Quote:
Originally Posted by RB
It doesn't work that way Rally because the same logic can be used for the 1200mm if you put it on a Canon 1.6x body.
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True to the extent that on the 1.6x camera you have more effective focal length - I assumed a 35mm frame - Got me there !
Canon (APSC and 35mm sensors)
1200 x 1.0 = EFL 1200 f5.6 @ <> $90,000
1200 x 1.6 = EFL 1920 f5.6 @ <> $90,000
Vs
Olympus (4/3rds sensor)
800 x 2.0 = EFL 1600 f5.6 @ <> $10,000 (320mm behind !)
EFL = effective focal length at equivalent 35mm
But the crop factor does yield a real increase in image magnification at the CCD
In the case of a 4/3rds sized CCD as used by Olympus - that is the full image circle at the CCD and the Olympus lenses are designed only for that image circle - so you are not actually losing any area of the image at all.
I am not sure if the focal plane was moved in the Sigma 800mm for the Olympus mount version or not - it was a very long time coming after the Canon and Nikon mounts so who knows ?
The other thing is the Olympus lenses are telecentric and designed for digital although the Sigma is only 'optimised' for digital but does have all the antireflective coatings needed for CCDs (but not needed for film)
Whereas I suspect the older Canon design has neither a true telecentric light path nor the coatings - but being a long focal length the light path is probably telecentric enough for that not to matter.
Its all moot really, and I fear a hijacking of the OP's thread !
. . . but for someone who wants this sort of reach (sporting and wildlife) its a real consideration that is cost effectively satisfied without loss of image quality or speed by using that combination of 4/3rds camera and lens.
I would be game enough to venture that the IQ is at least equal or better, simply due the use of coatings which will enhance contrast - but I havent looked at the Canon MTF charts - if they exist for digital.
Its just about poinmting out that cheaper options exist for the common man to achieve the same sort of result without any loss in IQ or speed.
Cheers
Rally
PS - plus you can actually carry the Olympus rig around on a tripod with a gimbal mount by yourself !