Hmmm, doesn
Hmmm, doesn
An awful lot of electrons were terribly inconvenienced in the making of this post.
Gear Photos
Originally Posted by Dr Croubie
It's not really about the amount of light, nor is it completely controlled in firmware. Daniel previously explained using a nice analogy, so I'll just paste his text from this thread: "<span>Imagine you are looking at the world through a 3cm cardboard tube. There is a 1cm hole in a wall, so when you look through the tube your view is restricted by the hole, not the tube. If the hole is expanded to 3cm, you'll have the maximum 3cm view possible. If the hole is expanded to 10 cm, the view is restricted by the tube, not the hole, so you can still only see 3cm. <span>The high precision f/2.8 autofocus sensor can only look at the world through an f/2.8 tube. If there is an f/5.6 hole in the wall, AF wont work. If the hole is expanded to f/2.8, then it will have an unobstructed view and work normally." Now, there's a little more to it than that, because f/2.8 is not a hard limit. But f/5.6 wouldn't work, even in bright sunlight. Nor does f/11 on an f/5.6 sensor with taped pins. Have you ever tried the pin taping? I did, with the 100-400mm + 1.4x II, and in bright light it's ok, but very slow and tends to hunt a bit, while in dim light it fails. Live View works, and is faster. I suspect Canon won't let it try because it's not very reliable, so from that standpoint, it's partly firmware.
It really seems that Canon took a stab at your idea, although not in quite the way you intend. Rather than relying on something variable, like amount of light, they coded in a known quantity - the lens you're using. As you can see on this translated page, they're pretty specific about which lenses can activate which AF points. The wide, fast primes and the 24-70mm only get one of the f/2.8 points, not all 5. The 28mm f/2.8 only gets the inner rows of f/4 points, and uses the outer rows of f/4 points at f/5.6. Since all these lenses have the same image circle, it must have to do with other optical properties that make those lenses less optimal with the higher sensitivity points. With some older, variable aperture zooms (and the 800/5.6) you start to lose even the f/5.6-sensitive points at the edges, dropping form 61 points to 47 points.
Macro lenses also 'suffer' - the 50mm f/2.5 and two of the100mm f/2.8 macro lenses L and old non-USM) don't even activate any f/2.8 points (they are f/2.8 lenses, right?!?), and the 100mm f/2.8 Macro USM doesn't get f/2.8 or even f/4 points. The 180mm f/3.5L Macro not only fails to activate f/4 points, but only gets the central 33 points out of the 61 available f/5.6 points. Probably not a big deal as MF is the norm for macro shooting, but I'm curious as to why the macro lenses take such a bit hit on AF point activation.
Maybe on the 7D. But on all the other APS-C bodies, the AF points are etched onto the focusing screen. I'd think it would be pretty confusing to see them there, but not be able to select them. Imagine the tech support nightmare if they sold an xxD or xxxD with an EF-S kit lens, and users not being able to select some of the AF points they clearly see in the viewfinder.
It's not the movement speed of the secondary mirror, it's size of the secondary mirror that limits the vertical extent of the AF point spread. <span>There is limited space behind the main mirror, based on the necessary geometry (i.e. the main mirror has to be at a 45° angle to the incoming light, and the secondary mirror has to be behind the main mirror and at an angle of 90° to the main mirror, so it's length is limited by the distance between the main mirror and the image sensor). You can see that in this cutaway schematic:
That's why the 1D IV, 7D, and 1D X all have about the same vertical extent. As seen in the diagram I posted, the 7D, 1D IV, and 1D X have the widest horizontal spread, and it's the same for all of them. That suggests they are hitting the limit of how far apart they can be (yes, that's relative, and the actual spread of the AF points on the 7D is much less - but then, all the components of the mirror box are scaled down, too, so the limits are relative just like the spacing). And again, except on cameras with a transmissive LCD (currently only the 7D and 1D X), inactive AF points can't be hidden.
John
So this discussion gets confusing, as I am trying to figure out what the 1D X article is telling me in relation to the 500mm f4.
This is what the 1D IV book says:
Maximum f/stop: f/4
High-precision, cross-type AF with the center AF point is possible. The remaining 44 AF points will be horizontal-line sensitive only.
Which with the 1D IV I take this to mean I have one Cross Point and it is the center point only. Any other chosen would be second best, albeit that would probably be good enough.
So am I interpreting the 1D X charts wrong on the article, which I take it to mean we would get 21 cross type points instead of just one?
The 1D IV has a function with the supertele you can program the little button on the barrel and get several functions, one of which shrinks the size of the 1D IV center point, this is a good function for small birds in the bushes. I wonder if the 1D X will have the same function, I haven't found anything on this yet.
On another note
This is what the 1D IV book says about certain lenses
The following lenses and lens combinations have a maximum aperture of f/4, but cross-type focusing on 39 AF points is still possible as with lenses having an f/2.8 maximum aperture.
