Choosing a guide scope or OAG

[kalasinman]

I've been using an OAG and have been ok with the issues that come with that choice, i.e. a very narrow FOV.

I recently bought a special lens for a 3x4 degree FOV with my DSLR and decided to get a dual mount rig from ADM so I could mount a 50mm f/3.5 guide scope.

While waiting for the ADM part to arrive, I tried using the guide scope with the 150/750 newt instead of the OAG. While I found the huge FOV to provide a wide choice of guide stars, I wasn't impressed with the accuracy of guiding, or the lack of it.

With the OAG I can achieve RMS of .5"-.8" with 1.5" only with bad seeing that yields poor images anyway. With the 50mm guide scope 1.5" RMS is typical  Not happy with that, as my imaging scale is around 1.3"

I reason that a guide scope with a FL greater than the 150mm+ of the guide scope and less than  the 750mm with the OAG, could yield enough FOV to yield better selection of guide stars and the narrower FOV than the short guide scope would mean a better guide pixel scale and thus more guiding accuracy.

Would the venerable ST80 be what I'm looking for? Low price and weight would be considerations as well. Thanks for any advise.-Jack