On Thursday, September 21, 2017 at 5:58:42 PM UTC-6, wrote:
To get back on topic.......Questar has made 5.25 inch prototypes. But they
cannot keep pace with the orders for 7s now. My 3.5 is over 30 years and still
going strong. Tremendous service support; maybe the best in the industry.

That's the thing. If Questar were an ordinary manufacturer of telescopes at
ordinary prices, making something larger than 3.5" - small enough that observing
possibilities are limited - and smaller than 7" - too heavy and expensive for a
Maksutov-Cassegrain - would make sense, as such a size would be more likely to
be popular.

But because they aim at very high quality, the number of telescopes they can
make is limited. In the sizes they _do_ make, they're getting more demand than
they can handle, as you've noted. And because of the price premium, how popular
any given size might be can't be assumed to be the same as what one sees in the
sales of telescopes that are much lower in price.

Even so, I suspect that a 5.25" might be their next product, and if so, it will
be very successful. But I'm not holding my breath - it may be more than ten
years before it happens.

John Savard