Lets put aside the quality of the glass for a second, as although this goes up by price, it does get to a point that even a mid range scope is well in excess of what we need for air guns at under 100m for arguments sake, and as everyone's eyes and opinions are different, it's actually hard to measure or quantify.

The big issue with scopes is more to do with adjustability, accuracy, repeatability, smoothness and precision of the optics/mechanics/reticle and overall function - and that's the bit most people overlook.

For back yard plinking a £35 scope is just fine, you may want to get a better one for hunting or low light conditions, and these then tend to add money to the mix Start to look at range finding and your into big mags and clearer optics, your now looking at mid priced scopes as a minimum, and the appropriate mounts will cost more than your hunting score for rabbits at 30m And we are not done yet, when you start to look at precision and repeatability then your looking at 1/8MOA adjustability, and it then needs to actually reflect these adjustments, so more money, and actual testing rather than just trying in the field. Your looking at box testing the scope by the click at you regular distances, so for BR as an example, your looking at 25m and every click representing just under 1mm, which is what you want for this type of shooting - but does you scope deliver, and are you and your set up good enough to test it in real life?

So many times when doing BR I'll adjust my scope by one click, and it does not move the POI at all, another click and it suddenly shifts 3mm Even an expensive scope does not guarantee this level of precision, but it should have a far better chance of doing it than a £25 Amazon special

So although brand, reputation, price and quality are good metrics to set you on the right path, the use of the scope plays a major part of the decision making process, along with price and the actual performance of the scope in all areas.

Let's just assume a really cheap scope will not perform like a dearer one - because they don't! But in saying that, it's possible to get a good mid priced scope which is better than a poorer high end scope - and that is where it gets difficult, because just like individual barrels perform differently with different pellets, the sum of the parts of the internals of a good scope do not always add up to the end result in an even manner, so trial and error are required to find a good one.

So in summary - not all scopes at any price point are equal, and although price is not a guarantee of a better scope, with a bit of research it can at least put you in the right ball park for a scope which is suitable for the purpose your buying it for