Light intensity stability in Saunders VCCE enlarger?

[Peter Collins]

I am about to do some testing and want to know how stable (in terms of brightness/lumens) the light source is in the Saunders VCCE enlarger.

For example, does it warm up over seconds-to-minutes and slowly get brighter?
or
Is it pretty much fully bright as soon as energized?

Bearing in mind that I will expose a sheet, develop and fix it, then check it, there may be 7 - 10 minutes between sheets exposed. Should I leave the enlarger on and cover the light with a lens cap?

Tips and tricks please. Even facts to back them up!

best,

[ic-racer]

Use a 'standard' meter and measure the light reflected off your baseboard.

That is the method I used for this chart. Later I got a dedicated enlarging meter and the results were not much different.

[Jon Shiu]

I don't know the answer, but it is not designed to be left on all the time as it will get too hot. Uses a 200 to 250 watt quartz-halogen bulb.

Jon

[Drew Wiley]

With most simple circuits like this, the halogen lamp will have a brief warmup, a
dependable plateau, and a slight fade or drift at the end when switched off. For critical work like color printing, first cycle the lamp a few times, but only about
30 sec each time; then try to print for at least 20 or 30 sec. But black and white
printing is a lot less fussy. Generally the warmup is about 4 sec or so, and the
afterglow only a few sec. If you have a dependable voltage stabilizer built into the
system, you won't have any trouble. But if you're going to just leave the bulb on
and pull the lens cap, better have another enlarger too, because something is
going to melt inside. Might need a fire extinguisher too!

[ic-racer]

This is the graph I had mentioned, though I may have misunderstood your first post. I thought you were referring to a cold cathode head. If you have a halogen head, then it likely is voltage regulated for even output, but you would only know for sure by looking at the schematic of the power supply. Even if it is not voltage regulated, the light output will be very stable over time.

Durst put a shutter on some heads, but it only makes a difference with short exposures. Durst also pre-warms the bulb in some heads (but it does not light).

Perhaps you concerns over leaving the lamp on and changes in intensity are from reading or hearing something about cold cathode heads.

[Chuck P.]

I have the VCCE 4550XLG with the voltage stabilizer and it is a lovely machine, never had any issues with the consistency of light output.

[Henry Ambrose]

No facts about change in light output but from lots of use I don't see a problem with my VCCE. Maybe if you were using 1 second bursts of light there might be some proportionality problems but at normal exposure times I don't think you will see it at all. I know I don't. And if the first .010 seconds of on-time varied in intensity it'd never show in a print that was exposed for 20 or 30 seconds.

If this really bothers you, use your hands or a card to block the first few seconds of light. But then you're back to "imprecision" just as you were "if" the light output had a lot of ramp up time. I think you may be chasing a problem that does not exist.

We use our hands, cards, screens and other tools for dodging and burning in a grossly imprecise way, counting seconds or watching a timer. I'm sure I make errors in those techniques that overwhelm anything the enlarger does.

[nolindan]

The application note on the Darkroom Automation web site will let you determine the lamp warm-up/cool-down times for enlargers with incandescent (PH21x or halogen) lamps:

http://www.darkroomautomation.com/su...2LampDelay.pdf

With an incandescent lamp the time between prints will make no detectable difference in your results.

An incandescent lamp does have a slight long-term warm up that increases the light intensity over a period of a minute or so, but the amount is around 1/30 of a stop.

(Please pm me if the document displays with an odd 'Space Cadets' font)

[Drew Wiley]

For exposures under ten sec I prefer either a light integrator or some kind of closed-loop feedback circuitry to measure the light. Anything longer than that and it's rarely
an issue unless you're doing extremely fussy work like color separations or precise
colro dupes. Basically, it's a non-issue for ordinary work.