by Scott Fairbairn
This discussion concerns a topic that is often debated amongst photographers. All digital cameras have a sensor that is used to capture your image. These sensors are not however, created equal in either size or in quality.
You may have heard the term 2x (times) or 1.6x magnification factor applied to a particular camera. There is even a professional camera with “2x” mode. The big question is “what does this mean and what is the impact on nature photography?”
In the good old days of film photography, the camera of choice was often the “35mm” SLR. The film captured images that measured 24mm by 36 mm wide. When digital SLR’s began to replace film, it was too costly to make a sensor that size, so manufacturers made sensor size’s much smaller.
The image at the beginning of this article shows the relative size of popular sensor sizes that exist today, compared to the original film size. The red box represents the traditional 35m film image size compared to the popular sensor sizes today(Nikon uses 1.5x which is very close to the 1.6x). To date, there are only a couple of digital SLR’s that have sensors the same size as the original film image size(Canon 1DsMII and 5D).
The digital magnification that is thrown about refers to a perceived magnification that is obtained by using one of these smaller sensors. Let’s have a look at the comparison images below. (Note: Images are for comparison purposes only, do NOT compare colour or sharpness between cameras!)
All three images were taken at the exact same camera to subject distance, same aperture and shutter speed, and same lense. The cameras were interchanged and images taken sequentially. These images are exactly what you would see on your computer screen.
The first thing you notice in this comparison, is that the image on the right(cropped sensor, Nikon and Canon 20D,30D lineup) has a much larger subject than the other images. For a bird or nature photographer, this can be a big plus as it means you can get a frame filling image farther from your subject than you could with film or a full frame sensor. This is great news because it is often tough to get closer to a wild animal without causing it to flee.
The next image compares full frame sensors to cropped image sensors in another way. So if we can get a frame filling subject at a farther distance than before, then we can also get the same image, at the same distance, with a shorter telephoto by using a cropped sensor. To better understand this, look at this comparison image.
The image on the left is via a 600mm lense using a full frame sensor, the image on the right is from a “cropped” sensor(aka. Canon 30D,Nikon DSLR) camera using a 400mm lense. The obvious advantage is you get the same image size with a less expensive camera and lense, and the 400mm lense weighs nearly 10 lbs less!
To summarize, you can get more “telephoto” effect with the same lense(compared to film/full frame sensor) by using one of the digital SLR’s with a “cropped” sensor. Of course this isn’t the end of the story, otherwise why would Canon be investing so much in developing full frame sensors? I also haven’t discussed camera resolution(megapixels) and sensor density(number of recording sites per surface area) yet. The short answer to the first question has to do with image quality. The promise of larger sensors is the ability to give better dynamic range(ability to record shadows and highlights), and lower digital noise at higher ISO’s. To this end, Canon’s full frame sensors deliver on this promise. The effect of megapixels and pixel/sensor density I will leave for another Tip’s installment!
by Scott Fairbairn
