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Re: [APML] Red / H-alpha work with film
> I was thinking of using a red filter in my mag 3.x
>skies and shooting say M42. I don't want to deal with TP and hypering
>etc so was wondering if E200 would be a reasonable film.
Yes, you can do this. I've done it under mag 5.5 skies and it works.
Naturally, it probably won't work as well under mag 3.x skies as under
darker skies, but it will work better than no filter at all.
> Scan the
>image and take only the red channel, then convert this to B&W. I hink
>you would end up with a decent looking B&W which one can do from the
>backyard.
If you shoot with an h-alpha filter, there literally won't be anything in
the other green or blue channels.
>I'm guessing a true H-alpha filter would have way to much a filter
>factor to consider film?
It depends on the width of the bandpass for the H-alpha filter. If you get
one of these 3 nm interference filters that the CCD guys are using, I don't
know how long you would have to go.
With a Lumicon h-alpha cutoff filter, I went 1 hour at f/2.8 under dark
skies on E200. Unfiltered I would have gone about 10 minutes. With the
IDAS LPR filter, I would go 20 minutes.
I think a number 92 or 93 red is virtually identical to the Lumicaon
h-alpha filter.
The less the red in the filter, the less benefit you'll get for light
pollution reduction , and of course, shorter exposures. Note that I'm not
sure if these red filters will filter out any light pollution from Sodium
vapor lights, the kind that give red skyglow. I'm not sure where their
emission lines are in relation to the cutoff for the filter.
You might want to consider a LPR (Light Pollution Reduction) filter such as
the IDAS filter. In my tests comparing the red channel from an h-alpha
E200 shot to an IDAS LPR E200 shot, there wasn't much difference.
Jerry
Astronomical photography: http://www.astropix.com
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