Step Wedge base (plus fog?)

[MacGregor Anderson]

I've been testing film speed and development times with a Stoeffer (sp?) step wedge. Expose for zone X with the wedge sandwiched in the holder just above the film.

Does the clear section of the step wedge block any light? Is there a base factor to it? An unexposed sheet of film has Film Base plus Fog. Yet all the testing stuff I've read online seems to be based on the assumption that the top zone on this step wedge is completely clear.

I don't have a densitometer or I'd test it myself.

Thanks,

Mac

[Eric Jones]

Hello MacGregor,

Mine reads .04 on my X-Rite 810 which is a little under 1/6 of a stop. Hope this helps.

Eric Jones

[MacGregor Anderson]

Thanks Eric. Answers my question perfectly. Not worth worrying about.

Love this place!

Mac

[Joe Smigiel]

"Not worth worrying about."

Mac,

That depends on what you are doing. In the context of our other discussion on the photo.net forum, the 0.04 density is not inconsequential when determining zone I and the effective EI by visual comparison.

It's importance diminishes greatly if you are talking about highlight zones, development times, printing times, etc., but it is very important when determining the film speed in the very thin densities associated with zone I and thereabouts.

Also note that the second step will be around 0.19, the third around 0.34, the fourth 0.49 and so on increasing by about 0.015 per step. After that critical first step, every two steps cuts the transmission in half since 0.30 density represents 1 stop of exposure.

[MacGregor Anderson]

Joe, good points there and thanks for sharing again.

I was perhaps being simplistic. It's just that 1/6 of a stop is half the smallest increment on my spotmeter or lenses. My developing time and temperature consistency is improving, but not to the degree needed for this sort of accuracy. Adding an additional 1/6 stop of error to the process is not good, but I suspect I'm nowhere near accurate enough for it to make all that much of a difference.

In saying it wasn't worth worrying about, I was just responding to the relatively low impact to my tests. At some stage I hope to improve my testing procedures to the level you discuss. But for now I'm trying to dial in my exposure and development to a point where I get much improved negatives that are substantially easier to print. The latitude of the film and the flexibility in the printing process makes this attainable without hair fine accuracy. I know, because I started using an F100 average matrix meter, then went to spot metering and to testing (without a step wedge, and purely visual analysis of results) and found a great improvement in my negatives. I never worked out accurate N+/- times, but did have a range of tests giving me a rough idea within a minute or two that helped me plot a film/development curve in my head, so to speak. These new tests are aimed at fine tuning that.

Why don't I just do it right the first time? Densitometer, shutter speed/aperature tests, a processing system with true temp control instead of a tank in a rubber tub with a so-so thermometer? Reciprocity tests (I shoot a lot of 1-50 second shots)? Filter tests? Reciprocity with filters attached tests? Cause I need way more time in the field. That's my number one priority. And I can only handle the testing one little step at a time or it starts to overwhelm.

Thanks again for your thoughts, here and on that other board. Very valuable advice. Unfortunately, I'm only a semi-capable "student" here who seems to relish repeating others' past mistakes to find out for himself that he should have listened to their advice in the first place.

Mac

[MacGregor Anderson]

I will probably open up a rough 1/6 stop to zone X and 1/6 for my next testing though.

[Andy Eads]

I have both the Kodak #2 and Stoufers step wedges. The nominal density increment between steps is 0.15 plus the gross fog (base plus fog). There is one area with no exposure and it reads about 0.05 optical density. So the readings from each step procede as follows: 0.05, 0.20, 0.35, 0.50, 0.65, etc. Hope this helps.

[MacGregor Anderson]

confirms Eric's test, off only by .01.

Suprised this doesn't come up more in threads on the wedge. I think I've read every one on the internet by now. Though maybe I missed it before.

Thanks for your help.

mac