6922Re: H-alpha filters
- Apr 1, 2002--- In ccd-newastro@y..., "remi lacasse" <rmi.lacasse@s...> wrote:
> Hi,Yes. It's due to different thickness of the glass.
> A few months ago I received my H-alpha filter from SBIG.
> It is the Standard type and I would like to ask 2 questions to
> the group or to those who have used the same type filter before:
> - I am using an ST-10E with the filter installed in the empty slot
> of the CFW-8 but the focus point is very different from the
> other filters. Is this normal?
> - Is it possible to use (find) a guide star and if so what is theminimum
> magnitude through the filter? Or will I need an external way toguide
> when using the filter?You'll need at least one of the following:
* a very bright guide star (use TheSky or similar)
* long guiding integrations (e.g. 10 seconds)
* a guide scope or OAG with separate autoguider (expensive)
* the SBIG TC-237 upgrade (expensive)
* more aperture
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