Adjusting scopes for closer focus/parallax?

[Martin Luber]

Howdy

I have a Simmons 6-20 44 scope (japan) with a dot reticle that came on a used 22 rifle. I’m finding that it won’t adjust for parallax or focus at 50 feet. I’m wondering if anyone has been successful in moving the front lens out n any scope? Shouldn’t take much. Probably lose nitrogen seal and may not even be possible to do. Perhaps there are adapter lenses to bring it in? Thoughts? Thanks

[gc45]

Personally I never had much luck with Simmons scopes, being a Leopold and Zeiss guy. Parallax and focus can be a real challenge, tough at 50ft, especially using a 6x20. Don't know what you mean by "moving the lens out" but it sounds like a disassembly of the scope, and if so, doubt you want to do that for fear of ruining the scope. Maybe you are shooting an air rifle and if that is the case, I would talk to the guys in that business, see what they suggest. You might need a different scope and for air rifles only at that short range. My only Air gun has an older leupold VariX-III scope but I shoot it at 50yds where the parallax adjustment works very well for me. I have used a 12x scope as well, one have Parallax adjustment and at 15yds with the same air rifle. Hope you get some better answers than mine.
Good Luck

[Winger Ed.]

Unless you get a scope made for air rifles, you probably won't have much luck.
Regular rifle scopes I've seen have a minimum of 50 yards to be free of parallax.

[gloob]

I've only managed to adjust one kind of scope for distance/parallax. The kind where the objective is held in by a thin threaded aluminum ring/carrier. The entire ring screws into the front bell, and typically there are 2 tiny slots on the edges for a wrench. The hard part is making a wrench to barely clear the ID of the bell and it has to also be curved to clear the lens. Yes, IIRC screwing the objective out makes the focal distance shorter. Screwing it in makes it longer.

[Kestrel4k]

Easy if the front lockring isn't glued on; the adjustment doesn't break any seals or lose inert gas charging.
Went down to 15 yds for two of mine, others have been to 25 yds & back; never an issue.
Have done something like a dozen of my Leupolds; once you get the knack of it, it only take 5 minutes or so.
Leupold doesn't even notice or care when a user-adjusted scope goes back through their service center for other modifications.

[dverna]

Easy if the front lockring isn't glued on; the adjustment doesn't break any seals or lose inert gas charging.
Went down to 15 yds for two of mine, others have been to 25 yds & back; never an issue.
Have done something like a dozen of my Leupolds; once you get the knack of it, it only take 5 minutes or so.
Leupold doesn't even notice or care when a user-adjusted scope goes back through their service center for other modifications.

Now that is something I would never have thought as easy or even doable. Love this forum.

[Martin Luber]

Thanks! I plan to use the whole setup for rimfire SporterRifle, not air. I see the notches in the seating rings and can make a spanner to work them. I suspect there is a ring under the obj lens too or maybe the lens has its own ring mount that l can adjust? Yes the objective lens has to move downrange if you will . Springer type air rifles break standard scope reticles by the way. Something with how the piston and slams and bounces a bit .

[Kestrel4k]

Feel free to post pics of the front end; many is the time I've looked at the front of an older but well-made scope and thought; hmm should I ?
I confess to only doing my Leupolds, since I'm just not interested in messing about with other scopes much.

[uscra112]

The only Simmons I have is not adjustable. And it's parallax-free at about 40 feet. Why I haven't binned it I don't know.

[Nobade]

You can make any scope adjust up close by stopping down the front of it. Same concept as lengthening the depth of field on your camera by stopping down the lens. Years ago I made a screw on cover to fit common scopes with a half inch hole in it that made it easy to test them close. You can do the same thing with a paper cup with a hole punched in it or some electrical tape. Of course you lose a lot of light gathering so it only works in good light but you can focus down to the end of the barrel if you want. BTW, if anybody needs a high power scope that will work up close, say 20 feet or so, the Vortex Golden Eagle F class scope is amazing for that. I don't know why they made it able to do that but it can and you can easily shoot flies with your rifle if you want to.

[45_Colt]

Strap wrenches and a little heat (hair drier) usually does the trick to get the objective bell loose and off. Can then rotate the objective lens assembly to set the parallax/focus for the required distance.

I know this can be done on Leupold scopes (as Kestrel4k posted), and IIRC, Bushnell. Not sure about others except for Burris, which can not be easily adjusted.

Removing the objective bell doesn't release the inert/dry gas. So no harm, no foul. And just gently hand tighten the objective ring when re-installing it.

45_Colt

[gloob]

This thread gives me some hope to adjust some of my other scopes.

I assumed the ones with a screw cap on the end of the objective must have a second "nut" behind the lens to lock it in place, else how would they be calibrated at the factory? Seems a strange way to make a scope, relying on the focal distance ending up perfect when the cap locks down tight against the housing.

