70D and third party lenses

[bjanusch]

In the case of the lenses mentioned, the Tamron 17-50 non-VC uses LensID 161, which is Canon's code for the EF 28-70mm f/2.8L - and that lens is on the above list of lenses with limited compatibility. Likewise, the Sigma 18-125 uses LensID 6, which is Canon's code for the EF 28-70mm f/3.5-4.5, also on the above list.

To fix this issue, Canon would need to update the 70D firmware to deliver full compatibility with those old lenses.

The lenses don't show up in camera as the wrong lens. They show up as just the focal range. Perhaps I don't understand your comment?

I was mostly trying to give real usage examples of how these 3rd party lenses perform.

[neuroanatomist]

The lenses don't show up in camera as the wrong lens. They show up as just the focal range. Perhaps I don't understand your comment?

I was mostly trying to give real usage examples of how these 3rd party lenses perform.

AFAIK, there's no way to know how those lenses show up in the camera - the camera doesn't display the lens used, the focal length (which I'd really like if it did), etc., just the exposure settings.

The way it works is the lens firmware reports a LensID to the camera, and the camera has a look-up table that inserts a description, and both are recorded in the EXIF. I don't believe that Canon has entries for 3rd party lenses in that table - why would they? When you view the file on your computer, most image viewers/RAW converters have their own look up tables that try to assign the correct lens make/model based on multiple fields in the EXIF, and failing that, they just report the focal range with no make/model info for the lens.

The camera's look up table determines how the camera behaves with that lens mounted, in regards to the AF system. For example, if you put a Canon 1.4x TC on an f/5.6 lens on the 7D, the camera will not attempt to autofocus. But, if you put a piece of tape over three of the 10 contacts on the teleconverter, the camera won't know there's a TC attached, and it will AF (sometimes successfully). Some models of 3rd party teleconverters allow the same behavior without taping the pins. As stated above, with the Tamron 17-50 non-VC, the 40D/50D/60D and 7D peripheral AF points do not function as cross-type AF points - vertical or horizontal lines can only be detected separately, not simultaneously. That's not because of anything optically wrong with the Tamron lens, but rahter because those cameras 'think' the 17-50/2.8 is actually the EF 28-70/2.8 lens. Since the 70D inherited the 7D's AF sensor (and likely the relevant bits of firmware), I'd bet that the 70D also activates the off-center AF points as lines and not crosses.

The real world example of the lenses you mention is good information. My point is that the reason you're seeing limited compatibility with those 3rd party lenses isn't due to the performance of lenses themselves, but rather to the fact that the camera 'thinks' those lenses are actually old Canon lenses.