Home Forums Hunting & Shooting Ask The Gunwriters Adjustable objective lense

What if any are the advantages of have an adjustable objective lense.

Elimination of parallax.

And, to a lesser extent, being able to focus the image/reticle at shorter ranges--but that is also related to parallax.

Depends on the use, most centerfire scopes are set for 100 yards and work well over many distances. Rimfires set at 50 yards if fixed. I have found I prefer an AO or side focus now. Easier to get a clear focus and not dependent on distance to the target.

What I have is a Leupold vari x 2 3x9. Looking to put on either a 257 Roberts or 35 Whelan. It has different yardages on the outside of the objective lense. If I set at 100 is that ok?

The yardage markings in my experience are rather subjective. What you want is clear focused target. It might be the 100 yard mark and it maybe a bit more or less. Every scope and set of eyes are a bit different.

Yep, the yardage markings are not only VERY approximate, but parallax can also vary some with atmospheric conditions.

So, rather than craning my head around checking for parralax I should just set the side parralax/focus to the sharpest setting?

You can check for parallax error easy enough and find the actual setting on the adjustment by trial and error but without firing a shot of course.

I buy scopes with adjustable parallax ring these days. Only one has settings that are correct for my eye. The distance setting is always much greater than the actual distance on all my other adjustable scopes - shows a consistent trend for my eye.

Setting it at 100 is not a bad sort of an idea, but the way to do that has nothing to do with the markings on the scope. Start by setting the eyepiece focus first. You do that my aiming toward the sky, ideally in low light (where your pupil is more dilated and hence better able to pick when the reticle's focused). Adjust the eyepiece, looking away frequently, until the reticle is as dark and sharply focussed as you can get it.

Then, using your maximum magnification, aim at a target 100 yards away, and adjust the objective focus, again looking away frequently, until the target image is sharp. You can confirm that you have "dialled out" parallax at this distance by moving your head around behind the scope without moving the rifle (you need a steady rest for this) - parallax will show up as movement of the reticle with respect to the target. You need to adjust the objective until there's none of this movement. Once you have the objective adjusted such that there's no parallax the scope is parallax-free at 100, regardless of what the graduations might say on the AO.

For most of your hunting, especially at magnifications at the lower end of the scale, you can forget about it after that. You'd only really notice the difference in short-range precision match shooting, or perhaps at really long range, and even then it won't amount to much if you have a consistent eye position behind the scope.

Not necessarily - you may still need to adjust the focus. Both settings affect each other to some extent.

Yep, and the focus adjustment on the ocular lens can also help eliminate parallax. It doesn't have as much effect as side- or objecitve focus, but it can definitely help.

Love your John Steinbeck quote MD. E

Thanks, O!

Thank you everyone for all the helpful information. I'll put it all to use when I get it all together