How to Take Deep-Sky Astrophotographs

"How to Take Deep-Sky Astrophotographs"," However, this does require the acquisition of extra equipment and skills.
 Added to this, an eyepiece with crosshairs will be needed for guiding the telescope.
 Also, any tiny errors in polar alignment will need to be counteracted in the north-to-south direction.
 When piggybacking with a medium-power telephoto lens attached to the camera, precision guidance is not essential - just keep the guide star somewhere close to the crosshairs.
 Guiding corrections are best delayed rather than for them to be made suddenly or irregularly.
 But how is the telescope guided when it is being used to take a photograph through?

One method is to employ a separate guidescope that has a high enough magnification up to x 500, which is really far too high for proper observing.
 This is because the mirror in catadioptric telescopes tends to move slowly as the telescope tilts while following a star.


One way to get around this problem is to use an off-axis guider.
 The difficulty with using an off-axis guider is locating a suitable guide star- more often than not there is no nearby star brighter than magnitude 12 in the appropriate place.


Because guiding is a tedious chore, most CCD cameras can actually do it for you.
 Autoguiders replace the crosshair eyepiece.
 Or even by putting a single CCD to double use: to track and record at the same time.
 Then the two images are combined, and so on over and over again.