Will the 7D Auto-focus at F8?

Discussion in 'Canon EOS' started by john_catapano|2, Sep 2, 2009.

  1. Does anyone know? If it does, I’d be tempted to get one for bird photography. I could then put a TC 1.4 on my 400/5.6L and turn the 7D into a 896mm bird-killing machine with auto-focus.
    Also, will the 7D mount a BG-E2 vertical grip from a 30D (probably not, I’m sure)?
     
  2. Technically yes, if I read the specs correctly. As for how accurately and how fast it would focus you'll have to wait until you get yours to find out.
    No, the 7D has its own grip, aptly called the BG-E7 (I think).
     
  3. Canon's information on it, both on canoneos.com and in their press release, refers to f/2.8 (for high-precision mode on the central sensor) and f/5.6 (for all sensors). Nowhere does it say f/8. Therefore, it's very safe to assume it will not AF at f/8. This shouldn't be a surprise. No consumer or semi-pro EOS DSLR has ever had an AF system designed to work at f/8; only the pro 1D/1Ds bodies have. No consumer EOS film SLR ever had it, either, and only one semi-pro film body (the EOS 3) ever did.
    Canon's specs say that the appropriate battery grip for this is the BG-E7. I haven't seen a specific statement saying that grips from other models don't fit, but usually a new grip means the old ones don't fit. So I wouldn't bet my life that the BG-E2 isn't compatible, but I'd be surprised if it were.
     
  4. You would think that in the 11 years since the EOS 3 came out, F8 AF would have become a little more widespread... IMO it has MORE application for consumers and amateurs (with their slow lenses and TCs) than pros (with their F2.8 lenses). Yes, that's a generalisation, but I think a reasonable one.
    Certainly I only bought the 2X II TC because my EOS 3 could make use of AF when using it (on my 300 F4L IS and 70-200 F4L). That TC has gathered a LOT of dust (performance and lack of AF on subsequent bodies)...
     
  5. No AF at f8 for the 7D. They have to give you some reason to buy a 1D camera. If they gave you everything the 7D you wouldn't buy a 5D MkII and if they gave you everything in that you wouldn't buy a 1ds MkIII
     
  6. I used my EOS 3 with a 400 5.6/1.4x and AF was worse than using MF.
     
  7. Hmm, yep - sure would shift a helluva lot more 1.4x/2x converters if they could go to f/8. As above, got them for my EOS 3 with a 300/f4.
     
  8. AF at f/8 would of been nice for 500/4.5 + 1.4x TC.
     
  9. That's why I use a Tamron 1.4x with my 500/4.5. AF works well and image quality (at least with APS-C sensor) is just about the same.
     
  10. Enlighten me please, what is the issue here? Is it that f/8 (due to TC effect) is too dark to achieve accurate AF?
     
  11. A camera like this just won't AF with a TC and an f/5.6 lens, Mark.
     
  12. Gotcha. Learn something new every day here :)
     
  13. Puppy Face, either you're much better at MF than I am or your EOS 3 was much worse than mine. I got lots of keepers with EOS 3 AF using 1.4x + 100-400L combo, and the 400/5.6 should be even better. Also, not long ago I dug my EOS 3 out just to compare its AF with 40D, and the oldtimer won hands down. Now I'm hoping the 7D would finally bring better AF than EOS 3 (apart from f/8) at similarly-sized body (EOS 1 series are too big for me).
     
  14. "I used my EOS 3 with a 400 5.6/1.4x and AF was worse than using MF."
    That's bad news, because the AF on the EOS-3 is better than on the 20D/30D/40D/50D...
     
