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First proper image - Whirlpool galaxy M51

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I'm reasonably pleased with this but there's lots to improve. Needs to be less noisy for one.

Unguided Canon 50D, 20x43s subs 5xdarks, ISO800, used DSS and Photoshop CS3. Thanks to @carastro for her guide - it was very useful indeed.


Edited by Yearofthegoat
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Thanks @spillage!

Not yet but intend to shortly.

I got a 70mm Barska scope off the 'bay for £11 so am sorting out a suitable bracket. Then I'll attach a GPCAM mono to it for guiding. If the 70mm is no good (have already had to shim the plastic focuser as it waved about in the breeze so am not expecting much!) I have my eye on an Antares Versascope 60mm, which will also make for a better finder than the 6x30 one that came with my 150PDS.

The above is a cropped jpg, the original stacked final has coma in the corners (stars look like tadpoles) but the centre is okay, so am not sure if I'll go to the expense of a coma corrector just yet.

The big thing I want to improve is how 'grainy' it looks - it seems to me to be colour noise? I can play more with NR but of course it removes some detail, so better to not have it in the first place. Lower ISO and longer subs maybe? Will certainly try that once guiding is set up.

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Yes @carastro it did, much appreciated.

I know my way round Photoshop levels and curves, but it was good to have a guide as to the order to do things. I still need to play more with DSS settings. For example, that image was stacked with 'Kappa whotsit' rather than 'Average', which is supposed to prevent the out of memory error in DSS.

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Once you start guiding use dithering and have a go a ditching your darks and only using bias and flats in DSS. If it works for you then you can spend more time gathering your light frames.

Might be worth trying use more darks.

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kappa-sigma should be fine. I would not use DSS for making any adjustments to the final image. You can try pixinsight or startools before you purchase.

I think pixinsight is a 30 day trial and startools is unlimited but you cannot save the results.

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1 hour ago, Yearofthegoat said:

I'm reasonably pleased with this but there's lots to improve. Needs to be less noisy for one.

Unguided Canon 50D, 20x43s subs 5xdarks, ISO800, used DSS and Photoshop CS3. Thanks to @carastro for her guide - it was very useful indeed.

Depending on how your camera actually handles ISO, I personally would actually increase the ISO quite a bit, and then either decrease the sub length (to allow more subs in a night), or increase the sub length if your mount allows it, to gather more light.
I've found with my nikon D5200, that increasing the ISO helps me collect a lot more data, and bringing it out without having to stretch it as much, which also brings the noise level up. As long as you have enough subs to basically neutralise the noise, it should be fine. I mostly do ISO 6400, and then do as many subs as I can. At least 30.
Also try with and without darks, that can again be camera dependant. For me personally, I pretty much HAVE to use darks, if I want a good image :)

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Dithering through the mount. I do this through apt which is connected to phd2/eqmod using the default settings.

I think the basic explanation is that any errors on the camera side will always remain in the same place and your image will move. DSS removes the static errors leaving you with cleaner data.

With the canon I would go not further than iso1600. I found iso800 is the best for me.

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Yes, even in normal non-astro use I try to stay 800 or below due to noise - usually colour noise.

I expect I can lengthen the subs even if not guiding - will see how that goes. The noise really only show itself when stretching the image, so I'll look at that again as well.

I can totally see how this AP hobby gets addictive.

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Try capturing more subs. With the reasonably short exposures you are taking you could afford to capture more and this will help boost the SNR. Having said that, it's a good first image....well done.


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