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

I am with Bob on this. The need to use one second test in all my years of
printing was limited to small RA4 prints. No other material has such a
critical need for tests. I would almost always just make several full
guesses for those time any way. 

Test made by turning off the light requires too much manipulation as well
for where I come from. Push the button once and starting counting. Perhaps
it is my hours spent playing music, but it just seems natural to use a
counting method that integrates my mind and body.

Light integrators should work well enough as its error should stay the same
and the user will get it right by observation which is ALWAYS the bottom in
printing.

Eric

Eric Neilsen Photo
4101 Commerce Street, Suite 9
Dallas, TX 75226
214 827-8301
 
http://ericneilsenphotography.com
SKype ejprinter
 
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Nicholas O. Lindan
Sent: Wednesday, December 19, 2007 10:59 AM
To: pure-silver@xxxxxxxxxxxxx
Subject: [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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