Exposure time when using Multigrade Paper and Colour Head
Apologies if this is a silly question, but I'm pretty new to this.
I've got a Jobo C6600 Enlarger and colour head. It works fine when printing on multigrade paper, except that the exposure times when using filtered light compared to full white light seem much longer.
What is a normal time for printing using a colour head at, say, a grade two filter?
I got my values from here , do they look correct?
I've only just started to print my own pictures in the Darkroom so simplification is appreicated
P.S, what is 'extension factor'?
I couldnt load the link from my phone but basically when using filtered light there will be an increase of exposure time that will be needed to get more density. This varies from paper to paper and the correct filtration chart for your variable contrast paper should be included in your box of papers.
It is best to make test strips until you get familiar with your head and paper brand. Grade two filter is usually equivalent to standard white light in contrast, going up increases contrast, going down decreases. You can go both ways for split printing.
Extension factor has to do with the relationship between the distance of a light source and intensity of it. The further the light, the less intense, such as when raising the head up, you will need longer exposure.
The chart you linked to uses a combination of both hard and soft filtration (magenta and yellow) for each grade. This method is designed to keep exposure times about the same for each grade. However, in doing so, it uses a lot more filtration that just using either magenta or yellow, and causes longer exposure times. By "multigrade" paper, if you mean Ilford's Multigrade, there are filtration charts included with each pack or box of paper that gives individual values for yellow or magenta as well ans the "balanced" method. It's also on their website (see below)
Adding any filters will increase exposure times compared to white, unfiltered light. There are no "normal" printing times, as there are too many variables: paper, enlargement size, light source, density of negative, etc. So, you have to meter and/or make test exposures for each negative and print size anyway. To me, this negates the advantage of balanced filtration and the longer exposure times. I would recommend using the single filters.
The Ilford literature uses "single colour" and "dual colour" to refer to the yellow or magenta (single) or both (dual or balanced).
The chart looks pretty good to me. You shouldn't have to increase time much, if at all. Once you do a test strip (I almost always start on a grade 2) and you see that your blacks hit a rich black, that will likely be your time. After that you will just be adjusting for contrast for mid-tones and highlights. This is generally speaking though. If you test at grade 2, but it's actually a grade 5, keeping that same time but raising the contrast can suffocate shadow detail and you might have to lower the time a bit. So, you may have to adjust your time as you increase or decrease time to control density of shadows and highlights more accurately, but it won't be far off.
It really depends on your workflow. I like to develop for higher contrast so that I can squeeze out 20x24 prints of any 35mm negative a I choose and never really print smaller than 11x14. So, at 11x14, I test at #2 and it's generally not far off...16x20 I test at #3, 20x24 at #4....I'm usually pretty close so my times don't vary much, if at all, when I use a colour head.
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The increase of Magenta to make the paper more contrasty gives only slightly longer times - if you look for the shadows getting real black. If you have a test strip and choose the first time with real black in the perforation area, then this time is nearly the same if you add 30% Magenta.
The first thing I try to find out with test strips is this minmal time for maximum black. Then I control the highlights with the help of the contrast, usually I need more Magenta. The strip with maximum black and nearly perfect highlights is the base of evaluating my exponation plan. It is easy to understand and works fine.