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Taking Advantage of Crop Factor

Should I get a Canon 5D MKII, 7D, or 1Ds MKIV ?  This is a question I am often asked when someone is looking to buy or rent an HDSLR.  There are several trains of thought that seem to be the main focus from one camera to another, and usually the conversation boils down to a low light and sensor size issue.  Yes, the 5D MKII has a significantly larger sensor over the 7D, and it does have better low light capability as a result, but there are other factors to be considered.  The focus of this specific blog entry is to address the factor of crop with the 7D and 1Ds MKIV, and how this can be seen as a positive rather than a negative.  I say this because I often hear people complain about using full frame lenses and the focal length multiplier as though this is a bad thing.   With regard to wide angle — yes, it greatly reduces your focal length options.  On the telephoto end, however, is where this can be a huge advantage. Before I go any further I will explain crop factor (I have seen several people try to explain it so I will keep it as simple as possible): When you use full frame lenses on non-full frame cameras (7D APS-C and 1Ds MKIV APS-H for example), the image appears bigger (magnified) because the field of view is smaller giving the lens a focal length multiplier.   If you are shooting sports or nature subjects on stills or HD, you will want to leverage the focal multiplier of 1.6x of the 7D and the 1.3x of the 1Ds MKIV.  The benefits are — you do not require a telephoto adapter or 2x or 1.5x extender.  The reasons for avoiding both are due to loss of 1 – 2 stops of light and the possible introduction of aberrations (chromatic and otherwise), flaring, trapping dust between optics, weight, etc.  You can always add a 2x extender onto a crop camera to get even tighter on your subject if applicable. Here is a brief breakdown of some common telephoto focal lengths when coupling a full frame lens with a 7D: 85mm = 136mm,  100mm = 160mm, 135mm = 216mm, 200mm = 320mm, 400mm = 640mm, 600mm = 960mm & 800mm = 1280mm Now if you apply a 2x extender like the Canon 2x EF Extender II your 960mm (600mm) will become a 1920mm (with a loss of 2 f stops ). There are factors to consider when using these new-found focal multipliers.  First thing to remember is that your foreground / background relationship does not change.  The lens properties remain the same unlike if you switched to a different lens. Second, you want to ensure that when using long lenses like the 100mm and above that you have some form of image stabilization built into the lens or a sturdy support system.  I managed to use the Canon 600mm this weekend on loan and threw it on my 7D for a 960mm equivalent focal length.  To use a multiplier like this requires you to either trigger the camera via remote or hold your breath while shooting as any bump, wind, etc. on the lens amplifies.  I had to use a heavy-duty video tripod with the release plate mounted to the lens foot to get anything useful on video.  This, of course, was an extreme field of view and not typical with focal lengths under 300mm. A large benefit for crop factor is for use with macro video and stills.  I shoot a lot of macro HD video of everything from insects, reptiles, textiles,  products, etc.  Macro functionality even with the focal multiplier is retained — which is important.  This can be handy when dealing with subject matter that may dangerous (shooting scorpions), or jumpy (see frog below), or when you just need more detail or a closer view without losing any stops of light.

Green Frog with 160mm equivalent field of view. (JPEG still pulled from HD Video shot on 7D w/ 100mm f/2.8L Macro IS  @ f2.8 shutter 50, ISO 320 *scaled down from 1080)

If you are going to focus shooting HD video of  nature or sports, you should  take a look at the Canon 7D and Canon 1Ds MKIV as alternatives to the 5D.  The crop factor will save you the weight of lugging around a 400mm or 600mm lens, plus it will save money (long lenses are expensive), and it will keep you more inconspicuous when needed.

Mike Sutton, Senior Account Manager Twitter: @MNS1974