  15. Enlighten me please, what is the issue here? Is it that f/8 (due to TC effect) is too dark to achieve accurate AF?
    No; it's not about how much light comes in the lens. If it were just about light levels, then any camera that could AF with an f/5.6 lens in a modestly-lit room would have no problem with AF with an f/8 lens (or even an f/16 lens) on a bright sunny day.
    It's about geometry. I can't explain it very clearly, but here's the basic idea. The lens projects a cone of light. The smaller its aperture, the narrower the cone is. Each sensor in the AF system is actually two sensors, one sampling light from one side of the cone and the other sampling light from the other side. The farther apart those two sample locations are, the more accurately the AF system can do its job, but then the wider the cone needs to be in order for it to reach them, and if the lens is slower than the AF system is designed for, its cone is narrow enough that it misses the AF sensors. (This last bit is the reason why the high-precision AF sensors in some bodies only work with lenses that are f/2.8 or faster.) f/5.6 is a reasonable compromise between these two goals in most cases.
    Now, the sensor hardware itself will work with lenses that are somewhat slower than f/5.6; there's a bit of leeway in the design. If the body knows that the lens is slower than f/5.6 (remember, the lens communicates this to the body, and if you use a Canon TC with a compatible lens, the body knows the effective aperture of the entire system), it will shut off the AF system, regardless of whether it might actually work; presumably this is done so that they can avoid having to hire a whole bunch of call-centre employees to explain to disgruntled customers why AF is flaky with slow lenses. If the body doesn't know the speed of the lens, however, it will try to AF. This is how third-party zooms that are around f/6.3 on the long end work: they lie to the body and say they're f/5.6, and there's enough leeway in the design that it does usually work. This is also how some combinations of lens and TC that are too slow may in fact work: if the body doesn't know (e.g. because you're using a third-party TC that doesn't tell the electronics that it's there), the AF system remains active. But it may or may not actually work.
    FWIW, I once tried using the Canon 1.4x II with the Canon 28-135/3.5-5.6 IS USM on an Elan 7E. This lens is not officially compatible with TCs, and I don't recommend trying it because you will end up with the rear element of the lens striking the front element of the TC if you zoom the lens (even accidentally) too far toward the wide end. But at the long end, there's enough clearance in the back of the lens for the TC's protruding front element to fit. Anyway, with this particular combination, AF simply did not work. It tried its best, but it could not focus on anything, due to the lens+TC being a stop slower than what the AF system was designed to handle. Without the TC, in the same conditions (same lighting and same target), AF was quick and reliable.
     
  16. WOW, thanks for the explanation Steve! You really do learn something here everyday!
    Ed
     
  17. There might be a possibility for AF: If it supports contrast based AF in live view mode, the AF sensors are not used. In this case AF is independent of the aperture, i.e. F8 or even F32 would work.
     
  18. I have a Tamrom 1.4x TC that works well with all EF lenses inc 28 135 as the body simply does not see it, I use it with 300 f5.6 often with no issues,Not all 1/3 party TC`s are missing these communication pins tho, Steve did you block the extra pins on the canon TC? this also stops the body seein the TC, my guess should be ok well in `AV` anyway. Regarding f8 lenses if available that would be another reason to unjustify the `1` series
     
  19. Nice discussion, this was new to me. I knew AF is more difficult at smaller apertures, and why, but not that most cameras decide for you that you can't use it. This should be really easy to fix by adding a custom function to the menu. There's a good candidate for a firmware update here, Canon!
     
  20. Steve did you block the extra pins on the canon TC?
    There's no need to do this with the combination I mentioned. The 28-135 is not compatible with the TC, so it lacks the extra pins needed to know that the TC is there. That's why the AF system tried to do its job even though the lens+TC combination is beyond the body's f/5.6 limit. If I'd tried this with, say, a 100-400 (which is compatible with the TC), then yes, I'd have had to cover the extra pins in order to make the AF system try to do its thing.
     
  21. Steve, my 400/5.6 and TC 1.4 are both Canon. Which pins do you have to cover to engage the auto-focus, and how do you cover them? Do I set the camera to manual mode?

    It would be nice for Canon to add a custom function for this as Allard suggests. When you're doing bird photography auto-focus is kind of an important feature to have, and it would be nice if I could add that TC 1.4, which would boost my focal length from 640 to 896. I guess this is how Canon gets you to go out and drop big bucks on 500mm and 600mm lenses!
     
  22. I have a 50D and use a 2x converter on the L series 100-400 f4-5.6. Autofocus is disabled but if you go to live view and switch to live mode focus which uses contrast detection it will do auto focus well past f8. I can only assume the 7D will do the same. It is slow but it seems accurate. Its no good at all for moving objects or somethng that may suddenly dissapear before you shoot. I think a custom function for this would be a good idea too. They already have the 2 highest ISO settings on CF access because they wont guarantee image quality that might be expected by an inexperienced user. If they made "AF enable above f8" available as a custom function they could similarly tag it as 'experimental'. As experienced photogs I think we would be happy to put up with the risks.
     
  23. Yes it will, but it will only do it live view mode. I tried it today with my Canon 100-400 and Canon 1.4. It will autofocus in both still and video live view mode.
     
  24. Like Bob and Chris I have had no problem using the with Tamron 1.4x tc with a 5.6 lens (the 70-300 f4.5-5.6 at 300mm). Sometimes 3rd party lenses have their advantages other than cost.
    At the risk of re-invigorating and ages old dispute, your 400mm becomes 560mm with the converter but it does not become 896mm simply because it is on the 7D.
     

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