Thanks Bernard. it does occur to me that most shots with the 70-200 or even 300 mm. lenses that are to be stitched are at near infinity anyway (if for no other reason than depth of field) and stitching should be relatively painless even with a bit of positioning error - as long as it isn't huge - with the lens collar on as I move the camera from horizontal up for the stitch, the angle is about 20 degrees without any overlap so say 15 degrees. With the centre of the lens a good 6 inches above the centre of the ball head, this amounts to approx. 1.5 inches (gee, this is the first time I have used a trig calculation since university (say 38 years) (guess, that education wasn't wasted after all).
OK so 1.5 inches back or forward if the subject is 100 feet away (with the 70 mm. lens), then the image size changes by1.5/(100*12 inches)=.00125. This ratio multiplied by approx. 1500 pixels from centre to edge of the narrow side of the sensor, gives the pixel error at the corner assuming you line up the middle of the two images stacked one above the other - this amounts to 1500*.00125=2 pixels.
That is, at 100 feet with a 70 mm. lens tilted up to do a second row of images, the error induced by not using a 3D pan head is two pixels on the far left, two on the far right, zero in the centre. Of course, you could angle the camera up then slide the camera forward 1.5 inches and reduce that pixel error to negligeable. Guess I won't be hanging my 70-200 off the 3D pan head, I can save it for stitches with wider lighter lenses.
