Its amazing the things that can jump out at you at times Aragorn. Thats how I discovered my meade was out of collimation.
Before I put the hartman mask on the other night I defocused the star first and noticed the Secondary wasn't centred in the defocused image on the laptop, even though I had a quick check through an eyepiece earlier in the night. Its a lot easier I've found to look at the laptop screen and adjust rather than reach down to the opposite end of the scope while I look through the eyepiece. Plus I feel its more accurate as I have a larger image to work with when its "really" defocused (within reason
) and I can up the gain and still see it, whereas in the eyepiece its not so easy at times.