David:
The Canon 2X I use is the APO model, with either EOS 1D mark II or 20D.
Yes, you're using the center of an enlarged image circle with it, but the
converter itself introduces aberrations.
I don't use either 400mm f/4 DO IS or 500mm f/4L IS wide open with the EF
2X II because the image quality is usually pretty marginal. I really need
to close down at least 2/3 stop to get something sharp. (And when I need
that much lens, there can be difficult conditions like falling snow or poor
air quality to degrade the image, or my focusing.)
I much prefer the Canon EF 1.4X II. (Mine's pretty beat up, but still quite
functional.) The image results are much better than the 2X, plus I get a
brighter viewfinder image and working autofocus at f/5.6 with either f/4
telephoto on the 20D.
It may be the Telyt's simple telescope design minimizes aberrations because
there's less glass AND the light rays have a straighter path.
I really needed the 1D mark II's autofocus with this shot at 1000mm (EF 2X
II + 500mm f/4L IS):
http://tinyurl.com/4srw8.
I'm always impressed at the high quality of your work with manual focusing
at such high magnifications.
Mark Bohrer wrote:
David:Surprisingly, Mark, it's not a whole lot different. Since the early 60's it's been known that the longer the focal length the less effect a converter has on the sharpness. Two factors... [1] the angle of the rays is narrower or straighter or something (very much so in the Telyt's case, with the cemented pair way out in the front) and [2] you're only magnifying the central bit of the prime lens... where it's at it's best.
I bet the barefoot 400mm lens is sharper than the 800mm setup with the 2X converter. I try to avoid using the 2X if at all possible. Nice climber on the tree... and without spikes too!
Now, a technician would prove that there is degradation - and of course there is... but with the 400 Telyt it's not really noticeable in the photos. BTW: the one problem with the early 70's vintage converter I use is that there is some significant vignetting with the Telyt. The APO converter does not have this problem. (The smaller sensor of the 20D also cures the problem!)
Still, I prefer the "barefoot:" Telyt simply because the finder is **so** much brighter at f6.8 than f13.6! Much, much easier to focus in dim light.
As for the climber... well, we all know they can... but it's rare to see one doing so!
Thanks for your comment and for taking the time to look. :-)
-- David Young, Logan Lake, BC CANADA. Personal Web-site at: http://www3.telus.net/~telyt Leica Reflex Forum web-page: http://www3.telus.net/~telyt/lrflex.htm
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