Forgive me if this has all been answered before ....
I'm calculating the magnification I would get with a TeleVue 2x 1.25" Barlow.
Given the backfocus distance with a Canon 600d fitted with T-ring is 55mm from sensor to front flange of T-ring, then if the front flange of the T-ring mates up to the top surface of the Barlow (I think that's right), then it looks to me like the the magnification factor will be 2.8x. going from TeleVue's chart below.
Does that sound right or do I have one of the measurements wrong?
http://www.bintel.com.au/ckfinder/us...erIncrease.jpg
