In the old days SLRs used a mirror to view thru the viewfinder. This mirror flipped up out the way when you took an image (same as a DSLR does today). The Mirror "slap up" just prior to the shutter opening sometimes caused vibrations and blurred images well some people thought this as an issue. This depended upon a lot of factors.
Of course DSLRs have the a mirror as well but we mainly use "liveview" focus by locking the mirror up and allowing light onto the sensor. However if you leave it down you can also focus in the old traditional way...thru the viewfinder. But this is tedious cumbersome and not as accurate. With live view you can enlarge the image and output it to a lappy for more refined focus.
DSLR Mirror slap can induce some vibrations which may blur the image...so sometimes mirror lock feature is used with a vibration delay...which can be set in APT to delay the shutter actuation.
However...full mirror lock operation in APT (and backyard EOS) is not available via the USB lead for digic 3 cameras ie; 450D/1000D (you need an extra serial lead)...read
APT instructions on this. Digic 4 cameras can do all this via the one USB lead.
Anti vibration is really not required as the camera is attached to a scope; mount all which add mass and dampen vibrations. Also the images we are after are dim so any vibration will not generally be seen. APT is controls the camera "in virtual mode"...using a few software tricks and with this you should, for a digic3 camera, set mirror lock off in camera custom functions and APT anti vibration pause to zero.
If you do not do this you can get some really funny d
ark patches and light leakage into the sensor. (the link may not work for all as it's part of the APT yahoo group) or my trials on this...
here.
Finally the view finder also has a reverse path to light to travel and this can also cause light leakage on to the sensor issues. So cover the DSLR viewfinder with the supplied rubber patch. Also turn the rear liveview screen off when taking images as this can cause "amp glow" like hot spots on the sensor (heat).
Sorry for the long read but hope this helps.
I saw you image as thought straight away..." a mirror lock/anti vibration pause" issue.