EF17-40mm f/4L USM, EF24-105mm f/4L IS USM, EF70-200mm f/2.8L IS USM + Extender EF1.4X II, EF200mm f/2L IS USM + Extender EF2X II, EF300mm f/2.8L IS USM + Extender EF1.4X II, EF400mm f/2.8L IS USM + Extender EF1.4X II
This kind of muddiesthe water and what was being explained about the f2.8 points and how many can be used. With my 500mm there is 1 point, with these combinations I can have as many as 39. It would make sense that Canon would focus intensely on these lenses to make them more diverse, since they are the bread and butter of the big league sports photographers and it is one of the best advertisements they can have.
Looking at the charts for the 1D X are we loosing some of the f2.8 cross points that we have going from the 1D IV to the 1D X?
Rick
Rick,
The 500mm f/4L IS and 600 f4/L IS will now have 41 cross type points on the 1D X. These are the blue and pink squares in the article below:
http://translate.google.com/translate?sl=auto&tl=en&js=n&prev=_t&a mp;ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fcweb. canon.jp%2Fcamera%2Feosd%2F1dx%2Ffeature-afae.html&act=url
The 1D-X will still have spot focus for the super-telephotos and they have also added in camera support for spot focus for many other lenses.
Rich
Rich
I thought it might mean 41, but I wasn't sure if that is what the chart was trying to say. Our 1D IV booksayswe have one "High-Precision" cross type point when using the 500mm (f/4). I wonder how this would apply to the 1D X, if all points are considered equal ie: "High-Precision" or are the blue points going to be superior to the pink points?It looks like an improvement over the 1D IV, but it can't be a giant leap for me since my keeper rate for in focus pics is very high out of the 1D IV already.
Those moving from the 7D or 5D II will think they found the holy grail of AF systems if they make the move to a 1D X. Wich I guess they have since it will be the best available on a Canon.
Rick
<span>
<span>Yes, you're losing some f/2.8 cross-type points, but gaining more f/4 cross type points. So, with an f/2.8 lens on 1D IV, you get 39 cross-type points, but with an f/4 lens you only get one cross-type point, with the exception of the list of lens and TC combos you posted above. With an f/2.8 lens on a 1D X, you'd get 25-41 cross type points (depending on lens), and you'd also 25-41 cross-type points with an f/4 lens. With an f/5.6 lens on a 1D IV (such as your 500/4 + 1.4x TC), you get zero cross-type points, whereas on the 1D X with an f/5.6 lens, you get 15-21 cross-type points (usually 21, as would be the case for the 500/4 + 1.4x).
<span>
<span>Something of a trade-off here. Prior to the 1D X, Canon bodies with a high-precision AF point only had one, the center point. On non-1-series bodies, that center point is high precision with an f/2.8 or faster lens, while on the 1-series, it is high precision with f/4 or faster lenses. The 1D X has 5 high precision points, but they require an f/2.8 or faster lens. So, your 500/4 on the 1D IV had a high-precision center point, whereas on the 1D X, your 500/4 will not activate a high precision point at all, not even the center one.
Lots of confusion here, lots of jargon. Time permitting, I'll try to post something that makes some sense of it all...
I think it will be helpful once they get the owners manual on line. Many of the questions everyone will be answered then.
Here is something I wonder as well. It has always seemed to me that the AF points and specifically the center point on the 1D IV covers a noticeably larger area than the 7D or 5D II seem to. I wonder with the new 1D X if the points will be smaller and much finer, since you are gaining so many new points.
Keep in mind I am not talking size of the etchings that you see when you get confirmation. I am talking actual area that the point focuses on which seems to be a larger area than the etching.
It's hard to say. The 1D IV and 1D X have approximately the same coverage, and the same number of 'columns' (11), but the 1D X has more 'rows' (7 vs. 5). But, how much 'blank space' between points exists on the 1D IV sensor? No idea...
John,
Isn't it true that if we have 41 cross type points that are f/4 sensitive on the 1D X, thenthose same 41 points will alsobe cross type points that are also f/2.8 sensitive. So, sincethe MKIV had 39 cross type points and the 1D X has 41 cross type points, then it means that we are actually gaining 2 extra f/2.8 cross type points and that we are not losing any.
In addition to gainingtwo moref/2.8 cross type points, we are alsoupgrading 5 points to higher precision "dual-cross" type points, out of the total 41 cross type points.
I don't think that the MKIV had any dual cross points, but I believe that you mentioned that the 7D hadone dual-cross type point at the center.
It's amazing that a lot of the 7D technology has found it's way to the 1D X or that the1D X technology made it's way to the 7D for testing. Either way,I always thought that the 7D was pretty advanced.
Thanks!
Rich
The blue points will bebetter than the pink points,for those using slower lenses. The solid blue points are newer dual cross type points, which means the point is an X with a cross layed over it. So, those will provide the most precision.
I don'town the 500mm f/4L so I never realized that, that lens only used one cross type center point. My 300mm f/2.8L IS with or without the 1.4X extender had 39 cross type points available on the MKIV. I agree that people using the500mm f/4L IS and MKIVcombo, never seem to have any complaints about it's AF ability.
I just thought of a new feature. Wouldn't it be cool if the focus points inside the viewfinder lit up "different colors" to let you know which type of focus point you were using, similar to the focus point graphics that we're looking at on the above link?
Rich
Posting Permissions
Reply With Quote