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What is a full frame sensor?

Posted by Matt on August 23rd, 2007 filed in Beginner Tips, Digital Photography Hints & Tips

In my last post on new Canon cameras I mentioned the EOS-1Ds has a full frame sensor, whereas the new 40D doesn’t. Some of you may be wondering what this means.

For those of you who remember film cameras (yes, they still exist) you’ll know about 35mm film – the most common film size used in consumer cameras. Each frame of the film is 24mm x 36mm, ironically over 35mm along the top! The picture taken with film cameras fits into this space, and is printed to make your photo. With digital cameras electronic ‘film’ is used – the CCD. This CCD sits in exactly the same spot as the film used to, but the main difference is that it doesn’t ever move (this is why dirt can become an issue, something we’ll discuss in later posts).

Comparison of film and CCD sizes

So a ‘full frame’ CCD is one that is exactly the same size as the old 35mm film – 36mm x 24mm. This is less common than smaller sensors, mostly because smaller sensors are much easier and cheaper to make. In the case of the 40D (and it’s siblings the Canon 20D and 30D, as well as the Rebel range) the CCD is 28.6mm x 19.8mm – a format called APS-C that is roughly 7/9 as wide and 5/6 as tall. So not only is it a smaller area, it’s also has different proportions to 35mm film – it’s slightly wider.

What does this mean to you? Well, a full frame sensor generally products sharper, more detailed images as it has more space to resolve the details in the image – although with a good APS-C camera you’ll probably not notice that much. What you will notice is if you use your old film SLR lenses on your new digital SLR, as there is an effective magnification of about 1.6x – eg, your old 50mm lens now behaves like an 80mm lens. This is not so good if you like wide angle shots, but great if you’re into long distance zoom lenses! That said, the photo you take full frame with an 80mm lens is not the same as that you take with a 50mm on an APS-C camera, it is just a cropped image that gives the impression of greater magnification. Life is never simple.

Now you know what a full frame sensor is, and some of the issues that can arise. You may now be adamant you want a full frame camera like the Canon EOS-1Ds, but be prepared for some sticker shock – they are much more expensive due to the cost in producing the sensors. If you have the chance try out an APS-C camera to see if you like it, chances are it will be fine for your uses and you can spend the extra money you save on a high quality, fast lens that is a much better bet for improving your photos.

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