M27 3rd July 2008

[Starflyer]

Here's my first attempt at M27 and my longest exposures to date.

Taken last night with my Skywatcher 130PM and SC1 toucam. 40 x 30s subs, 10 x 40s subs and 5 x 35s darks, stacked in DSS, levels and curves (sort of) in CS3. Stars are big and blobby and the nebula is very grainy, but it's a start.

Ian

[dogfish]

Hi Ian

I think that's great given what you're using (and a lot better than I can do). Can't wait to see what you can do with better kit.

Cheers, Martin

[steppenwolf]

Its a very good start, you've captured a lot of detail and some good colour. The star size is a function of seeing, sampling (pixel size V focal length) and focus. Your focus is perhaps a little 'soft' and your sampling is 1.9 arcseconds/pixel with your set-up so the stars will be relatively high resolution which, of course, means that they will include more pixels - resolution is a bit of a double edge sword!

Yes, there is some grain in there but more subs. will resolve that for you - I like the image, you should be pleased with it!

[Starflyer]

Thanks for the comments Martin and Steve

Steve, can I ask how you calculated the sampling?

Ian

[steppenwolf]

Hi Ian, the calculation is as follows:-

(206.265/Focal Length in mm) X individual pixel size in uM

[LostNSpace]

Nice image Ian

Had an attempt at taking the grainyness out of the image using Pixinsight......

Process tab/General/SGBNR..........tick the box in Luminance mask and then tweak clipping

(click to enlarge)

Great little program and i think it was Mike (Yfronto) that brought it to our attention :salute:

Mark

[Starflyer]

Thanks Steve, not that I'm any the wiser now , where does the 206.265 come from?

Thanks for taking the time to tweak it Mark, it looks much smoother now, I'll have to download and have a go with Pixinsight, it has definitely removed the grainyness

Cheers,

Ian

[Sam]

Very nice image Ian.

[Starflyer]

Thanks Sam

[legion48]

Great capture Ian. I imaged this one for the first time a few weeks back. I was surprised at how easily I could see it visually.

[steppenwolf]

Thanks Steve, not that I'm any the wiser now , where does the 206.265 come from?

Dividing pixel size by focal length results in an answer in radians. We need to work out the value in radians of our field of view. Apparently, there are 2pi radians in a circle. Therefore, there are 57.29578° in one radian, so there are 57.29578 x 3600 arcseconds in each radian. Multiplying by 206,265 converts radians to arcseconds. Why 206,265 and not the 206.265 I showed you earlier? This is because we are working in uM not mm for the pixel size.

Confused? Me too

[Starflyer]

Thanks for the thorough explanation Steve, is there a primer anywhere that shows / explains the calculations needed for choosing a suitable camera to match a certain 'scope?

Thanks Tony, I found it easier than M57 to see visually but harder to image. At 15-20 seconds M57 was clearly visible on the screen but M27 was hardly there using that length of exposure . BTW I'm still enjoying your old 'scope

Cheers,

Ian

[gary1968]

Thats a great image Ian, maybe next time we meet you can pass on some tips in the old imaging lark mate.

Cheers,

Gary

[Starflyer]

Thanks Gary, I'll no doubt see you at Kielder this Autumn for a beer or two and a Kashmiri lamb shank

Ian

[RobH]

That's a really good start there Ian

One thing that I think may help is to not be quite so severe with the black point as it looks rather clipped.

If you don't push the white point and black points quite so hard in the processing, you should end up with a smoother image and some more faint detail, although it won't be quite as contrasty.

Cheers

Rob

[Starflyer]

Thanks for the kind comment Rob and the processing advice.

Ian