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The Siamese Twins (NGC4567/NGC4568) with the Edge 11.

RobH

By RobH
in Imaging - Deep Sky

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RobH

RobH

Posted
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This seems like my first image in ages!! Certainly it’s the first that hasn’t been beset by a plethora of cameral issues!!

The Siamese twins (NGC 4567 and NGC 4568, also known as the Butterfly galaxies for obvious reasons) were discovered by the man who seemed to discover almost everything, William Herschel, in 1784. They are part of the Virgo cluster of galaxies, and based on their redshifts, are 120 million light years away.

Although they look like they have collided, there are no tidal tails or distortions of either galaxy, so it may well be that they haven’t yet actually hit (or at least they hadn’t 120 million years ago, when the light started its journey!)

The image was taken with my new Edge 11 SCT at F10 (2800mm FL), and is exactly the sort of target I wanted a large aperture long focal length scope for, as I find interacting galaxies fascinating, but many of them are very small.

The camera was an Atik 16HR, and all subs, including the luminance were binned 2x2. It’s not normal practice to bin luminance subs, but at F10 the scope is very slow, and at that focal length the resolution is limited by the seeing, and so there was no loss of quality with the subs binned, but a considerable increase in sensitivity which made up for the slow F-ratio.

I managed to get a couple of nights of luminance data, but it looked like I wouldn’t be able to get any colour before I went away for work, but right at the eleventh hour I got a clear night, and managed to grab enough data to add colour, although the image really needs lots more data in general, and I’ve had to pull a few tricks out of the hat to reduce noise generally throughout the processing.

Luminance was 23 x 6 minutes, Red and green-14 x 4 minutes each, and blue was 21 x 5 minutes. Total imaging time-5 hrs 55 minutes.

Imaged on the 23rd April and 3rd May 2011.

Another thing I tried with this image was shooting some RGB subs of a relatively clear area near the target specifically to image the light pollution, which I then could use as a kind of LP flat frame, and subtract from the image. In the past I’ve simply equalised the background levels, but I found that doing it using the new method meant that I had a lot less work to do colour-wise during processing. I haven’t perfected this yet and need to experiment a bit more but the method seems quite effective, and on a target that has enough clear sky surrounding it, a LP sample could be taken directly from the image and then resampled to match the correct image dimensions before being applied.

Cheers

Rob

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Whippy

Whippy

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That's a superb first light for the Edge 11 mate :). I'm intrigued by this 'colour' flat process you tried. I've almost resigned myself to not doing any more RGB due to the increasing LP here so if this is a decent workaround I'm all ears!

Tony..

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barkis

barkis

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What a wonderful looking object this is Rob.

I'm pleased you overcame the problems that beset you, to allow you to image this, it's a winner in anybodies book. Must have an APOD shout too.

That Edge is going to be a winner for sure :).

Seems you might need to produce a a tutorial on the techniques employed once you've perfected them

Ron.

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RobH

RobH

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Thanks guys....I have another couple of images to process over the next few weeks (most data taken with my TMB) and will play around with the LP flat technique some more. Once it's working properly I'll addd a tutorial to my website.

I got the idea after I'd shot some images with my new DSLR (I haven't owned one before). I was pretty shocked by the amount of LP, and found a couple of LP removal techniques on the web. I got to thinking about LP filters, and decided to have a bash at using photoshop and sampling the general LP levels and then subtracting them using 'colour burn' with 'inverse' checked.

It seems to work well, as long as it's not applied at 100%, as it clips the blackpoint when applied that hard.

As local LP is much the same most nights, it seemed to me that creating a generic LP sample for each main direction should allow me to use the samples for any images taken in those directions.

Basically what I did is this.....I shot 4 subs each of RGB at the same exposure length as the lights (These were flat frame and dark claibrated in the normal way.),

and combined them into a RGB image with no stretching applied.

The few stars on the images were removed using the clone tool, and then a gaussian blur applied to remove any noise.

Cheers

Rob

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swag72

swag72

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This is a lovely image - Aren't the Edge scopes though marketed as being ideal for imaging as you can easily remove a mirror and go from f/10 to about f/2.8? Is that not a major selling point and would make life easier for you not having to image at f/10?

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johnh

johnh

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Glorious detail right to core and interesting technique, knew you were suffering withdrawal from loosing the 14" so glad the C11Edge can deliver. Newish ACF v C11 Edge HD - wondered what you'd prefer?

John.

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RobH

RobH

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Aren't the Edge scopes though marketed as being ideal for imaging as you can easily remove a mirror and go from f/10 to about f/2.8? Is that not a major selling point and would make life easier for you not having to image at f/10?

They are indeed, but of course at F2 (that's the ratio you get with a hyperstar in place of the socondary) you then only have a focal length of 560mm....fast as heck but you don't get the image scale for the very small objects.

I plan on using this scope at F7 and F10 using my H18 binned 2x2 as there will be no resolution loss due to seeing conditions and that'll give me a fast enough imaging train even at F10.

John....my choice was between the 12 inch ACF and the Edge 11.....the ACF gives a corrected image over a curved focal plane but the edge has a true flat plane, and it's native focal length, plus the focal length at F7 (I have just got an Astrophysics reducer which isn't a field flattener too) gives me the image scale I'm after for the sort of targets I'm interested in.

I did look at the GSO Ritchey Chretiens, but would have to deal with diffraction spikes with that type of scope, and I'd rather add them if I want them (as I9 did on this :))

Cheers

Rob

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ollypenrice

ollypenrice

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Whheeee, that is exciting! It really does open up another world when you can get a focal length like this to work - as you resoundingly have done here. Trouble is, you do need the mount!

You are going to be struggling to know what to image next now that you have all those tiny targets within range.

Brilliant debut for the C11.

Olly

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rich_t

rich_t

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Fabulous image there Rob with new scope, I still havn't been able to put a decent image together with my 8" Edge scope, mainly because of the F10 ratio and the long wait for Celestron reducer for it. Will be interested to see how you get on with the AP reducer.

Did you use an OAG for this or did you find the mirror locks sufficient to use a guidescope with image shift?

Cheers,

Rich.

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RobH

RobH

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Hello Rich.

I tried using my lumicon OAG, but had a lot of problems and got fed up with faffing about so I stuck my Tal 100 on top and used that as a guidescope. (for various reasons, I couldn't use my SX OAG). I found the mirror lock to be good, but not perfect, and there was a small amount of image shift, but not noticeable on 6 minute subs.

Cheers

Rob

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