Results: Astrophotography with the D800E

Started Jul 20, 2012 | Discussions thread
RicksAstro
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Re: Quite the climb up the learning curve
In reply to JC1306, Jul 20, 2012

JC1306 wrote:

AnakChan wrote:

Tell ya what, it was challenging :D. polar alignment took me more than 1 hr (but I was working in the southern hemisphere, and at dusk, Octans was hard to find.

The other problem I had was my tripod was too light...I had the Gitzo 1541T, Acratech Ultimate Ball head. And I kept kicking the damn tripod :D. So that meant dismantling everything and polar alignment again.

Ha! I can one-up you on polar alignment. On the Astrotrac the polar scope is held in place magnetically. Nice idea but bad execution because the magnets are working upwards, against gravity. This means that if you slightly bump the tripod, the polar scope falls out. Or, if you bump it while polar-aligning, the scope will fall out, poke you in the eye and then fall to the ground. I have no idea why they didn't design it so that you slide it in from the other side so gravity helps keep it in place.

For my next session I'm going to give drift-aligning a try, it's supposedly pretty easy once you get the hang of it and gives better results .

Jarno
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Photos at http://jarno.smugmug.com

I never found the need to drift align, even doing very detailed deep sky work at long focal lengths. With low read noise cameras, I found it was better to do many shorter images rather than fewer longer ones. As long as you get the sky background well above the read noise, going much longer gives little benefit.

The more images you have, the better SW with Sigma type of combining works to throw away outlier noise and thermal noise. And actually some drift between the shots allows the Sigma combine to work even better, since the stars move compared to the fixed pattern (mostly thermal) sensor "noise".

And the shorter exposures allows you to not saturate the brighter stars, retaining their color much better, giving you an effectively expanded dynamic range through stacking (using floating point) many images. The stars themselves can be very beautiful and have rich colors from deep red to bright blue. But long exposures pegs the brightest ones at bland white.

It goes against many of the traditional thoughts I know, but I very seldom ever took dark frames, instead relying on more images (not wasting time on darks) and used SW signal analysis (Sigma combine and bad pixel mapping to remove the hottest pixels) to minimize noise.

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