the pro photographers that I spoke to said it was the way to go ,reasons given smaller lighter and cheaper also optically better than 16 mm and same resolution with less pics ,
Sorry - i don´t know which kind of "pro photographers" you know - but this is complete nonsense
10,5 shaved is a circular fisheye on FX - and a fullframe fisheye on DX.
That means: a circular fisheye on FX gives away a big part of the D800`s resolution due to the much smaller covering the frame.
You save ONE or TWO shots. That means: you save about 10 seconds of shooting-time. WOW
Using a 16mm Nikon fisheye you shoot 5+1=6 shots - the resolution is about 190 megapixels!
So: it´s just the other way around compared to what your "pro photographers" say:
1) the Nikon 2,8/16mm fisheye is an optically very, very good lens.
2) you don´t need to use it to it´s outer borders becaue it´s a fullframe fisheye: 180° diagonally.
3) A shaved 10,5mm on FX means to to exhaust it to the rim of the projected image. Approching the rim
of it´s projection the performance of EVERY lens in the world weakens drastically. Using the rim itself - that´s what you do by stitching such images - it´s defintely worse: massive loss of sharpness and tons of geometrical-/chromatical abberations.
1) you need to take ONE or TWO shots less. Yes.
2) this saves you about 10 - 15 seconds in shooting . . . but:
3) you loose MUCH resolution - because the image on the sensor is MUCH smaller being a circular projection. About 40% of the sensor is uncovered=black.
4) because of that the resolution of your final result is about half the size as it would be using a 16mm fullframe-fisheye on the D800 . . .
and that for saving just 10 or 15 seconds of shooting time??
Best regards to your "pro photographers" - maybe they´d be better off baking cookies, biking, fishing or whatever instead of being "pro photographers" . . .
(sorry - an irony i can´t refuse reading your lines)
btw.: the 10,5mm fisheye even isn´t relevantly cheaper than the 16mm fisheye!
Using a 10,5mm fisheye on a D800 is like driving a Porsche on third-hand tires . . .