Hi Mark,
I'm assuming that the finder you currently have is an 8X50. It could be either the right angle or straight through styles, but both of these can be focused.
Here's a link to how to go about it.
Finderscopes can be a very personal thing. I've got two of these 8X50 finders, one of each style, and they are great, even in light polluted areas like where I live in Sydney's east, as they have enough light gathering grunt to overcome the urban lights to be able to follow a star map easily.
Many folks swear by Telrads. I swear at Telrads,
. Like I said, very personal. Telrads ARE great, don't get me wrong, and there are star charts made specifically for them to the scale of the target image they project.
I prefer the simple red dot/spot finder (rdf). These project a holographic dot into the lens of the finder which allows both eyes to be used and there is no significant parallax movement making eye position less critical. Most nights I just use my rdf, even from home.
Some folks even load a couple, if not more, finders onto their scopes, such as an rdf and an optical finder. The rdf does the gross pointing, and usually that's enough. The optical finder does the fine pointing, particularly in a light polluted sky when you're aiming at a star poor region of the sky. I've got three finders on my 17.5",
You can also find finders of larger and smaller aperture. Again this depends on what you're after. One of the three finders on my 17.5" is a 76mm reflector.
I hope this helps.
Mental.
