Multi Grade Filters

I was simply trying to point out the primary differences between the filters, e.g., the #47B and #58 are only narrow band, passing and restricting at a fixed level, while the magenta and yellow, being subtractive filters generally come in different levels of bandwidth to restrict the opposite color at different levels. So, yes in a sense all filters work the same but also are made and used differently. I thought earlier there might be confusion.

I think we're all correct, but we haven't had a collective 'aha' moment yet... and that can be frustrating in these discussions.

RPC you can follow up with descriptions of how the density values of magenta and yellow in colorheads can be used to select the proper contrast...

I just have the one generality to point out...

One of the great things about all multigrade papers is their high contrast layer responds to blue and the low contrast layer responds to green.

Kind of neat that they all standardized on that one thing.

There's a lot of ways to deliver a mix of blue and green light to the paper.

Pure blue and green filters are easiest to understand how they relate to the paper, because they directly act on the respective layers.

But we are all accustomed to the magenta and yellow filters. I used to not think about it, I just followed directions. But when I learned about color a bit more, I realized how cool it was that they used magenta and yellow... not really because they are subtractive colors in the sense that magenta and yellow are subtractive colors for printing... (They're not doing color balancing or color separations). Instead they are really just doing you a favor. Using magenta and yellow obfuscates which light that is acting on the paper until you know magenta is red + blue. The magenta filter acts on the blue layer of the paper and it acts on the blue and red sensitive cones of your eye. The yellow filter (red+green) acts on the green layer of the paper and the green and red sensitive cones of your eye.

Only the blue and green light is doing anything to the paper. The red is only added to help you see. I think that's a really cool trick.

When you increase the magenta control in a colorhead, you insert more magenta filter into the light path, subtracting more green but the level of blue stays about the same. Since the green is reduced compared to the blue, contrast goes up in a print. When you increase the yellow control, you insert more yellow filter into the light path, subtracting more blue but the level of green stays about the same. Since the blue is reduced compared to the green, contrast goes down. Both are usually used in pre-determined combinations to keep exposure constant from one contrast change to another.

Right RPC, the subtractive filters are often referred to as... magenta is minus green, yellow is minus blue and cyan is minus red. We don’t use cyan in this case because red doesn’t do anything to the paper.

But this explains why the cyan colored Aristo cold light source doesn’t totally fail... it has the blue and green needed to do the job.

I believe RPC is trying to point out that the #58 and #47 filters transmit only green and blue, respectively, and remove all other wavelengths except for the narrow bandwidth of light they transmit. A set of typical VC filters attenuates the amount of blue or green light, with the extreme filters, #00 and #5 being the sharpest-cut filters (i.e., blocking almost all of the blue and green light respectively) while the intermediate filters transmit a mix of blue and green light in varying proportions.

There are no filter sets that are "blue" and "green" that are designed to do the same thing really, i.e., deliver a varying amount of blue and green light to VC papers but cut out other wavelengths. Certainly, something like that could be developed, but likely won't since it would not be as useful as the current Multigrade-style filters that also transmit red and thereby make viewing the image on the easel easier, which is helpful for dodging/burning.

Systems that use a mix of blue and green light (the Ilford head?) allow for continuous mixing of green and blue by using just those colors, adding what is dialed in in the chosen proportions. Dichro heads do the same thing, but by subtracting blue or green from the full-spectrum light source (as do the Mulitgrade filters). The result is the same.

For split-printing, i.e., using varying exposures of the extremes, printing with a combination of #00 and #5 filtration is really much the same as using a combination of #58 and #47 filters as far as the paper is concerned.

One reason for me to use the #47 filter instead of my usual dichroic heads is that I can get a tad bit more contrast from the #47 than maximum magenta. That has more to do with the inefficiency of the magenta dichroic filter than anything else. Sometimes I'll insert a #58 or #47 for dodging or burning when I don't want to fiddle with the dichroic filtration. I'll just switch the head to "white light" and burn or dodge through the appropriate filter.

Best,

Doremus

I have true RGB narrow-band colorheads, a traditional YMC colorhead, a blue-green cold light, hard 47, 47B, 58 and 61 glass filters, and can pretty much replicate results with any of these options on current VC papers.

Bill Burk said:

I think we're all correct, but we haven't had a collective 'aha' moment yet... and that can be frustrating in these discussions.

Click to expand...

I’m guessing the core problem is it’s not intuitive that the colors our eyes see may not be the actual wavelength of the light. So two setups look green to our eyes, but have different amounts of the green wavelength light that the soft emulsion sees.