[pure-silver] Re: Determining lamp delay / ramp-up

"BOB KISS" <bobkiss@xxxxxxxxxxxxx> wrote:

Nicholas Lindan wrote:
> There is an application note on the subject of determining
> an enlarger's lamp turn-on time on the Darkroom Automation
> web site:
> http://www.darkroomautomation.com/support/AppNotePH212LampDelay.pdf




1) Don't many timer-controllers have integrators built in


No, because then they would have to be called 'integrator
controllers'.  Timers are different from integrators - they
are not the same except that they both control the lamp.
About 1/3 of the graphic-arts integrators on the market
(well, now sitting in the back of surplus warehouses) were
designed by my firm.  I really do know the difference.


wouldn't they compensate for any ramp up?


I thought that _was_ the whole point of them.


2) Due to the intermittency effect, the photographic effect of 10
five-second exposures may not equal the photographic effect of one 50 second exposure 

The effect of 20 one second exposures - including lamp delay -
is about 5%.  So any intermittency effects would have to be less than
5% in 20 exposures.  I don't know of many people doing 20 progressive
test strips and I would not recommend such practice.  At a more
modest 5 exposures the effect would be close to nil.
A 50 millisecond lamp delay time, from looking at the time output of the lamp, certainly looks about right - see the graph at the bottom of the app note. When 50 milliseconds is added to each exposure then 20x1 seconds == 1x20 seconds to within 0.005 OD on grade 5 paper. I don't know how much closer you want to get... 

That doesn't leave much room for intermittency effects.

I suggest intermittency effects with photographic paper are
not relevant.  What is being seen is timer error and/or
uncompensated lamp delay and it is blamed on intermittency
when it should be attributed to erraticity.
Timing additive exposures individually with a GraLab or metronome will not work very well: a GraLab can't be set to better than 1/2 second, times to worse, and the motor and mechanical linkages introduce their own - variable - delay time; timing with a metronome introduces the body's response time, about 0.1 second in a child and 0.5 second in an older adult. Claims of intermittency effect using these methods are really a complaint about one's old age or the adequacy of one's timer.
To completely avoid this, I set the timer with the metronome, ticker, or beeper on, to, e.g. 50 seconds. With a black piece of paper I cover all but one narrow band of the test strip. I then move the black paper every 5 seconds. 

I don't think that would work very well if you were pulling the
paper back every one second.  And if you were to do the thing
in as coarse as 1/2 stop intervals you would, for a 16 second
exposure, be pulling the paper at 5, 3, 2.4, 1.6, 1.2, .8, 2
seconds -- not the sort of sequence that comes easily to mind
or trips lightly from the tongue of a metronome.

However, if you are doing test strips by hand your method of
pulling the paper back every 5 ticks is probably the best method as the errors are not additive. A metronome would be more accurate than looking at a timer display/dial as sound-to-action response time is faster and more consistent than vision-to-action response time.
Everyone should certainly do their test prints the way they want to and I would not presume to tell anyone to follow my particular methods. 

The timer in any case has the ability to do additive equal-stop
test strips or a series of individual equal-stop test prints. With lamp delay compensation either method is _very_ accurate. 

==
Nicholas O. Lindan
Cleveland Engineering Design, LLC
Cleveland, Ohio 44121

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