Re: DIY light source for 10X10" enlarger.

"Richard Knoppow" <dickburk@[EMAIL PROTECTED]
> wrote

> If one uses an enlarging meter the variations of fluorescent lamps with 
> temperature is of much less importance.

If only it were so.

The problem of lamp warming isn't mitigated by a meter - there
is the same variation in lamp output between metering
and exposing as there is between pre-warming and exposing.

A meter will compensate for slow variations due to lamp
aging, room temperature variation, and seasonal or dinural
voltage fluctuation.

A compensating timer/light integrator in combination with
an enlarging meter is a self-defeating mess:  The effect is
to double the error and to do it in the wrong direction - the
dimmer the lamp the more overexposed the resulting print.
If the lamp dims the meter will indicate more exposure
is needed - the integrator will extend the exposure time
on it's own to compensate for the dim lamp and as a result
compensation is applied twice - a 10% dimming of the lamp
will result in a 10% over exposure to the material.

The only real solution for cold-light woes is to stabilize
the light output with either a closed-loop regulated head
or some means of keeping the lamp at a constant operating/
idling/off temperature.

-- 
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http://www.darkroomautomation.com/index2.htm
n o lindan at ix dot netcom dot com