Adam said:
Sorry Rik, that just doesn't make sense. Can you explain to me why the distance between your anchor point and your eye changes just because someone turns down the lights?
The one fixed thing in all of this is the relative position of your draw hand and eyeball. I have NEVER had to change the height of my peep when going from indoors to out. Yes, the height of my bowsight changes, and I change the extension too, but I only adjust the extension to correct a sight pictures that changes when I come indoors.
Incidentally, if you ask around you'll find many compound shooters will tell you their sight pictures changes depending on whether they are shooting in full sun or deep shade.
Adam
The light doesn't have anything to do with it...
Let us say the relationship between the peep and the reference point is fixed. The relationship between the eye and the reference point is fixed. The relationship between the eye and the target is fixed (for target shooting). The sight-block moves. So the angle at which your eye is looking past the string changes. If the sight-block moves less, then the angular change is less, so faster bow and carbon arrows will see less of an effect.
Similarly, smaller changes in distance will produce less sight-block movement.
A diagram shows it more clearly
(funny I've got drawing and diagramming software and it's
still quicker to draw it by hand and take a picture :sigh
If you don't want to move the peep, then the only way out is to alter another fixed relationship, say the reference-point/eye one. So in effect you change the position of your eye, by shifting your drawing hand (and as a result; the peep) in relation to it. This is okay (and unavoidable) for small changes - going down a distance on a FITA, for example. Depending on setup, the amount of change may not be great enough to be noticeable - a small fraction of an inch down.
Basically, you've got a straight line from your eye to the target and need to put the scope and the peep somewhere on this line. That's four points, two of which (eye and target) are more or less fixed in absolute terms. Of the other two, one can (has to) move - the scope. The last point (the peep) you get in line by fiddling with the angle at which the bow ends up.
There are a number of variables which would affect how much movement you'd see. The speed of the setup and sightmarks, I've already mentioned. The distance from the peep to your eye would also have and effect (closer = less movement).
This all ignores any effects (good or bad) due to light changes. I'd guess that lower light conditions would make it easier to find an angle at which you could see through the peep (less movement needed) as your pupils would dilate. But that's just a guess.
Any photographers out there care to comment?
Sorry for the essay...