Any word on the compatibility with the 70D's dual pixel AF and third party lenses? I remember reading that Canon spent a year working on the algorithms for all the different lenses. Does that mean that it is the 70D that has be compatible with the lens not the other way around? For example, even if you upgraded the firmware on the lens does the firmware on the 70D also have to be upgraded to be fully compatible?
Hmm......good question.
I use my Tamron 17-50 quite a lot on my 70D and it works fine through the viewfinder. Live view is a whole other story. Something about the live view AF causes this lens to hunt in little chunks at a time until it eventually focuses. I'm talking minutes. The lens also works OK in video until your focus target changes significantly and then you may as well just stop recording.
The story is almost the same for the Sigma 18-125. The AF motor on that lens is a little bit better than the Tamron and it has a similar hunting issue in live view. It seems like the logic on 3rd party lenses is for the AF to front focus, step in until back focused just a little, and then step back to lock. The Sigma is about a 5 second process.
The speed of the AF motor in the lens will likely be the difference maker in how well each lens works in live view. The Canon lenses are much better, but the crappy motor in the 50mm 1.8 II struggles to keep up in Live View as well.
I believe this has little to do with lens firmware or AF motor speed. The Dual Pixel AF on the 70D isn't even compatible with all Canon lenses. The following are listed as having 'limited compatibility':
- EF14mm f/2.8L USM
- EF24mm f/1.4L USM
- EF100mm f/2.8 Macro
- EF400mm f/2.8L USM
- EF500mm f/4.5L USM
- EF600mm f/4L USM
- EF1200mm f/5.6L USM
- EF16-35mm f/2.8L USM
- EF17-35mm f/2.8L USM
- EF20-35mm f/2.8L
- EF24-85mm f/3.5-4.5 USM
- EF28-70mm f/2.8L USM
- EF28-70mm f/3.5-4.5
- EF28-70mm f/3.5-4.5 II
- EF28-80mm f/2.8-4L USM
- EF28-80mm f/3.5-5.6
- EF28-80mm f/3.5-5.6 USM
These are older lenses (for example, the 100mm macro listed is the older non-USM version of the lens, not the current 100L or 100 non-L USM lenses). It's relevant that 3rd party lens makers reverse engineer their lenses to work with Canon AF systems by assigning them a Canon LensID code for an older lens. This issue has reared it's head in the past, such as when several Tamron lenses were discovered to activate the off-center cross type AF points of the 40D/50D/60D/7D only as single line points, and not crosses, and Canon subsequently acknowledged that the same issue affected a set of older lenses. I'm not aware that Canon ever addressed this via a firmware update for those bodies.
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?Originally Posted by neuroanatomist
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.
Oh shucks...it's not compatible with the EF 1200mm f5.6L. Guess that one is off my "to buy in the future list." Oh wait, I don't have a 70D, nor will I ever be buying one.
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Thanks Neuro! I appreciate the detail of the answer. I just learned a lot about how my camera works (BTW - Where would one go to find such detailed information about camera firmware?). I have seen a couple of reviews of the 70D with the Sigma 18-35 1.8 and it performed nicely with the DPAF. Obviously the new Sigma would use a newer Canon LensID so I imagine that is why it is performing well.
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