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Rosette - a first light, a typo, and a small coma issue


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Hi all, here's the first light from my new modded 1100D:

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Rosette Nebula by glowingturnip, on Flickr

21x 300s lights at ISO1600, darks, flats and bias, equipment as per sig, Pixinsight processing

To say that I'm pleased with this camera would be a total understatement - it's soooo so much better than my old Nikon D80.  No amp glow and much less noise and a wonderfully clean master dark, so much easier to process !  And that's before all that lovely Ha goodness too.  APT worked very well with it, respect to Ivo, and license duly paid for :smiley:

As for the typo - this wasn't actually supposed to be the Rosette Nebula at all - I was going for the cone nebula and xmas tree cluster, NGC 2264, but made a note of it wrong as NGC 2246 which is part of the Rosette - it wasn't until the day after when I was checking the lights that I realised something was strange, I recognise that cluster...  Slightly annoying, I've already done the Rosette once, and my wife even framed it for me for my birthday, and of course now this is my better version, ho hum.

I'm slightly concerned though that I have some coma showing, as you can see from the unprocessed corners below, and that the coma seems to be asymetrical.  I'm using a Baader MkIII CC, and the scope was laser-collimated at the start of the session.   Would appreciate any input from you knowledgeable folks on this.  The target was off to the right of the frame so the stars are unfortunately not as round as I'd like, and I had to do a bit of minor offset surgery in the very top-right corner.

post-30803-0-29559400-1425647043.jpg

Anyway, hope you enjoy,

Cheers,

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Looks amazing. Check to see if the focuser tube or anything in the optical chain is sagging at all. I sometimes have that issue imaging with my canon on my Newt. That said you hardly notice really. Great work on the editing. You could play with the luminosity a bit to bring out even more detail.

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This is truly a spectacular photo, near magazine quality to this amature's eye. It never ceases to amaze me the quality of pics posted on this forum. Looks like that new camera is definitely a winner! I imagine this is only the first of many great pics you'll capture and hopefully share with the members of SGL...  :smiley:

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@toxic - excellent thanks, I've just mailed FLO to check it's the right one, then will definitely order.

@scorpius - thanks very much, I'm blushing !  I must admit I was very pleased myself with how this came out, definitely my best so far.  Amazes me how long I've been struggling with that hugely inferior D80 which is now relegated back to holiday snaps.  Now I need to work on getting permission from my wife to upgrade my rubbish mount...  might take some time...

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checked with FLO - it seems that their standard EOS t-rings (not the protective one), which are 10mm thick, will give the correct 55mm spacing for a CC without any additional spacers.

That being said, my t-ring was a cheap Chinese one from eBay, so may well not be the proper thickness, I've ordered a proper one now !

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I've ordered a knackered 1100d from eBay for £80 which I'm going to modify (won't auto focus apparently, never know it might be modded already ;) ). Whilst I won't get anything as good as your image due to my alt az mount, I can practice until I order a heq5 in summer.

After seeing your image I can't wait to try it out!

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This is a very nice effort with a DSLR. Your coma corrector is not set at the right distance from the sensor plane so you need to experiment with distancing in one millimeter increments you also have sensor orthogonality issue, this is very common in Newtonian imaging . I found that I my Baader CC is very sensitive to distancing and infact I have not used it for a long time as I prefer the SW CC.

A.G

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That really is good. I wonder if a very slight adjustment to the anti-aliasing values might help. There is just a hint of darkness around the stars which might tune out.

Olly

Thanks very much Olly, that really is praise indeed coming from you  :grin:

I see what you mean about the stars - I've given them a very slight stretch through a starmask for the below, hopefully looks a little better.  Not sure what you mean about the anti-aliasing, is there a tool for controlling that in post-processing ? 

post-30803-0-08617000-1425757379_thumb.j

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This is a very nice effort with a DSLR. Your coma corrector is not set at the right distance from the sensor plane so you need to experiment with distancing in one millimeter increments you also have sensor orthogonality issue, this is very common in Newtonian imaging . I found that I my Baader CC is very sensitive to distancing and infact I have not used it for a long time as I prefer the SW CC.

A.G

Thanks AG, I'll see how I get on with the new t-ring when it arrives, and go from there.

For the sensor orthogonality, which I was suspecting as well since that coma isn't symmetrical, I assume that's down to collimation of the secondary mirror ?

To be honest, I've not been able to adjust my secondary - those three little collimation allen screws are in there really tight, and I can see the whole spider vane assembly trying to twist if I try and loosen those screws.  When I laser-collimate, the laser spot on the primary is just outside of that little doughnut, rather than inside it.  Should I persist and try and get those screws moving ?

I guess the focuser mechanism will give a bit of skew to things as well, it's just a bog-standard focusser with thumbscrews.

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