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I posted this in response to NSS's not silly question in that thread too - but on reflection I feel it might help as a separate thread on its own... thus this one.
How the Oly 4/3 crop factor x2 works.
A lens's focal length is fixed and doesn't change, regardless of what camera body it is used on. If it's a 70mm lens, then it's a 70mm lens on a Canikon, Oly or Sony; or if it's a 35-100mm, then it's still a 35-100mm on whatever body it is used on.
All that changes on each body (in essence for purposes of this thread), is the amount in the center of the image that the sensor actually sees.
Let me see if I can explain this with the aid of a few diagrams, in terms of sensor size and crop factor.
Let's say this strange image of a piggy on a marble floor is what the lens actually sees. IMPORTANT: Remember, a lens projects a round image - not a square one!!
This round 'image' is then ultimately projected through the rear of the lens, and physically onto the cameras sensor. This next diagram illustrates two sensors; green being what the FF camera sensor might see, and blue being what the Oly sensor sees. It's simple physics here folks... the 4/3 sensor is smaller and thus less of the image is projected onto it by the lens as compared to the FF sensor.
And now, just to separate what each sensor 'sees'. Physically, the FF is larger and contains more of the overall picture i.e. a greater field of view whereas the Oly shows less of the overall picture i.e. less field of view.
However, if we now take a look at what we see through the viewfinders of each camera... we see a bigger pig in the Oly camera compared to the FF camera because of the reduced field of view as explained in the text above. Thus the apparent increase in focal length.
Which hopefully explains why there's the x2 crop factor in 4/3 equipment. The same lens but different sensor size has yielded less of the overall image being seen by the sensor and an effective increase in focal length. However, if it is 'zoom-in' you want (as opposed to 'zoom-out') - in the case of crop sensors, this can be interpreted as... less is more!!
Of course, there are many other factors that come into play here; photosite density, noise, capability of the lens to resolve more detail (which in ZD glass - is so) - but for a simple explanation - these diagrams should explain why we as Oly users get in closer to the subject as compared to FF cameras.
Please shout if there are questions...
Enjoy the piggie!
How the Oly 4/3 crop factor x2 works.
A lens's focal length is fixed and doesn't change, regardless of what camera body it is used on. If it's a 70mm lens, then it's a 70mm lens on a Canikon, Oly or Sony; or if it's a 35-100mm, then it's still a 35-100mm on whatever body it is used on.
All that changes on each body (in essence for purposes of this thread), is the amount in the center of the image that the sensor actually sees.
Let me see if I can explain this with the aid of a few diagrams, in terms of sensor size and crop factor.
Let's say this strange image of a piggy on a marble floor is what the lens actually sees. IMPORTANT: Remember, a lens projects a round image - not a square one!!
This round 'image' is then ultimately projected through the rear of the lens, and physically onto the cameras sensor. This next diagram illustrates two sensors; green being what the FF camera sensor might see, and blue being what the Oly sensor sees. It's simple physics here folks... the 4/3 sensor is smaller and thus less of the image is projected onto it by the lens as compared to the FF sensor.
And now, just to separate what each sensor 'sees'. Physically, the FF is larger and contains more of the overall picture i.e. a greater field of view whereas the Oly shows less of the overall picture i.e. less field of view.
However, if we now take a look at what we see through the viewfinders of each camera... we see a bigger pig in the Oly camera compared to the FF camera because of the reduced field of view as explained in the text above. Thus the apparent increase in focal length.
Which hopefully explains why there's the x2 crop factor in 4/3 equipment. The same lens but different sensor size has yielded less of the overall image being seen by the sensor and an effective increase in focal length. However, if it is 'zoom-in' you want (as opposed to 'zoom-out') - in the case of crop sensors, this can be interpreted as... less is more!!
Of course, there are many other factors that come into play here; photosite density, noise, capability of the lens to resolve more detail (which in ZD glass - is so) - but for a simple explanation - these diagrams should explain why we as Oly users get in closer to the subject as compared to FF cameras.
Please shout if there are questions...
Enjoy the piggie!
. Is the image circle of a 4/3 100mm lens, as measured at the sensor plane, the same in the 4/3 system as it is for a FF 100mm lens in an FF system? That's what your article implies. I've had a scour of the net for the relationship between focal length, distance to focal plane and the size of the image circle but without success.
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