multigrade filters or colour head filters - advice needed please
I have been using a Durst M670 colour enlarger and a set of multigrade filters for B&W work. I have noticed that some of the filters appear faded in areas (I have no idea how old the set is) Would it be better to use the dial up filters in the colour head for contrast control, or should I buy a new set of multigrade filters. I would be grateful for anyones advice.
Much easier to use the colour head. The multigrade filters have a 2-3 year life in use according to Ilford but of course that depends on how much you use them. Ilford publish the filtration needed for Durst enlargers.
I agree that the inbuilt filters in a colour head are far easier to use. The only real compromise is the inability for the colour filters to do the extreme grades, that is grade 5 and grade 0.
If you have a situation where you can use the filters, then keep them and use them for the rare occasion that you need the extreme filtration, you will have the best of both worlds.
with Ilford's filters you can use the same exposure for filter grades 00 to 3,5 and roughly double for 4 to 5. Does this apply to colour heads as well?
step wedge and test
I calibrate my dichroic head for new papers (actually in my case, usually very old papers) all the time - it takes one sheet of 8x10, and then my analyser gets me to a great print the first time.
I project a stouffer step wedge to about a 2.5" square size piece of paper. My Omega head goes from 170Y to 170 M in this series and for a first pass I go 30 units at a step- ie 170y, 140Y... 35Y, 0, 35M, 70M... 170M.
Label each piece with the filtration used for exposure- pencil, sharpie, etc.
Develop and process all in the same manner. Once dry, make note of the first non black step , and first non white step for each value of filtration. I use a 1/3 stop step wedge, so each step is .1 units of density.
You will find that usually the highest magenta filtration needs more exposure, to give an equivalent exposure to less contrasty filter settings. The solution is to figure in neutral density for all the settings that need it to get equal exposure. Then you can change paper grades by varying the filtration, and the highlight exposure will not change.
I look at the lowest non wihte step from the range of exposures with differing filtration, and then work out how many steps worth of ND is needed.
To do this, I measure the light value of a step that is being projected, and then measure the light output when the lens is stepped down 2 stops. Since I have a 1/3 stop step wedge, this is eqaul to 6 steps on the wedge. Yesterday, for example, I found that 12.4 seconds was the f/8 exposure.
Two stops down was 50.1 seconds. Not quite 4x, but don't worry. Now back to the open aperture, in my case f/8 Dial in C, Y and M, all to same values, until the time reading on my analyser reads 50 seconds (yes Cyan, because the analyser probe reads colour) In my case I found that it took 42 units of each to get 2 stops of light fall off. - so for me each 1/3 stop works out to 7 units. You can do this without an analyser, it just takes longer, with a series of prints needed to make the first non white when dry move 6 steps if you have a 1/3 stop wedge.
So now I know that, for instance, that first non white for me happened at 20 on the 170M, and at 14 for 0 filtration. So I need 7x6 steps of filtration to have equivalent exposure. - so my 'corrected' filtration for 0 is now 42Y 42M.
I do the same comuptations for all the other test exposures. Then I can see, for me at least, that for the paper in question, it doesn't get any softer beyond 140Y. It also tells me that without adding in extra 'offboard' filtration I will not get a harder than 4 contrtast grade. This is typical of old paper - they loose cointrast with time.
I go back to my tabulated filter data and assign which filter setting corresponds to the ISO paper range for each contrast. This data is on the sheet that comes with every type of paper Ilford ( and usually others) sells.
my real name, imagine that.
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There are two charts for Durst colour heads & VC paper filtration, one using a single filter the other using Dual filtration and constant exposure times for the majority of Grades. One is available on-line, see the library on the Darkroom Magic website.
I have a colour head on my DeVere but I use an under the lens Ilford Multigrade filters.
I can very carefully slide the filters in and out of the holder without disturbing the head - something I am guaranteed to do with changing the colour filtrations
If you are not split grade filtering then there is no advantage - if you are then this is a BIG plus point
I do use the heads in built colour filters but only as a variable ND filter to keep the exposure times sensible.
Thanks for the information - I am using Ilford MGIV paper - I have found the values for the various paper grades for the durst, should I also be dialing in filters for grade 2, given as 36Y, 46M, as a matter of course when doing test strips etc (I haven't been as I understood the paper printed as grade 2 without any filtration) but it will surely make a difference. Also should I have been using the grade 2 filter under the lens all along - maybe that where I've been going wrong?!
If you use the Gd 2 filter or dial settings you keep a constant exposure if you move to Gd 1 or 3. It doesn't matter.
You should be aware that Durst has used two standards for color enlarger filtration over time, one with maximum 130 Magenta and one with maximum 170 Magenta. There are different contrast filtration recommendations for each type.
Since it's hard to format tables for presentation on APUG, here are the Ilford Multigrade paper numbers in comma separated value form for you to plug into your favorite spreadsheet for formatting and printing:
Grade, Durst (170M), Durst (130M)
Note that these are for Ilford MG paper. Other papers will have their own characteristics and potential contrast ranges. I'd recommend Steve Anchell's Variable Contrast Printing Manual from Focal Press.