Wednesday, April 20, 2005

H-alpha exposure

I've been exploring last two days, my wife has just delivered our baby and I'm spending time with them, and I managed to get sometimes with my scope when they're sleeping in the afternoon.

Back to my queston, I used a webcam, a Ranger, SM40 with BF10.

I found that prominence and surface detail requires very different exposure setting.

I found that, surface detail reveals itself at the lowest exposure among all the h-alpha details, the correct range is very narrow and the image on the display will be red (normal) and it's quite hard to see it bright day light even I cover myself... maybe my eyes are too weak on red...

on pushing up the exposure, surface detail will be washed out and prominence will come into the view. Again, the correct exposure range is quite narrow, or else you saturate the brightest part very easily.

the funny thing is, if I further push up the exposure, the surface detail will re-appear, but this time, it's in orange but not red.

H-alpha should be red, I was puzzled and I spent time to think of it... why is that?

My preliminary thought is that, due to the high exposure setting, h-alpha signal got sneak into the G and B channel of the webcam. At this setting, normal R channel will be saturated, and so with G and B signal, the surface detail re-appeared. Prominence is about right in R channel as well.

Any idea, comment? Thanks...

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