Equipment

Buying a Camera for Astrophotography

 
Telescopes
Cameras
Eyepieces

There may come a time when you want to start taking pictures of what you see with your telescope. There are many ways to do this (see Astrophotography), some easier than others. Whatever you do, you'll need a camera of some kind.

Film or Digital?

In general, film is better for astrophotography. At the moment, digital camera technology doesn't allow long exposures (greater than about 30s) because the heat generated causes interference and disrupts the components (I think I've seen it done with some kind of cooling mechanism, but that goes way beyond my experience and the scope of this article!) Film can be left to absorb light for hours, which lends itself to the low-light context of astrophotography.

That is not to say, however, that there is no place for the digital camera in astrophotography. Brighter objects can be easily photographed with a digital camera, and in fact lends itself to the beginner more than film, as it has the considerable advantage that you can see the picture immediately after the picture has been taken. This helps you to learn the technique much quicker as you don't have to wait for your film to come back from the lab to see what does and doesn't work. Realistically, the beginner is limited to the afocal method with a digital camera, which means simply placing the camera up to the eyepiece and taking the picture. However, excellent results can be acheived with this method, subjects such as the Moon and Planets and some of the brighter clusters (harder) are good for digital cameras.

With film, however, long exposures can be taken, this includes star trails and piggyback photography, both of which can yield excellent results even for the beginner. Also an SLR with a removeable lens can be attached directly to the camera for the prime focus and eyepiece projection methods.

Digital

  • The more 'pixels' the better. A digital picture is made up of millions of different-color pixels (picture elements) to approximate the image. Obviously, the more pixels the camera has the sharper your image will be. Remember though, the more pixels, the bigger the file size will be and thus the less pictures you can store on a particular-sized memory.
  • Make sure it has the ability to let you choose the shutter speed. The camera is not designed to operate under the low light situation of astrophotography, so will not be able to correctly set it'd own settings. You'll have to set the shutter speed yourself.
  • Most should have it, but make sure it's got a 'timer' function. Often, presssing the button to take the picture is impossible, as you vibrate the camera in doing so and ruin the shot. A timer means that you can press the button then steady the camera ready for the shot.
  • Zoom is helpful. Don't be fooled if the advert promises fantastic zoom capabilities- this is digital zoom which reduces image quality drastically (all it does is crop the image and magnify the remaining part, meaning that less pixels are being used and therefore reduces the quality). Optical zoom is 'real' zoom, having no effect on the image quality. This is typically up to half the advertised digital zoom, but sometimes it has none at all, so make sure you check.
  • Battery life: Digital cameras are notorious power hogs, often draining a set of batteries in an hour or two. It is very frustrating just when you've finally lined up a perfect shot for the batteries suddenly to die.
  • For more ambitious photographs, such as the planets or close-ups of individual moon craters, holding the camera in your hand becomes impossible due to the vibrations. A tripod or some such support is worth considering here. Scopetronix (I'm sure there are others as well if you look around) do a handy little device which attaches your digital camera to the scope directly, meaning you don't have to touch the camera and, if your scope has an auto-guider it means you can use that to keep the object in view. Depending on it's accuracy you may be able to try longer exposures of 15-30 seconds. If you plan on doing a lot of digital camera photography then it's worth considering.

Please note I am talking about ordinary high-street digital cameras and not CCD's, these are specifically designed for telescopes and slot into your eyepiece. I would not recommend this for beginners- start off with the much simpler methods before you start to spend a lot of money. If you do require information on these, Al Kelly's CCD site is very good.

SLR

For most astrophotography you need an SLR camera. 'SLR' stands for single lens reflex camera. It has three major advantages over other types of camera:

  • What you see threough the viewfinder is exactly what will be focussed onto the film- you are actually looking through the lens. With other cameras you look through a viewfinder just above the lens. This is essential if you mean to attach your camera to a telescope in any way.
  • Most SLR's have removable lenses, meaning that they can be attached to a telescope, using the scope's optics instead of a lens.
  • They let you take full creative control of the shot, and allow long exposures.

SLR's come in may shapes and forms, from the modern all-singing, all-dancing models to 1970's mechanical cameras. There are lot's of them around, and the older models can often be picked up for a good price. You don't need much from the camera for astrophotography, in fact, it could be said that less features it has, the better. The problem with newer cameras is that they have an electronic shutter, which drains the batteries very quickly. I have one of these (I bought it for ordimary photography as well) and you really do pay for it in batteries, getting only about 2-3hrs exposure out of it (ordinarily this would take hundreds of thousands of photos, with hour-long exposures in astrophotography they go very quickly.) So if you're looking for one now, get an old, mechanical one, they're cheaper and you'll save a lot on batteries.

Things you need from your SLR:

  • Get an older mechanical one!
  • They all should, but just make sure you can manually set the shutter speed, and that it has a 'B' or 'BULB' setting
  • Make sure that there is a cable release available for it, you'll need one of these for most astrophotography.
  • If you plan on coupling it to you're telescope in any way, make sure there is a T-ring available for it. It's not the end of the world if there isn't as there are ways round it such as universal camera adapters, but it does make things simpler.

That's it really, you don't even need a meter as these don't work in such low light anyway. In fact, it's worth looking out for good cameras with broken meters selling at a reduced price.

Accessories

Another of the great thing about SLR's is the availability of hundreds of accessories for them. There are some camera accessories that are almost essential:

  • Cable Release. This means that you don't have to touch the camera to take the picture, and you can lock the shutter open to do long-exposures. If you do have an electronic SLR this will be an electrical wire, and you'll have to look up the right one for your model (and pay a lot for it!). If you have a mechanical one, it'll probably connect to the release button, and I think they're all pretty standard, and can be bought from any photographic shop.
  • T-ring. A T-ring connects to you camera's lens fitting and has a standard thread on the other side to fit to any telescope adapter which connects to your eyepiece holder (there are lot's of telescope adapters, but they fit all T-rings and most eyepiece holders.) There are many different fittings, the two main types being bayonet (line up and quick twist like a light bulb) or screw-fit (screw in like, well, a screw!). You have to get the right one for you're camera's fitting. If you're not sure take it to a photographic shop and they'll tell you. Usually you can buy a t-ring for you camera's manufacturer that will fit most of their cameras (as an example heres one for Minolta cameras). If there is no T-ring available for you're camera, there still ways to connect to a telescope, there are universal camera adapters availiable (try Scopetronix)
  • Tripod. A useful thing all round really, keeps camera still, points it in any direction. Useful.