Re: [APML] Red / H-alpha work with film

["Brian Larmay" <astrobri@ameritech.net>]

Jerry,

Do you have any examples of your attempts?
I'm very curious of comparison shots between the hypered TP and the E200

Thanks,
Brian

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----- Original Message -----
From: "Jerry Lodriguss" <jml@astropix.com>
To: <astro-photo@seds.org>
Sent: Wednesday, September 18, 2002 10:10 PM
Subject: 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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