Originally Posted by what barn door
Thanks Brian, I have some cheap Hawke scopes lying around that insist on moving zero every dozen or so shots, I will mess about with one then cut it up. Incidently I did cut a cheap scope up some months ago and was appalled to see a very flimsy leaf spring in situ, no wonder that damn thing was unreliable with a boinger.
I think you'd be shocked if you saw inside even some of the more expensive scopes out there. The Leup comps have plastic cogs for the parallax adjustment wheel apparently. I'm not rich enough to cut up a Leupold to find out how true that is, but that's what I've been told. (Pete Dutton told me)
I think you can get lucky with a scope and find that centring the turrets gives you a reasonable rough centre, but more often than not I've found that it's quite a bit off and you're much better off just using the mirror trick. It takes seconds and if it's good enough for the Leupold factory, it's good enough for me.
There's a few scope cutaway photo's on this very forum - a Weaver and a Nightforce
For those who can't be bothered to click on the "Tips, Tricks and Tutorials" sub forum and then click on the very first sticky post at the top of the forum... here's a link to it you can just click : >> CLICK HERE <<
Going back to what I said previously about how much difference Optically Centring a scope makes.. I think that if you're not aware of what the internals of a scope look like and operate, it's easy to fall into the trap of thinking that turning the turret from one extent to the other moves the internal lenses to such an extent that you're now looking through the outer edges of some of the internal lenses. If you look at the cutaways though you'll see there's not actually a huge amount of movement going on internally. What you're actually doing is changing the angle of the lens at the front of the erector tube to refract the light in a slightly different direction. So although it's true that you're probably not getting the absolute best possible sight picture if your scope isn't centred, the difference in quality isn't likely to be noticeable to the human eye.
I do believe there is a consequence of not optically centring though, and so far no one has mentioned it in this thread - and that's the exit angle of light at the ocular lens. I'll be honest and say that thinking about it it seems quite obvious now, but I didn't twig onto it until I fixed a camera to the end of a scope to take some photos. I found that if the scope wasn't optically centred, I didn't get a clear picture round the edges of the sight picture with the camera mounted directly behind the ocular lens, and could only get one if I twisted the camera slightly in it's mounting bracket. When I get the time (and can be bothered) I'll do some proper investigation into it and share my findings.