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Bode's Galaxy


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Hi there,

Just back from another enjoyable trip to Astro Adventures in Devon. Unfortunately, we only experienced one clear night- however, we have come back with this image, which we are fairly pleased with. It does need a reprocess to get rid of a stubborn satellite trail; we are also thinking of gathering some H-a data at home to add. It consists of 10 x 10 minutes in luminance, 12 x 5 minutes in red and 10 x 5 minutes in blue and green, taken with my Atik 460 EX, through an Intes Micro MN71 7" Mak-Newtonian, and processed in Pixinsight. It was also processed without darks or flats. I am especially pleased with this image, as I have been having some difficulties with processing images taken with this camera, as discussed at length on another thread, and am hoping that this issue is now cured- so far as I can see, the problem seems to be related to noise reduction. Any comments gratefully received.

Dave and Zoe

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You have some fantastic detail in there but I worry about colour and the "comet trails" of the brighter stars. It is an artefact I haven't seen before and the first thing that comes to mind (correct me if I'm wrong) is astigmatism. If it is, it is almost certainly caused by the primary mirror clamps being too tight, thus warping the mirror glass some. Mak-newts are great, and I have just gotten one myself (190MN). I did put it in the shop first thing in order to change the focuser, and as I had the primary out I chacked the clamps and they were very tight. Again, your problem may not be astigmatism, but if it is, it is easily corrected.

I would like to see some more punch in the red and the blue in the image (personal choice, of course). I found the satellites ;). What you should do to get rid of them is use sigma clip in the stacking in PI. It will get rid of everything that is not in the same place in all subs. Of course, if you sigma clip you will have to dither your exposures so that hot pixels remain stationary while stars move around a few pixels between exposures. PI has a fantastic sigma clip!

All in all, a nice result! More to pull out for sure with more experimentation.

All the best,

Per

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OK, first impression is that this is a darned impressive image. It comes in strongly with something to say. As Per says, the optics are at fault with those one sided spikes radiating from the stars. I suspect that Per's analysis is right but I'm no expert on Mak Newts.

I think the black point is clipped a little aggresively. Personally I think a Ps value of about 23 is good for the background sky.

Galaxies tend to have little colour contrast so need a helping hand (cheating!!) but I tend to lift the middle blues and the higher reds in Curves.

Anyway a great result. You have resolution right into the core, which isn't easy and deserves a low bow!

Ollu

Edited by ollypenrice
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Hi,

Many thanks for all the positive replies. Funnily enough, the image was stacked using sigma clipping, which got rid of two trails but not the brighter one. I did actually use curves to lift the blues more and saved it as a separate image, but dithered over which I preferred! We are hoping that some H-a will improve the image too. We know that the stars are not quite right...

Zoe

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Winsorzied sigma clip needs to be set during the image integration in PI. You can find it under the pixel rejection tab...

The optics definitely need to be looked at since as you know the stars aren't right at all and its very distracting in the image. The galaxy looks great and you are getting some nice detail coming through to the core.

This just goes to show that extended object are very tolerant of optical issues but your not going to have any success with open cluster and globular clusters any time soon, well not until you solve the optical issue. If the scopes under warranty I'd take it back to the point of sale and ask them to fix it for you? If not and your not comfortable performing the necessary surgery on it yourself, try taking it to an astronomy club I'm sure someone can help you.

(Per is right, it sounds stupid that the clip tightness can cause this issue with a thick primary mirror but it can! I have experience a similar issues with my own newt)

Good luck

Edited by Darth Takahashi
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Hi,

I did use Winsorized Sigma Clipping in PI, which still didn't remove that last trail- quite peculiar... As the scope belongs to Astro Adventures, there's not much I can do about the stars! Just about to reprocess minus the satellite'd image.

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