SleazyRider
Member
I've been eye-ballin' a Nikon Buckmaster scope with "side focus" and it got me to wondering: How does focus differ from adjustable objective (AO), or are they synonymous? In advance, I appreciate the help!
Focus/adjustable objective: what's the diff?
- Thread starter SleazyRider
- Start date
- Status
short version, AO (rotating a ring around the big end of the scope) is very slightly superior optically, but practically impossible to do from behind the scope. So for tactical/practical shooters, the side focus (usually a knob on left side near elevation and windage knobs) is much more ergonomic and the way to go. For benchrest shooters, it's AO. AO is also usually a bit cheaper, but not as cheap as a fixed parallax where there it is not adjustable at all.
SleazyRider
Member
Thanks for the reply. Is the fixed parallax out of focus at ranges other than the one at which it is set?
Jim Watson
Member
Not enough to matter except for a dedicated target outfit.
Understand, focus is not the main purpose of the AO or side knob, it is a parallax adjustment. Twiddle the ring or knob until you can move your head behind the ocular lens and the crosshairs not move against the target. Then you have the target and reticle in the same focal plane and a minimum of aiming error as you shift position.
I say "twiddle." The graduations on the AO ring are not very accurate. I have one scope that reads 77 when correct at 100. And the side knobs are so coarse that many (like my Leupold) are not graduated at all.
Understand, focus is not the main purpose of the AO or side knob, it is a parallax adjustment. Twiddle the ring or knob until you can move your head behind the ocular lens and the crosshairs not move against the target. Then you have the target and reticle in the same focal plane and a minimum of aiming error as you shift position.
I say "twiddle." The graduations on the AO ring are not very accurate. I have one scope that reads 77 when correct at 100. And the side knobs are so coarse that many (like my Leupold) are not graduated at all.
Worth saying again.
And, as posted, the side parallax can be adjusted without moving from the shooting position.
For someone who will set up at a certain yardage and not move, there is no advantage to the side AO, and a front OA adjustment is as good or better as far as ease of adjustment.
Outlaw Man
Member
Excellent replies here. About all I can add is that an AO might add enough to your scope diameter at the objective to require higher rings. It's such a small difference it rarely matters, but on the right scope and the right rifle (or maybe it's" wrong" scope and rifle), you might eat up all your clearance.
SleazyRider
Member
Many moons ago I overheard my fifth grade teacher telling another teacher that I was the "slowest study she's ever seen," so I thank you for all your patient replies, which I've read over and over again until I finally got it. Thank you all!
- Status