split grade mystery (at least to me)

The specs in the sky are scanner bed induced - not UFOs, do not be alarmed.

Could be contrast reciprocity failure related to light intensity.

You should try keeping exposure time constant and vary intensity (f stop) to see how that works.

PE

Think about it. The difference between 2" and 4" is one stop. The difference between 4" and 6" is half a stop. The difference between 6" and 8" is a third of a stop. The difference between 8" and 10" is a quarter stop, etc.

That's why some people like timers like the "Stop Clock" that allow you to adjust exposure time easily in stops rather than seconds.

"The difference between 2" and 4" is one stop. The difference between 4" and 6" is half a stop. The difference between 6" and 8" is a third of a stop. The difference between 8" and 10" is a quarter stop, etc."

I never though of it that way. I'm glad I posted this. Thanks very much for the insight.

Looks to me that what you call Right to Left @ 2 seconds is really backwards. Seems your left most strip received no exposure. Are you revealing paper as you step across or covering paper with each step? The difference is major.

If you are sliding your cover sheet from (CORRECTION should have read "R to L") revealing paper, you simply are ganging up density behind you. If you cover the paper with each step you are protecting the previous step and will see the 'net' result of the additional time.

As David has said, your increments are also misleading. I work with stops as measured in time. I work from a base exposure of 7.5 sec and cover that, add 1.4 sec (combined = 8.9), cover, add 1.7 (10.6), cover & add 2.0 (12.6), cover and add 2.4 (15), cover and add 2.9 (17.9) and continue to as needed. Or start at 15 sec base and go frome there.

Your print, to me, looks as if you revealing paper when you should be covering paper. I hope I've made myself clear.

First, I exposed the whole print for 5 seconds with the 0 filter. I started on the right side, covering all but the last .75" and exposed for 2 seconds , the I moved the card to the right .75" and exposed for a further 2 seconds and so on from right to left. The print is under exposed on the far right because of the filter frame.

I've had exactly the same confusing results. I was extremely surprised to see little difference on my test prints when printing at G5. I never thought of it in F stops or in terms of covering the paper, rather than what I normally do which is to uncover.

Thanks David and Bruce for giving me something to work on tonight and thanks unclebilly for posting this.

I am not at all sure we have answered Unclebilly's query. When I look across the print I can see practically no difference in the print density at all. I appreciate the difference in stops decreases as pointed out by David but even so, I'd have expected a greater difference in density from what is 7secs( 5 secs overall +2secs) and is the 1st division to what is 13 divisions more, each of which is 2 secs.

Doesn't moving from L to R and covering as you go or R to L and uncovering as you go merely reverse the progression of densities? So in simple terms of 1 sec divisions L to R and covering gives 1 sec, 2 sec etc and R to L and uncovering gives 5 secs, 4 secs etc?

Thanks for the posting Unclebilly. This has a lot to teach us in terms of split grade printig and diagnosis. So much so that I believe its worth a thread.

I tried the method of covering the paper and there is a noticeable difference in areas of the test strip. More importantly this translated well into the actual print.

Pentaxuser, I agree that this should be in a thread. There has been a lot written about split grade printing on APUG but the piece of advice about test strips plus the F stop explanation has really helped.

when I look at the image on my screen the description makes absoutely no sense.

to me it looks liek each step is equal the previous, with a dark line inbetween each step. really, the look about equal to me.

Infact, I think it is quite amazing and interesting...

corey