Modern DSLRs can be used for astrophotography with varying degrees of success. One issue which affects them all, however, is the fact that the camera sensors are sensitive to infra-red and this is a problem for normal photography. To counter this the manufacturers typically include a filter in front of the sensor which cuts out infra-red and the very deep red end of the visible spectrum. These filters have the dual benefit of protecting the sensor and, in recent models, it is this filter which is shaken ultrasonically to help remove dust.
The trouble is that for deep sky astrophotography that filter also cuts out very useful light including hydrogen alpha emission lines in nebulae. Here are two shots (courtesy of Hutech) which illustrate the issue (standard filter on the left and modified filter on the right).
No dark frames or flat field frames applied
As implied by the source of the images above, one company that has addressed the problem and offers modified DSLRs is Hutech
. They have just released an EOS 40D with a with Type Ib astronomical filter and are due to release an EOS 40D with a clear wideband multi-coated filter in the next few weeks. The product announcement page is here
. The price is around $1800 which isn't too much of a premium to pay if you need the functionality. In my view a modified 40D with it's remote live view and focus capabilities is the best of the DSLR pick for astrophotography. Such a camera can also be used for normal photography provided you add a specially designed filter between the lens and body but doing so prevents use of EF-S lenses.
Sorry if this sounds like an advert. In a way it is but I am not aware of another company which modifies cameras in this way so it isn't as though this post is putting other companies at a disadvantage. However, if anyone else does know of such a firm please let us all know and I'll don the sackcloth and ashes!