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M45 - The Pleiades


x6gas

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I've been to'ing and fro-ing and fro'ing and to'ing as to whether to post this image but I've finally decided to stick it up here as I am interested in comments about what's causing the halos.

I shot this while I was waiting for the Rosette to get above the trees and was basically experimenting with 5 minute subs (I have generally used R subs of 2 minutes with slightly longer values for the other filters).

I didn't bother shooting a luminance but I am seeing again huge halos on the blue subs.  I'm not sure if this is atmospheric (from thin, high cloud or water vapour, it was a pretty humid night), or from the scope or filter, or camera.

Anyway, there was nothing I could do to kill the halos in processing so I stuck some diffraction spikes to try to draw the eye!  Framing is also all wrong, but I didn't want to mess with the orientation I had for the Rosette.  So not by best work, but nice to have another Messier object in the can...

4 x 300s subs for each channel through 2" Baader filters for a total integration time of an hour.  Combined in AstroArt 5.0, registered in RegiStar, and processed in CS5.

Scope: Tak 85 FSQEDX

Mount: CGEM DX

Camera: Atik 460ex

Guiding: IMG0H, Atik OAG, PHD.

post-11821-0-36682600-1389284304_thumb.p

Thanks for looking, Ian

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Ian, are you sure it's the filters and not the cameras face plate?  You probably already know how to work out the distance of the offending surface from the chip but just in case here is a link.  http://www.astrodon.com/articles_faq/articles_faq/press_release:391,355,49

Mike

I have no idea at all what it is Mike!  Thanks for the link, though, that looks like an interesting read... a quick skim does point the finger at the sensor window.

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Baader 2" CCD filters Olly.  (these ones).  Do you have a theory?

I did, but it's wrong!! Your blues are of the 'teal' hue and that's the hallmark of the Astrodons. I think you might look at the red channel which might be underplayed somewhat. There's a red star in the tail or streamer of stars leaving the main cluster, for instance, and some hints of red in the deep background which you might be able to drag out. You seem to have nice deep data and your optics are as corrected as they get.

I'd colour sample the background sky in the upper left (since there isn't a lot of background sky going begging around the SIsters!) My own target is 23/23/23 in RGB. That's personal of course.

Again, super image.

Olly

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I have no idea at all what it is Mike!  Thanks for the link, though, that looks like an interesting read... a quick skim does point the finger at the sensor window.

With all the money charged for these CCDs you'd think that the manufacturer could use a properly coated piece of glass to reduce reflections or is the problem more complicated than this?

A.G

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With all the money charged for these CCDs you'd think that the manufacturer could use a properly coated piece of glass to reduce reflections or is the problem more complicated than this?

A.G

I don't think so, Baader claim no reflections at all for these filters, they must be confident otherwise they are wide open to wholesale claims for refunds.  I reckon the camera makers are just skimping.

Mike

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Ian, are you sure it's the filters and not the cameras face plate?  You probably already know how to work out the distance of the offending surface from the chip but just in case here is a link.  http://www.astrodon.com/articles_faq/articles_faq/press_release:391,355,49

Mike

Thanks again for the info and the link, Mike.  Does indeed seem to suggest that the sensor window is the culprit.  Might drop Atik a line to ask about this and I am also going to check to see if I have the same issue on my 490ex.  I'm amazed if the sensor window doesn't have an AR coating but who knows...

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  • 2 months later...

I don't think this necessarily has anything to do with Atik's chip window. I know I'm a fan but I'm a fan because I've never had this kind of thing!

I've used a Baby Q with Atik 4000 and FSQ106 with Atik 11000 (and, in the past, assorted scopes and an Atik 16HR) I've also imaged with guests' various Atik cameras, notabaly a few 460s. One of these was in another Baby Q, not mine. I have never, ever, seen this effect before. It's very strange and very annoying, of that there is no doubt. But it is not characteristic of Atik cameras and doesn't ring any bells with Baader filters, so something odd is going on. Perhaps something highly specific.

In a word, I'm stuck.

Olly

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Many thanks for bringing this thread back from the dead Olly - it's posted in the wrong section really and should be in "Image Processing, Help and Techniques"

... so something odd is going on. Perhaps something highly specific.

In a word, I'm stuck.

Olly

Me too!  I've not yet done a scientific experiment logging exactly what kit I am using but I seem to be having the issue with both of my 4 series cameras, on both of my FSQ85s, and with two sets of Baader narrowband filters (I only have one set of RGB filters...).

Interesting discussion. Made me Google a bit and stumbled on this: http://www.astronomik.com/en/news/astronomik_halo_free_filter_halo_problem/

Maybe Baader has had some faulty batches too perhaps.

But as this is a 4 month old topic. Has the OP tried further and maybe already solved it?

Alas, Guillermo, no I've not solved it and the issue remains something of a mystery.

Using the logic and equations in the Astrodon article on halos, I've calculated the distance between the reflecting surfaces to be ~1.2mm and the filters are 2mm thick - which seems too far out - which is why I am suspecting the sensor window on the camera but in honesty I don't know and as Olly says it doesn't seem to be a problem for other people very successfully using the Atik 4 series / FSQ85 combination.

I've offered a set of 1.25 Baader filters I can spare for a while to see if it's a batch issue.

I think Baader would also respond if contacted. They are a serious firm.

Olly

That's very, very kind of you Olly and you are a true gent :icon_salut:.

However, my next steps are to try shooting without a filter in the filter wheel at all and possibly to dust off my 383L+, and my TS90 Apo (I definitely did not have this problem with the Baader filter / 383L / TS90 combo).  So plenty to try but I may well take you up on the offer to borrow another filter set if I draw a blank.

Thanks again everyone, Ian

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