Until about 10 years ago the primary way to take a picture through a telescope was with a film based camera. Ideally this is done as a long exposure (5-90 minutes) with very sensitive film. This places extreme demands on the telescope's mount and drive. It requires that one manually check to see that the telescope is tracking it's target or use an electroninc autoguider for the same purpose. This is what Jeff Ball does to take his beautiful pictures of nebula in the Milky Way. The film camera (either 35mm or "medium" format) gives a big field of view.
Now one can use a CCD camera for a similar purpose. A CCD is up to 10 times as sensitive (maybe more I'm no expert) as film. This allows one to take much shorter exposures to image objects in deep space. But if you want color images you may have to take 3-4 sets of pictures through various filters as the high end CCD cameras are all black and white. Still one can take black and white snapshots of 10-70 seconds. But I was afraid that for me even this standard was to high to meet. Of note, the CCD camera has a much smaller field of view then the 35mm or medium format camera.
More recently using adapters from companies such as
Scopetronix . You can attach your
home digital camera to your favorite medium to low power eyepiece and take
pictures with that.
The picture of Jupiter to the left was taken by Jeff Ball with a Nikon Coolpix (900 something) through a 14mm Televue Radian with my 20" Obsession from Greasy Ridge, Ohio on 11-12-01. The scope was on a Tom Osypowski aluminum equatorial platform.
When you use an eyepiece in front of your camera's lens it yields greater magnification than when looking through that same eyepiece with your eye. This is good for taking pictures of planets and other small things as it magnifies them. Accurate polar alignment is important to keep the planet in the camera's field of view when imaging at high power. Digital cameras can shoot in color but have limited low light sensitivity so initially they were used to take pictures of the sun, moon and planets. More recently people are doing longer exposures and going after deep sky objects. This is the site of a person who has "tricked" his camera into taking 32 second exposures. He has added (stacked) some of these together and has produced some interesting views of deep space objects. The Digital_Astro group on Yahoo has much more detail on imaging with a digital camera for either long term or short exposures. With the Cannon D60 series cameras it is amazing what people are doing. This camera has low chip niose which is important for long term exposures.
The last method is the one that I chose, Video Astronomy. The idea is
that with a video camera you can just hook your camera into your telescope and
take pictures.
Well the average home video camera is kind of heavy so people either: place the
video camera on a tripod next to the eyepiece, use a special mount, use a
lighter camera such as a "web cam" or security camera (usually optimized for low
light situations), or use a specialized camera designed for astronomy such as
those sold by ADIRONDACK . A problem with
video cameras is that they are limited in their sensitivity to low light and
have been limited to images of the sun, moon, and planets. But now with its "Stellacam",
Adirondack may have created a bridge system between traditional video and CCD,
This black and white camera is more sensitive then most video cameras and it has
the ability to add up on the video chip up to 128 frames (which at 30 frames a
second is what a 4 second image?). This allows one to record some of the
brighter Deep Space Objects as well. With brighter objects like star clusters I
often take several images and average them to reduce the noise. With dimmer
objects like nebulae I have added up to 300 - 2 second frames which puts you out
at a 10 minute exposure!
Ah, with programs like Astrovideo the distinction between a CCD camera and a video camera begins to blur. However most video cameras and web cams are not cooled so chip noise buries (hides) the signal of dim objects and limits your ability to image them. This can be overcome to a degree by using "dark frame subtraction" to get rid of the noise. There are at least 2 companies who are making "CCD" cameras that are Peltier cooled (drops chip temp by 15 to 20 degrees C and reduces chip noise). The first is Starlight Express whose cameras based on color and B&W video chips are sold by AVA . These come from Europe and have many software programs dedicated to them. The new comer is SAC. They have been making peltier cooled camers in the USA for only a short time. They run their cameras with astrovideo.