More Elements Aren’t Always Better
Today’s lenses are marvels of design with low dispersion and aspheric elements, supersecret submolecular whatchamacallit coatings etc. I notice more and more the marketing people touting stuff like 63 elements in 45 groups!!!!! in their brochures. One thing we sometimes forget is that every air-glass interface in a lens is going to reflect a fraction of light (usually less than 1%, often as little as 0.2%). That stray light bounces around in the lens and can cause flare, loss of contrast, and ghosting (reflected sunspots in the picture).
The top lens above has 23 elements, the one below it has 12. Below are the flare tests done by Bryan Carnathan at The Digital Picture for those same lenses, 23 element lens on the left, 12 element lens on the right.
Of course lens coatings help minimize flare and the manufacturers are quick to tell you the new versions of some lenses have “supernano” or “subwavelength” coatings that are better than old coatings. They aren’t quite so quick to mention that usually just a single surface in the lens has the new coatings. The other lens surfaces are coated the old way.
Only the back of the front element in this lens actually has the new subwavelength coating. The other 15 glass-air interfaces have standard coating.
It doesn’t mean lenses with more elements always have more flare and ghosting. But there is a general tendency that they do. Older lens designs with older coatings have the same tendency. So an old lens design with old coatings and lots of elements can have major problems shooting with the sun in the field.
One other point about all that reflection that may be happening: reflected light isn’t getting to the sensor, so the f/# (which is a theoretical calculation) may be quite different than the T/# which measures actual transmission. An f/1.4 lens may, or may not, actually let f/1.4 worth of light hit the sensor. (Actually, it definitely won’t, but more on that later.)