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Summer Triangle Challenge

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Seeing was actually quite good this particular night so decided to image my favourite galaxy M51.
Here are the acquisition details:

Date: 2017-05-02
Mount: EQ5 Pro
Scope: SkyWatcher 130 PDS
Camera: ASI 290MM (from FLO earlier this year - love it!!!)
Lights: 553x8s
Darks: 173x8s
Gain: 400
Binning: None


Post processing was done in DSS and then GIMP. Also used an application I wrote myself to remove the background gradients and ampglow. It is similar to how DBE works in pixinsight but less advanced of course. I have a thread over here about it (sorry in swedish): http://astronet.se/phpBB3/viewtopic.php?f=13&t=14890

I can upload a ZIP of the raw files if anyone would like to try out some short exposure image processing :happy7:

Also have an image over in the huge 130PDS thread that uses these subs along with some from april (so can't use that image here...). It does look better with less noise.


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1 hour ago, Galen Gilmore said:

That is an amazing image for such short exposure times! 

is there a reason your using such short exposure times? Because I'm getting the same equipment you have, an EQ5 and a 130PDS.

Thanks a lot!

The reason for short exposures is that it makes everything so much easier and less expensive. Since these new CMOS cameras have so low read noise there is no need for long exposures that is required with most CCD cameras. Long exposures either requires guiding (which is a pain in every possible way not to mention an extra expense) or a mount that costs a lot of £££. You could even use an Alt-Az motorised mount to do short exposures :icon_biggrin:

Another good thing is that it has made it possible for me to image even on nights with windy weather. Sure, I have to throw away a couple of subs those nights but imagine the pain of trying 5 minute exposures and have them ruined by a gust at the last second, NOT fun!!


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1 hour ago, cuivenion said:

Fantastic image. I thought that images like this were only possiblle with much larger apertures when using such short exposure times.

Thanks! Yes, I was skeptical as well, but truth is I have had so much fun ever since I got this camera :)

I did at lot of testing in the beginning, more information in this forum thread (sorry swedish again): http://astronet.se/phpBB3/viewtopic.php?f=15&t=14495


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5 hours ago, SvartSork said:

I can upload a ZIP of the raw files if anyone would like to try out some short exposure image processing

Oooh yes, please!  Would like to compare my gradient removal with yours!

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@AKB ok will do. Just that it will be several GB in size so need to find somewhere else to upload it  :(

I'd say that is the main drawback of short exposures - you need a lot of disk space and patience while stacking.. 

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10 hours ago, AKB said:

Thanks. In fact, just to compare gradient removal, I guess the raw stack would be a start (you don't remove the background on each sub separately, I assume.)

Here is the full set of lights and darks if you are still interested (or someone else is). It is 2 GB compressed :icon_biggrin:
I used 553 of the lights subs but there are some hundred more in the ZIP file. Just pick the ones with best FWHM and score and you should have roughly the same set as I used in DSS.



41 minutes ago, Ant said:

 That's incredible!


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Well, here's my attempt using 262 subs.  It's only that number because it became rather tedious to manually pick the alignment stars for each sub... there seems to be quite a bit of movement between each.  You don't dither?

Also, this camera is not cooled??  Amazing data!

I may have stretched it just a bit too far, but you can clearly see some small fuzzies in the background – not sure of their actual designation.

Basic processing chain was:


  • Grade image quality, picking those with HFR below 2.25
  • Align, simple translation with manual star selection (rejected just one with satellite trail)
  • Stack


  • Background removal (homemade, fully automatic with no manual placement – perhaps like ABE??)
  • Stretching (mixture of automatic and manual)
  • Noise reduction - weak bilateral filter and ONR ('Olly Noise Reduction' – raise lowest end of curve)

Nebulosity (again):

  • Slight star reduction
  • Image rotation
  • JPG generation

So, really, very similar to usual processing, just that there are a lot more files!

Thanks so much for letting us have a play with this.


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  • 3 weeks later...
On 2017-07-12 at 02:21, sharkmelley said:

8sec exposures!   It's a lovely image and an excellent example of how sensors with low read noise are changing the rules of the game :)

Thanks Mark!

I have another version with almost double number of subs that looks much better:

Cant use it though since half of the subs are from april :(


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