print meter

[Doremus Scudder]

2 x 3 second exposures is not twice 1 x 3 second exposure though.

?? Not sure what you're getting at here.

If you compare 2 x 3 second exposures with 1 x 6 second exposure then 2 x3 seconds should be lighter

Indeed, there is likely an intermittency effect at play, although slight with papers, that would make two three-second exposures slightly less than one six-second exposure, not to mention bulb ramp-up time, etc.

One need not use short bursts of light to make a test strip, however. One could easily leave the enlarger light on and simply cover the stripes of a test strip progressively; that's exactly what I do, counting seconds as I go. The real point I was making is that the exposures for the test-strip stripes should progressively lengthen in order to achieve a uniform exposure difference between stripes.

Best,

Doremus

 

[Nicholas Lindan]

Sorry to say, but I can not find any intermittency or reciprocity failure in photographic papers.
http://www.darkroomautomation.com/support/appnotereciprocityandintermittency.pdf

I think folks who do encounter effects are doing so because their enlarging timer isn't properly compensating for lamp warm-up/cool-down. Even a PH212 bulb requires a 50mSec (0.050 second) adjustment for every on-off cycle. Finding the correct adjustment isn't hard:
http://www.darkroomautomation.com/support/AppNotePH212LampDelay.pdf

Warm-up/cool-down compensation with a cold-light head can be problematic. A compensating timer is a must. For the most consistent results the lamp needs to be kept full-on and an electro-mechanical shutter used to control exposure.

 

[Doremus Scudder]

Nicholas,

I think you're likely correct, and that the true cause of "intermittency" has more to do with the warm-up time of the bulb used or other issues with the timer. That still makes a difference, though.

I step on my footswitch with a card under the lens, let the bulb stabilize for a few seconds and then begin my exposures by removing the card. Timing is done by counting seconds to the metronome (my timers are permanently set on 99 seconds - as high as they'll go). I like print exposure times in the 20-30 second range, or longer to eliminate even the small error in timing by removing and replacing the card (although, as a trained musician, I'm pretty sure I can hit sixteenth notes at 120bpm, meaning I'm accurate to 1/8 second or thereabouts).

I have compensating timers for my cold-light heads, but they're all in storage; I prefer my color heads and halogen bulbs these days.

Best,

Doremus

 

[Nige]

There's times when I bump the magenta by 10, increase the exposure by 0.5sec then half way through the exposure decide to dodge a section, then add a burn which I hadn't considered...