If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
two kinds of Multigrade filtering?
I've been using Ilford Multigrade paper and filters for years, with the
filters, in the above-neg position, being the usual (so I hitherto thought) range between 1 and 6 in 1/2 grade increments, ranging in colour from a light orange to a dense pink. However, recently in a charity (thrift) shop, I picked up an Ilford set thinking it would be good for my new large-format enlarger which needs an under-the-lens filter holder which this box has. On examining it, I see it looks rather older in design, says Ilfospeed Multigrade on the box, and the filter inserts are graded 1 through 7 in whole grades and range from a pale tobacco green (grade 1) through nearly colourless (3) through mauve to a dense purple (7). The calculator dial that was in the box gives least filter factor for the 3 - about half a stop - and higher amounts towards the ends of the range. My existing ones seem to have a slightly rising filter factor per grade, or at least for the pinker (hard) grades. What have I got here? An earlier incarnation of Multigrade, or something optimised for a different lamp spectrum? (I understood the principle of Multigrade was balancing two separate green-sensitive emulsions through differential spectrum control, is that correct?). My regular enlarger is an MPP condenser with the standard 100W pearl bulb, and MGIV paper prints and grades just fine using the orange/pink set. I've not yet tried this new lot on a print yet to see what it actually *does*. Further information greatly appreciated! Tony Clarke |
#2
|
|||
|
|||
two kinds of Multigrade filtering?
"Tony Clarke" wrote in message ... I've been using Ilford Multigrade paper and filters for years, with the filters, in the above-neg position, being the usual (so I hitherto thought) range between 1 and 6 in 1/2 grade increments, ranging in colour from a light orange to a dense pink. However, recently in a charity (thrift) shop, I picked up an Ilford set thinking it would be good for my new large-format enlarger which needs an under-the-lens filter holder which this box has. On examining it, I see it looks rather older in design, says Ilfospeed Multigrade on the box, and the filter inserts are graded 1 through 7 in whole grades and range from a pale tobacco green (grade 1) through nearly colourless (3) through mauve to a dense purple (7). The calculator dial that was in the box gives least filter factor for the 3 - about half a stop - and higher amounts towards the ends of the range. My existing ones seem to have a slightly rising filter factor per grade, or at least for the pinker (hard) grades. What have I got here? An earlier incarnation of Multigrade, or something optimised for a different lamp spectrum? (I understood the principle of Multigrade was balancing two separate green-sensitive emulsions through differential spectrum control, is that correct?). My regular enlarger is an MPP condenser with the standard 100W pearl bulb, and MGIV paper prints and grades just fine using the orange/pink set. I've not yet tried this new lot on a print yet to see what it actually *does*. Further information greatly appreciated! Tony Clarke Curious, if the filters have not just faded they would still be transmitting the same colors to the paper. Modern VC paper has two emulsion components (Ilford has three), a low contrast one sensitized to both blue and green and a high contrast one sensitized only to blue. For low contrast one exposes using green light, which the high contrast emulsion does not see, for high contrast both emulsions are exposed by using a filter which transmitts only blue light. For increased visibility of the image on the baseboard this is a magenta color-difference filter (transmitts all colors except green) rather than a green filter. Modern filters are also balanced so that the effective paper speed remains constant although in two ranges, one for grades up to 3.5 and the other, half the speed, for higher contrast. Earlier filters required a change in exposure for each grade. I suspect what you have is a very old set of filters. It may work on modern paper but the grade spacing may not be right. Also, both Ilford and Defender (later Dupont) made the first variable contrast papers, along about 1940. I am not sure of the Ilford paper but the colors required for the Defender paper were the reverse of modern stuff. -- --- Richard Knoppow Los Angeles, CA, USA |
#3
|
|||
|
|||
two kinds of Multigrade filtering?
Tony Clarke wrote:
[...] the filter inserts are graded 1 through 7 in whole grades and range from a pale tobacco green (grade 1) through nearly colourless (3) through mauve to a dense purple (7). The calculator dial that was in the box gives least filter factor for the 3 - about half a stop - and higher amounts towards the ends of the range. [...] Multigrade papers work by combining green and blue sensitive emulsions. Your filters vary from transmitting green light, through to transmitting blue light (plus red, which of course doesn't contribute to the exposure). So it sounds as though they will work perfectly well. I guess this is an early version of multigrade filtering, which was later replaced by filters which don't need the exposure calculator. "Normal" filters also transmit red light (the low-contrast filter is yellow, vs your green filter), which helps make the image more visible without affecting the exposure. There's a history of Ilford Multigrade at http://website.lineone.net/~mauricefisher/Darkroom/Multigrade.html Though it doesn't mention a system with green filters, it's interesting to see that the order of the filters has changed, with earlier versions of multigrade used yellow filters for the hardest contrast grades. -Tim |
#4
|
|||
|
|||
two kinds of Multigrade filtering?
