In Damians last post he mentions that he has just taken possession of a monster of a new lense and that due to him using it on a Canon 350D, a cropping APS-C DSLR body (not a full frame 35mm DSLR such as the Canon 5D) there will be a “multiplication factor” that makes the output appear to be even more powerfully zoomed.
What exactly does that mean?
Well with a “prosumer” or entry level DSLR you do not get a full sized sensor. The side effect of the smaller sensor is the resulting image is “cropped” but it can be thought of as “zoomed”…
While it doesn’t really, it is common to think in terms of the focal length changing in order to understand the difference in captured image size. The decreased coverage resulting from using a smaller sensor will proportionally match what you would get when using a longer lens on a larger sensor. For instance, the sensor size in Nikon digital SLR’s is around 16mm x 24mm which is two-thirds the size of a frame of standard 35mm film at 24mm x 36mm. Since the film frame is therefore 1.5 times the size of the sensor (the inverse of two-thirds), we will get the same coverage on our Nikon sensor as we would by using a lens with 1.5 times the focal length on 35mm film. The narrower angle of coverage the longer lens will yield mimics the narrower coverage produced by the smaller sensor. Because of this, some people talk of this as being a “focal length multiplier” for digital. Since the effect is produced by the sensor size and the lens focal length doesn’t really change, “crop factor” is definitely a more correct term.
In practical terms this means my Canon 350D with 50mm lens is working at an effective “pseudo focal length” the same as a 85mm on a 5D. Weird huh?
Originally the promise was that these smaller sensors would reduce the price and make for a smaller and lighter overall package without sacrificing too much of the demanded quality. In actual fact there is not much difference in size and weight, and the quality difference isn’t so great that an average-Joe photographer should be put off, but there is definitely a difference in price.
The difference in price might be more down to the full frame backs are only aimed at the pro market and the entire field is pretty much owned by Canon. Nikon do not even have an answer to the EOS 5D or EOS 1Ds Mk II at all. Nikon are restricted by having third parties involved in their sensors and so only make APS-C cameras, while Canon having their own CMOS designs and manufacture capability produce both sizes.
To really mix it all up, lense manufacturers have lines of product that cater just to the APS-C owning crowd. These lenses, unlike your standard 35mm SLR lenses, will only work with the cropping sensor bodies. A 35mm digital lense really is 35mm, and often are smaller and lighter than the standard equivalents also. This can certainly be an advantage but does mean if/when you upgrade to full frame you will not be able to repurpose your lenses as they will not fit.
Of course many people make the argument that APS-C are plenty good enough. It is generally agreed though, outside of Nikon, that the same number of pixels on a full size sensor will give better image quality. Whether the difference in quality justifies the increase in price is for only you to decide but personally I am happy with my Canon 350D output … currently.
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