D800E night sky shots

Started Mar 21, 2013 | Discussions thread
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Re: D800E night sky shots: Fabulous. ISO?
In reply to Jack Hogan, May 15, 2013

Hi Jack,

There are different approaches to nightscapes. I have been experimenting with different settings and have pretty much come to a conclusion.

Firstly DXO Mark rates D800E ISO at something like 2910. I looked up what they mean by that. They mean there is no appreciable drop in signal to noise ratio at that ISO. After that it falls and it affects image quality. So they say up to ISO2910 there is no image quality degradation.

Is that ISO1600 the point where gain kicks in referenced somewhere?

As far as the 2 different approaches goes you have 3 choices:

1. Camera fixed on a tripod and take the longest image you can at the widest aperture before chromatic aberration, coma affect the image. Use the highest ISO to get the brightest image before star elongation wrecks the image.

2. Mount the camera on a tracking mount and take a longer exposure but now the foreground blurs if its too long. So you either do a composite image where the foreground is layered afterwards (some don't like these shots as there are so many fakes on the net) or you compromise between blurred foreground, bright exposure, optimimum ISO and dynamic range, lowest noise, good colours, no chromatic aberration (or minimal) and no coma.

3. Take several images the same and stack them.

I have done all 3 approaches and worked out an optimum setting for each. For the fixed tripod ISO6400 which is still quite low noise (especially in winter) to my eye gives the overall better result as ISO3200 is too underexposed at F2.8 and 30 seconds at 14mm. You could take several and stack them as an 3rd alternative which is how deep sky telescope images are taken. You could use a lower ISO then and preserve more IQ. I did experiment with ISO12800 and whilst the images were brighter the drop in Dynamic Range was becoming noticeable and highlights were starting to blow out.

It also tends to vary depending on the lens as well. I have some tracked images that turned out very nicely at lower ISO as you suggest. ISO1600 is indeed a good ISO if you can track but too dim for 30 second shots.

You can also make a master dark frame and not use long exposure noise reduction to speed up the process.

Next time I have it out I'll try the multiple stacking with a master library dark approach and use it on a panorama so I can compare results.

Greg.

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