APS-C VS Full Frame

All of us know that Canon 5d3 is around the corner and maybe it will be launched in August or maybe September (I’m wrong! 5d Mark III is announced on 2nd March 2012 ). This time I got confused about the difference between aps-c and full frame camera. All I know is full frame will give us more depth of field and it is wider because it doesn’t have crop factor. I asked someone at canonrumors and he gave me a brief and full explanation (thanks to neuroanatomist).

This what he has told me and I will explain it in my own sentences , APS-C VS Full Frame sensor :

First, sensor size affects two things :
[1]. Field of view (FoV). Also FoV affects 2 things :
—a. Focal Length (object framing)
—b. Depth of field
[2]. Light gathering for the sensor.

These will be explained one by one.

Field of View Difference Between APS-C and Full Frame

[1a]. FoV affects focal length

I take this image from photo net. You can see there, the same image will have a different field of view thus affects only focal length. It won’t affect depth of field yet (in this example -> full frame uses X lens compare with aps-c uses X lens). Why we can get this result? Aps-c has 1.6x crop factor. So if you mount 50mm on full frame camera, the focal length is 50mm. If you mount 50mm on aps-c camera, you must multiply it with 1.6. 50mm becomes 80mm. That is why the field of view of aps-c is narrower than fullframe.

Depth of Field Difference Between APS-C and Full Frame

[1b]. FoV affects depth of field

I take this photo example from http://www.flickr.com/photos/8413680@N08/4096725884/lightbox/
It will describe this point perfectly!
After looking at point 1a, you will think that you can use different lens to have the same focal length. Yes! It is right! To have the same focal length as full frame + 85 mm, you can use 50mm on aps-c camera. Now you get the same focal length but not the same DoF. Why?

There are 3 factors that influence DoF :

  • lens aperture (wider aperture gives shallower DoF)
  • subject distance (closer subject to camera gives shallower DoF)
  • focal length (longer focal length gives shallower DoF)

Okay, you’ve set your aperture to the widest, you have the same subject distance, but don’t forget the last thing! While having the same focal length, full frame has 85mm lens on it and aps-c only has 50mm on it. So full frame automatically gets a better depth of field.

[2.] Light gathering for the sensor

Full frame camera has a bigger sensor. Bigger sensor gathers more light then smaller sensor. That’s why full frame performs better when it uses higher ISO. Full frame sensor will have 1.3 stops less than aps-c sensor. That means  if you use ISO 2000 on your aps-c camera and ISO 3200 on full frame camera, you will get the same noise level.

 

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