford 500-600.
Was the light source only of the Blue/Green spectrum, or did the filtration system filter out all (including Red) but either Blue or Green.?
Thanks Again

The light source is two fairly powerful, full spectrum halogen lamps.
One of them is directed at a fairly efficient dichroic interference filter that only reflects back (into the mixing chamber) green light, and the other is directed at a fairly efficient dichroic interference filter that only reflects back (into the mixing chamber) blue light.
I don't think efficient dichroic interference filters were available (at least readily) when the original transmission based, magenta and yellow variable contrast (or even colour) printing filtration systems were first designed.
And there certainly weren't any narrow spectrum blue and green light sources available back then - they all depended on filtration.

 

[CMoore]

Yes - the later Ilford Multigrade 500 and all the Ilford Multigrade 600 light sources are good examples.
If your original source is tungsten or halogen, it was probably at one time both cheaper and easier to use magenta and yellow filtration than to attempt to filter out all but the relatively pure green and blue. In addition, I find it slightly more difficult to focus and compose on the easel with a blue-green source - I wish that the Ilford heads added some red when in "Focus" mode.

That is very interesting. Thank You.
I am not a technical person, and do not have a vast knowledge of enlargers, so ............. is there no "Easy" way to by-pass the filtration system when focusing.?
Doesn't my Beseler Color Head have a lever that allows a person to do just that.?
Sorry if i am way off base with this.
Thanks

 

[MattKing]

That is very interesting. Thank You.
I am not a technical person, and do not have a vast knowledge of enlargers, so ............. is there no "Easy" way to by-pass the filtration system when focusing.?
Doesn't my Beseler Color Head have a lever that allows a person to do just that.?
Sorry if i am way off base with this.
Thanks

The dichroic filters in the Ilford Multigrade heads don't move - they are fixed in place. The system adjusts the amount of green and blue light (or magenta and yellow light, in the older versions), by electrically or electronically adjusting the amount of light hitting those filters.
In the Beseler colour head, you adjust the results by rotating more or less of the filter into the light path. If filters can be moved (by hand, in the case of the Beseler colour head) than they can be moved right out of the light path.

 

[AgX]

Thank you, Matt !

I got the 500 manual, but never looked into it as that head seems rather obscure here.

 

[MattKing]

Thank you, Matt !

I got the 500 manual, but never looked into it as that head seems rather obscure here.

For clarity, the Multigrade 400 head (which I actually own and use) and the earliest Multigrade 500 head (which I have in storage) use magenta and yellow filtration. The later, blue-green heads offer a grade 5 upper contrast limit, whereas I need to use supplementary filtration to achieve that.

 

[RalphLambrecht]

It is very possible i misunderstood, but..... are there enlargers that use a Green and Blue filter rather than a Yellow and Magenta filter.?
Thank You

not aware of any brands but it would work,green giving you a very soft grade and blue a very hard grade.

 

[cowanw]

My Zone Vl enlarger has blue and green bulbs. So not filters

 

[John Koehrer]

Aren't blue and green used in split grade printing?

 

[CMoore]

Aren't blue and green used in split grade printing?

Well, i use Y and M in split printing.
From what i read here, practically speaking, G and B are the "Same" thing.

 

[ic-racer]

Philips PCS 150 uses green and blue.

 

[AgX]

Not quite. See post #2.

 

[ic-racer]

Starting from blackness, a blue light darkens the shadows. A green light darkens the highlights.
Starting from white light, a magenta filter lightens the highlights (by removing green). A yellow filter lightens the shadows (by removing blue).

 

[DREW WILEY]

There are several misunderstandings present certain on previous posts. Blue-green cold lights are primarily white light with some blue-green output, either mixed or in parallel tubes. Ordinary subtractive colorheads are primarily white light too, well, tungsten-halogen, so somewhat warmish per spectrum, but full spectrum, in which blue is removed by variable degrees of yellow filtration, green removed by magenta filtration, and red removed by cyan filtration. But at least some white light always gets through anyway. Dedicated VC heads are the same concept, but simply have the cyan filter removed, since VC papers don't respond to red anyway. Additive heads require a narrow-band method to deliver pure blue, green, and red light. This makes their filtration far more dense, requiring a far more powerful halogen source per lumen output, then some way to balance the simultaneous activity of three different colors at the same time. The primitive Phillips enlarger did this via rheostats, so the light output was quite anemic. Later, Beseler came up with a xenon pulsing flash tube head, analogous to serious graphics RGB Xenon systems so hot they had to be cooled with water jackets, but intended for convenient home use instead, and vastly weaker in output. The third method requires very sophisticated electronic feedback controls to selectively pulse banks of halogen bulbs respectively distinguished by pure R,G,or B narrow-band dichroic filters over them. A dedicated VC system would simply omit the bulb and filter of the red position, or else put a colorless UV filter in its place for sake of white light focusing. I have 8x10 enlargers of all three categories : blue-green cold light, subtractive CMY, and pulsed additive halogen RGB. I can do VC papers with equal ease with any of them, as well as split print VC selectively using only G versus B channels of my additive heads, or by using a hard 58 green versus 47 blue glass filter over the lens of my cold light option. Either this afternoon or tomorrow I'll be printing VC paper with smaller 6X9 negs, so will use my smaller 5X7 RGB additive colorhead installed on a Durst 138 chassis, instead a big 8x10 rig. My own additive heads are custom designed to avoid the extreme heat output caused by the handful of commercial designs of the past, which included a Durst 10X10 system never marketed for commercial lab use, but used by an NSA spy plane 9-inch aerial film facility in order to deliver truer color than that of other options, along with extreme detail. There were six of them, and they ran so hot that every six months the filters had to be totally replaced by a contracted specialist at a sum maintenance cost of about $200,000 a year. That included his travel expenses. But if all this is simply too much detail, just reference the previous post by Ice-Racer, which gives the gist of it.

