Rosette - Hyperstar, Fast Ha filter, colour camera

[MarkS]

Yes, I know you shouldn't take H-alpha with a colour camera, but this is an experiment I did Friday night to see how deep I could go in a short session.

C11 Hyperstar with SX M25C cooled colour camera and Baader f/2 HighSpeed filter i.e. the passband has been pre-shifted to overcome the usual reduction in contrast on fast optics. Baader don't publish the bandwidth but I think it is around 10nm since that is roughly the frequency shift at the edges of the f/2 light cone.

18 x 600sec exposures i.e. 3 hours total integration time.

Stars are egg-shaped (and hence fine detail is blurred) because of the usual SCT mirror shift while passing through the meridian and I just did a very quick stack without calibration frames.  But this is just a proof of concept.



Full size version here:
http://www.markshelley.co.uk/Astronomy/2014/rosette20141219.jpg

When you consider that the colour camera is only recording 25% of the available photons, I think the results with a mono ccd could be quite outstanding.

Mark

[RobertM]

I don't see why you can't take Ha with a colour camera, sure you will loose a bit of resolution and gain a bit of noise but it sure makes the camera more flexible; it's nothing that can't be retrieved with more subs.

The image looks quite promising but I think 600s is pushing it a bit without a mirror lock of some kind.  I found 120s produced round pointy stars unguided on an EQ6 but that could probably be extended with guiding, don't know quite how far though.  The image also looks ever so slightly out of focus.

The highspeed filter looks promising but it's difficult to tell without a comparison.  I think that if the passband shift was that great then my 5nm Ha filter would be completely off band and I wouldn't get anything.  I even get OIII through my 3nm so the shift must be well under 2nm for that to happen.

Robert

[Fay]

Very nice Mark!

Fay