PF-80ED vs Kowa 663 (1 Viewer)

I am in the market for my first scope and these two are on the top of a very short list.

I came across the following thread message:

Given this limitation of the PF80, would the 663 seem as bright as the PF80 over a significant portion of its focus range? Does this focuser issue also impact the exit pupil just as if the actual objective were the sizes mentioned?

This is an unfortunate feature of the PF80 but if you are mostly looking far out it won't be an issue.

Brightness has to do with magnification and transmission so long as your eye's pupil is smaller than the exit pupil of the scope. Not the size of the exit pupil.

The size of the exit pupil has more to do with comfort and ease of placement of the eye. So an 80mm scope will give you a more comfortable eye placement at higher magnification than the same magnification on the 66mm.

Of course the size of the exit pupil depends on the magnification and the size of the unobstructed objective.

Assuming similar transmissions for the the two scopes the PF80 should be as bright and more comfortable than the 66mm Kowa at any focus range.

The problem with giving any definitive statement depends on the transmissions of the two scopes. The size of your entrance pupil. And the magnification you use.

the Kowa 663 is SIGNIFICANTLY smaller and lighter. These scope aren't really in the same "class" beyond price.

The larger Pentax, as noted above, should be slightly brighter and more comfortable in terms of viewing, but IMHO the optical differences should be so small overall that practical concerns should take over.

For example, if you will EVER be traveling or hiking with your scope the smaller scope is a no brainer. The PF-80 is a big lug of a scope. I would only get it if you will mostly be stationary (e.g. seawatching or scoping mudflats and you carry the scope in the trunk of the car) and want the utility of plentiful, interchangeable eyepieces.