This recent appearance of a Questar Field Ranger 3.5 on eBay prompted me to wonder about the general characteristics of this model. Out of all the current offerings that Questar makes available, is the Field Ranger the closest thing that Questar makes that is most comparable to, say, the current Celestron C90 or Orion's 90mm Apex? Aside from obvious variations in quality between a handmade and mass produced scopes, it seems to me that the Field Ranger is maybe the least complex Questar that is out there for this size category. I'm thinking specifically in terms of a lack of control box.
Would one be able to achieve focus if a 90-degree diagonal were placed in the visual back? Can one even put a 90-degree diagonal in the visual back? Is the Field Ranger's "visual back" indeed a visual back? I see that the Questar Brandons thread into it, raising questions in my mind about whether someone could attach a standard 1 1/4" diagonal. Or is the Field Ranger designed only to accept an eyepiece with no diagonal?
Questar clearly this scope with surveillance applications in mind. But that in itself doesn't necessarily mean that it can't be used as an astronomical observing instrument.
I should add that these questions are purely academic on my part. I don't have any interest in pursuing this scope for purchase. Instead, I'm merely curious.