I have an 80mm f/6.3 tabletop achromat since 1973, and refurbished in 2012 and is almost the most used scope for me. I have observed more deepskies the last few years with it than all the forty years before. Color errors are not that bad, so I can use it even for planetary views up till 130x.
Despite having a 16" Dobson, which captures 25 times as much light, it is amazing what such a small scope shows. The much wider field is a big advantage.
Here is a possible explanation as to why a much smaller scope is amazing in what it shows. I have no idea if this concept passes logical tests or if it is so much blather (illogic). Feel free to correct my idea or shoot the argument down.
Comparing the light gathering of the small scope vs the larger scope is one way of looking at the issue.
Another way is to compare the light gathering of the human eye and the telescope in use.
If we assume an exit pupil of a human eye of 7mm the area of light gathered is 38.45... sq mm.
An 80mm telescope is gathering 5026.54... sq mm.
The 80 mm telescope gathers about 132 x as much light as the naked eye.
Other factors include thresholds and "envelopes" of sensitivity. The human eye and ear do not pick up sensation below a minimum, and will become saturated -- or even damaged, if the sensation is too intense.
An 80mm (or 30mm? 10mm?) small telescope delivers light in the zone over minimum sensation. But, visual planetary, lunar, and few bright stars with even small telescopes can be too bright.
The limiting factor is not the telescope, but the eye.
Over time humans have adopted telescopes astronomy that work within the eye's minimum threshold.
Edited by Littlegreenman, 17 May 2020 - 02:14 AM.