Re: Travel to Greece: do you regret not bringing a certain lens?

Roger N. Clark (change username to rnclark) wrote:
Alfred Molon wrote:


Another point, it's advantageous if the lens is as close as possible to the sensor, especially for wide angle shots. That is the case with all compacts and a camera like the Sony R1 for instance, but DSLRs have a swinging mirror which prevents placing the lens too close to the sensor.

I don't see that as an advantage.


It's an advantage for the lens designer for two reasons.

First, simply allowing the added freedom of a lens element
close to the film can never hurt. It might not be needed,
but it might indeed be needed.

Second, and why it is important for wide angles, is the
"symmetric principle", which basically means that
a lens which is completely symmetric (and thus, of course,
is a 1:1 macro) cannot have certain third order aberrations.
A normal lens does not have symmetric object and
image distances, but this principle still applies. It is why
Super Angulons (and plain old fashioned Angulons for that matter)
are such great very wide angle lenses, despite being
only 8 (or 6) elements. They make use of this principle.

Doug McDonald
.

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