View Single Post
Old 13-09-2008, 08:40 AM
RB's Avatar
RB (Andrew)

RB is offline
Join Date: Aug 2005
Posts: 22,097
Originally Posted by rally View Post
1200 x 1.6 = EFL 1920 f5.6 @ <> $90,000
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.

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.



PS - plus you can actually carry the Olympus rig around on a tripod with a gimbal mount by yourself !
I agree that there are cheaper alternatives, I'm not arguing money, LOL just about any lens on the market is cheaper than the Canon 1200mm.

My point is that a crop factor is just that, a crop of the actual FOV and does not yield any 'true' magnification, for example on any of the main stream crop bodies by Canon, Nikon etc.

The Four Thirds system developed by Olympus & Kodak tried to achieve a hybrid magnification factor by combining a smaller sensor and 4:3 aspect ratio as opposed to 3:2 and then developing specific lenses for that sensor to achieve the 2x factor.
Yes they added special coatings and made the lenses telecentric but making a sensor smaller is not going to help noise performance IMO.

How popular is the four thirds system amongst professionals?
Do you see many used at events like the Olympics where they need the image IQ and reach? Don't think so.
Would I want to use a four thirds system for my astro imaging.... no.
I would and do however use Canon DSLRs and lenses for my purposes.

I suspect that the Four Thirds system is an alternative for those that just want a more compact system but is not really preferred in the main stream amateur and pro sectors IMO.

The image quality of the new Nikons and hopefully soon Canon bodies are by far the best to date.

It's also no coincidence that medium format achieves even higher IQ than any of these, why?

Sorry I know it's become a drawn out discussion but it's good to discuss things, and I'm not by any means an expert but love to hear other opinions and share ideas.

Reply With Quote