Halogen Bulbs And Green Fringe

Mitch640 · Post by **Mitch640** » Fri Aug 05, 2011 3:42 pm

I know achromat lenses will cause green and purple fringing. I have had some luck reducing this effect by using a lower voltage level and longer shutter time. Could it be possible that an aging Halogen lamp could cause more green or purple fringe? I don't know just what they do as they age.

ChrisLilley · Post by **ChrisLilley** » Sat Aug 06, 2011 12:04 am

Could you post some images showing this reduction that you are seeing from the lower voltage?Presumably the outpt spectrum of the lamp is different in this case?

Mitch640 · Post by **Mitch640** » Sat Aug 06, 2011 1:50 am

Chris, I will do some tests today and post the results. I know I have some already, that I kept in my files, but I did not make note of them as low or high voltages.

I am curious if it's a possibility though, as the lamp in my Fluophot is the one that came with it when I bought it, and who knows how old it was then?

Mitch640 · Post by **Mitch640** » Sat Aug 06, 2011 8:06 am

The test seems to be inconclusive. Two images taken at lower voltage, 8v, seem to show about the same amount of green.

1. ISO 100, 1/60"

2. ISO 100, 1/1200"

But, one image at ISO 100 and 1/400" shows a lot less green, but is over exposed at 11v.

Still, this does not answer the question of what an old bulb might be doing. I will have to put a new one in and try again.

g4lab · Post by **g4lab** » Sat Aug 06, 2011 11:25 am

I doubt this effect is a result of something happening in the lamp.

There are some changes that can take place as a quartz halogen lamp ages.
Slight differences in color temperature.(as hot spots develop on the filament) If operated at too low a temp there can be tungsten deposits on the envelope, but these act like a neutral density. (if the halogen cycle fails to operate due to low voltage operation or over cooling with a fan)

The green in your shots looks like some kind of optical effect to me.

Mitch640 · Post by **Mitch640** » Sat Aug 06, 2011 12:19 pm

I do know the green and purple fringe are due to the glass used in achromatic lenses. It was expected and all my achromats do it to one degree or another. My one Plan Apo is pretty much free from the fringing, but when I use strong light, even it will show some at different times, but nothing like this.

I was just curious if some of it came from the halogen lamp itself though. Just a thought. Maybe I will get my answer when I change this old one out.