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watch said:
It has to do with the exit pupil location of these lenses.
AF sensors are all about angles, not the quantity of light. F/5.6 sensitive AF sensors have a 10 degree offset (two sensors "looking" at opposite edges of the lens circle from the back) and f/2.8 sensitive AF sensors have a 20 degree offset. With lenses such as macro lenses, the exit pupil moves farther away as it focuses close, putting the edge of the circle outside the view of the AF sensors. The sensor is "blind" to the image, so the camera has to switch to an f/4 or f/5.6 AF sensor.
Same thing with the 24-70, which has an unconventional backward zoom, with 24mm extending the lens and 70mm making it shorter. At least, that's my hypothesis with this lens.
I suspect the 24-70 Mk II will be able to utilize these double cross points.
The great news with this sensor is all of the f/4 sensitive cross points. I think this AF unit is going to be one of the best ever marketed by anybody. The D800's sensor is nothing but f/5.6 AF points, other than that single f/8 center point.
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wickidwombat said:
Well I said my hypothesis as to precisely why is a guess, but in any case, it is all about the location of the exit pupil.
That doesn't mean AF will be any less accurate with these lenses. The f/4 points are all cross-type, and they'll likely actually be looking close to the f/2.8 exit pupil. In any case, the 16-35 is going to have a lot of DOF most of the time.
I really wouldn't worry about this with any of the mentioned lenses. Unless I was one of the 24 people who owns the 1200 f/5.6L and saw that only 33 AF points work at all.
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Loswr
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Thanks for the nice explanation!
I think the new AF sensor sounds like one of the best ever, from anyone. But I've also considered that there might be a large bit of marketing hype here about 'more accurate' f/4 sensors vs. 'less accurate' f/5.6 sensors. Nikon seems to do fine in the accuracy department, with 'just f/5.6 sensors'. The underlying assumption is that the density of the pixels in the line sensors are equivalent, but what if that's not true?
Consider: the prior 1-series bodies starting with the 1DIII have many f/2.8-f/5.6 crosses (two lines with different baselines), but the center AF point is f/4-f/8. Does that mean the center point - the one where you most want accuracy - is actually less accurate because of the 1-stop narrower baselines? Canon says it's not, that it has the same accuracy at f/4 as the other points at f/2.8, because they use a sensor line with twice the density of pixels to compensate for the narrower baseline. So, what if Nikon's AF systems use higher-density sensor lines for relatively greater accuracy at f/5.6 compared to Canon's f/5.6 lines? I have no evidence that this is the case, just tossing it up for consideration, given that Canon has already played this card.
Regardless, it is fair to say that this AF system is Canon's best to date - and even though I'm getting a 1D X, I'm really glad they're using the same AF sensor in the 5DIII as well, especially after my experience with the 5DII's AF.
Stephen Melvin said:
I think the new AF sensor sounds like one of the best ever, from anyone. But I've also considered that there might be a large bit of marketing hype here about 'more accurate' f/4 sensors vs. 'less accurate' f/5.6 sensors. Nikon seems to do fine in the accuracy department, with 'just f/5.6 sensors'. The underlying assumption is that the density of the pixels in the line sensors are equivalent, but what if that's not true?
Consider: the prior 1-series bodies starting with the 1DIII have many f/2.8-f/5.6 crosses (two lines with different baselines), but the center AF point is f/4-f/8. Does that mean the center point - the one where you most want accuracy - is actually less accurate because of the 1-stop narrower baselines? Canon says it's not, that it has the same accuracy at f/4 as the other points at f/2.8, because they use a sensor line with twice the density of pixels to compensate for the narrower baseline. So, what if Nikon's AF systems use higher-density sensor lines for relatively greater accuracy at f/5.6 compared to Canon's f/5.6 lines? I have no evidence that this is the case, just tossing it up for consideration, given that Canon has already played this card.
Regardless, it is fair to say that this AF system is Canon's best to date - and even though I'm getting a 1D X, I'm really glad they're using the same AF sensor in the 5DIII as well, especially after my experience with the 5DII's AF.
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neuroanatomist said:
You're welcome.
Stephen Melvin said:
neuroanatomist said:
It is possible, but after the 1D Mk III AF debacle, I'll bet Canon has put everything into this AF unit. They know this is their last chance to prove themselves.
neuroanatomist said:
Well with the new sensor, the "X" points are only active at f/2.8. I think it's fair to say that it's designed to have the most accuracy with these center points.
neuroanatomist said:
I am, too. Frankly, it's much more efficient to spread that over a few million 5D's than 100,000 1D's. I never understood why they felt the need to develop completely different AF units for so many camera lines. At worst, why not give the lower lines last year's AF from the higher lines?
