Canon EF 70 - 200 f2.8L IS USM Zoom lens

[cfranks]

I've fitted this lens to my QSI683ws and ask is there any way to reduce the aperture from the (apparently) fixed 2.8 to, say, 4.5 or so? I think I read somewhere that mounting it on a Canon camera, taking a long exposure at f 4.5 and removing the lens while the exposure is underway will leave the lens set at 4.5! Seems very dodgy to me so I thought I would ask the experts here.

Charles

[troypiggo]

Not dodgy, just inconvenient.

Only other way I can think of is to make an external aperture. Ie a circular disk over front of lens. Some use cardboard for simplicity. Other DIY lens cap mods or use filter step rings.

[cfranks]

Thanks Troy, I was going to try that. I bought a 'nested set' of filter reducer rings to try when the clouds go away. I know nothing about the construction of these lenses and didn't know if there is a variable aperture built in that the camera controls electronically. Hence the naff question!

Charles

[Octane]

Don't remove the lens during an exposure.

Instead, stop down the lens to whatever aperture you desire, press the depth-of-field preview button on the side of the body, and, then remove the lens while the button is depressed.

H

[troypiggo]

D'oh. What H just wrote is what I had in my brain that you had written in the OP. Completely misread your method. He's right. For once. :P

[Octane]

lol, cheeky.

H

[cfranks]

Thanks Octane, that was what I had read before!! I don't feel too much of a dummy now, just a bit forgetful!

Charles