Originally posted by Cipher Stop any modern lens down a couple of stops and the images will be pretty much the same.
Originally posted by Fenwoodian This is an old myth that gets rehashed over and over again. I do not agree.
Unfortunately, there is an undeniable element of truth behind this. Within the double Gauss lens design family of which there are many, many, derivatives*: Optical performance will indeed be effectively identical, providing the variables of shooting aperture, optical coatings, exact optical geometry of the lens elements, and number of aperture blades in the optical design remain the same.
Compare a Zeiss Tessar** to a Planar, Summitar, or a triplet variant and even if the variables of optical coatings, optical geometry and number of aperture blades are preserved - you will get
distinctly different results. Various optical designs have inherent advantages and pitfalls - some have superb control over distortion, but have limited options for the designer to reduce chromatic aberration, some designs have excellent control of distortion and colour aberrations, at the expense of horrendous amounts of field curvature and astigmatism.
When you stick within the lens design family the statement holds true. However, in this age of innovative and Über-corrected lenses using novel Aspheric elements and exotic glass types, the lines that used to distinguish lenses are becoming...a little blurry.
*A shining example of which is the classic 7 element SMC Takumar 50mm f/1.4
** the M and the DA 40mm f/2.8 lenses are in the Tessar family... Pretty much all f/2.8 compact primes in the 40-49mm FL range are Tessars, It's a cheap and efficient design.