On 2010-07-04, Bob Engelhardt wrote:
Bob Engelhardt wrote:
I've been meaning to ask about that (red dot parallax). ... - I
thought that no-parallax was a main feature of red-dots. ...

I did find something about this: Aimpoint says that their red dot is
parallax free at 50 m & beyond. At less that that, there is parallax.
I.e., the dot needs to be held in the center of the sight. It's not at
all obvious to me why that should be, but there it is.

Because the focus point is beyond the dot, so there is a
difference as you shift the angle.

As an example -- for certain kinds of things, the old Nikon F
had among the various interchangeable focusing screens one which was
clear in the center with a fine '+' there. For lenses which had too
small an aperture (really long lenses, typically) you would have the
normal focusing screens darken instead of show focus splitting. But
with the clear and '+' screen, you put the camera on a tripod (needed
anyway with that long a lens) and move your eye from side to side as you
focus. If the focus is right on, there will be no motion between the
object being focused on and the '+'. If you are focused too close, the
'+' will move one way relative to the object, and if you are focused
beyond the subject, the '+' will move the other way.

So -- the Aimpoint is probably focused at something a little
beyond 50 m, and is close enough from 50 m out to infinity. The red dot
takes the place of the '+' in the Nikon focusing screen.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---