Got it, it sounds extremely useful. I will be ordering tonight. So I would be compensating slightly for exposure changes in all grades of filters, instead of Ilfords statement of the same exposure for 00-3 1/2, taking out all other factors like light intensity etc.? Does there become a point where you have a standard exposure time for the initial print of the wedge, Or is that the guesswork still involved? Would you print 12 test strips using each 1/2 stop filter grade for each new batch of paper based on using the same filters, or just 6 in full stop increments?
Thanks for the great info, this tool is actually helping me understand the process of figuring out the proper exposure better.
Some papers are faster than others, but they're mostly all within a stop or so of each other. What might surprise you is that for a given paper, the apparent speed with one type of light source can be markedly different when you switch to a different light source. To keep the explanation simple, let's take a look at fixed grade papers. Fixed grade papers are very sensitive to blue light and less so to other parts of the visible spectrum. The cold light on my Beseler enlarger is optimized for graded papers and glows with a distinctly blue case, but does not appear very bright on the baseboard. If you measure it with a meter, it shows decidedly less bright than the incandescent and halogen lamps of my other two enlargers. Yet it prints blazingly fast with fixed grade papers. Why? The output of the lamp is heavily biased towards the blue end of the spectrum, precisely where the paper is most sensitive. The blue end of the spectrum is rather poor from incandescent lamps and all that light energy is for naught, since the paper can't really see it to well.
The biggest difference in speed between different types of variable contrast papers will be if you are comparing a neutral to cold tone paper against a warm tone paper. Warm toned papers are a lot slower in general, sometimes as much as two stops slower than a neutral toned paper from the same maker. It's the nature of the beast.
It shouldn't take long to figure out a good starting point for the initial unfiltered print of the step wedge. The first print of the step wedge will probably be off. Figuring out how much more or less exposure you need is as easy as counting the steps since the wedge is incremented in 1/3 stop intervals. Need to move it up or down 3 notches? Double or halve the exposure. See the attachment for compensation factors. The table goes from -4 to +4 stops of compensation by time. Simply decide how many stops you want to add or subtract, look up that number in the "F stop change" column and multiply your exposure time by the factor in the "Comp Factor" column. Don't change anything else. Change only the exposure time.
I print a copy of the step wedge for each filter in the set, including the 1/2 grades. You'd be surprised where the changes fall sometimes. It doesn't take much paper to do this, but it does take a bit of time. If you're using 8x10 paper, you can cut 10 strips from each sheet, each 1x8 inches. That's more than enough to print the step wedge. You need 13 strips altogether, but cut 20, because you'll need a few to dial in the initial exposure and to allow for the inevitable mistakes. Mark each one on the back with the filter number. Mark the strip made with no filter stating so, and include the head height, aperture and exposure time for reference. Once you have that dialed in for one paper, most other papers will come close to that - usually within a stop.
This is really a lot less complicated than it might appear to be. Once you actually get a visual on how this works, it will become almost intuitive.
