View Full Version : Step Wedge Tests

John Clifford
14-May-2006, 12:15
Does anyone have information about the kind of contrast profile one gets for various b&w papers using a step wedge and color filters. I have just finished such an exercise on Arista II and Dektol 1:2. I was surprised to find that the greatest change occurred at the higher and lower ends of the filter range with very little change happening in the middle ranges. In fact my overall contrast ranged from 14 steps to 8 steps (pure white to pure black) but from filter #1-#3
(5 Kodak filters) I only get a one step increase. Is this normal?

Tom Westbrook
14-May-2006, 14:57
What light source are you using?

BTW, A good resource for info on paper testing (among other things) is Way Beyond Monochrome (http://www.users.zetnet.co.uk/ktphotonics/wbm.html). It's a great reference for B&W darkroom people.

N Dhananjay
14-May-2006, 19:55
Are you using a cold light? Cold lights put out a lot of light towards the blue end, and thus typically produces higher contrast than incandescent light sources. Also most filter sets are designed for incandescent sources. Thus, when you use a cold light, you will typically notice a compression of contrast with the high end filters. That is, with an incandescent source, the contrast grades will be evenly spaced. However, with a cold light, you will find big jumps at the low end (e.g., moving from 1 to a 0 filter will produce a big drop in contrast) and very small jumps at the high end (e.g., moving from a 5 to 6 filter will increase contrast by an infinitesimal amount). Typical solutions are using a 30CC filter between the light source and negative or split printing.

However, from your description, it sounds like you have the opposite problem, big jumps at the ends and very little in the middle. I'd start by examining the filters and how well they work with your light source.

Cheers, DJ

Brian Ellis
14-May-2006, 20:04
It's normal to see the middle stay roughly the same from one filter to another. The filters are "contrast" filters so it's the two extremes that will be most affected. I don't understand what you mean when you say that from filters 1-3 you only got a one step increase. Increase in what? You did pretty well to get 14 distinct steps with at least one filter, I don't think I did that well with my Aristo VCL 4500. One of the reasons I switched to printing digitally is that I can scan and print a 21 step wedge that shows 21 distinct steps, something I had been able to do in the darkroom only with van dyke brown printing.

John Clifford
20-May-2006, 07:28
"from filter #1-#3
(5 Kodak filters) I only get a one step increase"
What I meant is when using a #1 filter I can count 11 steps on my print of the Stouffer Step Wedge. When I use a #3 filter I can count 10 steps. I count from the first black that merges with its neighbor to the the first white that merges with its neighbor. I guess my real surprise is that I need only use about 7 of the filters out of the twelve to attain all available contrast variation on the Arista II paper.
In reply to the other question I use an incandescent bulb and condenser set up.