On Digital SLR’s, when mounted with a lens of given focal length, you would have noticed a considerable change in the Field Of View, when compared to a film camera. This is nothing but the “Crop Factor”.
The field of view (also field of vision, abbreviated FOV) is the (angular or linear or areal) extent of the observable world that is seen at any given moment.
Let’s consider the prime 50mm lens:
The field of view through a lens when mounted on a 35mm film camera versus a Digital SLR differ noticeably and this is because of the “Digital Crop Factor”
Traditionally, the medium to capture images on a camera was film (which was 1.4in or 35mm wide) and lenses were built for 35mm medium but when Digital SLR’s came into existence the sensors in DSLRs were not 35mm – it’s not because they couldn’t but making a sensor of 35mm increased the production costs and hence the cost of the camera – thus manufacturers came up with an optimal sensor size that would be cost affective and thus appeal to the customers and DSLRs were born. However, a DSLR has to be backward compatible too i.e. they had to mount traditional lenses – that was not a problem however, the field of view would drop because the capturing sensor is not of the same size
By how much would it drop? let’s see a few examples
For Canon EOS 350D the sensor size is 22.2 x 14.8 mm
For Nikon D70S the sensor size is 23.7 x 15.6 mm
The formula to calculate the crop factor is just divided the sensor size by 35 (because 35mm should be the designated sensor size)
For CANON EOS 350D DSLR the crop factor calculates to 35/22.2 = 1.6
so now the field of view, for a 50mm lens, on a D-SLR translates to:
field of view = focal length of the lens X crop factor
i.e. field of view fov = 50 x 1.6 = 80mm (i.e f.o.v is equivalent to a 80mm lens)
wow!! it’s almost become a tele photo lens? – not exactly
Note that the focal length remains the same but the field of view of this lens now becomes the equivalent field of view of a 80mm lens.
If you are a DSLR (serious amateur level) user and if you are going to buy a lens then don’t forget the crop factor otherwise you end up picking a high quality expensive lens expecting to have a f.o.v equivalent to the focal length but you’ll end up with much lesser. So plan your buy keeping the full frame sensor in your mind.
Invest in expensive lenses only if you are going to switch to a full frame sensor in the future.
For Nikon and Fuji D-SLR users the crop factor is approx: 1.5
For Canon D-SLR users the crop factor is approx: 1.6
