novice questions on 25mm and 40mm

[savuti]

hi again,

thanks for good advice (I promptly downloaded DOF-table to my palm tx).

Now, I´m wondering about what,exactly, is meant by the notions "normal" lens (i.e a 50mm in my former SLR world), and, on the other hand "rectilinear" (apparently, a 12mm lens from VC is considered rectilinear). Should this mean that the 12mm does not distort faces on short distances? (I don´t really think so). Or does rectilinear simply mean that not all straight lines will be curved on all photos (as opposed to fisheye-lenses)?. Is my 40mm nokton fairly "normal" on close range face photos, or do the laws of optics define 50mm as the widest lens with such caracteristics (whatever "normal" means)?

I´m living far away from any developing lab, so have to wait for a mail order lab to develop negs, and I´m shooting away before getting the first results. Being a lousy photographer wanting to get better, I´d just like to know what to expect, and am impressed by the response last time.

By the way, I absolutely love the bessa and the 25mm snapshot skopar, not yet sure about the 40mm nokton and the 75 mm color heliar, but everyone seems to like them, too.

Kind regards,
Olav

 

[JeremyR]

There may be more formal definitions for each, but...

For practical purposes, rectilinear basically means "not fisheye." Technically it probably means that straight lines are rendered as straight lines. I'm sure someone will jump in and correct me if I'm wrong. 😀 A 12mm rectilinear will certainly "distort" faces and other objects not in the center of the frame--this is just the nature of the ultra-wide-angle beast.

Normal is just a term for those focal lengths between "wide angle" and "telephoto." I don't think there's a strict definition in terms of focal length; depending on who you ask you may hear anything in the range of 35mm to 70mm or so (in 35mm format). 50mm is right about in the middle of this range, so that's what you'll probably hear most often referred to as a "normal" lens.

Cheers,
Jeremy