Basic imaging requirements

For those interested in imaging and image processing with DSLR, CCD, webcam or film.

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Robin Scagell
Posts: 1061
Joined: Sat Jul 24, 2004 12:12 pm
Location: Flackwell Heath, Bucks, UK

Basic imaging requirements

Post by Robin Scagell »

In reponse to the question 'What do I need for basic imaging of the planets and some Messier objects through my 150 mm scope with HEQ5 mount', I wrote the following, which may be of use to others who are thinking of dipping their toes in the murky waters of imaging. It is very basic and others might like to write additional material to amplify particular aspects....

You'll need different cameras for planetary imaging and deep-sky imaging. Webcams are perfect for planetary imaging because of their ability to capture a video stream from which software can select the best images. But webcams are not in general very sensitive, so rather than try to adapt them as some people do, it's better to have a separate camera for deep-sky imaging.

At one time, people dipped their toes into the waters of webcam imaging using off-the-shelf webcams, notably the Philips ToUcam and its successors, but these are no longer available new and there are no simple replacements. You can get results of a sort using even the simplest webcam with its lens removed and taped to the eyepiece barrel, and for the outlay of about a fiver it's fun to do this and to get some useful experience in focusing and grabbing images. But the controllability of the cheap instruments is poor, while the more expensive ones don't have readily removable lenses and may be equally hard to control for astronomical use.

The only replacement for the Philips range is the Celestron NexImage (£134), which is the same camera and comes with 1¼-inch adapter. There are also the Meade Lunar and Planetary Imager (£86), and the Sky-Watcher Acuter (£60), which do not enjoy such good reputations.

You will, however, get better planetary results with DMK cameras, starting at about £300, or Lumerera Skynyx cameras, which cost at least double that though I don't know who distributes them in the UK.

For deep-sky imaging, you can start with any DSLR camera but for better results you really need a cooled CCD camera, which can cost rather more than most DSLRs. Atik, Artemis, Starlight Xpress and SBIG all have their adherents and I'm no expert so you'd have to take more advice. Ian King, of Ian King Imaging, would be a good person to ask, and he can also advise on software. There is also the Meade Deep Sky Imager (£356), which is uncooled and of limited value, though it can give tolerable results with its clunky software. But I'd recommend starting with a DSLR if you have one, to get experience.

You'll find, for example, that the drive of the HEQ5 isn't good enough as it stands for unguided long-exposure imaging, and by long-exposure I mean more than about 25 seconds. You need to correct for the periodic error, which then requires an eyepiece with crosswires and subsequent problems with retaining the corrections from one night to the next. Or you can use a separate guidescope and imaging device, which introduces problems of finding a guide star near the object you want to photograph.

With all cameras, either planetary or deep-sky, there are single-shot colour options, but the best results come from mono cameras plus a filter set. To get top results with all cameras, you have to get deeply involved, and pay a fair bit of money. It's best to stick to the objects that are easy to photograph wit the equipment you have, get good results with those then push the boundaries a little.