Converting ilford single grade into split grade chart/formula for a given paper ?

[GABRIELE TURCHI]

Hi there
i am wondering if anyone knows how to convert ilford single grades exposures into equivalent split grade exposures for a given paper (i assume there might a be a formula for each given paper ?)

the reason i am asking is because i prefer "find" my image tuning single grade exposures but than i wish i could split it in order to dodge (during 0 and/or 5) during the first exposure ...

ps: i am not a fan of making test strips for 0 and 5 in order to start that way ..i

thanks
g

 

[Bill Burk]

I bet you could get a Stouffer scale and expose it (by contact) to a variety of ratios of times under Blue and Green filters...

Create a graph curve of the results in terms of “green/blue ratio to LER”. (Log exposure range). This curve could tell you any green/blue ratio for any desired contrast grade... You could check the LER of the graded papers but you might not have to since the data sheet should give it.

 

[Sirius Glass]

Bad news single grade paper cannot be converted to variable contrast papers.

 

[Pieter12]

I will assume you are asking about using VG paper.

I'm not sure about this as I can't seem to locate the reference, but I recall that equal times for 00 & 5 will give you a grade 2. Using f-stop timing, for each stop of exposure you add to the 5 filter, the grade goes up one grade. For each stop less with the 5 filter, the grade goes down one. Something like that--you might have to add more time to get grades 4 and 5. Hopefully someone with more knowledge of split-grade printing will be able to chime in on this and correct me.

 

[koraks]

Equal amounts of blue and green will yield grade 2, and apparently if you increment the ratio by multiplying with about 2, you step up/down a grade. So a ratio of 1:1 G:B would be grade 2, 2:1 would be grade 1, 4:1 would be grade 0 - conversely, 1:2 would be grade 3, 1:4 would be grade 4, 1:8 would be grade 5.
At least that is my understanding from this here; page 81: https://users.wfu.edu/~jrpickel/pdfs/split_grade_printing.pdf
The problem is how to determine what the output of your enlarger is in terms of blue/green light - naturally, if either color is significantly more powerful, this stands in the way of simply interpreting the exposure ratios as time ratios. Furthermore you may want to consult datasheets of papers for further information although they are generally annoyingly non-specific on the matter of exposure scales of individual emulsions within the same paper.

On a side note, see also here for info on variations in local contrast in VC papers: http://www.darkroomautomation.com/support/appnotevcworkings.pdf

 

[cowanw]

Just to make the point that the Grade 2 or 2.5 combination may not be the equivalent of equal exposures of blue and green. My Zone vi enlarger is comparable at grade 2 of Ilford under lens filters as equal to 22% blue exposure and 78% green exposure.
My suggestion would be to use a step tablet (or any negative you choose) and expose it at each grade of combined light, recording time, and then recreate the print with split light, recording new times for each. Then you would have a table of conversion. ie your analyser says grade three at 14 seconds; consult your table and you divide the time between blue and green as per the percentages you have tested to work.
Here is what I discovered with a Zone vi enlarger which is an additive Blue/Green system, but the principle stands. See post 2
https://www.largeformatphotography....ble-Contrast-Enlarger-any-advice-for-new-user