On 3/24/2020 12:33 PM, Ken Norton wrote:
Some data from old Modern Photo reviews...
They may be referencing back to this review. Where else are they going to get
accurate measurements?
I'm assuming that their tests were done at infinity focus?
Good assumption, as there is no other common ground for comparison.
It's
actually a little more tricky with the measurements because a
traditional lens design that focuses through extension will generally
get a little longer as it is focused closer.
Except for those with floating elements, I don't see how this is possible.
But an IF (internal focus) lens will get shorter (wider angle) as it is focused
closer.
Ah so true, and a shame - the closer you get, the shorter the working distance gets, bad juju. The Canon 60/2.8 macro
was closer to 40 mm at closest focus.
And then there are the various zoom lens designs which have a lot of
variation depending on what end of the range they are on.
The RX10 IV zoom is a a great example, with good close focus/mag. only at 24,
50 and 600 mm
Take the OMD 14-54 as an example. There are two crossover points where
the lens behaves quite differently. It's like three different lenses
in one. Depending on which of the three focal-length ranges you are
on, the lens will either get longer or shorter as it is focused.
". . . longer or shorter . . ." is ambiguous in this context - physically? in
focal length?
Doesn't matter, but a pedant is . . .
Also, did MP measure the angle of coverage from corner to corner or
from side to side?
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. I long ago made my own spreadsheet for to allow comparison across FL and format.
There's a nice calculator here. <http://www.bobatkins.com/photography/technical/field_of_view.html>
So the eSIF says the possibly mythical 18/3.5 lens that started this and has an actual FL of 18 mm, has a 100° AoV, but
the horizontal AoV is 90°.
Their chief tester wrote a white paper on his techniques, I think. Maybe you
should find it. :-)
I Dunno Moose
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What if the Hokey Pokey *IS* what it's all about?
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