Originally posted by Franky2step when considering the SR algorithms, I think about the rule of thumb for shutter speed vs focal length, eg, 100mm lens, minimum shutter speed 1/100th. so.....I read somewhere that an aps-c dslr should use the 1.5x rule where 100mm lens needs 1/150th...just wondering about that
That is different from entering focal length for SR. The hand held speed is based upon acceptable sharpness of a print blown up to 8x10 inch from 35mm negative. If you consider using an APS C sensor, which crops the middle out of the frame, to get to 8x10 print you enlarge the image further, this is why the hand held speed needs to be increased for APS C sensors.
Using shake reduction if you have good technique will allow the rule of thumb to be pushed about 2-3 stops, although once, hand held, I shoot a 500 mm lens using SR at 1/40. That is about 4-1/2 stops slower than the "Rule"