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

DEAR NICHOLAS,
        Two things:
        1) Don't many timer-controllers have integrators built in and
wouldn't they compensate for any ramp up?  
        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, depending on many factors.  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.  This way, if I like the look at
20 seconds, it really IS 20 seconds not 4 shots of 5 seconds.  So, unless
you want to expose your entire print in 4 shots of 5 seconds each, you may
be comparing apples and oranges.  My method also eliminates the repeating
problem of ramp up because this only happens at the beginning which is the
greatest exposure band at 50 seconds and, even without an integrator, it
will be a nearly insignificant part of that maximum exposure.  I think
Richard Knoppow will confirm these observations.
                CHEERS!
                        BOB  

-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Nicholas O. Lindan
Sent: Wednesday, December 19, 2007 8:38 AM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Determining lamp delay / ramp-up

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

Although aimed at users of the Darkroom Automation timer, the technique
can be used with other timers.  Delay is only important when making
multiple additive exposures - such as test strip prints where the paper
is progressively covered.

When making test strip prints the lamp delay time should be subtracted
to the determined exposure.  The correction is:

 Corrected time = determined time - (number of the correct strip - 1) * 
delay time

If the lamp delay is 0.16 seconds and strip #5, 17 seconds, is the
correct exposure then the corrected time is:

 17 seconds - (5 - 1) * 0.16 seconds ~= 16.5 seconds

Incandescent lamps have a short delay time, a PH212 has a 0.05
second delay time.  Cold light heads can have significant delay
times that vary with the temperature of the lamp and the time
between exposures so test prints should be made in a very consistent
manner in order to be able to compensate a cold light head.

Some timers have their own parasitic delay time that adds to the
lamp's delay and makes additive exposures quite inaccurate.  The
technique described also compensates for the timer delay.

--
Nicholas O. Lindan
Darkroom Automation
A Unit of Cleveland Engineering Design, LLC
Cleveland, Ohio 44121

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