Canon's EF-S lenses have adopted an optimized optical system and mechanical structure to accommodate an APS-C size sensor that is smaller than a 35mm full size sensor.
For digital SLR cameras with an APS-C size sensor, the image sensor size is smaller than the 35mm film format, so the 35mm equivalent lens focal length is 1.6 times the actual focal length and the angle of view is shifted to the telephoto-side. For example, if a 50-mm lens is used with an APS-C size camera, the 35mm equivalent focal length is approximately 80 mm.
The following cameras are compatible with EF-S lenses:
EOS 7D / EOS 60D / EOS 50D / EOS 40D / EOS 30D / EOS 20D / EOS 20Da / EOS REBEL T2i, EOS 550D / EOS REBEL T1i, EOS 500D / EOS DIGITAL REBEL Xsi, EOS 450D / EOS DIGITAL REBEL XS, EOS 1000D / EOS DIGITAL REBEL Xti, EOS 400D DIGITAL / EOS DIGITAL REBEL XT, EOS 350D DIGITAL / EOS DIGITAL REBEL XT, EOS 350D DIGITAL
When attaching an EF-S lens, align the EF-S lens with the white, rectangular EF-S lens mount index on the camera. When attaching a lens that is not an EF-S lens, align the lens with the red EF lens mount index.
Note:
Features of EF-S Lenses
Thanks to the following reasons, Canon's EF-S Lenses have been able to achieve optimized performance despite their compact and lightweight designs.
- To accommodate the sensor size of APS-C DSLR cameras, the image circle (the circular area in the image plane formed by the cone of light transmitted through the lens) has been made smaller.
- To accommodate the smaller quick-return lens of the cameras, the back focus (the distance from the rear element of the lens and the sensor) is shortened further (short back focus) than that of the regular EF lenses.
Reference:
EF-S lenses have a mechanical configuration that makes it so that they cannot be mounted on cameras that are not compatible with ES-S lenses.
In addition, a protective rubber ring is attached to the back end of EF-S lenses so that the camera body is not damaged even if you try to attach the lenses to non-compatible cameras by mistake.
