The original plans for the Questar telescope were for a 13cm (5") unit. There are various stories as to why the 9cm (3½") model was the one actually introduced in 1954 and they range from the inability of Cave Optical (and, later, Cumberland Optical) to make the optical elements in quantity to the realization that a 13cm product would be significantly heavier than a 9cm one (the Questar 7, an 18cm aperture 'scope, even the newer "lightweight" model, is quite a beast at more than 8kg for just the optical tube assembly).
Here's a copy of an image of the specification sheet that I found floating around the WWWeb:
I note that the F:ratio (with camera) is near F:16. This is in keeping with some newer designs that emphasize longer focal lengths: rather than inserting additional optical elements to achieve greater magnification, any add-ons are used in to achieve the opposite - lower power and wider field. Nonetheless, I see, also, that the control box incorporates a 1½ power amplifier or "Barlow" (Only 1½X?! Is that just a nod to history? Maybe a focal reducer would be a better accessory?). The 40mm central obstruction for the secondary mirror is about the smallest that can be implemented and still illuminate an entire, full frame (35mm) sensor. The internal focusing mechanism is mentioned but not detailed. In spite of some image shifting during focusing (and the infamous "mirror flop" during long exposures - not just a Questar issue), the Questar's thimble is quite rugged and offers an extraordinary focusing range (my Vixen, mentioned below, without accessories, cannot achieve focus on anything closer than a half kilometer). I wonder if the internal secondary rather than external "dot" will be used now that the Gregory patents have expired.
I owned a Questar Duplex (9cm) for some years. I eventually sold it when I realized that, with the associated "portable" pier, the rig was nearly as cumbersome as my 20cm (8") Vixen (I'll NEVER sell that!) and just could not compete in convenience and optics (Yes, Questar mythology aside, as the racing axiom goes, "There's no replacement for displacement!" / "You Can't Beat Cubic Inches!").
Additional advice from a wise astronomer (not me): "Buy the biggest, baddest mount you can afford ... AND CARRY!"
I visited the Questar WWWeb page (
https://www.questarcorporation.com/ ) and, even after some searching, found no mention of a Questar 5. The original post is from 2017, and I note that the Questar Corporation was founded four years before the first Questar Standard was offered, so we could have another couple of years before formal announcements. The original design was revolutionary and has endured well. There's now a lot of technology out there (things like automatic plate solving and atmospheric distortion correction) that set a pretty high bar for a new Q5. We'll see...
