Toronto Photography Meetup Group

I was thinking the other day that it might be a good idea to turn off my lens image stabilizing when doing long exposures of the CNE rides. This got me wondering what the 2 diferent IS modes were for. In picking up my manual for my Canon lens I came across this other unrelated section about the "Infinity Compensation Mark" which compensates for shifting of the infinity focus point that results from changes in temperature.

Anyone know what this 'tool' does and how/when to use it?

I've wondered about it myself, and come to the conclusion it's not something that is suitable for manual adjustment, it's just something the camera AF system uses to have different infinity focus positions for the lens elements depending on the temperature, so that if you ever have to look at the focus distance, this whole range of positions is actually infinity focus for the lens.

It's not like we could go "Oh, it's -20

I don't think the distance scale on the AF lenses has any practical purpose.

I know when to use it, but my current viewfinder is useless for manual focusing, so is the scale more or less

You have it on all long or large telephoto lenses. I think that with such a large piece of metal and glass you can have thermal expansion and contraction of the lens due to the ambient temperature. By not having a hard infinity stop but allowing it to turn slightly past the infinity mark on the lens barrel you allow the user to still achieve infinity focus while compensating for the temperature effects on the lens.

Another infinity compensation mark found on old manual focus lenses was made for use when using infared film in your camera. The infared wavelengths focused at a different point compared to visible light and this was marked on lenses. So you would focus your camera visually and then turn the lens to the dot or mark and take your picture.