First LRGB attempt: M27

[NigeB]

Hi All,

I acquired a used Atik 460ex mono + filter wheel and filters a couple of weeks ago to replace my OSC camera. I spent most of a clear night sorting out OAG spacing and dealing with a weird problem where the filter wheel isn't recognised by Windows 7 if it's connected to a hub along with the CCD and Lodestar guide cam. But in the end I got things working and had a go with M27 before the dawn came. I took 2 x 300 second exposures in each of L, R, G and B through the TOA-150. Aligned and stacked each channel in Registax, then combined in PS CS4 and adjusted curves - nothing else. Here's the result:

 

 

No darks or flats; I know there's not enough signal in here, so it's a bit noisy, but I was still mighty impressed with the performance of the Atik kit. Criticism welcomed.

I took some Ha data as well, but have yet to manage to get this to look right when used in the L channel (am following the Starizona directions on combining Ha with RGB). Still, with this weather, it looks like I'll have a couple of months without the inconvenience of clear nights to get in the way of processing...

 

Nigel

 

[laudropb]

Very nice image.

[Physopto]

That's a really good start. Which scope did you use?

 

[NigeB]

Hi Laudropb, Physopto,

Thanks! This was taken with a Takahashi TOA-150, using an off-axis guider with a first generation SX Lodestar.

Nigel

 

[ollypenrice]

That is mighty impressive! The resolution is delicious - as we might expect from a TOA150.   Colour balance is lovely right through from the background to the stars. For such short data this is ridiculously good.

If Starizona are telling you to use Ha as luminance ignore them! Ha, as you know, is red - so it should go in the red channel. You can't just replace the red with Ha because the stars are smaller, the background darker and not all the red emission is passed by the filter. So the trick is, in my view, to add the Ha to the red by splitting the channels, pasting it onto the red then changing the blend mode to Lighten. This means that the Ha will only be applied where it is brighter than the red. It won't do any subtracting and will leave stars and background as they were. What is more, only the brighter Ha will find its way into the image. If, when you stretched it, you called a halt to the stretch once it got to look noisy in the darker parts then you may well have a bit left in the data from the point of view of adding it to red. While it is pasted on red in blend mode lighten you can give it a bit more of a lift in Curves to see what you can get away with. I would then follow the same process to add OIII to green and blue (since it sits on the GB border.)

Olly

PS Using Ha as luminance on this target would be a particularly bad idea since there is so much attractive blue nebulosity. If you illuminate this in red light you'll kill it.

[Physopto]

That is a really nice scope so not too surprised. Your guiding must have been spot on and the conditions very good. For a total of ten minutes in each channel the result is  amazing. From what I can see you haven't cropped at all.

I was also interested in what Olly said about the processing. I am going to have to spend some time learning about PS.

Just think what you will achieve when the Ha is added.

Derek

[NigeB]

Hi Olly, 

Wow, many thanks - that's praise indeed! I am much encouraged by your comments. 

The Starizona web page I'm using is this one: 

https://starizona.com/acb/ccd/software/ps_hargb.aspx   

Reading it again, their advice seems to be consistent with yours and outlines the same process of adding the Ha into the R channel with use of Lighten blend mode, application of curve adjustments etc. But I'm going to start again and follow your steps instead; perhaps I've made an error along the way (when I followed the Starizona steps, I ended up with a very grey-blue version with occasional red highlights. Curve adjustment didn't help much, but I wondered if I was hitting the signal limits of the data). I've shown a jpeg'ed version of the Ha frame below. I'll try some reprocessing over the weekend and post an update.

Thanks again,

Nigel

 

 

 

[NigeB]

11 hours ago, Physopto said:

That is a really nice scope so not too surprised. Your guiding must have been spot on and the conditions very good. For a total of ten minutes in each channel the result is  amazing. From what I can see you haven't cropped at all.

I was also interested in what Olly said about the processing. I am going to have to spend some time learning about PS.

Just think what you will achieve when the Ha is added.

Derek

Hi Derek

Thanks! It seemed like a pretty steady and clear night.

I'm heartened by your comment on guiding - I've been experimenting with mounting my C11 alongside the Tak; a side-by-side approach didn't work (lots of flex and long damping times), so I've now got the C11 piggybacked on top, and the result is much more stable. The M27 image was taken in this configuration, so it seems that the tracking isn't badly affected. But the focal length of the Tak is quite forgiving (1100 mm); I suspect imaging at 2800mm f/10 is going to be a different matter...

I have cropped a little bit - I have the smaller (=much cheaper!) of the Tak field flatteners, but I still get some distortion at the corners of the frame. 

This is the first time I've used PS for astro imaging, and I'm impressed; even though I have an old version on an old machine, it seems to cope well with the file sizes and is really nice to work with. Am sure you will enjoy the experience!

 

Thanks

 

Nigel

 

[AndyUK]

As Olly said "For such short data this is ridiculously good"... and for your first LRGB, doubly so !  Very impressive indeed... Thanks for sharing (and showing what's possible for just 40 mins total integration time!)

[ollypenrice]

10 hours ago, NigeB said:

Hi Olly, 

Wow, many thanks - that's praise indeed! I am much encouraged by your comments. 

The Starizona web page I'm using is this one: 

https://starizona.com/acb/ccd/software/ps_hargb.aspx   

Reading it again, their advice seems to be consistent with yours and outlines the same process of adding the Ha into the R channel with use of Lighten blend mode, application of curve adjustments etc. But I'm going to start again and follow your steps instead; perhaps I've made an error along the way (when I followed the Starizona steps, I ended up with a very grey-blue version with occasional red highlights. Curve adjustment didn't help much, but I wondered if I was hitting the signal limits of the data). I've shown a jpeg'ed version of the Ha frame below. I'll try some reprocessing over the weekend and post an update.

Thanks again,

Nigel

 

 

 

Have a care with that slightly saturated streak in the lower half. 

If you can find the imaging time, more Ha in longer subs would find the tantalizing outer shell which extends far beyond the main nebula. We're seeing bits of it here already.

Olly