I purchased the TC-17EII to use with my 70-200 mm nikon lens and D800 camera and the autofocus always worked great. I was lucky to obtain the new 80-400 mm lens and tried the TC with it. There was no problem with autofocus between 80 and 200 mm but after that there was only continuous seeking with no focus point ever achieved even in bright light. I am a new photographer (less than a year) but love the equipment and wonder if I am doing something wrong or if the TC or the lens is not compatible or is defective? Has anyone else had this problem? Thanks so much for your input!
I've read about that restriction a number of times before, but I don't understand why it is (I don't suppose I'm alone). The D800 will not AF at any aperture if the light is too low (which has to be very low indeed), so what's going on inside the camera/lens to physically prevent AF from not working with certain lens/TC combinations?
It is still about the amount of light that reaches the AF sensors. The 80-400 is a 5.6 lens – add the TC17 and you get a max aperture of f/9.5. That small aperture just doesn’t allow enough light for AF to work. f/9.5 reduces the light transition by about 3x.
I've always questioned that, Dave. As an example...
Put a TC20 on an f/4 lens and it is working f/8. Use an f/5.6 camera, like D300 or D700, to focus.
Put a TC14 on the same lens and camera, and it is only one stop brighter.
If it is strictly a matter of the amount of light, then the TC20 should focus just as well as the TC14, but with one stop more light.
My experience says that that is not true, both in the light level that the camera even thinks it found focus, and in the quality of focus. I can focus a TC14 + f/4 lens in quite dim light, where a TC20 needs many stops more light, I think.
YMMV on this. I think is an interesting discussion/issue.
It think the TC complicates things some by an inherent loss con contrast caused by magnifying the image.
Each converter produces a little less contrast than the one before. Although the TC2E III is a close match to the TC17E II.
It is also possible that the camera firmware is tweaked to act differently with the TC's. On the D300S my 400/2.8 moves painfully slow with the 2x TC even though it still has f/5.6. With the D800 it has improved and the 2x focuses more like the 1.7x.
Tue 26-Nov-13 02:27 AM | edited Tue 26-Nov-13 02:36 AM by jamesvoortman
As I understand it from an article I saw, phase detection autofocus relies on light coming in through the peripheral parts of the lens and it compares left with right, or top with bottom. Once the aperture gets too small it reduces the width of the light path between subject and sensor. Width of light path seems to be the issue, not brightness.
In this particular case, the 80-400 is a variable aperture lens that is f4.5 at the wide end and f5.6 at the narrow end. With a 1.7 TC fitted it becomes a f7.4 to f9.5. At some point in the zoom range, the magical f8 aperture is exceeded and AF is no longer viable.
On some Canon cameras AF is disabled by firmware at apertures beyond f5.6 or f8 (depending on the body) presumably to limit wear and conserve battery power because the lens will tend to hunt and chatter if you continue trying to get focus in such circumstances. Older Nikon bodies are not "hobbled" like this but maybe some of the newer ones are, for the greater good of lens and battery?
Another thing to be aware of is that the D800 has only 11 out of 51 AF sensors that are f8 capable. The others are all f5.6 capable. If you ensure to use only the f8 sensors when focusing with this combo, you may have better luck than if using the f5.6 sensors.
Sun 24-Nov-13 09:36 AM | edited Sun 24-Nov-13 09:37 AM by nrothschild
Although technically this combo is a half stop past the camera's spec'd limit, I don't ever recall anyone reporting that an F/4 lens with the TC17 would absolutely refuse to focus...
I have shot my TC17 with my 500/4 AFS and 300/4 AFS, on a D300 and D700, and probably other older bodies. It is not exquisitely accurate (very inconsistent). But it works, more or less.
I have even AF'd with the TC20E-II and f/4 lenses. That needs very bright light, but it does not totally refuse to focus, as described here, in bright light. And again, my experience is consistent with others.
I don't have the lens and body in question here. I just think it would be interesting to see if others report the same. If they do, then the "rules have changed", perhaps? I only posted here because I think this is an interesting observation and subject. This is the first f/5.6 lens, I think, that even mounts to an unmodified Nikon TC?
Thank you all for your thoughtful and insightful answers to my question. This forum never ceases to amaze me. Hopefully, other neophytes will read the topic and benefit from your expertise as well! I intend to explore the TC with manual focus. Thanks again.
