first ever widefield - what's wrong?

[c3po]

hi all, well i've finally landed myself a DSLR - a Sony Alpha 200 10.2MP - and a half decent lens, a Sigma 28-70mm F2.8 so i can really start with getting my teeth into AP.

so, anyway, with LOVELY clear skies last night, my equally lovely wife and my new acquisition, i headed out to a relatively dark site to try my hand at a few static wide-field images to stack in DSS later since i didn't have a T-ring or telescope attachment yet. I set the tripod out, attached the A200 and lens, pointed roughly at Cygnus and opened the zoom out to the full 28mm, focussing as best i could (its bloomin' hard ain't it!!). Then i attached my wired remote timer and pushed in for it to do 25 subs of 20 seconds each - i'd have loved to go longer, but even with 20 seconds i noticed some slight trailing. Lights done, and 10 darks of the same ISO and exposure completed, i was done...This morning, DSS was opened up and all the images entered and off it went....all done, off to Photoshop and do some basic levels and curves adjustments - I think I did it right!?!

The below image is what I've ended up with after a bit of tweaking in PS CS4. The bright lower left area is caused by the LP from my town (Carterton) & RAF Brize Norton both within 3 miles of where we went.

stacked wide-field (Cygnus region) by Si_3po

looking at it now, i can see i didn't focus well enough, and there's still some trailing...any other comments would be much welcomed!

[JamesF]

Particularly around the top edge it looks to me like you have some stacking artefacts (and perhaps around the top of the left edge too). I'd crop those out and then redo the black point to see if that helps.

Even if you're only taking 20 second subs, I'd take some longer ones initially (45 seconds, say) to get the framing sorted. I reckon you could have moved the image down the frame a bit in this one and got more of the "width" of the Milky Way in the frame. If you're able to take a few at your expected exposure length and look at some of the stars close up on a laptop, that might help with the focus, too.

The light pollution is a pig. Even when it seems minimal visually it manages to creep into long exposures quite heavily. I have almost none that's apparent here visually, but in an image I took of the southern end of the Milky Way recently it's got across almost the entire frame I've bought a 2" Skywatcher LP filter and a couple of step-down rings to fit the kit 18-55mm lens that comes with the 450D and for the 50mm f/1.8 to see if that helps. Unfortunately it's been cloudy ever since. If you have Photoshop, Gradient XTerminator may be your best bet for getting rid of it in an existing image.

James

[Daniel-K]

quick play is cs3 with some noels actions to get rid of the LP great start carry on, if you camera is just on a static tripod you will get trailing unless you invest in a tracking system like astro track or you can make a barn door mount

[c3po]

.

[JamesF]

@James - the camera is 2nd hand, and the person I got it from says the sensor has slipped downward very slightly following the camera being dropped. This affects how I have to frame things as I have to aim the camera lower than

I see. In that case it might well be worth taking a longer exposure shot first to see how the framing looks.

James

[c3po]

Thanks for the guidance guys, much appreciated. I'm away with work until next weekend now, so I'll revisit this image then.

@James - the camera is 2nd hand, and the person I got it from says the sensor has slipped downward very slightly following the camera being dropped. This affects how I frame things as I have to aim the camera lower and take the picture - its harder than it sounds! But yes, I agree it could have done with better framing! Maybe I need an angled magnifying viewfinder add on (the a200 doesn't have live view) to help; do these even exist?

@Daniel - this was a test image to see what I could do with the camera. Regards tracking, I've started reading up on drift alignment and piggybacking which I'll try next. Then I'll look at getting a t-mount for the camera for DSO's ant the learning starts again. In fact, this while procedure had been a massive learning exercise for me as only when I was reading the DSS stacking tutorials and Photoshop adjustment guides did I realise I should have been shooting in RAW! So I'm guessing the JPEG compression hasn't helped my image any.

[c3po]

Yikes double reply - blame my silly Android phone! Don't know what happened there...

[JamesF]

It's not just the compression that's the issue with JPEG. Based on your settings for white balance and so on the camera will modify the JPEG image when it creates it, whereas the raw image is as close as you can get to "as it came off the sensor" which means you have complete control over how it is processed.

James

[GlassWalker]

"angle finders" certainly exist, although I'm not sure about the choices for Sony. e.g. I used to have a Canon one, that had two level magnification also.

[c3po]

Well, I just got a 'failed' notice from the Nova Astrometry solver...can anyone suggest why? looking at the image I can clearly see the "Coat Hangar" near the top right corner, also clearly visible are Sagitta and Vulpecula in the top right, Delphinus in the bottom right, the front legs of Pegasus on the far bottom left and finally the neck of Cygnus right along the top edge.

Would re-stacking with a better sigma ratio work to combat the trailing and clear up the blur?

[c3po]

i thought i'd have a 2nd go at stacking in DSS and then try the Astrometry solver again. Well, luck paid off and although there's less colour in the MW, the Nova astrometry server did it's job and gave me this:

stacked image(2nd attempt) - annotated by Si_3po, on Flickr