Autofocus I cannot get the AF to work when I mount my sigma DL macro super 70-300mm lense on my EOS 350D. Do you know what is wrong, and how can I fix this?

Sigma makes their lenses with a variety of camera mounts. If you get the lens with a Canon mount then yes, it will fit any EOS Rebel camera body. A lens with a Pentax mount, for example, will not fit a Canon camera.

Sigma makes lenses with a variety of mounts. As long as you get one with a Canon mount it will work on your 600D. A lens with, say, a Sony mount, will not work on a Canon camera.

Sigma makes lenses with a variety of camera mounts. A lens with a Pentax mount, for example, will not fit onto a Canon camera. Assuming you get the lens with the Canon mount, then it will work on the EOS 350D with full functionality.

If those lenses have a Nikon mount then they will fit on the D3000 and D3100. However, the D3000 and D3100 lack a focus motor. If the lens does not have the focus motor then you will not have the autofocus capability. Sigma calls their focus motor the HSM; if the lens does not specify HSM then they do not have the motor.

Assuming you get the lens with a Canon mount, yes. Sigma makes lenses to fit a variety of makes, but each one has a different mount. A lens intended for a Nikon, for example, will not fit a Canon.

All after market lenses are specifically designed for a brand of camera. They are for Nikon, Cannon, Minolta etc.. They can not be cross branded just as you could not use a Nikon made lens on a Pentax.

You can't, not as far as I know.

Getting functionally useful adaptors from any other brand to Canon EOS is difficult as the register distance from the sensor to the lens is the deepest of all current lens mounts. Adaptors therefore require expensive optical correction in order to preserve infinity focus ability and given that the adapted lens will still be substantially crippled most owners aren't prepared to pay for such an adaptor. In any case, the additional optical elements will reduce optical quality.

Due to similar electronics, it is possible to physically convert a Sigma mount lens to EOS by fitting an EOS lens bayonet but it's a skilled job requiring fabrication skills and even then there's no guarantee that the lens will communicate correctly with all EOS bodies. In practice, due to the scarcity of Sigma mount lenses the conversion is usually the other way around.

Yes, if you get one with a Canon mount. Sigma makes their lenses available with a variety of mounts; a lens with a Nikon mount, for example, will not fit on a Canon camera.

Are you sure you bought a lens with Canon AF mount? To me it sounds like you got one with a mount for a different camera.
Does the mount on the lens look like this?


If it doesn't, you got the wrong version of the lens. If it does look like the mount in the picture, your just mounting it incorrectly.
If you hold the camera with the lens mount facing you, the red marker on the lens should be in the 12 o'clock position, lining up with the red marker on the lens mount on the camera. The turn the lens clock wise, about an 8'th of a full turn, and the lens should click into place.
I hope this help you!
/Chris

Here is Nikon's specs of lens compatibility for the D40X:


Compatible Lenses*: Nikon F mount with AF coupling and AF contacts Type G or D AF Nikkor:
1) AF-S, AF-I: All functions supported;
2) Other Type G or D AF Nikkor: All functions supported except autofocus
3) PC Micro-Nikkor 85mm f/2.8D: Can only be used in mode M; all other functions supported except autofocus
4) Other AF Nikkor*â¹/AI-P Nikkor: All functions supported except autofocus and 3D Color Matrix Metering II
5) Non-CPU: Can be used in mode M, but exposure meter does not function; electronic range finder can be used if maximum aperture is f/5.6 or faster
6) IX Nikkor lenses cannot be used
*â¹ Excluding lenses for F3AF

They do not recommend 3rd party lenses, ever