70-300 "L" and a TC on a T2i?

Discussion in 'Canon EOS' started by robert_thommes|1, Sep 27, 2014.

  1. In researching the use of a 1.4X TC on my Canon 70-300 "L" lens connected to my Canon T2i, I've been getting mixed responses. So I ask, does anyone here know definitively if a 1.4X TC (probably either the Kenko or Tamron; as the Canon TCs do NOT work)will retain AF connectivity when placed between my Canon 70-300mm "L" lens and my T2i Digital Rebel?
    If it will, what sort of IQ defficiency might I anticipate?
  2. In all probability it won't as your maximum aperture will be f/8 (at 300mm) to small for a T2i to auto focus.
    I suppose you could tape some of the contacts but the focus will still be hit and miss.
  3. I cannot answer your question directly as I do not have the same equipment as you. However I can tell you that with the latest 1.4 Kenko DGX - the X is important - the maximum aperture is displayed as f/8 if the lens has a maximum aperture of f/5.6 and the exif data correctly shows the lens plus converter combination for both focal length and aperture. Nonetheless, both a 20D and 40D body will attempt, and sometimes succeed (in good light) to focus the lens. Suggest you look at reviews on Amazon for the DGX converter for EOS, several reviewers have reported success with various combinations.
  4. You can answer this yourself better than any of us who don't have the manual for that camera. The effect of a 1.4x telextender is to reduce light by one stop. Your manual will tell you the minimum aperture at which your AF system will function. It may vary from one AF point to another. Your lens has a maximum aperture of f/5.6 at the long end, which means that with a 1.4x extender it will function as f/8 at that length, regardless of whether it registers as f/8. So, that means that to AF at 300mm, you will need at least one AF point that can function at f/8. I very much doubt you have this--even the 5D Mark 3 didn't have this with the initial firmware--but your manual should say.
  5. Neither the T2i, nor my 20D, nor my 40D, will attempt to autofocus with a Canon lens and a Canon converter when the effective maximum aperture is f/8. With the exception of a handful of bodies, the Canon system will shut down the autofocus when the maximum aperture is smaller than 5.6; but that is to ensure reliable, accurate, and consistent autofocus. Whether the autofocus is good enough with the Kenko converter depends entirely on what the user thinks is 'good enough.'
  6. While I own neither the 70-300 L (although I've used it several times), nor the newest Kenko 1.4x, in the past (say, ~ 6-7yrs ago), I used the 75-300 IS w/ a 1.4x Kenko TC. The amount of light passed through is the same as your set up, although the body was an XTi.
    The AF was spotty at best. In very good light, the AF would function properly, and with only a small negative impact on focus speed. By the time you got down to cloudy daylight, especially when the subject area was one of low contrast, it was hit or miss - or hunt. Anything less than that, and AF would fail completely to obtain lock. While I can only hope that your T2i has improved AF sensitivity over the XTi (your T2i's AF working range starts at -0.5 EV, even though the XTi's is the same), I wouldn't expect drastic improvement over my experiences. - Oh, and I wouldn't even try in anything other than center point only.
    As far as the optical quality goes, you'll see a significant hit, especially at the long end. The good news is that the 70-300 L is very very good, so, even if you take it down a notch, depending on your subject matter, the additional reach may give better results than simply cropping - though I'd probably steer away from images with high contrast (say a BIF, or a bird against the sky), as, in those cases, simply cropping will likely give you as good, or better results.
    Frankly, on that body, you are going to kill all the benefits of having spent $$$ on the L. If you really need that FL, you'd probably be better off simply trading the 70-300 for a 100-400 - certainly your images, and your blood pressure, will thank you.
  7. I appreciate the responses. As a result, I feel I would be best off in simply not persuing this option at this time. Cropping may be MY best option until I feel the real need to possibly purchase a lens with a longer focal length.
    Thanks again,
  8. While not officially supported, Bryan at The-Digital-Picture.com has experimented, and the Canon EF 1.4x III extender does work with the 70-300 L from about 250mm to 300mm, which is mostly where you want it, anyway.
    Look at his review of the 70-300L lens, and search for "1.4".
  9. Yowza! 'kaThunk!' LOL, while technically it seems to work, I don't think I'd choose to mount any combination of lens & TCs that, with a reflexive zoom twist would cause two elements to whack together!
    Just so we are clear here, Bryan is saying that you can only physically mount the Canon 1.4x and 2.0x TCs with the 70-300/3.5-5.6 IS L when the lens is zoomed in to and past 250mm (and that when you do so, the TC is completely ignored by the camera - allowing AF to occur -albeit verrrrrry slowly). If you, while the lens is mounted on either TC, zoom back out to ~250mm, the internal elements (more specifically, at least one of their mounts) strike each other!
    Since, zooming is often reflexive, and fast, it doesn't become a question of if damage will occur, but merely when, and how bad! This of course is unless, like Bryan, you 'engineer' a zoom stop out of gaffers tape or some other way to limit travel to 250-300mm- at which point you might as well buy a 300/4 L IS!
  10. Cropping may be MY best option until I feel the real need to possibly purchase a lens with a longer focal length.​
    Robert, I don't know how often you shoot the 70-300 at the short end, but, if you shoot a lot at the long end, you might be surprised at the prices for a good f/4 constant aperture prime, such as the EF 300mm f/4, with or without IS.
    For all I know, an f/4 constant aperture lens may be able to handle your auto-focus needs, even on the T2i. I have shot the EF 70-200mm f/4 non-IS lens on the T2i, and I was pleasantly surprised at the results, but if you shoot a lot between 200 and 300, you might at least want to consider the 300mm f/4 constant aperture prime. Let's face it: most of cannot afford the EF 300mm f/2.8, and f/4 sure is a lot easier on the arms and hands, not just the pocketbook. In addition, perhaps you really do not need the teleconverter.
    Just a thought. . .
  11. I was unaware that the 1.4x and 2x would work with the 70-300L when zoomed out. I tried them both on when I bought the 70-300 a few years ago, they didn't fit and I never thought about it again. But I just tried them now and they both fit when zoomed to 300. But not something I would do except in a pinch because, as pointed out, the natural reflex of zooming back would cause an expensive crunch. And I have a 400/5.6, so not something I really need to attempt.
    So, I just tried the autofocus. With a 60D, the 70-300L at 300 mm will autofocus with 1.4x (Mk1) in good outdoor light, but not particularly quickly. Indoors in poor light it can't autofocus. The 70-300L attempts to autofocus with the 2x (Mk1) but NEVER achieves focus. Just goes back and forth then stops. Ditto with a Tamron 2x.

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