So's I took a closer look and the cap on the bell of the scope is just a cap. There's a lens carrier with the wrench slots underneath it.

[Kestrel4k]

Yes those two slots for the objective lens assembly are in most scopes, once you start looking for them.
And yes, they need to be able to be calibrated at the factory, so, ...

[popper]

Like nobade said, put a 'stop' in front. Won't hide much FOV and cheap.

[Willbird]

I did it years ago with a junk Bushnell Phantom where the lens came loose in the first place. IMHO moving the front lens in that instance changed the distance at which it focused. My dad had a couple Lyman Target Spot scopes and it was easy to work the Adjustable Objective on those and understand what was going on there. Some mfg used to sell a 50' adaptor to install onto a scope ?

https://www.sportsmans.com/hunting-g...pter/p/1700027

By the look of that one the situation is that you need to move the objective further away from the shooter, not something that can be achieved just by shifting the lens in the existing scope tube.

[popper]

Focus is to adjust the scope to see the reticle clearly. Parallax is to adjust the scope LOS to compensate for barrel (projectile) LOS. At close range, just aim LOWER. Problem solved. At factory loads in rifle, worst you get is an inch off.

[gloob]

Focus is to adjust the scope to see the reticle clearly. Parallax is to adjust the scope LOS to compensate for barrel (projectile) LOS. At close range, just aim LOWER. Problem solved. At factory loads in rifle, worst you get is an inch off.

Popper, I can't make heads or tails of your post.

Screwing the eyepiece in/out will adjust the focus of the reticle (on the most common type of scopes, which are second-focal plane).

As far as seeing the target clearly at any given distance, parallax and focus are basically synonymous. When the target is perfectly in focus, there will be no parallax error. (With an AO scope, you should adjust your focus/parallax on your highest magnification, if you have time, for the best accuracy.) Most rifle scopes are set for 100 yards, and this is close enough to perfect from maybe 50 yards out to infinity. But as you get closer, the focus/parallax gets increasingly finicky. The lens must be adjusted out in increasingly larger amounts for every step you get closer. On adjustable scopes, for instance, you have to turn the dial a way bigger amount to go from 10 yards to 5 yards, compared to adjusting it from 50 yards to 45.

And if you get way too close, you have to aim higher, not lower. That's due to the difference in bore axis and sight axis (I assume what you mean by LOS), which is not what parallax is about. The problem that occurs when focus/parallax is off is that the target and the crosshairs are only aligned when your eye is consistently and perfectly centered. If you try to shoot a non-AO rifle scope at 10 yards (and you ignore the blurry target), when you move your eye a mm off center to the right, the crosshairs will move more to the right than the target does (but a target that is 100 yards away will move exactly with the crosshairs). So your shots will not land on the crosshairs, even if you were to adjust or compensate for bore-sight axis or LOS. You could lock the rifle in a vice, and depending on how you look through the scope, the crosshairs will wander all over the target potentially causing misses that are inches off from where you expect, even though you're only 10 yards away! That's the problem with parallax error. It doesn't matter that much for most rifle shooting. It matters a lot if you are trying to shoot a mouse with a half inch kill zone at 15 yards away.

This is why airgun shooters don't use fixed objective rifle scopes for sub 50 yard shooting. Fixed objective airgun scopes (the kind that are packaged with rifle/scope combos) are typically fixed somewhere between 15 and 35 yards.

[Martin Luber]

I did it years ago with a junk Bushnell Phantom ….snip…

By the look of that one the situation is that you need to move the objective further away from the shooter, not something that can be achieved just by shifting the lens in the existing scope tube.

Wouldn’t shifting the obj lens out in the existing tube do exactly what you said? Thanks

[popper]

And if you get way too close, you have to aim higher, not lower.
If your scope (for example) is zero'd @100 yds and you shoot 50, the bullet will travel ABOVE the scope LOS, to the target. Parallax is by definition, the difference between barrel LOS and scope LOS.
As for focus, near target (reticle) needs to be in focus, the eye will accommodate far targets (depth of field).
For iron sights your focus is the front, peripheral will align it with the rear notch and depth of field takes care of the target.

[PopcornSutton]

Can I ask a question about these "stops". Are these an added on piece that fits in front of the objective lens and essentially just has a smaller hole to look through? I recall the early March scopes came with a screw in piece for the objective end that had about a half inch circle/hole in the middle. I don't believe it had anything to do with parallax, but focus issues in bright light.

I have an older Leupold straight 8 power scope I use for squirrel hunting, but the AO won't go closer than 25 yards. When you get a closer shot, it's blurry and parallax is obvious.