1dx is it all hype or the camera we have been waiting for?

[Axilrod]

I wonder if the exclusion of f8 is in part to sell big lenses that have come out?

I think it's more that it's easier to lock focus at f/8 vs. f/2.8 (much more shallow depth of field at f/2.8, harder to focus).  I think the reason the previous poster was saying it wasn't for him because an f/5.6 lens with a TC loses a few stops so it would end up having a max aperture of f/8 and he wouldn't be able to use AF.  I could be totally wrong..

[briansquibb]

I will need to sell both my 7D and 5DII to get the 1DX so I am counting on it to have at least (preferably better) the autofocus capabilities of the 7D and at least (preferably better) the IQ (at 3200 or so) of the 5DII. I shoot as a hobby (most of the time) so I am not too worried about having a backup body. Too give you an example, I shot my daughter's basketball game yesterday and put my 70-200 IS II on the 5DII and shot at ISO 3200 / 2.8 / 1/500th and put my 50 1.2 on the 7D and shot at ISO 1600 / 1.8 / 1/500th. Here are two sample shots, 1 each from the 5DII and 7D set-ups. Can you guess which is which with looking at the EXIF data?

It was pretty easy to guess which was which - the first has more wa perspective and a grainier bg then the second. I get the point you are trying to make though.

As a 1D4 would meet your requirements as stated then I would be very surprised if the 1DX didn't

[NotABunny]

I wonder if the exclusion of f8 is in part to sell big lenses that have come out?

I think it's more that it's easier to lock focus at f/8 vs. f/2.8 (much more shallow depth of field at f/2.8, harder to focus).  I think the reason the previous poster was saying it wasn't for him because an f/5.6 lens with a TC loses a few stops so it would end up having a max aperture of f/8 and he wouldn't be able to use AF.  I could be totally wrong..

Focusing is always being done at the minimum F of the lens; this ensures that the maximum amount of light is used in order to accurately determine the focus. The aperture of the lens changes only when the shutter button is pressed. So, in this case the problem is that if the minimum F of the lens becomes 8 (because teleconverters are added), the camera can't focus.


http://www.cambridgeincolour.com/tutorials/camera-autofocus.htm

For SLR cameras, the number and accuracy of autofocus points can also change depending on the maximum aperture of the lens being used, as illustrated above. This is an important consideration when choosing a camera lens: even if you do not plan on using a lens at its maximum aperture, this aperture may still help the camera achieve better focus accuracy. Further, since the central AF sensor is almost always the most accurate, for off-center subjects it is often best to first use this sensor to achieve a focus lock (before recomposing the frame).

[briansquibb]

For SLR cameras, the number and accuracy of autofocus points can also change depending on the maximum aperture of the lens being used, as illustrated above. This is an important consideration when choosing a camera lens: even if you do not plan on using a lens at its maximum aperture, this aperture may still help the camera achieve better focus accuracy. Further, since the central AF sensor is almost always the most accurate, for off-center subjects it is often best to first use this sensor to achieve a focus lock (before recomposing the frame).

With a 1 series body all points are high sensitive with lens of f/2.8 or faster

With a 1d4 series body all points are high sensitive for the following f/4 combinations (I would gues the same or better for the 1DX):

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


Brian

[neuroanatomist]

Could also mean that Canon might start looking at lower f stops on their lenses. Say f2.8 as a base, not f4 like is the current standard.

No, in fact, Canon is trending the other direction.  While previous 1-series bodies required f/2.8 lenses for multiple cross-type point (with some important exceptions that have 39 cross-type points at f/4 on the 1DIV), the 1D X has 41 AF points that are cross-type with f/4 lenses.

[neuroanatomist]

With a 1 series body all points are high sensitive with lens of f/2.8 or faster

It's important to distinguish between accuracy and precision.  Accuracy is 'closeness to true' whereas precision is repeatibility.  So, a system can be accurate but imprecise (meaning you get the right answer on average, but any one measurement can be way off), or precise but inaccurate (meaning you get the same answer every time,but it's wrong).  Here's a diagram that illustrates the difference:



An f/2.8 point is more accurate than an f/5.6 point, because the baseline is wider.  The f/4 center line in 1-series bodies achieves the same accuracy by using a sensor line with twice the density of 'pixels'. 

The center point on most Canon bodies, including the 1-series, are 'high-precision' AF points.  That specification means that point is precise to within 1/2 to 1/3 of the depth of focus for the max aperture of the attached lens, depending on body (depth of focus is the sensor side equivalent of depth of field, it's measured in µm in front of/behind the sensor).  Other points that aren't 'high-precision' are specified to be precise to within one depth of focus.

The issue gets confusing because Canon's marketing literature often fails to distinguish accuracy from precision, using the two terms as synonyms (not uncommon in lay speech/writing, but IMO poor practice in technical documentation).  I clarified the issue for myself in an email exchange with Chuck Westfall. 

A cross-type point just means the point is sensitive to phase differences in two orientations - it means achieving a lock is possible with more kinds of subjects.  Being 'cross-type' says nothing about accuracy or precision of the AF point.