Another try with Astrotrac

[Scubapauly]

HI Folks

I managed to get out into the desert last night for a play with the Astrotrac. I was using Nikon D7000 with Sigma 17-50mm F2.8 lens.

I shot 20 x 50 sec images at F4 ISO 800. Also 6 Black frames same settings.

The images were stacked in DSS and the result once stretched is below.

But if I take one of the RAW files and process in PS I seem to get a much better image every time.

It was only around 8:30 in the evening and the Milky Way hadn't quite broken the southern skies so I wasn't expecting anything amazing. I just thought it would have been slightly better than I got.

The skies here are so clear and bright that really long exposures blow out the sky. Is this still a problem when using black frames???

I am trying to get things right using a wide lens before playing with the 70-200mm and 2x extender.

Paul

[StuartJPP]

Hi Paul,

Is 20:30 late enough for it to be properly dark where you are/were i.e. past astronomical twilight? There seems to be quite a gradient present.

With regards to the images, I think that the 1st (stacked one) is less noisy than the single frame image and the colour seems better. Was the 1st image in the sequence similar to the last image or did they progressively get darker as the session went on?

The ground in the 1st one will be out of focus because it is moving with respect to the stars (not sure if that is what you mean by the single shot being a better image).

Additionally you seem to have some dust bunnies (sensor dust) which are visible on the bottom middle of the image, this can be eliminated by the use of flats.

Looks great where you are, lots of potential.

[Scubapauly]

I think you nailed it. I don't think it was dark enough.

I expected the ground to look fuzzy in the stacked, as you say rotation etc.

Dust is a nightmare here especially out in the desert. Quick lens changes or stay with what you've got!!! Good job I bought a cleaning kit with me this shift.

Thanks for the reply.