I have heard many people say that the Nikon DSLRs have no cross-type AF point on two sides, the points only lie in the middle/central area. The 51-point system (15 cross-type) of Nikon, named after 3500, can be date back to the year of 2007, begins first of D3. The AF system of D4 right now is the improved version. Besides, the 39-point system (9 cross-type), 4800, also has the fatal weakness: no cross-type point on two sides. However, for Canon, the ellipse 45-point AF system, which can be date back to film times, and which reaches the strongest condition: 39 cross-type points and 6 line-type points on EOS-1D MK IV, has been abandoned by Canon, and replaced by the newly 61-point AF system.
Why should I emphasize that the 45-point system on 1D4 is 39 cross-type and 6 line-type? Because Canon had the assist points before. 5D2 has 9 AF points, but some people say it has 9+6, the 6 is assist points. When it is in 1D MK3 or 1Ds MK3, the ellipse 45-point AF also has assist points. It has 19 cross-type AF points and 26 line-type assist points (cannot be selected by users). Maybe the 19-point system on EOS 7D comes from the 1D MK3. When it comes into 1D MK4, more cross-type points and no more assist point. Maybe it can be made into all 45 cross-type points and no line-type point, for it is on purpose by Canon why it didn’t do that. It is F5.6 line-type plus F2.8 line-type, when it is F2.8, it comes into cross-type. Besides, the center point can do cross-type AF under F4.0, and AF under F8.0. In some particular situation, all the 39 cross-type points can do cross-type AF under F4.0. In the opinion of now on, it may be a little older, for it has no dual cross-type point, the newly 61-point AF has 5 dual cross-type AF points. It could have the dual cross-type AF point, for EOS 7D before it already has. Why should it have the dual cross-type AF point, what is the purpose of it?
The dual cross-type AF point on EOS 7D, is designed for focus accurately. But there is only one on 7D. Theoretically, when using F2.8 lenses, it is the only one point which can do AF accurately. Though it makes F2.8 lenses essential to have cross-type AF points available when using the EOS body of 1D MK4, in final using it, almost every point can been used for accurate focusing. The mainly purpose of dual cross-type AF point is for high precision focusing, but it have reached the goal by cross-type AF point on 1D MK4, so making the dual cross-type on 1D MK4 may be redundant. However, we have to admit that it makes F2.8 lenses, or at least F4.0 lenses essential, or we have to accept the fact that there will be no cross-type AF points.
So, the 61-point AF that contains 5 dual cross-type points has appeared, and applied on EOS-1D X, which is the first time for 1 series bodies to have dual cross-type AF point. And the number of dual cross-type point increased to 5 from 1. At first I didn’t got it that why it is vertical 5 points in central, and why it is not cross-type 5 points, or matrix 9 points. In this time, Canon has added F4.0 sensor, and it comes into 2 lines in each sides, 4 lines in total. When it comes in F4.0, it will have cross-type points in two sides. (PS: much better than Nikon, it won’t have ever.) When using F2.8 lenses, I think it will also have better precision than F5.6 sensor.
However, when the 61-point AF meets the extreme-conditioning ellipse 45-point AF, degeneracy has emerged: number of the AF point which works under F2.8 and is more accurate has decreased to 5 from 39. The 20 points under F4.0 may work better under F2.8 than F5.6, and new technology may make it more accurate for non-F2.8 sensors. But in theory, at least the AF points work under F5.6 in 61-point AF, 61-5-20=36, they are not accurate enough in the situation when aperture is under F2.8. Regarding the future, no matter of the speed or ability of focusing, or the accuracy of final shot, the dual cross-type AF point has more advantage than the normal cross-type one.
I have heard this saying: if choosing between 1D MK4 and 1D X, someone will still choose the former, for it is more mature. There has been several firmwares for 1D X, and solved many bugs. If we prefer the AF point which is dedicated under F2.8, it is surely degeneracy. Besides, the X-sync of 1D X has decreased to 1/250s from 1/300s of the APS-H format 1D MK4. I don’t know whether it should have an X-sync of 1/300s for APS-C, for APS-H already has. Maybe it is the last one for 1D MK4 that has APS-H format and ellipse 45-point AF in 1-series EOS bodies, but it may be back somewhere and somehow. It is hoped that EOS 6D would use the 19-point AF of 7D, but it uses the 11-point AF mod by the one in 5D2. EOS 7D was the first one uses 63-zone metering system who is not 1-series body. 45-point AF is still 1-series exclusive, the situation may change now. 1D X and 5D MK3 have used the new 61-point AF, which makes the 45-point AF a high-end accessory no more. The rumor of EOS 7D MK II has said that the AF may not be the 61-point one, but it will not get poorer performance than using 61-point one. In the tradition of 7D and 5D2, the sensor smaller, mechanical performance better. 5D3 has FF and high performance, so 7D2 should has an APS-C sensor and ultra high performance. Usually, more AF points, better. 45-point AF has lesser point than 61-point has. The prediction of Impress Japan has listed in Japanese (some Japanese font is Chinese
) with the saying of 7D MK2 has the AF point of more than 40, it should be the improved version of ellipse 45-point AF with some experiment technology. In my opinion, Canon goes on an experiment of dual cross-type AF point on the 45-point AF, which has more than ever. How about the 45-point AF making of 19 dual cross-type points and 26 cross-type points? Haha. And when it is mature, makes 61-point AF with more dual cross-type AF points. Why EOS 6D still has no dual cross-type AF point? Because the experiment on 6D is -3EV light focusing.
In future, when the number of AF point works under F2.8 is more enough, it could have a selection of “only using high precision AF points” when using F2.8 lenses, just like “only show cross-type AF points” in 61-point AF. Quote and modify a saying: Canon don’t want users having a DSLR that has not cross-type AF points enough when using, and has no F2.8 sensor for high precision focusing when using F2.8 lenses; Canon is working on to make it reach the altitude of usable for amount and distribution of the F2.8-sensitive AF points. PS: how about the altitude of distribution of Nikon’s cross-type AF points?
The type of sensors, line or cross or dual cross, the precision of sensors, F5.6 or F4.0 or F2.8, the combination of the two is surely an art.
Attachments/picture NO.1: Original
Attachments/picture NO.2: The reason for it is vertical 5-point, and why it’s not 7-point
Attachments/picture NO.3: Extreme conditioning?
Attachments/picture NO.4: Ellipse 45-point on 1D MK4. Left is under manual select, and right is under auto select. I don't got it that when auto selecting they are not cross-type.
PS: Bugged when uploading pictures...
when convert the rest two png into gif, it can be uploaded, no access denied...