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Old 18-02-2012, 01:49 PM
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OIII filter and bloated stars

Any tips on minimizing bloated stars that you get with OIII filters in images? Best dealt with at capture time or post-processing?
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Old 18-02-2012, 02:43 PM
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I don't get bloated O3 stars. What brand is your filter?

Here's a zoomed crop of the same star, S2:Ha:O3, and the Ha is a little dodgy.
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Old 18-02-2012, 06:32 PM
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G'day Robin. Filters are 13nm Astronomics. Can't post images today, will tomorrow. Not the stars bloated per se, more like a halo around them. Seem to recall Greg Bradley(?) talking about it once as though common. Maybe I was mistaken or misunderstood. But my OIII subs do have this halo.
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Old 19-02-2012, 07:54 PM
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I don't see this Troy. One tip, don't shoot O3 under a bright moon. You can mostly get away with S2 and Ha but try and time the O3 for when the moon isn't in the sky for a better result.
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Old 19-02-2012, 08:05 PM
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I was about to bet they were Astronomiks the moment you used the word Halos. I had halos, switched to Astrodons and the halos went away.

http://www.astrodon.com/products/filters/narrowband/

The good news is that they have acknowledged the problem, and you might get a free upgrade, see here:
http://www.astronomik.com/en/news/as...r_halo_problem

Alternatively, you could try adding an IR filter and see if the halos disappear.
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Old 19-02-2012, 10:50 PM
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Thanks for the link, Peter. Interesting. Checked my Ha filter and no halo, but the OIII and Hb do show similar halos to that second link. Scope is only f/7.5.

Robin - no moon around when I used the OIII this time, but good tip for future. Thanks.
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Old 20-02-2012, 08:34 AM
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Quote:
Originally Posted by troypiggo View Post
G'day Robin. Filters are 13nm Astronomics. Can't post images today, will tomorrow. Not the stars bloated per se, more like a halo around them. Seem to recall Greg Bradley(?) talking about it once as though common. Maybe I was mistaken or misunderstood. But my OIII subs do have this halo.
Is this the kind of thing you're describing as a halo?
This is a cut from an O3 stack.
Peter
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Old 20-02-2012, 08:48 AM
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Yes, that looks like it. It's making all stars look cyan.
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Old 20-02-2012, 10:42 AM
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If that is it, then it is the trademark Astromoniks effect (older filters only).
Try an additional IR cut filter if you don't want to return the filters for replacement.
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Old 20-02-2012, 12:20 PM
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Thanks Peter. I'll be testing all of them thoroughly and returning/swapping them if no good. Really appreciate the link and experience. Thanks.
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Old 20-02-2012, 09:27 PM
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As a matter of interest and, perhaps, comparison, the filter that produced the halo in the image a loaded yesterday was a Baader. Tonight, I swapped it out for one of those Orange Bright brand OIII filters and the same star did not produce any visible halo.
Peter
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Old 21-02-2012, 12:08 PM
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I'd be really interested to know if an additional IR cut filter would remove the effect on the Baader if you ever get a chance.
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Old 21-02-2012, 12:57 PM
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Quote:
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I'd be really interested to know if an additional IR cut filter would remove the effect on the Baader if you ever get a chance.
I do have a Baader UV/IR cut filter but they won't fit in the filter wheel if they're 'stacked' so it will have to wait until the opportunity arises. But like you, I would be interested to see the results.
Peter
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Old 17-03-2012, 01:05 AM
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Managed to sneak some test shots on Sirius in between the clouds tonight. These are stretched a lot to highlight the halos. Some pretty weird patterns in there. 5x1m subs each. Left to right is Ha, Hb, L, OIII, SII.

Anyone able to help diagnose them? I do see the Astronomics filter issue that Poita linked above at least in some of the shots. Imaging train was 10" Newt, MPCC, all Astronomics filters, and QSI583ws.

On a side note, how does the collimation and field flatness look to you? Any signs of issues there?
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Old 17-03-2012, 08:19 AM
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I'd send them back to Astronomiks and get the replacements before their offer runs out.
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Old 17-03-2012, 08:58 AM
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Definitely doing that mate. Thanks so much for the pointer. Wouldn't have known I could get them replaced at their expense if it wasn't for you.
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Old 26-03-2012, 12:04 AM
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Sent off those images and the other details Astronomik asked for last weekend. Heard back from them on Friday. They're doing an analysis of my images next week. They told me that in their preliminary look, there was some halos from the filters but also some reflections from the MPCC.

Bit puzzled about the MPCC comment since they don't show up in the Luminance image, which was also shot through the MPCC.
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Old 26-03-2012, 10:53 AM
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Take the MPCC off and fire another image to them.
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Old 26-03-2012, 11:55 AM
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Intend to. In fact, tried last night but my mount had other ideas...
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Old 04-04-2012, 08:11 AM
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I heard back from them last night. They're saying there's 2 different reflections/halos in there. The tight inner ones around Sirius are caused by the filters, the larger reflections (with the spider vanes showing) are caused by the MPCC. Kinda what we already knew, but the good news is that they're sending me out a replacement set of "no-halo" filters!

Must thank you guys again for your links and help.
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