RE: [APML] H-alpha solar photography nightmare

[vega <vega@ulisse.it>]

>===== Original Message From "Bert Katzung" <katzung1@attbi.com> =====
>Hi Emmanuele:
>I think the Lumicon H-alpha has a pretty broad bandwidth (around 10 nM or
>greater?) for sun work unless it's a special filter that I don't know about.
>The Lumicon H-alpha filter that I have is a standard non-solar filter for
>imaging H-alpha nebulas and it has a pretty wide bandpass. As you know, the
>DayStar and Coronado solar filters work down around 0.3 to 0.8 nM bandwidth.
>I believe the non-solar H-alpha filters that have been mentioned recently on
>the CCD lists for solar prominence imaging were Custom Scientific's 3 or 4
>nM bandwidth filters.

Hi Bert,
according to the filter's manual, the filter _is_ designed and intended for 
visual use (see my post in response to Chris Cook), and I'm quite surprised 
that nobody has never heard about it. It has a bandwidth of about 1.5 
angstrom, i.e. 0.15 nM. The Coronado filters and the like have bandwith lying 
around 0.3 to 0.8 (as stated on their website), which means between .03 and 
.08 nM (1 nM = 10 angstrom).

>I'm a little unclear on how you positioned your filter(s). If I understood
>the recent CCD posts correctly, you should use a regular solar filter (eg,
>Baader film) over the objective (just like solar visual observing). Is that
>what you mean by the "IR prefilter"? The H-alpha filter should go at the
>camera end. Add neutral density filters of any type as needed to get the
>exposure up to something you can achieve with the camera you're using. (I
>haven't tried solar imaging with an H-alpha filter of any kind, so I'm
>speculating here. I am interested in trying my CCD camera on it, though.)

In fact, the Lumicon solar filter comes with a prefilter, mounted on a 
telescope cap, that absorbs 95% of the incoming infrared radiation: then, the 
remainder has to pass through the actual filter, which is mounted _before_ any 
eyepiece or any astrophoto gear. The actual filter is cylinder about 1 cm 
(.4") high and 10 cm (4") in diameter, which is intended to fit onto 1.25" 
tubes. Then it also has a small knob, by means of which the user can adjust 
the filter's tilt by +/- 3 degrees. This fine tuning should allow for better 
viewing (shooting?) of fine chromosphere details.

Does it make sense now?

Emmanuele


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