BIRDER'S JOURNAL
January 3 , 2013

SUBJECT: When a Camera's Crop Factor Makes a Difference

Quite often photographers are lured into thinking that a sensor's crop factor magnifies an image, producing more "reach." This is not the case. As an example, if photographer (A) was using a DSLR with a 10 megapixel, 1.6x cropped sensor and photographer (B) had a 26 megapixel full-frame sensor camera, which photographer would obtain the best resolution of a bird shot at the same distance using the same lens, assuming both sensors had the same technical specs.?

Photographer (A) would look in his viewfinder and find that the bird would almost completely fill the field of view while photographer (B) would look in his viewfinder and find that the bird was much, much smaller.

Photographer (A) might be lured into thinking that his image would contain much more detail compared to the image produced from photographer (B)'s camera.

In fact, both cameras would produce the same amount of detail of the bird. The difference between both photographer's cameras is nothing more than the field-of-view. Photographer (B) would have a much wider field-of-view, but the pixel density would be identical to photographer (A)'s camera and therefore produce identical detail of the bird.

So the next time you hear someone say "I like xyz camera because the crop factor gives me more reach.", Set them straight. It's not the crop factor of a camera that determines "reach." It's the density of sensor's pixels that will produce greater "reach" or resolution.

Please note: In the above example, I purposely chose to have both cameras with equal pixel density. The 10 megapixel camera's sensor is smaller compared to the full frame sensor but if it were manufactured into a full-frame sensor, it would equal 26 megapixels. (10 x 1.6 x 1.6 = 25.6 Megapixels)

And now that I have stated the above, I retract everything I just stated...That is...When it comes to video!

Most if not all DSLR manufacturers today offer video. Usually it's either 1080p (1920 x 1080 pixels) or 720p (1280 x 720 pixels). In all instances video resolution is much less than the DSLR's full resolution and in most cases the manufacturers average the pixels across the entire sensor. This basically dumbs down the sensor to make the entire sensor only 1280 x 720 pixels if we were to shoot 1080p video.

Because manufacturers choose to use the entire sensor to emulate 1080p or 720p, we are forced to use the field-of-view as our source for video production.

Using the scenario found at the beginning of this article, photographer (A) would be the clear winner compared to photographer (B). Photographer (A)'s video would have much greater "reach." His video would show the bird up close, while photographer (B)'s video would appear much more distant.

Let's now take a look at a real world example of how the camera's crop factor plays a huge role when it comes to video.

The following video contains footage from three different cameras: Canon 5D Mark III, Canon 7D and the new Panasonic Lumix GH3. All were shot using the Canon 600mm II f/4 IS L lens from a set distance to a suet feeder.

The Canon 5D Mark III has a zero crop factor, while the 7D has a 1.6x crop factor and finally, the Panasonic Lumix GH3 has a 2x crop factor. Oh...and let's not forget about the Panasonic GH3's teleconverter feature that only uses the camera's center pixels to produce a video. This feature does NOT average the pixels across the sensor. It uses the center pixels only. This has the effect of doubling the resolution! Gosh, I'd love to see Canon incorporate this into their firmware. Why they do not do this is beyond me! They really are missing the boat by not using this feature.

Please note: The Panasonic Lumix GH3 with the Canon 600mm lens uses a dumb adapter. Image stabilization is not available. This is a bummer to be sure. (I am hoping Metabones will come out with an adapter this year that will allow for this.) As you will see in this video, the Panasonic Lumix GH3 when using the teleconverter feature, magnifies the image to the point in which image stabilization would have REALLY HELPED!

Here's the video:


—Alan Stankevitz

 

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