On 3/24/2020 2:46 PM, Ken Norton wrote:
I imagine corners, as that's the way all the makers write their specs. I've
always disliked that, as the wide dimension of the format as the useful number.
As the OMZ 18mm is such a highly corrected lens, I think that it's
usability is that of 18mm as compared to other similar wide-angle
lenses. Once we adjust other lens' images to the same linearity and
crop the results, their effective focal length is reduced.
A very interesting (to me, at least) characteristic of the µ4/3 lenses is that they are generally designed with linear
distortion undercorrected, to concentrate on better correction of other aberrations. Linear distortion is then corrected
in firmware for JPEGs and conversion software for Raw files.
As WA distortion is always barrel, that means the image gets wider when corrected. To maintain the nominal format
dimensions, the sides are cropped. AFAIK, DxO is the only Raw converter that gives the choice of retaining the full,
corrected width. I find the difference sometimes significant.
The Heliar 10/5.6 that I just wrote about is amazingly well corrected for linearity. DxO has a profile for it, but the
difference is minuscule.
especially true with the OMD line where the lesser-grade lenses may
have the same diagonal angle of coverage, but have more distortion.
This is where side-to-side (and top-to-bottom) measurements are more
valuable as they indicate what the "usable" angle of coverage is.
Diagonal assumes 100% image area too with varying H/W ratios. Cropping
to a common dimension (long edge) is the great leveler.
Yup. In my post today about xWAs, I was surprised to see the difference in vertical coverage with 6x12 film and a 60 mm
Super Angulon and 6x17 with the 90 mm, for essentially the same horizontal coverage. Obvious, but I'd not thought about
In all honesty, it's just so much noise. Grab the lens, and determine
whether or not it's wide enough and linear enough for you with low
levels of apparent correction.
Exactly why I'm trying the Heliar.
Broader Limits Moose
What if the Hokey Pokey *IS* what it's all about?
Themed Olympus Photo Exhibition: http://www.tope.nl/