Do You Have a Scope with a Fast-Focus Eyepiece? This Inaccuracy Prevention Tip Might Prove Useful
I just read a post about someone's buying a new Sightron scope that has a fast-focus eyebell or eyepiece. That jogged my memory. What follows below the dotted line is a copy of a post I did that concerns similar scopes on our gone-but-not-forgotten Yellow Forum back in 2005, (with a few minor changes for the sake of clarity). I can't believe it's been that long.
Anyway, my old post concerns scopes that have a fast-focus eyepiece, and something that could be hurting your accuracy, even by a lot. The post is still as relevant as ever, because, if anything, there are even more of these scopes being used and produced today. If you remember reading this, you can skip it here. There's nothing new in the text below. But, if you DON'T remember reading it, it's worth 10 minutes of your time. I say that because many of us will sink beaucoup money in our shooting rigs, whether spring or PCP powered, and we can still be shooting ourselves in the foot as to accuracy if this fast-focus scope idiosyncrasy is overlooked.
I hope this helps someone get maximum accuracy out of their shooters, whether air-powered of powder-burning, because it applies to both. If you've been struggling with getting precision-type accuracy from a shooting arm in spite of trying everything you can think of, this tip may be the thing that finally tilts things in your favor--if the gun in question has a fast-focus scope sitting on the top of it.
Do you have a fast focus eyepiece on your scope? By that, I mean where there's no locking ring to hold the occular adjustment in place, so you can just turn that little black ring-piece holding the lens closest to your eye to focus the scope? If you do, better check something.
Bushnell Sportsmans, Banners, Legends, and many other scopes have the feature. It IS convenient to use, and just fine if you perform a simple little fix, but I'm posting this because I've seen problems with them so many times, that chances are yours is hurting your accuracy if you leave it as is.
Two problems that can hurt accuracy (both caused by no locking ring):
1. Each shot will tend to gradually move the eyepiece from your preferred setting, a little bit at a time, so it slowly and insidiously goes out of focus. (Springers and other recoiling arms are more prone to this item than PCP's because of the former's firing recoil or jolt). As the scope goes out of focus, your groups will tend to open up, even though the crosshairs are still fairly clear. By the time it's bad enough so DO you notice an obvious change in focus, you've probably wasted several shots, blaming 'who knows what', when it was totally scope-caused. Yes, you can put it back to its original correct setting, but if that's all you do the same process will just start all over again.
2. Without a lock nut, the lens can also tilt side-to-side or up-and-down at will, as the gun knocks the scope around when fired, or if you simply bump or touch the end of the eyepiece (PCP shooters take note). That can change the sight picture A LOT, so once again, accuracy will definitely suffer.
To easily demonstrate just how serious the #2 problem can be, set the gun and mounted scope in a vise, or on another stable rest, not in your hands. Aim the crosshairs at something, 10 yards away is plenty far enough, and keep your eye on the target. Now lightly grasp the fast focus piece, being careful not to move the gun, and gently tilt the eyepiece side to side inside the scope tube, or up and down. If your scope is like more than 50 % of them, you will see the crosshairs move all over the target! No bueno!
I sight in with tunes, and it took a little while with my first fast focus scope(s) to figure out why the groups were often so lousy, or would shift to a different POI after several shots. Sometimes I still forget at first as I attempt to sight in, then I remember after a minute or two.
The fix is simple. You need to lock that eyepiece in place. A nice way to do it, that can be easily changed:
Set the fast focus to your liking, (the darkest clearest crosshairs at the scope's high power setting), then put a piece of regular masking tape completely around the circumference of the tube and eyepiece, pressing it firmly into place so the fast focus part can't move. Don't like the beige tape? Me either. Use a black magic marker to color it black--it disappears (don't get the marker on the lens!). Some use black electrical tape because it's already black, but I don't like the gooey residue that often gets left behind if you remove the tape.
There are more permanent things you could use to hold the setting, like using RTV sealant, but I like the easily remove-able tape. It's useful if you sell the scope, or your eyesight changes.
Anyway, if you haven't noticed it before, this information may make you a better marksman. (And all of my customers who read here, will know why I have a funky piece of tape on their nice scope when I send it back to them!)
Safe and Happy Shooting!
Ed, the Airgun TuneMeister