Parallax adjustment - at what mag. does it become important?

N

NativeCraft

New member
At what magnification (in a rifle scope) does having an adjustable objective become important? I'm trying to decide on a new scope in the 3-9 or 4.5-14 power range.

Will "lack" of a parallax adjustment possibly allow more light transmission in low-light situations?
 
Usually at 12x and up it becomes relevant. It has nothing to do with light transmission. Light transmission is strictly the result of the objective lens size and the quality of the optics internally.
 
But wouldn't an adjustable objective or some other method of adjustment require an extra lense or some sort of mechanism that would reduce light transmission a bit?
 
At close range using high mag you will be able to focus better Generally most fixed power scopes are set at 500 yds. At long range you will be able to focus on your target better. The better you can see, the better you can shoot. I have adj obj or side focus on all of my scopes.
 
There isn't a "right' answer to your question. It depends a great deal on your eye position in relation to the axis of the scope.

When you look through a scope, the objective lens projects an upside down/reversed image behind the objective (the 1st image plane).

The next lens or set of lenses (the erector cell) takes that image and flips it again so it's right side up, projecting it a little further down the scope (2nd image plane).

The next set of lenses (the zoom group) adjusts the image to the desired size, and projects it a little further down the tube (the 3rd image plane).

The 3rd image plane is where the reticle is, and the eyepiece focuses on the reticle and the image at the same time (when there's no parallax).

If the image isn't focused PRECISELY in the same plane as the reticle, you have parallax. If your eye is perfectly aligned and centered with the axis of the scope tube, it won't make any difference to you in most circumstances, but if your eye is off at all, it can cause you to miss.

Whatever error (parallax) exists in the image projected by the objective lens is multiplied by the power of the scope. In other words, if the objective image is 1/10 mm off (negligible), with a 36X scope it will be focused 3.6 mm behind the reticle, and that is a HUGE amount.

Parallax is corrected by moving the lenses forward or back, so AO has no affect on light transmission.

One thing you should be aware of with the side adjusting scopes is that you should always adjust them down. Take the adjustment to infinity and then back it down, i.e. you can adjust from 600YDs down to 200YDs no problem, but when adjusting from 200YDs to 600, you want to take it all the way up to infinity and then come back down to 600YDs.
 
"One thing you should be aware of with the side adjusting scopes is that you should always adjust them down. Take the adjustment to infinity and then back it down, i.e. you can adjust from 600YDs down to 200YDs no problem, but when adjusting from 200YDs to 600, you want to take it all the way up to infinity and then come back down to 600YDs."
nmleon, could you explain the reasoning behind this?
thanx
RR
 
Quote:
"One thing you should be aware of with the side adjusting scopes is that you should always adjust them down. Take the adjustment to infinity and then back it down, i.e. you can adjust from 600YDs down to 200YDs no problem, but when adjusting from 200YDs to 600, you want to take it all the way up to infinity and then come back down to 600YDs."
nmleon, could you explain the reasoning behind this?
thanx
RR



It is because of the "lash" or play in the system that moves the lens.

If you go from 200 to 600, the dial moveds the optics back towards the shooter, and recoil causes the lenses to be pushed forwards because of the slop.

But if you go from infinity to whatever range you need, the lens group is forward against the fork, so recoil just keeps it there.

So when using a side focus/parallax and going from a close range to a further one, go to the infinity stop, and then dial back (if more than one shot is needed).

.
 


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