Are all f stops created equal???

I have heard that with the 4/3's system, a 2.8f stop is not the same as a cannon or a nikon. Is this true? If so, can you tell me what a 4/3's 2.8f is equivalent to in cannon or nikon?

 

They must mean in terms of depth of field. I hope somebody can help you with the math, I have lost all my links on the subject of compairing depth of field for crop and full frame sensors.

 

It has to do with the sensor size.An easy example are P&S cameras. Most of the lenses on them are f/2.8, but the DOF wont be the same at the same focal length as an APS-C or FF DSLR.

 

If I'm not mistaken, I think with a larger sensor you will get a thinner depth of field. But for light gathering purposes, they all mean the same thing and will generally yield the same shutter speed for the same amount of light at the same ISO.

 

Sorry for the double post, but Canon makes point and shoots, lol. I think your meaning to say an SLR.

 

That's right

YEa sorry, fixed it

 

Aperture (f stops) are a matter of physics. They are all the same no matter what body they are on or what film or sensor size they are projecting to.

DOF however does change with the sensor size based. Here is a good read on the basics of lenses. Understanding Camera Lenses

 

4/3rds has a slightly smaller sensor than a APS-C camera (Nikons below D700, and Canons below 5DMkII), and a much smaller sensor than 35mm cameras.

That said in terms of being created equal, it's much of a muchness. Certainly you can get excellent depth of field out of a 4/3rds system.

As for being equivalent. There is no simple answer. The following variables affect DOF:
Angle of view
Subject to camera
Camera to background
Aperture
Sensor size affects the above variables in different ways in order to get the same shot.

 

I would point out that the 4/3 sensor is much smaller than APS-C" the 4/3 sensor measures 225 square millimeters, which I would describe as "significantly" smaller than Canon's 1.6x APS-C, which measures 329 square millimeters in area. Nikon's 1.5x APS-C sensors measure 370 square millimeters.

A full-frame d-slr sensor is 864 square millimeters, making the 4/3 format very much smaller--3.84x smaller in area than FF or FX digital. The upshot is that the 4/3 format uses very short focal length lenses,which have deep depth of field; with many 4/3 focal lengths, it is very difficult to get selective focus. The smaller the format, the deeper the depth of field at each focal length range: super-wide, wide-angle,normal,short telephoto,and super-telephoto.

The Kodak Disc Camera was invented as a film format that would be so small that absolutely NO focusing of the lens would be needed to create depth of field that extended from about 18 inches to Infinity. The Kodak Disc film format had a negative area of 11 x 8mm. The old mini-Instamatic 110 format had a negative area of 17x13 millimeters; not coincidentally, the 4/3 format sensor measures 17.3 x 13 millimeters, so you might equate the 4/3 format with shooting on the old Instamatic format.

The advantage of the 110 format and the 4/3 digital format is that even wide-ish apertures like f/2.8 have deep depth of field. On a 4/3 camera shot at f/2.8 the depth of field at more than a few feet distance with a normal lens will be quite deep. The disadvantage of the 4/3 format is that it has deep depth of field at apertures like f/2.8 with a normal lens focused beyond a few feet. Double-edged sword one might say.

 

A 4/3's sensor is half the size of a full frame sensor.

Therefore, the DOF on f/4 in FF can only be achieved in f/2.8 (one aperture stop down; ie, the diameter of the opening opens 2x wider).

The lens diagraphm opens the same size on the 4/3's system as on a normal system, but the DOF is affected by the sensor.

 

And don't forget subject to background and camera to background ratio distances... both have an effect on apparent DOF.