Focal length and 4/3 sensors

[Dan Cattermole]

Right! After a bit of arm twisting here we go.

Basically, and noticeably I have my OM 50mm f1.8, and an OM 35-70mm f2.8 macro lenses that I've bought recently with an OM to 4/3 adaptor.

I had a quick mess around with the lenses (as ya do) to get some idea of focal lengths. Testing what was in frame etc. I've always been under the impression with older lenses if, for example you had a 140-600mm film lens then that (in a full frame digital sensor) makes it a 70-300mm, so in affect, halving it..... (please do correct me if I'm wrong)

Now, my great little noisy little 4/3 sensor seems to project the focal length as it should be.... Digital lens or not.... So, if I put my 14-42mm digital lens on, and put it to around 35mm, it has the same focal length as my 35-70mm OM lens at...... 35mm of course.....

Should it be different or am i bieng retardation?? Lol

 

[Hamish Gill]

Roight... That's a confusing question so I'm going to make it simple

Your sensor has a 2x crop factor

So, your 14-42

To get the same focal length on a 35 mm camera you times that by 2

The lens that would give you the same effective focal lengths on a 35mm camera would be a 28-84mm

Focal length is a constant it is the size of the sensor that is smaller in your camera

Because the sensor is smaller you are effectively croping

A 14mm lens would be very wide on my camera but as your sensor is smaller it would e that same as cropping the image from my camera to give an equivalent of 28mm

Does that make sense?

On your camera a 50mm lens gives you the same as what I would get if I put a 100mm lens on my full frame camera!

 

[Hamish Gill]

A 140-600 lens would give you an equivalent of 280-1200
A 70-300 would give you 140-600