550d Zooming during movie

Started Feb 26, 2010 | Discussions thread
caterpillar Veteran Member • Posts: 7,643
Not all zoom lenses are parfocal

skanter wrote:

caterpillar wrote:

Also, the lens has to be parfocal. It means, it must maintain the initial focus otherwise, there is added work to re-acquire focus.

Is this listed in specs - or, how can one accurately test if a lens is parfocal? All prosumer videocams I've used are parfocal, not sure about zoom lenses I use with T2i.

Not all lenses are parfocal. Most L lenses are. But there is no guarantee as I have not tested all the Ls. But I know some consumer grade lenses are NOT parfocal. I know my 70-200 f2.8L IS is. You can test it by zooming in to the max, say 200mm at the widest aperture, AF and lock focus, Shift the lens's AF to M or manual, take a picture. Then pull out the zoom at the widest FL, also at widest aperture, take the picture. Go to your PC or MAC and download the images. If your image is in focus at 200mm as well as as it's widest FL, well in my case it's a 70-200mm lens so it's 70mm, the lens is parfocal.

You may also try to visit the Canon lens web site. It may be listed there. Not sure though. But you can always test.

  • Caterpillar

'Always in the process of changing, growing, and transforming.'

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