Wolfgang said:
How are you sure that the lens itself stops down linearly?
canon's chuck westfall explains the problem in detail:
<
http://digitaljournalist.org/issue0508/westfall.html>
Q: My EOS 20D in aperture priority mode with manual diaphragm lenses
exposes properly at f/2.8 and f/4, begins to overexpose from f/5.6 to
f/8, then comes back down around f/11. How can this be possible? Is
there a solution besides using an external meter?
A: The EOS 20D focusing screen is optimized for superior brightness
at moderate apertures from about f/3.5 and smaller, compared to
conventional ground glass designs. This makes the viewfinder image
brighter and easier to focus manually at those moderate apertures,
but the trade-off is that it passes disproportionately more light to
the metering system. When a Canon EF lens is mounted to an EOS
camera, a variable exposure compensation factor (a program curve, not
just a fixed compensation factor) for this phenomenon is fed through
the system in order to provide correct metering for all apertures.
However, when using a non-coupled manual diaphragm lens as you
describe, no such communication takes place, so the responsibility
for exposure compensation reverts to you. It's unnecessary to use an
external meter. Instead, you can take a series of test shots at the
working aperture(s) you plan to use, then analyze the test photos to
determine the most desirable exposure compensation factor for each
aperture. The 20D's auto exposure bracketing (AEB) function speeds up
the process of taking the test photos, and you can use the Info
palette in Photoshop to determine the most accurate exposure. If you
can standardize on one or two particular apertures you plan to use
(for maximum sharpness, desired depth of field, etc.), it will
simplify the calibration process by eliminating the need for tests at
other apertures.
to quote you, "I don't forgive not metering" to which i add "correctly."
what's odd about it? and why does it even matter?
Or is there, just *maybe*, a line break behind "Canon__Super_Teleph"?
i ran tcpdump while posting and you're right, it does add a line break
when wrapping outgoing text. however, it's not noticable in urls
because both newsreaders (one gui, one text based) as well as email and
even text editors that i use all detect urls, regardless of embedded
line breaks and even without delimiters most of the time, so at the end
of the day, it doesn't really matter if there's an extra line break or
not.
Show me the Nikon 50mm f/1.0, if you please. I want to see one.
nikon could make a 50mm f/1 if they thought it would be profitable, but
as canon found out, it probably isn't a worthwhile venture. nikon
users have modified even faster lenses to nikon mounts (see below for a
42mm & 62mm f/0.75), so clearly, there is very little that precludes
making one, other than a compelling business model.
<
http://www.muellerworld.com/exhibits/fast_lens/>
