You can take astronomical pictures with almost any kind of
camera. You'll be able to image the Moon and planets and constellations with
just a camera on a tripod. If you have a telescope,
you'll be able to image the Moon, and even close-ups of craters on the Moon.
To photograph deep-sky objects like galaxies and nebulae, you really need
a telescope on an equatorial mount to track the stars so you can use the long
exposures required for these faint objects. You can use a computerized
altazimuth mount to photograph brighter deep-sky objects. But for serious
long-exposure deep-sky astrophotography you need a serious telescope !
Don’t be put off trying to take astronomical pictures if you
only have a small pocket digital camera –they can still capture images of stars
Ideally you need to have manual focus so you can manually set the focus to infinity. Pictures of constellations are possible and Moon pictures through a telescope.
It is even possible to use mobile phones – especially for lunar pictures and some reasonable images of the moon are possible. You will need an adaptor to hold the phone to the telescope and you will find similar problems to other small digital cameras.
So why are images less good with small cameras ? Resolution is often poor and noise is high. This is because the optics tend to be poorer with small cameras, especially when lens wide open. Also the sensor chips are small and are often noisy – especially in poor light, leading to grainy images. We’ve probably all noticed this with the small ‘pocket’ digital cameras in low light. But don’t be put off – you can still take some nice photos even with a small camera.
But modern digital SLR cameras can
overcome the problems with using smaller cameras. They have much larger sensor
chips and better optics.
In November 2008 I looked into buying a DSLR. I found that Canon cameras had low chip noise and were becoming popular with amateur astronomers.
I purchased a Canon 450D which has 12M pixels on a chip 22.2 x 14.8 mm.
If you want to take some really good astronomical images do consider purchasing a DSLR. Secondhand ones are available on EBay etc at a good price. A new entry level Canon 1100D costs around £270, less in USA ! But it is possible to get show good some images with small digital cameras.
For the moon you can probably use your
camera on ‘auto’. Except for the moon, most things in the sky are faint, so you
need to maximise the amount of light getting into the camera. 3 settings on your
camera influence this:-
- Exposure – the longer the better but …..
- Lens – open as wide as possible
- Iso setting – higher the more sensitive but…
Therefore ideally you need a camera that has a manual option that allows you to change these things.
For exposure, DSLRs have a ‘bulb’ setting
that allows any exposure. Many small digital cameras have a maximum exposure of
15 seconds, but this is long enough to get some good images. If you have a
self-timer delay or a remote release, use that to avoid camera shake. Use your
camera screen to frame your image.
Do consider using computer control, which helps a lot and gives you more control
over the camera and settings. Canon & Nikon cameras come with a useful programme.
But there are programmes available tailored for astronomical use. I use
Backyard EOS which will control the
camera, including focus, image acquisition automation, etc.
You also need to set the camera lens and sensitivity (iso setting). For all imaging, except the moon, use a manual setting and have the lens as wide open as possible. This will be the lowest ‘f’ ratio, maybe f2.8 etc. The camera Iso setting changes the sensitivity of the camera’s imaging chip. Use a high iso setting for high sensitivity, but there is a caution – increasing the iso setting also increases the camera noise. Noise makes the pictures look ‘grainy’. Try iso 800 or 1600 as a starter.
Then you need to set the camera focus. For
the moon, which is bright, you can usually rely on the camera autofocus. For
everything else you need to manually focus. So you need to check your camera
handbook and work out how to turn off the autofocus. You need to focus the camera on
maximum distance or infinity. Some cameras have a ‘mountain’ setting for this,
in which case try this. If not, point the camera at the horizon and focus
manually. It might help to try this in the daytime first. For DSLRs, turn off
autofocus and set the focus to infinity – again check this in the daytime first.
Do use your camera screen to help with focus and zoom in to check your images are
focussed by seeing if the stars are pin sharp. If not adjust slightly and try again
until they are- that's the advantage of digital