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.

Bob

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.

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On Jul 4, 7:57*pm, 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.

Bob

Of course parallax helps us judge distances. But since it is not
needed from a the perspective of someone pulling the trigger at the
moment the trigger needs to be pulled it can be irritating. :-)
(Though it never bothered me when lining up my sight picture).

On my cameras my longer focal length lenses have relatively little
parallax than my shorter lenses because they focus so far out. But at
the same time the images they produce by default are relatively
"flat". The further the distance, the less parallax there is, and the
"flatter" the scene. So I'm wondering if there is a connection. :-)

I really need to get back into my Photography hobby to brush up on
what I used to know. :-)

One of my original goals was to machine a custom mount that would
allow the older FD lenses I have to be mounted on the newer digital
camera bodies.

Darren Harris
Staten Island, New York.