Using Variac's to dim 1k a 650w arri fresnels.... color temp?

[G.P.]

Ok so say you have an Arri 1K you'd like to bring down to say around a 600w or a 650 you'd like to bring down to something around a 300w....

Using a Variac: http://www.officebeyond.com/va-130-1000.html

How dramatic of a color temp change is there going to be when dimming the light sorce down to about half strength? Will this introduce horrible shifts to a warmer color temp?

I've always just used a 300 for a 300 and a 1k for 1k never really used a variac to change power going to the fresnel so I have no idea what to expect... anyone know?

Its just an industrial strength dimmer, no magic being done. So any know, or better yet have footage of this being done?

 

[Paul Hudson]

Generally 1/4 CTB will correct for a light a half brightness.

 

[Razz16mm]

This chart shows the relative shift of color temp vs voltage as a ratio multiplier for a tungsten halogen lamp.

Below 80% voltage color temp drops very rapidly with very little blue green spectrum.

My experience using a combination of dimming and CTB color correction is you wind up with a red/blue color cast with very little yellow/green. ND gels or wire scrims are better for reducing light output.

 

[Paul Hudson]

View attachment 35772


This chart shows the relative shift of color temp vs voltage as a ratio multiplier for a tungsten halogen lamp.

Below 80% voltage color temp drops very rapidly with very little blue green spectrum.

My experience using a combination of dimming and CTB color correction is you wind up with a red/blue color cast with very little yellow/green. ND gels or wire scrims are better for reducing light output.

Agreed! Scrims are much better than diffusion.

 

[G.P.]

Thanks guys that chart was perfect. Scrims and nets it is!

 

[Bern Caughey]

You also might be able to re-globe it with a smaller bulb, but I usually use scrims.

 

[slondon]

View attachment 35772


This chart shows the relative shift of color temp vs voltage as a ratio multiplier for a tungsten halogen lamp.

Below 80% voltage color temp drops very rapidly with very little blue green spectrum.

My experience using a combination of dimming and CTB color correction is you wind up with a red/blue color cast with very little yellow/green. ND gels or wire scrims are better for reducing light output.

Oh, thanks Razz, I've never seen such a graph before and it's very useful.

Here's the link: http://www.newport.com/Quartz-Tungsten-Halogen-Lamps/378263/1033/catalog.aspx