Rifle Scopes Understanding Scope Construction

[Bro Mo]

What are the optical pros and cons of different scope construction variables such as:

• Power: does a 3x multiple (ie. 4-12x) maintain optical quality better than a 6x multiple (ie. 2-12x) if everything else is equal?
• Objective: How does objective size effect optical quality?
• Length: Does a longer optic maintain optical quality easier than a short one?

All these things, I assume, make a short, high power factor, large objective scope more difficult/expensive to make than a long, low power factor, smaller objective scope?

If two scopes are the same price, is a long 5-15x42 going to be significantly different quality than a short 3-18x56?