Ah yes, that's the slightly confusing trap that I initially fell into. What you are describing relates to exposure, but AF always operates at maximum aperture, before the it closes down when the shutter release is pressed.
AF needs a lot more light to operate than the sensor needs to capture a correctly exposed image.
Yes, but f/9.5 is the maximum aperture of the 80-400mm/TC-17EII combination with the lens at 400mm. I think Brian's point is that combination in bright conditions will allow more light to reach the AF sensors than a lens/TC combination with an f/8 maximum aperture will in dimmer conditions - but the "rules" say the f/8 combo will AF but the f/9.5 combo won't.
>From what's been posted on here, it sounds like the D800 is >executing a command that has been pre programmed into it.
No, that's not it. At apertures smaller than the specified limit, the camera will usually attempt to focus - and will sometimes succeed. The f/8 and f/5.6 limits have never been "enforced" in Nikon cameras, lenses and TC's.
This is in contrast to Sigma TC's, which DO disable AF when the effective aperture is smaller than f/5.6 - with any camera.
Tue 26-Nov-13 10:39 AM | edited Tue 26-Nov-13 10:40 AM by Lunastar
Interestingly, my little AF-S 300/4 prime lens works very well with a 17TC. The AF is good on my D300 and even quicker on a D800. Of course, you are at f6.3 but that's usually no problem in decent light. And, the image quality is quite good.
As far as mounting one on an 80-400-I wouldn't suggest it as the image quality on a zoom is sure to degrade noticeably. A 14 TC on my 200-400/4 is excellent while the 17TC shows (to me) unacceptable image degradation. Plus, the 80-400 is at f9.5 where light gathering is really going to be at a premium.
The 17TC is really designed to work best with f2.8 glass and really shines with primes like the 300, 400/2.8's and the 200/f2.
I assume that giving the AF limit as a lens max-aperture value is just Nikon's way of trying to simplify things. I'm sure we've all experienced fast lenses failing to AF in low light and slow lenses AFing nicely in good light.
Nikon also gives their AF "detection" limit in EV (at 100 ISO), which is an absolute light value. The bodies that "AF with f/5.6 or faster" lenses are spec'd at -1 EV, which is the amount of light that would produce a proper exposure at f/1, ISO 100, 2 seconds, or any other combination of ISO, aperture and shutter that gives the same exposure. The bodies that AF with f/8 lenses are spec'd at -2 EV, one stop lower. (For reference, -3 EV is about what you would get from a rural landscape illuminated by a full moon, or nearly full moon. See this page.)
But surely the AF target factors into the ability to do AF, too. Just because the AF system can detect something at -2 EV doesn't mean that the thing you are trying to focus on will provide sufficient contrast to actually be detectable.
In the end, I'm not sure how helpful all of that is other than to point out that the situation is pretty complex, and any attempt to reduce it to a single number is going to be an approximation, not a hard-and-fast rule.
I found this thread very interesting. Personally, I don't have much use for TCs expect on the 600. So I can't add anything to this discussion.
Just a comment for the OP. I shoot the 80-400 and when I need more reach than the D800 combo, I use the D7100. Considering the pixel density, that combination is about the equivalent of the D800 80-400 and TC1.7. It has the advantage of also being f5.6. Focuses flawlessly and quick.
>I found this thread very interesting. Personally, I don't >have much use for TCs expect on the 600. So I can't add >anything to this discussion. > >Just a comment for the OP. I shoot the 80-400 and when I need >more reach than the D800 combo, I use the D7100. Considering >the pixel density, that combination is about the equivalent of >the D800 80-400 and TC1.7. It has the advantage of also being >f5.6. Focuses flawlessly and quick. > >David I also have the D7100 and 80-400 AF-S lens combo. Very happy with them so far. I was thinking of trying my TC 1.7X on this combo for Air Shows mainly Jet demonstrations. Lots of light, but Jets tend to get distance fast. 80x1.5x1.7=204mm, 400x1.5x1.7=1020mm 1.3 crop mode; 80x2x1.7=272mm, 400x2x1.7=1360.mm D7100, 80-400, TC1.7, 1.3 Crop mode gives an amazing range of 272mm to 1360mm. The lens is very fast to focus. Want to see if I lose auto-focus above F8.0.