using a stouffer wedge

[pellicle]

Hi

after my contact printing experience (recently posted) I thought I'd modify my system and then test this with a stouffer wedge that I happen to have.

The lamp I'm using is an 8w lamp incandescent lamp and combined with its location in a black "can" I made it works nicely. My exposure time seems to be around 10 seconds (on a negative). For my testing I picked a negative which has a decent black level and delicate highlights which are well spaced on the negative (which is not contrasty really)



I can make a pleasing contact print from this, but (perhaps strangely I don't know) I can't get much further into the range of my stouffer wedge than about 9 (with the remaining steps staying white).

the above image works out more pleasingly printed (to me) when I have my exposure such that I get step 8 being the last visible with tone.

I printed with a #2 filter for this test.

anyone think this is normal or "wrong"?

thanks

[Nicholas Lindan]

How many OD|Stops/step are in your wedge?

If it is a 21 step, 0.15 OD/step | 0.5 stop/step wedge then 9 steps is 4.5 stops which is about right for a grade #2 - #2.5 paper.

For Ilford MGIV RC, as an example: http://www.darkroomautomation.com/su...mgivrczone.jpg

[pellicle]

Hi

its a 21 step wedge, the same one I used to test my scanner here.

if I've understood what you've said right it means I'm not far off in my setup and technique now.

good to know :-)


does this mean that I'd not normally be getting anything as dense as the higher steps (and how would I print them?)

[fschifano]

Looks like you're getting close. Perhaps a tad more contrast, not much, maybe 1/2 grade from the look of the scan. Then again, I don't expect the scan to match the print too well.

[Nicholas Lindan]

does this mean that I'd not normally be getting anything as dense as the higher steps (and how would I print them?)

If you use a grade #00 filter then you can get 8 stops or so on the paper - or 16 steps.

If you increase the exposure by 5.5 stops then the darkest wedge steps will print as highlights on the print, but the first 11 steps will be pure black.

Normal negatives should not exhibit the same range of densities found on a step tablet. A step wedge is meant for testing, and as such it exceeds the normal limits.

[pellicle]

If you use a grade #00 filter then you can get 8 stops or so on the paper - or 16 steps....

thanks for that. I need to better understand how to use my stepwedge for testing and understanding exposures.

I'm aiming to try to understand the relationships between density on my negatives, density on the paper and how to predict better the best way to print a negative (without wasting too many bits of paper ;-)

[ic-racer]

With a 21 step wedge you can do a quick calculation without a reflection densitometer. Throw out the one that is "almost black" and the one that is "almost white." Count the number of slices between the two. Multiply this by 15 and you have the ISO(R).

Typical figures might be Grade 5 = ISO(R) 40 to 45; Grade 4 = ISO(R) 60 to 70; Grade 3 = ISO(R) 80 to 90; Grade 2 = ISO(R) 100 to 110; Grade 1 = ISO(R) 120 to 130; Grade 0 = ISO(R) 140 to 150; Grade 00 = ISO(R) 160 to 180.

[fschifano]

With a 31 step wedge, do the same thing and multiply by 10?

[CBG]

Could anyone offer a simple definition of ISO(R) ?

C

[ic-racer]

With a 31 step wedge, do the same thing and multiply by 10?

Depends on how far apart the steps are. On a 21 step wedge they are usually 0.5 stops apart. So that would be 0.15 log density change between each step (recall that one stop is 0.3 log, so half of that is 0.15 log density.

The ISO(R) values are computed as 100 times the log density the paper will reproduce.

So, if you get 6 gray strips, that is 6 x 0.15 x 100 = 90

These are rough estimates, but the ISO(R) values are ranges anyway.