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Old Apr 12, 2009, 5:59 AM   #1
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Question:
If I fit say a KIRON 28-105mm f3.2-4.5 35mm lens, via an MC to 4/3 adapter ring to a 4/3 camera, is the f number range effected like zoom crop factor (2:1 for 4/3 systems cameras), or does relative f number remain the same ?

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Old Apr 12, 2009, 6:52 AM   #2
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F-numbers stay the same, it will be still a f/3.2-4.5 lens, the FoV (field of view) of the lens will be the equivalent of a 56-210mm lens on a 35mm (full frame) camera.
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Old Apr 12, 2009, 7:55 AM   #3
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I took the liberty to copy my answer from a different forum here at Steve's:

garys17 wrote:
Quote:
In the Olympus E-520 manual on page 123 the following is stated:

"A Four Thirds system lens with f2.0 brightness, for example, is equivalent to f4.0 when converted to the aperture of a 35-mm camera."

Does this mean that the fastest Zuiko lens is actually f4.0?
You will notice the title of the paragraph is "Depth of Field" and that statement is correct. The DOF of my 35-100 f2 is the exact same as a 70-200 f4 lens being used on a full 35mm sensored camera.

If you are trying to gain additional DOF, of course, this is no problem at all. If you are looking to restrict DOF (make it narrower) then the big sensored high dollar camera will have an advantage.

Everyone has different needs. I shoot alot of telephoto and the shorter focal lengths the 4/3 sensor uses is a huge benefit to me. The 50-200 is nicer to carry than a 100-400 lens, and sharper to boot. Because the lens is shorter to get an equivalent field of view, the DOF is deeper, and that is something I generally like for shooting long. I normally want additional light so I can stop down to gain even more.

In total, no its not a f4 lens. Its a f2 lens that is half the focal length. The AF system is operating on f2 light. The viewfinder is illuminated with f2 light. Its a f2 lens! Becaues shorter lenses have greater DOF, it shares that characteristic with a f4 lens in 35mm format that has twice the focal length.


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Old Apr 12, 2009, 8:56 AM   #4
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mr.sneezy wrote:
Quote:
If I fit say a KIRON 28-105mm f3.2-4.5 35mm lens, via an MC to 4/3 adapter ring to a 4/3 camera, is the f number range effected like zoom crop factor (2:1 for 4/3 systems cameras), or does relative f number remain the same ?
The f-number is a function of the actualfocal length of the lens(independant of any 'Crop Factor') and the pupil diameter of the lens, and has nothing to do with the camera it's attached to. So, the f-number remains the same.
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