 

[John51]

Are the 2 emulsions in VC paper close in speed? iow, if the exposure was 50% blue and 50% green, would the result be close to grade 2?

I'm planning on experimenting with blue and green light on my condensor enlarger using a colour changing led bulb.

 

[MattKing]

Actually, variable contrast papers work because although the blue and green sensitive emulsions have the same contrast, they have different speeds.
Contrast is adjusted by varying the ratio of exposure to the more sensitive and less sensitive emulsions.

 

[CMoore]

Are the 2 emulsions in VC paper close in speed? iow, if the exposure was 50% blue and 50% green, would the result be close to grade 2?

I'm planning on experimenting with blue and green light on my condensor enlarger using a colour changing led bulb.

I was wondering the same... Thank You

Actually, variable contrast papers work because although the blue and green sensitive emulsions have the same contrast, they have different speeds.
Contrast is adjusted by varying the ratio of exposure to the more sensitive and less sensitive emulsions.

Thanks for answering that.

Does VC Paper simply NOT See (true) red light at all, or does it just react very slowly to it.
If you tested your Red Safe-Lights for 15 hours, would they fog the paper eventually.?
Thank You

 

[MattKing]

Does VC Paper simply NOT See (true) red light at all, or does it just react very slowly to it.
If you tested your Red Safe-Lights for 15 hours, would they fog the paper eventually.?
Thank You

Yes, and yes!
None of the standard black and white darkroom papers - VC or fixed grade - have significant sensitivity to red light. Only a few special papers - like panchromatic Panalure - have any significant sensitivity to red light.
But just because they don't have significant red light sensitivity doesn't mean that they can't be affected (fogged) by really high amounts of red light exposure.
And of course, red light sources are rarely purely red light. They usually have small amounts of non-red light "leakage".

 

[CMoore]

10-4..... thanks

 

[DREW WILEY]

I my experience, the low contrast sensitivity of most VC papers to yellow or green light tends to be about three or four times faster than the high contrast sensitivity to magenta or blue light. I don't know how much of this is due to how to how the emulsions are formulated, and how much is due to the fact that blue and magenta filters are significant denser than green or yellow ones of comparable hue saturation. Trying to factor alleged paper grade this way seems counterproductive, a waste of time. Grades meant something back when actual graded papers were mainly used. But even then they differed mfg to mfg. VC papers can be intelligently used even if one never heard of paper grades.

 

[koraks]

I my experience, the low contrast sensitivity of most VC papers to yellow or green light tends to be about three or four times faster than the high contrast sensitivity to magenta or blue light

I'm not sure if this is what you mean, but in my experience, it's the other way around. The blue-sensitive emulsion is ca. 3 stops faster than the green. I ran into this setting up my experimental RGB head for VC printing. I needed to attenuate the B array by about 2.5 stops compared to the G in an attempt to get the same exposure time for dmax across grades 1-5. Keep in mind that G leds generally have higher lumen efficiency than green (roughly twice), so the difference was in fact even a bit more than 2.5 stops. Hence my 3 stop estimate.
All this stuff is a bit difficult to figure out with online available information. Also experimentation with the regular M/Y filters generally doesn't yield much useful data, as the B output of tungsten/halogen sources is extremely low to begin with compared to the longer wavelengths, so much of the 'attenuation' I had to do is 'automatically' done by normal light sources due to their inherent characteristics. When working with known power levels for distinct parts of the spectrum and (roughly) known luminous efficiencies, this all becomes very apparent though. The same when working with an Ilford 500 head; notice how dim the B is compared to G, while exposure times for B tend to be conspicuously short.

 

[MattKing]

Keep in mind that G leds generally have higher lumen efficiency than green (roughly twice), so the difference was in fact even a bit more than 2.5 stops. Hence my 3 stop estimate.

Is there a typo in this sentence - did you mean to say Green LEDs have higher lumen efficiency, or did you mean to say Blue LEDs have higher lumen efficiency?
Aside from that, thanks for your post.
On a much less scientifically rigorous note, it makes sense to me that the Blue sensitive emulsion components are faster. For most split grade prints, the low contrast (green) exposure gets you most of the way there - all you need is a relative "smidge" of high contrast (blue) exposure to bring the result into form.
I find it instructive to prepare a good "straight" print using split contrast, "0" filter and "4-5" filter techniques and then make two separate prints of the same negative, one with just the "0" filter exposure used in the regular print, and the other with just the "4-5" filter exposure used in the regular print. You will see that almost all of the image is there in the "0" filter exposed print.