FT magnification & rangefinding

[brassgbits]

anybody got a clue as to the minimum magnification to range find to say 2 yards at 55 yrds. I have a Bushnell legend scope for HFT and I am pleased with the optics. So I was considering the 6-24x40 Elite with side wheel for FT.

Any comments

[Cocker (sp)]

To be honest, you would benefit from a little more mag.

Most scopes range well out to 45 yards, it defining the 45-55 that counts.

[Pavel]

You may get away with 24x mag but the norm is 32x. Of course, this depends a great deal on the quality of the scope. Burris are great at 32x but a Big Nikko, which I use, isn't ideal as it's more comfortable on 40x -50x.

Paul.

[Darren Petts]

24x is a little low and the sidewheel Bushnell isn't as good as the front AO version by some margin at rangefinding. As std they only focus down to 25 yds and after modding only come to 17 yds. Nice scope for hunting or HFT but relatively poor for FT. If you want bushnell quality optics then the front AO 8-32 is fine for FT and there are a couple in the sales section now.

[luddite]

I have a Schmidt and Bender 5-25x56 and while it will range-find flawlessly out to 50 yards it is not as good as a Burris 8-32x44 between 50-55. I would have to say that a minimum of 32x is required for precise range finding. However I do have an Air Logic 4-20x40 which will range-find almost as well as the Burris but these scopes are no longer available. So as a rule of thumb I would say 32 is usually the minimum required.

[RobF]

given similar quality lens specs and build, the rule is that the depth of field reduces with the ratio between mag and objective lens sizes...ie a 50mm scope on 50 mag ranges better than 25 mag...but given a smaller objective, say 40 you need less mag.

The limiting factor is the exit pupil which below 2mm (ish) starts to strain the eye or supply less light than it wants, which is why larger objective scopes benefit because they get more light in to start with.

Light transmission of the lenses is important because although the final exit pupil will be the same size on a 10-50x50 set to 50mag 10-40x40 (ie 1mm) the amount of light the 50 will gather to start with will be more so the image will be brighter which may help reduce eye strain and will provide better contrast which will help rangefinding.

Fixed mag scopes, having less lenses have better light transmission than zooms, given the same lens quality...but then better quality lenses in a zoom scope might perform better than a fixed mag of lesser quality...same is true of two different zoom scopes, even though one might have a worse zoom to lens ratio, the lens quality might deliver better results...and lens quality can even vary within the same make.

i'd say 25 mag is too low for most scopes...i haven't tried the 25 mag s&b...and the only 32 i have tried is a burris...but generally speaking you want as high a mag as possible and i'd say beyond 35 is a good start for a rule of thumb (exceptions prving the rule ), with the biggest objective, with the best lenses...given that most scopes have deficiencies in one way or another, and perhaps other problems (like not focusing below a range etc...) you can see that it's not such an exact science. A case of trying different scopes and seeing how they perform for you is probably the best route, rather than buying by numbers.

There's a thread in this forum about the usual FT scope suspects.

[Nick322]

Is there already more information about the rangefinding quality of the MTC viper 8-32x60 (certainly around 50 yards)?

Nico