"Tim" wrote in message ... Tony Clarke wrote: [...] the filter inserts are graded 1 through 7 in whole grades and range from a pale tobacco green (grade 1) through nearly colourless (3) through mauve to a dense purple (7). The calculator dial that was in the box gives least filter factor for the 3 - about half a stop - and higher amounts towards the ends of the range. [...] Multigrade papers work by combining green and blue sensitive emulsions. Your filters vary from transmitting green light, through to transmitting blue light (plus red, which of course doesn't contribute to the exposure). So it sounds as though they will work perfectly well. I guess this is an early version of multigrade filtering, which was later replaced by filters which don't need the exposure calculator. "Normal" filters also transmit red light (the low-contrast filter is yellow, vs your green filter), which helps make the image more visible without affecting the exposure. There's a history of Ilford Multigrade at http://website.lineone.net/~mauricefisher/Darkroom/Multigrade.html Though it doesn't mention a system with green filters, it's interesting to see that the order of the filters has changed, with earlier versions of multigrade used yellow filters for the hardest contrast grades. -Tim This thread is getting quite old but I will add to it anyway:-) The above article is very interesting. Ilford variable contrast paper had sensitizing reversed from the current type. I had thought that Ilford changed this in the early 1960's the article indicates the change was much more recent. The filers asked about seem to be for the older system where the blue only sensitized (non color sensitized) component was low contrast and the blue and green sensitized component was the high contrast one. This is the reverse of VC papers made over the last about 25 years. Both current Ilford and recent Kodak filters are for the system where the blue component is the high contrast one. I should also note that Defender Photo Supply in the USA had Varigam on the market about the same time as Ilford Multigrade, i.e., 1940. I think Varigam used the current system but am not sure. Defender had ties with both Kodak and Dupont (who eventually bought the company). Defender and Ilford must have been aware of each other's work. The idea of introducing some neutral density into the filters to equalize exposure is also quite recent, about 15 years ago I think. The usual variable contrast filters are complimentary rather than having the color of the light needed for exposure at a given grade. The idea is that the visual illumination at the baseboard for focusing and composition is much brighter. -- --- Richard Knoppow Los Angeles, CA, USA |
#5
|
|||
|
|||
two kinds of Multigrade filtering?
"Richard Knoppow" wrote
The filers asked about seem to be for the older system where the blue only sensitized (non color sensitized) component was low contrast and the blue and green sensitized component was the high contrast one. The way I understand the way the system works is that there are two identical low contrast emulsions. Both are sensitive to blue. One has a sensitizer added to make it sensitive to green as well as blue. Exposing one low contrast emulsion with green light gives a low contrast print. But exposing with blue light, to which both emulsions are sensitive, gives a high contrast print. Intermediate grades are made by exposing various proportions of blue and green. HD diagrams of VC materials often resemble a bumpy roller coaster ride because of the vagaries of the green sensitizer, the difference in the characteristics of the two emulsions and the match between contrast filters and emulsion sensitivity. Ilford adds a third cyan & blue sensitive emulsion to smooth out the response and expand the contrast curve. Green light exposes one emulsion, cyan exposes two emulsions and blue exposes three emulsions. If you look at the colors of the Ilford filter set and a CIE color diagram (or other 2-d representation of 3-color space) they form an arc, centered at red, going from orange to magenta. Grade 2 is a dusty pink - a combination of red and neutral density - on the line from red to the white center point. http://www.henrysturman.com/images/cie.jpg Information is from Mees and Ilford product literature. -- Nicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.darkroomautomation.com/index.htm n o lindan at ix dot netcom dot com |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
All kinds of cameras. | jim | Digital SLR Cameras | 0 | February 19th 07 08:08 PM |
All kinds of cameras. | shawn | 35mm Photo Equipment | 0 | January 19th 07 07:18 PM |
All kinds of cameras. | shawn | Digital Photography | 0 | January 19th 07 07:13 PM |
Scanned Slides: Filtering non-uniform edge discolorations | Acecliffy | Digital Photography | 4 | September 17th 06 02:48 AM |
Recommendations for spam filtering on RH9+ servers? | Norman L. DeForest | Digital Photography | 26 | November 25th 04 06:04 PM |