# 4/3 has no focal length advantage-correct him if he is wrong

Started Nov 15, 2008 | Discussions thread
Re: 4/3 has no focal length advantage-correct him if he is wrong

As others have said the 50-200mm is 50-200mm in several ways:

Actual physical dimensions
depth of field
perspective distortion

If one lens at 50mm projects an image of an object onto a 15mm squared area of > the sensor, then another 50mm lens should do the same. If one sensor has four > times as many pixels in that 15 mm squared area the final image will be twice as > wide and tall - twice the "magnification" four times the area.

If you put a 50mm lens on a 21mp Canon and a 50mm lens on a 5mp E1 and > took a picture of the same thing from the same distance the E1 picture would look > closer to the photographer. If you then cropped the Canon picture to 5mp, by > keeping the middle 25% of the area of the picture, you would have two almost > identical pictures. (2.4mp/cm2 vs 2mp/cm2)

The E-3 is 10mp. If Canon releases a 40mp 35mm FF camera you could do the > same thing. Until then you will get a magnification advantage with Olympus.

If you compare Olympus to a 10mp FF then it really is a 2x difference.

When you are comparing the output files of an Olympus 10mp at 50mm to a > Canon 21mp at 50mm, not so much. When you compare two pictures at 100% - > pixel for pixel - the object will seem larger with the Olympus but not really 2x > larger. (4.2mp/cm2 vs 2.4mp/cm2 = 1.75x magnification)

At least that is my understanding. If I am wrong please explain why I am wrong.

Thanks

Jon,

My understand after all the contribution to this thread is such:

A 50mm FF lens projects an image that covers the full surface area of a FF sensor while a 50mm 4/3 lens projects an image that covers the full surface of the 4/3 sensor ( which is half the size of the FF sensor )

In another words, because the FF sensor has double the surface area of the 4/3 sensor, it follows that the lens diameter of the FF is larger than that of the 4/3 ( by how many percent, I don't know), in order for it to be able to project a bigger image on the FF sensor.

Because the 4/3 sensor has only i/2 the surface area of the FF sensor, for the same 50mm lens, the 4/3 can only have half the field of view or angle of view, whatever you call it compared to a FF.

Therefore, using both a FF and a 4/3 camera and shooting from the same spot on the same subject, assuming the 4/3 sensor is 10mp, this 50 percent cropped image (relative to the FF) can take advantage of the full 10mp resolution of the 4/3 sensor. For the FF to match the same resolution, it needs a 40mp sensor.

However because a FF lens needs to project a bigger image on the sensor, it needs a bigger lens, at least in terms of diameter, which translate to more weight and cost.

On the other hand, for the same focal lens, my friend is right in that his field of view is double that of 4/3, and the 4/3 has no advantage in terms of reach.

That is my understanding after going thru all the contributions.

However, this understand seems to differ from that of Jon.

Could someone correct my understanding?

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