Relation between lens diameter and IQ
It appears that generally lenses with higher diameter (larger filter thread like 67, 72 or 77 mm) are much pricier than the lenses with comparatively less diameter (say 52 or 58 mm) and most of the cases they are better w.r.t. IQ too. Why it is so?
What may be the problem of manufacturing smaller diameter lenses with very good optics? Canon L lenses are also follows mostly the same trend. What is the technical reason behind this?
Small lenses are not as capable as resolving things as larger lenses. I have been messing around with amateur astronomy for a decade or so. Set up a 60mm lens telescope next to a 120mm lens telescope and look at the moon through both of them. Providing they are both equally nicely made, the 120mm lens will give a thorough spanking to the 60mm lens on details seen. This is simply an inescapable consequence of diffraction.
I have a telescope now with an 8" lens up front. Usually pointed at the sky, but I could use it to take detailed pictures of pine needles and spiders webs from a football field away. (Like these tiny snow crystals, easily 250 ft away:)
I wondered if the difference was evident with camera lenses and I finally got a bigger lens after all these years, a Canon EF 300 f/2.8 which has (I think) about a 115mm front element. I was blown away I have never captured detail like this from a camera lens before.
I am sure that Canon does make an all around superior effort with these big lenses, by any measure, but the fact is, it's got a big lens and it collects a lot of light. You could put the worlds finest 300mm f/5.6 lens with an 53mm front aperture next to this Canon 300mm f/2.8 (also set to f/5.6) and thanks to physics, the big glass is going to thrash the little one.
Here is one with a 160mm telescope, over 6" of glass up front:
Those spider webs (and spider legs) are probably 170 ft away.