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Looking good. I would go longer exposure and try wide open if lens aberrations permit. You hit a wall with earlier model cameras with their noise performance such that shots tend to be underexposed and ISO3200 is working it too hard. 20 seconds at F4 is not going to generate much signal.
If you try too much ISO most cameras can't take it and the image becomes noisy. Even if you use the newest and latest 30 seconds ISO6400 often looks overcooked and unnatural.
There's a limit to the look of images from any DSLR at high ISO. They tend to look underexposed, oversharpened, weak colour, overall - too stretched. Of course, its only a 30 second shot which in Astro CCD land would be a focus shot!
So that leaves you with the Vixen Polarie type approach where you can get 15 minutes or more exposure time with a good polar alignment and the high ISO noise performance limit ceases to be a problem. You shoot at lower ISO. Say 10 minutes at ISO400 F4 or 15 minutes ISO200 F4.
The results are chalk and cheese but its extra money for the mount and more work to accurately align it and more Photoshopping at the end.
Of course it adds a new problem in that trees etc become blurred. But that means careful selection of landscape in the shot and a separate short exposure higher ISO landscape series blended in using Photoshop.
Its another approach anyway.
An alternative if its a static scene would be take multiple shots and stack them. Quickly, as the Milky Way obviously moves.
Greg.
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