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50 mins of H alpha on the Rosette

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16 years 11 months ago #59860 by phoenix
50 mins of H alpha on the Rosette was created by phoenix
Was hoping to get 2 hours on this but cloud has lost me so many sub frames I have no idea what I will end up with.

farm3.static.flickr.com/2012/2195453154_9c16f94659_b.jpg

Kieran
16" ODK (incoming), Mesu Mount 200, APM TMB 80mm, SXV H16, SXV H9
J16 An Carraig Observatory
ancarraigobservatory.co.uk/

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16 years 11 months ago #59866 by philiplardner
Replied by philiplardner on topic Re: 50 mins of H alpha on the Rosette
Beautiful!

I notice an eccentric halo around the brighter stars - your stars seem round so your collimation looks ok, so I wonder what's causing this effect. An artifact of processing or an internal reflection perhaps?

Phil.

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16 years 11 months ago #59881 by dmolloy
Replied by dmolloy on topic Re: 50 mins of H alpha on the Rosette
im no expert, but looks like a beautiful image to me. although colour images are fantastic - I like these this B&W images - makes you look closely at contrast. Also in medium and largish scope its closer to what you might actually see....nice one Pheonix

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16 years 11 months ago #59925 by phoenix
Replied by phoenix on topic Re: 50 mins of H alpha on the Rosette
Phil the star halos in H alpha are down to the type of filter used. I use an Astronomik one. Astrodon claim their single substrate filters reduce internal reflections that cause the halos. I am no expert in filters so maybe some of the other guys have a better explanation.

Kieran
16" ODK (incoming), Mesu Mount 200, APM TMB 80mm, SXV H16, SXV H9
J16 An Carraig Observatory
ancarraigobservatory.co.uk/

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16 years 11 months ago #59928 by philiplardner
Replied by philiplardner on topic Re: 50 mins of H alpha on the Rosette

Phil the star halos in H alpha are down to the type of filter used. I use an Astronomik one. Astrodon claim their single substrate filters reduce internal reflections that cause the halos. I am no expert in filters so maybe some of the other guys have a better explanation.


Ok - that sounds reasonable... but it's strange that the halo isn't concentric around each star but offset slightly to the left. It suggests that the filter glass may not be perfectly perpendicular to the optical axis - as if it has been seated at a slight angle in its cell. If you decide to remove the filter glass from its holder/cell to inspect it you should use a fresh pair of latex gloves to avoid getting grease/acid on the filter. If the halo was concentric with the star you could conceivably remove it in Photoshop or similar. Just a thought.

Phil.

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16 years 11 months ago #59946 by phoenix
Replied by phoenix on topic Re: 50 mins of H alpha on the Rosette
Phil there is always a wee bit of play in these filters to allow for thermal expansion so the filter may be stuck in the cell at an angle. Might give it a wee prod with an ear bud (or small hammer :lol: )

Kieran
16" ODK (incoming), Mesu Mount 200, APM TMB 80mm, SXV H16, SXV H9
J16 An Carraig Observatory
ancarraigobservatory.co.uk/

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