Canon 7D oddities: half-mirror?

Discussion in 'Photography Equipment & Products' started by Derrel, Sep 3, 2009.

  1. Derrel

    Derrel Mr. Rain Cloud

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    From Canon's own web pages at Canon EOS 7D Digital SLR

    "Quick-return half mirror (transmission: reflection ratio of 40:60"

    Am I understanding that correctly, that the 7D will have some type of pellicle mirror that reflects only 40 percent of the light,and allows 60 percent transmitted light to go through the mirror and to the imager?

    I know they have a NEW, a truly NEW type of viewfinder screen; how does that work with this half-mirror with 40:60 transmission/reflection?

    One can also see from Canon's own illustrations that the 19 AF points are all still tightly-spaced in a centrally-biased diamond shape...still the same basic diamond-shaped array with all the AF points pretty much biased toward the very center of the frame and basically very limited AF coverage toward the edges of the frame. Why does Canon continue with this same, diamond-shaped array they have been using for years now?
     
  2. Garbz

    Garbz No longer a newbie, moving up!

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    I'm not sure what they mean by half mirror, but that's how pretty much all cameras work. Notice how the actual AF unit for the camera is in the bottom of the body? A lot of the light entering the lens passes straight through the mirror and gets reflected down to the AF unit, and the remainder actually makes it to the viewfinder.

    The only thing I can see that they are advertising there as truly new in the viewfinder is LCD overlay. But that's not really new either, D200 and other cameras have had this for years. Unless there's something I'm completely missing?

    Because the Canon AF team needs to be shot. From all the wonderful things Canon does this is always a let down again and again.
     
  3. inTempus

    inTempus TPF Noob!

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    I would say the new 19 point system is a MAJOR improvement and certainly not a let down in my view. That's all I wanted on the 5D2. I'm not sure you need 51 or even 45 points for effective AF on a camera. I prefer the simplicity of fewer points assuming you have proper coverage - which certainly appears to be the case with the 7D.

    [​IMG]
     
  4. Derrel

    Derrel Mr. Rain Cloud

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    I read the Robgalbraith review Rob Galbraith DPI: Autofocus, video and more

    and it seems that the AF system is a big step up from what the 5D and 5D Mark II has, but their testing shown that the system is good with static subjects, but that it has some issues with moving subjects.

    It's not a matter of how "many" AF points a camera has, but how they are deployed over the frame. For those who shoot peak action sports, the highly centrally-weighted AF systems found in most consumer bodies are simply not up to the task, like in the 40D and 50D, which Galbraith and other pro sports/event shooters do not feel is an adequate AF system for peak action sports.

    Heck, it's not a matter of how many AF brackets there are, but how sophisticated and capable the software and sensor system is: the 12-area with 9 cross type AF sensors of the Nikon D2 series bodies was a WIDE-area AF system that covered most of the frame, and had the multi-CAM 2000 AF module, with 2,000 data collection points. I think that was/is a preferable AF system on DX than the new CAM-3500 is on Full-frame.

    The problem,as Galbraith points out, is that the new 19-point system is basically tightly centrally-biased, with as he says, basically the same area covered as the 9-point diamond system used in the 40D and 50D; the problem with the 5D and 5D-II is that they too, use the same 9-point diamond array ported over directly from APS-C to FF, with no expansion of the AF area's size. That makes the 5D series AF *exceptionally* center-heavy, and makes it absolutely dismal for off-center action ,or even tall orientation portrait work under bad lighting. Nikon has a slightly similar situation,using 51 points that blanket APS-C (D300) from almost the entire left side to the right side of the frame, but on the FX bodies, the same AF system covers less of the sides and top/bottom areas of the frame.

    Here's a sample quote about the 7D's AF from pro sports shooter and web author Rob Galbraith:

    "Continuous focus using Spot AF, centre AF point, AI Servo and the EF 200mm f/2L IS, tracking a soccer player for a few minutes in fading light, the results showed promise but were ultimately inconclusive: through about 200 frames, the camera was able to hang onto focus properly for portions of several sequences, better than we've ever seen from the 50D, as well as deal with the AF point moving off the subject briefly. But it would also lose focus for several frames for no apparent reason, even when the AF point was right on the mark and the subject was moving at an easy pace."

    I own a 200mm f/2 VR Nikkor...that is not the way that lens focuses on my wide-area AF with the D2x...if a 200mm f/2 Canon has trouble focusing in lower light, then this camera's AF system *might* have some weaknesses for serious sports uses. But then again, the camera seems limited to ISO 1600, so it's clearly not being target as a sports shooter for indoor sports.
     
  5. Montana

    Montana TPF Noob!

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    I like how you keep compairing a consumer grade camera to a prograde.
     
  6. Antithesis

    Antithesis No longer a newbie, moving up!

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    I think working on a new AF system is something Canon should have been doing years ago. I used to own a 5D and a 20D, and the AF systems were the same. The same old 9 point, slow, garbage focusing system. My old D80 focused faster and more accurately than the 5D that cost 3 times as much when it was introduced. Large MP counts are nice and all, but if the camera has finicky focusing, what's the point? I hope that they at least got it right this time.
     
  7. Hobbes

    Hobbes TPF Noob!

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    huh... I have seen people saying that the 11point AF system in Nikon D90 is better than the all cross type 9point AF in 40D and 50D so I am kinda wondering how many of those 11 points are of the cross type...
     

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