#1  
Old 20-09-2018, 08:45 AM
tim.anderson (Tim Anderson)
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Join Date: Nov 2014
Location: Cowra
Posts: 213
Ngc253

The Sculptor Galaxy, NGC253, also known as the Silver Coin Galaxy.

Technicals:

Telescope: 254mm Newtonian, F4
Camera: ASI1600 monochrome
Images: 50 x sixty-seconds in each of L, R, G and B channels
Combined in Nebulosity and processed in Photoshop
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Click for full-size image (Sculptor2-2.jpg)
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  #2  
Old 21-09-2018, 07:25 AM
Placidus (Mike and Trish)
Narrowing the band

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Join Date: Mar 2011
Location: Euchareena, NSW
Posts: 3,719
Hi, Tim,

You're getting very good detail in the galactic fountain dust lanes there.

Looks like the focus was either not quite right from the start, or drifted during the imaging session. With an F4 scope, focus can be very touchy. Perhaps it would be worthwhile to refocus (using short test images) from time to time during the run. We focus by taking multiple 10 second test images on a suitably bright star (which might mean having to move well off the main target, and come back to it later) and choosing the position with the best FWHM. Other folk use a Bahtinov mask, or a 3-hole mask, or just find the position that gives the best image. It does mean that you have to have a way of actually seeing the test images at high magnification. Because your scope is such a fast instrument (a very good thing) you'll probably need to refocus much more often, especially early on in the night. Those dust lanes will look even better then.

It is also just possible that the collimation is off. You can check that easily by going even further out of focus, until you can see the shadow of the secondary mirror more or less in the centre of the star. It should be exactly central.

Hope all this helps.

Best,
Mike
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