From: "milton_aupperle" <milton@outcastsoft.com>

Date: September 11, 2011 4:29:42 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Color Balance

Hi Folks;

Just in case anyone is interested, here are my color balance ratios for my PGR Grasshopper (with ICX285 EXHAD CCD) using different filter combinations. I balance with a G1 or G2 mag 6 to 7 star that is +50° or higher above the horizon, shooting 250 frames with each LRGB filters at a constant exposure and gain. I then  align and stack each LRGB movie and have Astro IIDC measure the intensity of each stacked LRGB image. I do this twice, binned 1x1 and binned 2x2 just to make sure there are no discrepancies. This whole process takes about 45 minutes to do per filter set.

AstroDon "E" Series 1 LRGB Filters:

Luma 1.00, Red 1.723 , Green 1.00 , Blue 0.875

AstroDon "E" Series 1 LRGB Filters with Hutech IDAS LPR Filter:

Luma 1.00, Red 1.640 , Green 1.00 , Blue 0.650

AstroDon "I" Series 2 LRGB Filters:

Luma 1.00, Red 0.970 , Green 1.00 , Blue 1.180

AstroDon "I" Series 2 LRGB Filters with Hutech IDAS LPR Filter

Luma 1.00, Red 1.300 , Green 1.00 , Blue 0.910

So you can see what difference there is for exposure times using different filter sets and how much an LPR filter can change the balancing.

They way I use these ratios is that if I wanted to do a 10 minute exposure with the AstroDon "I" Series LRGB Filters and a Hutech IDAS LPR Filter, I would need exposures of:

10 min luma, 13 minute red, 10 minute green and 9.1 minutes blue.

and that would be close to proper color balance. Once your below about 45 degrees, you would also need to start compensating for G B atmospheric extinction:

http://www.astro-imaging.com/Tutorial/LRGB_I.html

TTYL..

Milton Aupperle