Coverin contact to stop a lens down

[GenDEM]

Hi there

Now bear with me here, I'm new to the SLR scene.

I have a 10D and I was tonight attempting to shoot an indoor soccer game with a 100-300 4.5-5.6 lens. Of course, at max zoom, the lowest I could go was 5.6...this lead to most shots being dark to avoid blur, even at 3200 ISO.

I've read in other forums that there are contacts you can cover on an EF lens to trick the camera into letting you stop down lower than the lens is rated. It sounds good...but there must be a reason why a lens is rated the way it is.

Before I go and try this for myself, can someone offer an explanation, or point me at one, of why lenses are rated with an f number at all, the ramification of shooting below the lens's rated minimum F stop, and if anyone does this in Real Life or if it's a half wit posting rumors that I fell for?

Thanks

[henkbos]

This seems magic to me: piece of tape and you gained 2 stops while the physical hole that the light passes through remains the same!
The only thing I can imagine is that the tape will stop passing that info from the lens to the camera and will somehow trick the exposure meter.

Curious to other responses.

[bluebomberx]

The purpose of taping contacts on lenses is to retain auto focus capability at f/8. Canon EOS cameras will not attempt to auto focus if the maximum aperture of the lens in reported smaller than f/5.6. This happens when using a 2x teleconverter on lenses such as the Canon EF 70-200 f/4 L. The tape prevents the aperture data from going back through the contacts on the lens mount, thus retaining auto focus because the camera will think it is still at f/5.6 or lower.

-Richie

[henkbos]

Ritchie,

Can you tell us which contact?

[bluebomberx]

I don't have a clue, but search around on the D30/D60/10D forums over at http://www.robgalbraith.com to find out. I haven't needed to do this with any of my lenses so never bothered to learn more than I already posted ;)

-Richie

[Roger_Cavanagh]

It's explained here:

http://www.fredmiranda.com/TipsPage/

Regards,

[Yance]

gendem wrote:
I have a 10D and I was tonight attempting to shoot an indoor soccer game with a 100-300 4.5-5.6 lens. Of course, at max zoom, the lowest I could go was 5.6...this lead to most shots being dark to avoid blur, even at 3200 ISO.


Physically the aperture of the lens can open so far, so if you set the maximum aperture that is what you will get. Stuck with the conditions you had for indoor soccer you will either have to use a flash or invest in a better lens, either an f4 or f2.8. There really is no other way around it.

[GenDEM]

Thanks for all the feedback. This shoot was an experiment that likely won't be repeated, but it has made me think a bit differently about lens selection...it's one thing to read about lens metrics, and quite another to see the effect of them right in front of you. Perhaps the 28-135IS would have been a better choice of a starter lens.

Thanks again