Another first autoguided pic - Horsehead

[Lee]

Hi all
Finally have my side/side setup running! PHD is one awesome piece of software.... Anyway - with clear skies, and the horsehead starting to clear some local light pollution, I thought what better target.

The pic is 1 hour (20x3min) of luminance exposure - DSI Pro II, ED80 at f/7.5, Astronomik UV/IR block filter. Dark subtracted and flat frame adjusted with deep sky stacker, exposures performed with Nebulosity. Guided through Skywatcher 100mm f/5 achromat, DMK21AF04.AS and PHD guiding. Outback cooler running, temp 20.0degC

I'm quite happy with it - guiding was excellent (and easy!), stars round, happy with focus (thanks to WO focuser) - but there are some black streaks - these only show up in the final histogram stretching stages. In the past I have had these much worse, and it was put down to dark frame temp-mismatch - with the Outback I thought this would vanish - maybe it has just reduced it a heap..... Any other ideas? I feel that more, longer exposures would increase signal-to-noise ratio, and avoid some need to stretch so much....

I would have done longer exposures, but I only had some pre-done 3 minute master darks!

Certainly a big improvement on my last years horsey.....

[gbeal]

I would still guess at the darks Lee. If you can, shoot the darks as you shoot the lights, if you know what I mean. I am lazy and have a selection of "library darks", but really the only way is to shoot them each night. With the 30 minute shots I use the library ones, but for something like 5 minutes or even 10 minutes I would shoot them every time. Try it and see.
Gary

[jase (Jason)]

Lee,
Indeed, a significant improvement to last years image. It looks like the you've tried to stretch the data too hard, thus introduced excessive noise. Possibly a darks issue. Look forward to seeing more.

[h0ughy (David)]

Nice go at it Lee, glad to see my borrowed stuff is working for you

[Garyh]

Well done Lee! other than whats already mentioned you have the focus and guiding spot on! Look forwards to the next shot!
cheers

[Ric]

Nice capture Lee. The guiding looks great.

Cheers

[Dennis]

Hi Lee

That is a terrific HH – nice round stars and sharp focus, well done.

It looks like the lines of the (few) hot and cold pixels seem to generally follow the same direction as the “noise” streaks. This makes it look like something is shifting between sub-frames?

Cheers

Dennis

[Aster]

Nice one Lee. It's nice to see some other DSI Pro images instead of all the Canon ones.

[Lee]

Originally Posted by Dennis

It looks like the lines of the (few) hot and cold pixels seem to generally follow the same direction as the “noise” streaks. This makes it look like something is shifting between sub-frames?

I've wondered this - but why only shift between exposures - the stars are all round, so I assume nothing is shifting during an exposure..... I think it is overstretched.

Originally Posted by Aster

Nice one Lee. It's nice to see some other DSI Pro images instead of all the Canon ones.

Thanks Alex..... Going to point my Ha filter at him soon, took some 10 minute darks tonight.....

[Dennis]

Hi Lee

A similar thing happened to me a long time ago, when I was using an SBIG proprietary function labelled “Track & Accumulate” with the SBIG cameras/software.

The SW, on the fly, stacks each sub-frame even though the mount is not auto guiding and the end result is that you obtain a combined image of say, 20 x 90 sec but it is not full frame. The image area is defined by the common area of overlap of all the sub frames and the non common regions outside the overlapped area (caused by drift) are discarded.

It was under such conditions I had similar streaks to you, as each sub-frame was shifted relative to its successor due to (small) tracking drift. This is probably a complete red herring though, as you were auto guiding?

Cheers

Dennis

[stlfiremedic35]

There is a guy that sells a photoshop plugin called astronomy tools actions. One of the things it does is remove vertical line noise the example he used looks just like the lines in the horse head picture. Over all a pretty good picture, more shots stacked may of helped, I am just going by what i have read, I dont have the hands on know how most of you guys do, not yet anyway. I have been useing data that was given to me by other people and practicing processing it with photoshop and ps tools. latter when I get a camera Ill work on that part of it. Wow photoshop is a tuff program to learn without a teacher. Hey have fun thats what its all about, Ken