@crojai wrote:
Actually I did find some information on the programming of the program mode which gave rise to my question. If you google 'program mode program line canon' you get a link to cpn.canon-europe.com which gives a really good explanation of this. It's just that I can't find the charts for the the 18-55mm. I've read before that the system is suppposed to try to select a shutter speed compatible with handheld shots as a start so I was pretty surprised it was so far out. I would really like to find the 'program line' for the 60d/ 18-55mm.
Thanks for all the input. I'm hoping someone out there can point me in the right direction.
I think you mis-understand the "program line". It pretty much gives you an idea of how the camera calculate aperture and shutter speed for automatic exposure if you are curious. By knowing the line of your lens, it would not help you with anything. But if you want, you can calculate and graph it for your lens.
Back to your original question, you asked why at 18mm your shutter speed is 1/30s and at 55mm your shutter speed is 1/15s. The Canon "program line" in short says that Aperture will not be increased at least until reciporal of focal lenght is reached. At 18mm, your lens aperture is 3.5 and and at 55mm your lens aperture is 5.6 which is 1 1/3 stop slower. Thus, for a given scene, your 18mm f3.5 1/30 will be 55mm f5.6 1/5s.
This is purely my speculation but I think the camera takes into account the IS on your lens. The camera thinks that with IS enable, you can shoot handheld at 2-stop slower. So instead of having to pump up the ISO (or the ISO already reached its limit), they just low down the shutter speed. The correct exposure is F5.6 1/5s. But the camera thinks "it's too slow, the shutter speed need to reach 1/focal length taken IS into account. So ISO will be increased until 1/15s". Again this is just purely speculation.
