Equipment I Use
I use a Canon EOS 500D SLR and have the following additional lenses: –
- Standard Canon kit lens 18 – 55mm EF-S, f/3.5 – 5.6
- Canon prime lens 50mm EF-S, f/1.8
- Canon 28 – 135mm EF-S, f/3.5 – 5.6
- Canon 100 – 400mm EF-S, f/4.5 – 5.6
- Canon Extender X 1.4 EF
This camera has an APS-C sensor which gives a cropping ratio of 1.6 and therefore makes each of the lenses above 1.6 X their stated focal length. The 28 – 135mm lens was created for APS-C sensor cameras and the focal length markings on the barrel correspond to the cropping factor being taken into account.
Having used Canon digital cameras for some years now, I have become used to the visual effects given by each of these lenses and I’m comfortable knowing their individual pro’s and con’s.
I also own a Canon EOS 3 film camera, which I use on occasions, which helped me understand the differences between full-frame cameras and cropped sensors.
Exercise: Focal Length and Angle of View
With both eyes open, take a shot of the scene when the image in the viewfinder seems to be the same size as the image in the eye not using the viewfinder. This will help determine standard focal length for that lens. Take a further 2 shots of the same scene from the same place; 1 at widest angle of the lens and 1 at full zoom.
Having printed the 3 images at A4, I compared them with the real-life setting and found that I needed to hold the standard image ~45cm from my eye for the two images to appear ~ the same size. The zoom image needed to be ~ 190cm from my eye, which was ~ the same distance as the camera sensor was from the subject when all the shots were taken; the wide image needed to be ~ 22cm from my eye. The printed focal length on the barrel of the lens for the standard shot was ~55mm.
Although I’ve used this lens on many occasions, I’ve never measured the distances eye – printed image – real life setting and was surprised at the correlations. Thinking about it, I now understand why this is true. I also realise that looking at images and comparing them with real life objects, along with printed focal lengths on lenses, are all APPROXIMATE.