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I have a late model 1Dmk3 and never had any problem with it's AF
I think only early models suffered from the debacle
I think only early models suffered from the debacle
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dturano
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while the lens i have may not take full advantage of my future camera I feel like its motivating to know my camera is ahead of my current lens gear. And that the results from my lens will excel on this body than its predecessor even if its not at its full potential.
To be honest, im not sure how to explain it but the overall thing i yearn for out of new cameras is to find that great photo i got from when i shot film. While i have printed my own work in a dark room, i find i overshoot and bank on qnty over qlty or the trust in my photo editing skills, while back when i shot film i would shoot and order prints, sit in my car at the store and look through them. It was a whole different experience. Dont get me wrong, i get amazing results from my gear, 50d, xt ( i love the colors ont his camera and refuse to drop it, the original black rebel xt after the rebel i believe 2nd gen from the silver one? it is a great camera even in what some would call dated) 7d. I dont care what anyone says, while modern cameras produce a wow factor film had a great feeling and which will never be reproduced, unless you shoot film
which i know some (they understand) hipster doofuses - who still do or went back for retro clients, hey where there is a market there is a job.
Sorry for the rant, just find it funny to see posts about auto focus, hdr, dynamic range, i appreciate the info and questions but i love the raw natural ability of a camera and manual features. I actually had a friend ask me why I wouldn't get a ti3, it has more dummy modes
While im not the greatest, consider myself more of a techie nerd and thats while ill upgrade. To be honest all these nikon d800 posts and 5d3 comps, if i had enough coin I wouldn't be on this site, i would be sitting back waiting for both new bodies. I have know some great photographers who use old gear and even what some would call amateur gear, no matter the brand produce great photos based on there knowledge and understanding of conditions.
Again sorry for the rant, its late i need sleep. cant wait for the new camera.....
To be honest, im not sure how to explain it but the overall thing i yearn for out of new cameras is to find that great photo i got from when i shot film. While i have printed my own work in a dark room, i find i overshoot and bank on qnty over qlty or the trust in my photo editing skills, while back when i shot film i would shoot and order prints, sit in my car at the store and look through them. It was a whole different experience. Dont get me wrong, i get amazing results from my gear, 50d, xt ( i love the colors ont his camera and refuse to drop it, the original black rebel xt after the rebel i believe 2nd gen from the silver one? it is a great camera even in what some would call dated) 7d. I dont care what anyone says, while modern cameras produce a wow factor film had a great feeling and which will never be reproduced, unless you shoot film
which i know some (they understand) hipster doofuses - who still do or went back for retro clients, hey where there is a market there is a job.Sorry for the rant, just find it funny to see posts about auto focus, hdr, dynamic range, i appreciate the info and questions but i love the raw natural ability of a camera and manual features. I actually had a friend ask me why I wouldn't get a ti3, it has more dummy modes
While im not the greatest, consider myself more of a techie nerd and thats while ill upgrade. To be honest all these nikon d800 posts and 5d3 comps, if i had enough coin I wouldn't be on this site, i would be sitting back waiting for both new bodies. I have know some great photographers who use old gear and even what some would call amateur gear, no matter the brand produce great photos based on there knowledge and understanding of conditions.
Again sorry for the rant, its late i need sleep. cant wait for the new camera.....
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woofmeow said:
As brian said perhaps the confirm beep may be better, but also for what it's worth, you wont be able to remove the focus screen (in the 5d3, not sure about the 1dx) so with faster lenses as shallow DOF, you may or may not be getting the most out of those lenses unless you use live view and DOF button used...
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Certain comentators seemed to have issues with later models as well, it's just that others couldn't reproduce themwickidwombat said:I have a late model 1Dmk3 and never had any problem with it's AF
I think only early models suffered from the debacle
.
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woofmeow
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briansquibb said:
Thanks for reply.awinphoto said:
I recently "switched" from 60D with katz eye focusing screen to EOS 1N film camera, with stock screen, and from my expirience (i shoot only with manual lenses) the 100% coverage stock viewfinder makes it so much easier to focus, compared to split prism, but small one.
So im aware about fixed screen in 5d3 and think i can live with it (and maybe katzeye will make custom one for it, like they did for 7d), i'm just curious about advantages in AF system that can help with manual focusing.
For example, focus confirm on my 60D lied often for few mm's, so i could not rely on it and was forced to use live view in most close-to-object situations. Maybe it was camera issue, something like front/back focus.
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