Sombrero Galaxy

M104, NGC 4594 in Virgo

Image exposure:
149 min 52 sec
Image field of view:
24 x 16 arcmin
Image date:

M104 is a very attractive target for amateur astronomers. Famed for its hat-like appearance, it is an edge-on spiral galaxy with an emphatic dark dust lane asymmetrically bisecting a very bright bulging nucleus.

At magnitude +8, the Sombrero is easily picked out in small telescopes. It is about 28 million light years away in the Virgo Cluster of galaxies, a regional association of more than 1,300 galaxies.

My 2½ hour image was built from 100 sub-frames of 89.9 seconds.

That’s odd, you might think. Why 89.9s and not a nice round 90.0s? The short answer is that the SharpCap imaging software measures the brightness of the sky background at that particular time and automatically recommends an exposure time and gain setting. My part in that particular process is to hit the accept button. 😊

I feel a rant coming on . . . .


Soapbox Alert

Here in Oz we are nearing the end of a tedious six week federal election campaign, with Prime Minister Tweedledum and Opposition Leader Tweedle-dee yelling insults at each other in debates. One of them wants to give workers a pay rise which is unacceptably high and the other wants to abolish pay rises for all eternity.

The Biggest Issue of our Time, Global Warming, is given scant mention. One of them wants to export more fossil fuels and the other wants to export only slightly less fossil fuels.

The current Australian Government is one of the worst in recent memory and it deserves to be kicked out. However, if that occurs they will be replaced by a party which was kicked out of government only nine years ago because it, too, was a shocker. The party which once rewarded homebuyers with 17.5% interest rates on their mortgages.

As for the covid pandemic, to sweeten people as the election loomed, they opened up last October and progressively dismantled all the restrictions and mask mandates which had kept us relatively safe. It gifted the virus a springboard to take off like a rocket and as a result Australia very quickly leapt from being one of the least infected countries to one of the world’s worst.

A small country with a population of just 26 million, Australia is now the sixth worst nation on the Johns Hopkins table of reported monthly infections – and covid, the Second Biggest Issue of our Time, is also not even an election issue.

Rant over.
It’s safe to come out.

Telescope:Meade LX-90 200mm Schmidt-Cassegrain
(deforked); 2000 mm f/l @ f/10.
Optics:Astronomik light pollution filter.
Mount & Guiding:SkyWatcher EQ6-R Pro mount.
Imaging camera:ZWO ASI 071 MC cooled.

Images © Roger Powell

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ABOVE US ONLY SKY : amateur astronomy in australia


  1. Very nice . . . I ran it through DeNoise because it looked a bit grainy . . .

    Then I doubled the size . . .

    I’m curious to know what you think. I assume this will go in moderation, and you don’t have to release it if you’d rather not.

    Liked by 3 people

  2. After some frowning I released it for display on this page – because I understand your motives – but not anywhere else please.

    The challenge with astro-image processing is not to over-cook the adjustments by making improvements to some parts of the image which can be to the detriment of other parts.

    The initial processing is done in the image control software at the laptop alongside the telescope, as the live stacking continues. The final tweaking is done later on my PC using different software.

    Processing is an art I’m still learning. There are many amateurs better at it than I am but I’m just astonished to be in a position to take these shots. Fifteen years ago I would never have dreamed of it!

    It really is an art too. I mean that in an ‘artistic licence’ sense, not just in the ‘skilled’ sense. Maybe a bit like the clever variations you sometimes publish of various objects, although I wouldn’t be quite so adventurous with my astro-images.

    I see many images taken by others using different equipment with different software, different techniques and a different idea of how the end product should look. Sometimes their images seem over-processed or under-processed to my eyes: the colours don’t sit well with me, the stars are too sharp or too fuzzy, the sub-frame exposure was too short or too long, the background should be darker or lighter, the galaxy could be brighter etc etc. – but in the end, it’s their interpretation of how the image should look. There’s no right or wrong.

    Another problem which I occasionally grapple with is finalising an image and after posting it up I notice it has over-processing flaws which I didn’t see before posting. This happens here on WordPress and also over on Flickr. For that reason I often pull back a little after stretching.

    As for noise, yes it can be noticeable sometimes – but mostly that is reduced by dithering during the acquisition phase and by using flats and darks. Subsequent software manipulation of noise can be to the detriment of other elements of the image.


    Liked by 3 people

    1. My apologies. I should have asked before manipulating your image, and, of course, those won’t appear anywhere else (you could also delete the comment as it’s primarily for you).

      I confess my motivation was more about the performance of DeNoise and GigaPixels and your opinion about the end product. I should have just emailed them.

      I think there’s a little banding occurring (probably because the original was already compressed once by WP), but not too bad.

      That said, If you’re looking for post-processing software, Two products I highly recommend are Topaz DeNoise and DxO PureRAW. The latter works only with RAW files, but DeNoise (which is what I used on the above) works with any file and they have a wide range of processing models and adjustments (artifacts are a problem with many noise-reduction algorithms).

      I assume your original files are of a higher resolution (and size) than what you publish, but if you are also looking to enlarge crops, Topaz GigaPixels works well. It’s not 100% great (it depends on the quality and features of the original), but works for most stuff I’ve tried it on.

      FYI, the Sombrero NASA original photo I had mentioned (11000×6500 pixels 211MB) was also noisy and this is the Sombrero NASA DeNoise version.

      Again, sorry about playing with the photo.

      Liked by 1 person

      1. I have to admit that seeing all the background galaxies almost detracts from the photo because it almost looks fake, as if someone just threw extra stuff in there to decorate around the subject.


      2. Yes the incoming images which are pre-processed during live stacking are FITS files. The stacked output file is either PNG or TIF.

        The SharpCap software has its own noise reduction process, which I’ve yet to test. You’ve given me a nudge and I’ll try it out after full Moon. Depending on the results, I’ll look at your suggestions after that.



  3. I don’t know if you have seen Ian Morison’s website (as you are based “down-under”) . But he is retired radio-astronomy professor who is also one of the most well-known amateur astronomers in the UK and is has written many books on astronomy

    It would be worth looking at as he has written various articles on image processing

    Liked by 1 person

    1. Thanks, Steve. I’ve bookmarked that site, it looks interesting.

      One characteristic of astrophotography is that there is such a variety of choice, for hardware and software for image acquisition and image processing and everyone charts their own path. Of course that leads to a huge variety of advice and procedures too!

      I hope however that some of the concepts on the site you recommended could be of some value.





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