Scope help

[FTRshooter]

Fred, that no longer computes.

You said: 'If a scope with fixed parallax adjustment was set for zero error at 200 yards, then the parallax error would be on opposite sides of the set plane but equal size at 300 or 100 yards and also equal but twice that size at 400 or 50 yards.'

Using you power of two progression,I believe that is analogous to a logarithmic scale, base 2,) setting up for zero error at 200 yards would mean the parallax error would be the same magnitude, simply opposite at 100 and 400. 100 yards is half the distance of 200 and 200 is half the distance of 400.) It would then be that at 50 yards,one quarter the distance from 200), the magnitude of the error would be the same as at 800 yards,of which 200 is one quarter.)

Certainly on my AOs, the difference between 300 and 1000 yards setting is minuscule compared to the difference between 100 and 300. Closer than that is an even digger displacement.

Help me understand your numbers, please.

 

[Fred Bohl]

FTRshooter

Sorry to have confused the issue so badly. Let me try to clarify what I was trying to say.

It would be possible to design a scope for zero error at 200 yards, so that the parallax error would be on opposite sides of the set plane but equal size at 300 or 100 yards and also equal but twice that size at 400 or 50 yards.

However almost all scopes are designed as afocal systems so that they are parallax free at infinity and behave as your typical AO shows. For this design if the objective position is factory set for 0 offset of the image plane,zero parallax error) with the target at 200 yard range for an example the offset for a particular scope would be +4 at 100 yard range,+ is toward the shooter and value is arbitrary to show relative magnitude), +8 at 50 yard range, but -4 at 400 yard range and and -8 at 800 yards as you describe. Note that the actual offset values are dependent on the design,i.e. focal length of the objective).

I hope this corrects my poor prior explanation and has not be too confusing or wasted too much of your time.

Note that the maximum aiming error that a particular parallax offset error will produce is dependent on several other design choices/compromises. These include but are not limited to: AO or side parallax adjustment, first or second focal plane reticle location, magnification,fixed or variable) and eyepiece type.

 

[FTRshooter]

Fred, thank you for the clarification. With your new set of numbers, everything now falls neatly into place.