Not Your Everyday Banana

by Bart Arondson

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I often hear about sensors being full frame (which I think means 35mm sized) and others being cropped (if they are less than that) such as APS-C sized sensors.

My question is what is so special about the size 35mm? Why is it used as the standard against which everything else is measured? Is it the largest sensor possible or does it have some other characteristic that makes it stand out?

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2 Answers 2

up vote 12 down vote accepted

For digital cameras, it's purely due to historical reasons - 35mm was the dominant size for film cameras and cinematography. As for why film cameras ended up with 35mm, I'd suggest 35 mm film and 135 film on Wikipedia as a good place to start. It's also worth noting that "35mm" is not actually the size of the image, which is 36x24 mm, but the width of the film.

It's certainly not the largest sensor available - a number of companies (Hasselblad, Phase One, Pentax) make "medium format" sensors which are larger than 35mm sensors.

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It's worth noting that 35mm is the largest sensor available at consumer prices (below $2000) - even slightly larger sensors (Leica S: 45mm x 30mm, Pentax 645D: 44mm x 33mm) carry a much higher pricetag. –  Matt Grum Aug 28 '13 at 12:10
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@PhilipKendall "35mm was the dominant size for film cameras and cinematography" Actually, that's not the whole truth. The dominant size for cinematography was 35mm film shot vertically (sprokets left and right) which gave a smaller frame size similar to APS-C or Nikon "DX", whereas the dominant size for stills photography was 35mm film shot horizontally, which is also termed the "135 format", and gives around double the frame size because your photos are laid out horizontally (sprockets top and bottom). So while the film was the same width in both cases, the frame size was quite different. –  thomasrutter Sep 2 '13 at 2:35
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Because the standard size for film cameras for a long time was 135 film which measures 35mm in width including the perforations and leaves enough space for a 36x24mm negative size. Since the Field of View (FoV) for any particular focal length lens is determined by the size of the film or sensor onto which the image circle is being projected, over time various focal length lenses became associated in photographers' minds with a corresponding FoV for that focal length when used with a 35mm film camera. By relating digital sensors of other sizes as a linear ratio to the size of a 36x24mm 'full frame' sensor, it makes the task of figuring the equivalent Angle of View (AoV) for any particular focal length lens a simple exercise of multiplying the the smaller sensor's crop factor by the focal length of the lens.

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Nice explanation, I would love it if you could expand on this please. You introduced some quite complex concepts here like FoV, AoV, crop factor and focal length. It would be good if this could be illustrated by diagrams and examples. –  Sachin Kainth Aug 30 '13 at 15:27
    
If you search this site for Field of View, Angle of View, crop factor, and focal length there is more than enough information already here including the charts and diagrams you request. If you have trouble using the search box, perhaps you could ask a question regarding that on the meta site. If that doesn't help you could try the chat room, where I'm sure on of the regulars such as AJ Henderson would be willing to draw you as many charts an diagrams as you wish. –  Michael Clark Aug 30 '13 at 15:58
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