View Full Version : p/a and ao ??

25-05-2004, 02:46 PM
iam about to buy a new scope and wonderd if anyone out there could tell me the difference between p/a and ao,which is the one that stops the reticle from being blurred? thanks

25-05-2004, 02:49 PM
PA = Parallax Adjustment, AO = Adustable Objective. They both make the picture come into focus.

Paul Hudson
25-05-2004, 02:51 PM
It's usually the eyebell adjustment that affects the clarity of the crosshairs.


25-05-2004, 02:54 PM
Agreed, I miss-read your post. The AO/PA will focus the subject while the EB brings the ret into focus.

25-05-2004, 02:54 PM
AO - Adjustable Objective.
PA - Parallax Adjustment.

So, AO is PA, but PA isn't neccessarily AO, because it could be Sidewheel!

Just to clear up confusion. ;)

Taff Williams
25-05-2004, 03:05 PM
I thought AO was "Aespherical Optics", a means of keeping more of the sight picture in focus towards the edge of the objective.

Open to criticism

Ogri the trog

26-05-2004, 08:26 PM
sorry fellas if I am being thick but I remember when PA was introduced and I understood it removed eye alignment error when set to the correct range - i.e. you could look through any part of the scope (within reason) and the shot would still hit the apparent middle of the crosshairs.

Using the PA for rangefinding through focussing is a later adaptation of the original purpose of PA which is therefore very different to AO.

As a non PA/AO scope owner someone tell me I am wrong??:confused: :confused:

Paul Hudson
26-05-2004, 08:33 PM
The Adjustable Objective lens is a means of Parallax Adjustment. It stands to reason that if you adjust the objective lens so that an object at a particular distance is in focus, then it is rangefinding no matter how you look at it...

Or have I missed your point?


26-05-2004, 08:45 PM
Er kinda missed it - you do answer a question that I had wether AO did the same thing as PA -thanks - my point though it still that this function can be used to ensure consistent accuracy coz if your eye is outta alignment but the PA/AO is set correctly then it doesn't matter - if however the PA/AO is not set correctly i.e. out of focus slighty and you don't have perfect eye alignment then the shot will go wide / high/low - irrespective of judging the range.

I don't see much written on here about this function of PA/AO- is is just that I am ignorant and everyone else takes this for granted (or have read the instructions with their scopes???)

Am interested as I need to buy a 'big' scope for my new PCP toy and would value alignment error minimisation more than range finding (which is just and added bonus of PA/AO for me)
Ta, Stu

Paul Hudson
27-05-2004, 06:35 AM
Ah... Stu, I'm one of those that takes it for granted.

Once the object is in focus (whether it be by adjusting the objective lens or twiddling the sidewheel) then the parallax error has been dialled out. It's a bonus that I can then read off the conveniently marked scale and it tells me the distance. Because the scope has been focused on the target, the crosshair appears to be "at" the target. The crosshair stays on the target no matter where my eye is in relation to the scope.

Of course, it's always better to be consistent with head position anyway :) .



27-05-2004, 08:24 AM
That's the winning answer - thanks mate -very interesting chat!