I sometimes get asked what is required to start off in astro-imaging without a telescope. The short answer is a camera and tripod - but of course it is a bit more complex than that. Any old camera will not do. Any old tripod will not do either.
I'll get to the camera details but let's review the tripod first, because this is simple but crucial. Its checklist of requirements are:
- Sturdy, to reduce vibrations.
- Collapsible, for easy transportation.
- Fine movement, to enable minimal aiming adjustments.
- Low centre of gravity, to reduce the risk of toppling when knocked.
You will be working in the dark, so you need to know where the knobs are and where the legs are (so you don't kick them). You also need to ensure the tripod never tips over, so I hang a weight on mine.
When I was out observing with MAS last month, a man was walking two dogs in the field - and they were not on leads. They both saw the red lights astronomers use, including the one I had hanging off the tripod, rushed towards us in the dark and bumped straight into my black tripod! With the heavy camera setup on top, it would have toppled over but for the attached weight.
The inconsiderate dog-walker then walked over and shone a white light around, destroying our night vision - but that's another story.
I've got three tripods. The first one is adjusted by loosening the thumb levers and was unsuitable for making the fine adjustments needed in astronomy. So I bought a trigger action tripod, which was an improvement but still not quite good enough. My third and best tripod so far has a long twist lock motion control arm and I am much more satisfied with it.
In a nutshell, don't spend hundreds or even thousands of dollars on camera equipment and mount them on a $30 tripod.
CAMERA AND LENS
My current setup: Canon 60D with Vixen Polarie sidereal motion tracker and polarmeter.
Astro-imaging has a number of mandatory requirements which point towards a relatively expensive digital single lens reflex (DSLR) type of camera. By all means try your luck with a point and shoot model but your results will be disappointing unless they satisfy the basic requirements:
- Remote trigger port, to eliminate camera shake when taking an image.
- Manual focus capability. Auto-focus will not work in the dark.
- Large size monitoring screen. Do not compromise with a small screen on the camera.
- Adjustable monitoring screen, because you will point the camera at some very awkward angles.
- "Live view", with digital zoom, to enable you to enlarge and focus manually on a bright object in real time.
- Automatic image review.
- Long exposure capability - a series of timed exposure options, at least up to thirty seconds.
- "Bulb" facility to take exposures longer than thirty seconds.
- Manual setting capability for shutter speed, f-stop and ISO. Auto selection will not give the desired results.
- Flash suppression.
- Image review with digital zoom.
To eliminate unwanted star trailing you will need to use a wide angle lens (I use a 10-24mm zoom focal length),) and the lens should have a wide aperture such as f/3.5. With a narrower field of view, f/2.8 or even f/2 or less if highly desirable (I use a 50mm f/1.4 lens). A manual setting ability is essential.
A focus indication scale on the lens is a great help - but simply setting the lens to infinity will not guarantee stars will be in focus.
A light pollution filter is a great tool to have but not essential for starting out.
Raw image capability is desirable when you progress to serious imaging.
You will require a remote shutter control attachment to eliminate vibration when shooting. You do need to buy one which works with your particular camera model. Mine was bought for an earlier model and sometimes interferes with some of the camera buttons.
An intervalometer is a very useful device for use as a shutter controller. You specify the exposure time, the number of images and the interval between each one.
My old Canon 300D, with intervalometer attached.
When observing with others in the field, a red filter is necessary on the monitor, to prevent white light annoying others.
A sidereal motion tracker is a helpful device which, once polar aligned, enables you to track objects for longer periods without star-trailing.
See the whole series, starting at number 1.
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