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I've read about and seen some rather sophisticated rigs for night sky photography that allow for ultra-long-exposure photos by counteracting the rotation of the sky by rotating the camera with it. The problem is mechanics for such rigs is rather complex, expensive and not entirely within reach of an amateur.

I was considering a different approach:

  • Set the camera on a firm tripod or whatever, leaving it motionlessly.
  • Use intervalometer in the camera firmware to take multiple photos of moderately long exposure, short enough that the stars don't blur into lines.
  • Save each as RAW so that the trace amounts of light captured in each of them don't get lost.
  • Either using more bright stars as markers, or even calculating the misalignment of the photos basing on movement of the sky and lens geometry composite the images in software, to obtain good images of the night sky.

Obviously I wouldn't get very far with high zoom images, as the field of vision would shift away long before I'd get enough light in for a good photo, but obtaining a photo of a fair section of the sky from a relatively wide angle lens should be doable.

Is such approach used or even viable? Is there such software "out there" already or would I need to write my own from scratch?

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Hubble folks use AstroDrizzle (drizzlepac.stsci.edu), which I know is designed to produce the highest possible quality results, but I know that it requires accurate pointing information. –  Donald.McLean Sep 30 '13 at 14:24
@SF, To me it sounds like you're wanting to stack multiple exposures into a single exposure, not create a mosaic? Is that correct? –  Luke Peterson Oct 10 '13 at 7:23

2 Answers 2

up vote 5 down vote accepted

What you are talking about is making a 'mosaic'. This technique is commonly used in astronomy to stitch together many images that are off-set from each other of some (apparently) large astronomical object (e.g., a star cluster or a nearby galaxy). In addition to covering a large field of view, making a mosaic generally also improves signal to noise where the images overlap.

One way to realign the images is to uses cross-correlation to find the optimal shift for consecutive images in order to align them. This can be done in common data analysis languages such as python (free), matlab or IDL (not free).

I have not used black-box software to do this, but here is a list of programs that might help: http://astronomyonline.org/AstronomySoftware.asp#CCD_Control_and_Imaging_Software:_

Hopefully some astrophotographers here can recommend some software.

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There are several ways to create mosaics. The most widely used by amateurs is probably Photoshop or GIMP. There are several tutorials on the web, and example of which is one on Astrophotography Tonight. Another good tutorial can be found on the Starizona web page. There is also a software called iMerge and another called Montage that are worth looking at.

There are also many panoramic image programs but they mostly work by distorting the images to make them fit. This may render nice photographs but they will of course not be geometrically correct.

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The problem with generic mosaic montage software is that it usually blurs/blends the images instead of summing them. Very dim objects remain very dim. Also, stitching 10 images in Gimp by hand is doable. Stitching 300 shot over 5 hours, one per minute - less so. –  SF. Sep 29 '13 at 23:17

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