BetterPhoto Q&A
Category: Problems with Photo Equipment - Tips & Tricks

F/Stop on Canon 70-200 f2.8 IS lens

So far, I've only tried it as mentioned above -- in low light outdoors or indoors where you can't use flash. For outdoor bright sun, I've reverted to my trusty old 75-300 f4.5-5.6, which is OK, but I'd like to upgrade to better glass and IS. I typically shoot in shutter priority, at speeds of 1/1250s or 1/1600s. ISO varies depending on lighting, dog speed, and dog color. I've read reviews that talk about stopping down to f4.0. I've also checked out other agility photographers' online work which includes EXIF data showing that they are using f stops of f8.0 or more in bright sun at similar speeds.

This seems like something I should be able to figure out, but I'm stumped. Or maybe I'm still missing the correlation between f stop, shutter speed, and ISO. Can someone help? At least with how to stop down the lens to f4.0 or less?

Any suggestions or comments would be greatly appreciated.

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July 03, 2008

First, follow this link and download a copy of the camera manual
http://www.cleaningdigitalcameras.com/pdf/EOSDRXT350DIM-EN.pdf
The title of the link is misleading, follow and you can get your own manual in a pdf version.

You stated you are using the camera in Tv Sutter-Priority AE however you are unable to alter the f/# and your always shoot using @ f/5.6.

Be advised that in Tv Shutter-Priority AE mode, the user selects the shutter speed (you have figured out how to do this) now you need to know that the camera’s chip logic AE (Auto Exposure) selects the proper f/# based on the light level (ambient light and ISO setting). In bright sun conditions, the built-in-logic is selecting small opening (large f/# values) like f/16 or f/11 etc. Otherwise your shots would be overexposed.

If you set the dial to Av Aperture-Priority AE, in this mode the user (you) selects the aperture and the AE (Auto Exposure) logic selects the appropriate shutter speed based on chip logic taking into account ambient light and ISO setting.

If you want complete freedom to set shutter speed and aperture you can set the dial to M Manual Exposure. In this mode the user is required to set both shutter speed and aperture. The wise chip logic allows you to observe the correct exposure. As you peer through the viewfinder, it presents an exposure indicator. Additionally, seasoned photographers often fall back on a separate, quality, handheld, light meter, and use its data to select aperture and shutter speed, for best exposure.

The bottom line, it won’t do you any harm to read the camera manual.

Alan Marcus (dispenses truly marginal technical gobbledygook)
ammarcus@earthlink.net

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July 04, 2008

Thanks for your reply. I have the camera manual and have actually read it, albeit 2 years ago when I first got the camera.

The rental lens didn't come with a manual, nor can I find it online. For some reason I was thinking that I had to do something manually to stop down from f2.8, as if it was perpetually set to that and only that. Must have been having a brain cramp.

Thanks for your technical gobbledygook of enlightenment. Knew it was an easy answer, but the forest was getting in the way of the trees.

Judy

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July 04, 2008