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Increased Aperture vs useability - the numbers don't lie
I will submit a Spreadsheet (a table), this evening, giving precise numbers for the relative Light Gathering Power (and telescope Magnitude Limit) compared to the relative Telescope Volume (and Telescope Weight), for telescopes of 8, 10, 12, and 14 inches of aperture.
[ obviously, the assumption here is an invariant mount design, a specific optical design and coatings, and a specific tube design(and materials) ]
The Light Gathering Power of a telescope increases a lot when we move from 6 to 8 inches of aperture, and also when we move from 8 to 10 inches of aperture. The L.G.P. gains between 10 and 12 inches of aperture are distinctly smaller but still quite noticeable to the eye.
In contrast, the modest L.G.P. increase that we get when we move from 12 to 14 inches of aperture is swamped by many other Very important factors such as: varying light transmission, varying eyepiece type, different levels of observer skill, etc., etc.
Telescope Volume and Telescope Mass :
These are usability quantifiers (numbers) that inexperienced people do not understand intuitively; even a slight increase in overall Telescope dimensions leads to a significant increase in telescope volume and telescope mass. And your lower back feels the difference!
Nearly every 14 inch telescope is a massive object that is hard to cart around. In fact, for rather a lot of people of middling observer experience, only 10 inches of aperture is about the upper limit for reasonable convenience and fairly easy transport & setup of the instrument.
I will shortly submit some numbers, in order to prove my point.
There have been a lot of terrible 14 inch telescopes around, and a lot of reasonable-to-good 10 inch telescopes around. For instance, many 14 inch Dobs, and also the very old model C14s, have really mushy star images, so some experienced observers actually prefer to look through a 4 inch apochromatic refractor, because of the crispness and contrast of its images. Mechanically and Optically, it is just that much harder to produce a really big Scope that performs well and has reasonable ease-of-use.
We all know a lot of people who own Giant telescopes that lie idle all the time!
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