I think you may find that it may be hard to get decent images with a DSLR on an ETX 90
You may need to get a lightweight camera instead..unless the gears have been replaced, in the past it was always hard to use a heavy DSLR ..the mount couldn't handle the weight
Go to mike weasner 's site for examples of images with an ETX 90
http://www.weasner.com/etx/menu.html