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I need some help understanding crop factor. I do get that the actual focal length doesn't change, but as far as field of view and how the image turns out is where I'm getting stuck. Anything that I've been reading online is not very clear on this subject. If anyone could explain how this works in a simple way, I'd appreciate it. :)

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marked as duplicate by mattdm, AJ Henderson, MikeW, Itai, Nick Miners May 17 '13 at 6:36

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
Take a look at What is angle of view in photography?. That's not exactly the same question, but the two are intrinsically related and once you understand one you'll understand the other. –  mattdm May 16 '13 at 22:06
    
Also see What is the relationship between focal length and crop factor?, which has a number of answers hopefully explaining in a simple way. –  mattdm May 16 '13 at 22:07
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3 Answers 3

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Crop factor is the ratio between a full frame sensor (36X24mm) and the sensor you're looking at.

Sensor Sizes

While the same photons go through your lens, a smaller sensor will only "see" part of them as you can see here:

CropFactorExample

The perspective does not change but because you're seeing only part of the image it seems that you magnify it, hence, 50mm lens on a camera with crop factor of 1.6 (meaning that full frame size/the sensor size = 1.6 )will act like 80mm lens on a full frame camera

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Interesting to note: there are many sports and nature photographers who actually prefer APS-C over full-frame, because they get that extra zoom "for free" (though it's actually at the expense of less light hitting the sensor, assuming the same megapixels). Crop-factor is also why cell-phone cameras can be made with such incredibly small focal-lengths without looking like a wide-angle lens. –  BlueRaja - Danny Pflughoeft May 16 '13 at 23:20
    
Note that though the perspective is not changed, when you look at your image on screen, or print an image, the full image is the box above labeled 'The sensor'. Therefore, it appears 'zoomed in', offering a bit of a telephoto effect. It is cropped compared to a full frame sensor, but of course there is no black letterboxing around the image. –  cmason May 17 '13 at 1:05
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Quick answer, the crop factor times the focal length is the visual equivalent of the focal length on a 35mm camera. So a 35mm, full frame sensor has a crop factor of 1 and crop factors either go up or down from that depending on their relative size. Greater than 1 is a smaller sensor (since it appears as if the focal length is longer compared to a 35mm) and bigger sensors are less than 1 (since it appears as if the focal length is shorter compared to a 35mm).

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Thank you everyone for your answers. I believe I finally understand this. :) –  Dani May 17 '13 at 3:08
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Crop Factor is the relation of the size of the camera's image sensor compared to the industry standard size which is 35mm film format which is called "Full Frame DSLR". To cut the cost of the Camera, manufacturers intend to make DSLRs with smaller imaging area thus the crop factor is conceptualized.

enter image description here

  • Black – Full Frame Red
  • Red - 1.3x Crop Factor
  • Yellow - 1.5x Crop Factor
  • Green – 1.6x Crop Factor

When you enlarge images to the same size from different sensors the ones with the smaller sensors will be enlarged more – making it seem bigger. When you install a lens (e.g. for Nikon, FX lenses) to a camera with a smaller sensor (e.g. Nikon: DX cameras) the lens is often said to have a larger equivalent lens size.

Here's a table of equivalent lenses when installed with different sensor sizes: enter image description here

For more information check these links http://www.kenrockwell.com/tech/crop-factor.htm http://digital-photography-school.com/crop-factor-explained

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