"Siddhartha Jain" wrote in message
ups.com...
Hi,

Given two lenses, one a prime (say 28mm) and the other a zoom (say
28-75mm) and both with an aperture of f2.8 -
- Will the prime be brighter than the zoom because it has fewer lens
elements?
- Will the prime be sharper wide open than the zoom at 28mm?

Ofcourse, a lot will depend on the particular makes and models being
compared but is there a rule of thumb?

- Siddhartha


In theory, zooms will always be somewhat below the quality of prime lenses.
Zooms typically have barrel distortion at one end of the zoom range, and
pincushion distortion at the other. Older zooms, especially those that did
not have decent multicoating, were more prone to flare and ghosting, because
of the light bouncing back and forth off the air-to-glass surfaces.

The margin of superiority of primes over zooms has narrowed, and many
photographers find the convenience and economy of one zoom versus several
primes to be more important than some slight degree of image degradation. I
have a couple of Pentax zooms in K-mount that do a credible job, and it
certainly is easier to carry two zooms than it is to carry 5 or 6 primes.
Thirty years ago, I bought a couple of third-party zooms for my M43 bodies,
and the results were just awful, relative to my SMC Takumar prime lens.
Colors had a grayish cast, saturation was less than on the OEM lens, the
aperture ring was operated in the reverse direction of my Takumar's (Pentax
does it "backwards"), the front element turned when the focusing ring was
moved, making polarizer use difficult, the lens front element was not the
standard Takumar 49mm or 58mm, making it necessary to buy filters just for
use in that lens, and the resolution was noticeably less than that of the
OEM Takumar.

The build quality was obviously less-good than the OEM lens. The focusing
was not nearly as smooth, the zoom ring was a bit on the tight side, the
lens barrel was not as sturdy and the lens lacked multicoating (this was 30
years ago). So, while I saved a few dollars, I got pretty much what I paid
for and no more. I ended up putting that zoom lens up on the shelf, where
it remains to this day, and I bought only OEM lenses after that. They cost
a bit more, but the level of satisfaction that I derived from them made up
for the higher price. And not a single one of the OEM lenses has failed, in
3 decades.

British landscape photographer and author Brian Bower noted that, while his
Leica R zoom lenses cost a lot more than non-OEM lenses, he felt that they
were a good value because they retained their accuracy after over a decade
of hard use. He noted in one of his books that the cheaper zoom lenses
might see the elements go out of precise adjustment and the zoom mechanism
might become very loose after a time, making it necessary to keep checking
the zoom ring to be certain that the zoom ratio has not changed from
whatever it was originally set to. Bower valued consistently good results
more than lower price. He made his living with those tools, and he had
little tolerance for lens failures.

My own take on it is that if the proposed use of the lens is of a very
casual nature, it is probably okay to go for the savings. But if top
performance and reliability are paramount, one really has to think about
whether the savings might be offset by potential future loss from
poorly-performing equipment. I would rather have only a couple of really
good lenses than a kit full of lenses of questionable reliability and
performance. It seems that, in my own case, virtually every time I have
tried to save money by cutting corners I ended up paying double.