Resolution describes in general the ability of a “system” to provide “details”. Systems can be anything, a thermometer , a speedometer in a car, a TV screen, a printer, … and last but not least cameras and lenses.
When people talk about cameras, easily a Megapixel race starts. The general optinion in the consumer market may be “the more, the better”.
Marketing is the big player behind the scenes. If my competitor offers 1 Mega-something and I can offer two Mega-something, this is usually reason enough for the subconcious mind of the consumer to go for the higher number.
Do we need to know the temperature with a resolution of 1/100 degree?
For half a century a VGA TV resolution (640×480 pixels) was just fine for us to get the “needed” information. These days HDTV and 4K resolution is a must. Again .. it’s nice to have, but is it needed?
A strange phenomenon in terms of resolution are ..
When a new TV with extra high resolution appears at the market, the prices are very high. This is because the manufactures obviously can sell it at that price and because the development costed lots of money.
Once this new resolution becomes standard, the prices drop considerably.
But as long as its not mass product:
High resolution = higher precision, better production machines, better inspection tools, better workers, .. needed, maybe even brand new production strategies)As a result: Low volume production -> high prices
In our daily lives we learnt:
The optical term contrast of an image is pretty much what we would expect from our daily use of the word.
The global contrast in the two images above is about the same, however the local contrast (the change from pixel to pixel) is less high in the lower image, because of the slight blurring.
Apart from the production quality, the resolution of a lens is limted by a physical effect called “diffraction”.
The “best possible” lenses are called “diffraction limited”, read : they are as good as allowed by physics … “only limited by diffraction”.
In short, diffraction is an (unexpected) change in direction of light particles that occurs if they don’t have neighbors “travelling” in the same direction. As a result diffraction occurs at the rim of a lens iris, at the surface of metal rods, threads etc.
As a side result we notice :
For diffraction limited lenses with an F# below the optimal aperture : The higher the F#, the higher is the DOF, the lower the resolution and thus the lower is the local contrast (= lower MTF) .
If lenses are not diffraction limited, increasing the F# makes means using more the center parts of the lens elements (which have lower aberrations). Therefore the resolution increases for a while until the critical aperture is reached, then it decreases.