Full Frame vs Crop Sensor

[Roxie2401]

Am I correct in thinking that a crop sensor is better for "Action" shots, like sports?  Is this because of the extended "reach" of the lens (multiplication factor) and does a crop sensor aquire autofocus faster?

Is a full frame better for static/stationary subjects like landscape, architecture, studio work where the subject does not move?

I'm trying to decide between a 5D MK II and a 7D and keep hearing that the 5D had/has AutoFocus issues.  (I know about the outter AF points not being great, but even the center point seems to lack the ability to aquire focus.

Or, is the difference in that the crop sensor is using a smaller portion (center) of the glass whereas the full frame is using more of the lens?

Is there a reason why so many people seem to have two bodies - crop and full frame?

I'm sure the Full Frame vs Crop has been discussed many times and maybe I'm just overwhelmed with too much data.

Thanks for any input.

[KeithB]

The only reason the crop sensor might be better for action is that the smaller pixel count *may* allow you to shoot more frames per second.

[SidSP]

The only reason the crop sensor might be better for action is that the smaller pixel count *may* allow you to shoot more frames per second.

Sorry, but I disagree. I see little or no direct relationship between frames/sec and smaller pixels. It's far more likely that the higher frames per second in the 7D over the 5DII it is due to the 7D having dual Digic IV processors.

I have both crop (7D) and FF (5DII).  I use the 5DII for everything but action shots (birds in flight, moving animals, sports, etc.)  My reasons for using the 7D with for birds in flight and sports are: (a) the extra reach of the crop camera over FF due to the 1.6X crop factor; (b) the higher frames per second in the 7D, due primarily to its dual Digic IV processors; and, (c) the superior and customizable focus modes of the 7D over the 5DII.

[KeithB]

Like most statements of fact about digital cameras, I think mine is now superceded.  I thought that Canon kept the smaller than FF but larger than APS-C  to keep the frame rate up for sports shooters?

[Bob Atkins]

I think it's easier to get higher frame rates on APS-C than APS-H and FF because (1) the image files may be smaller (though that's not always the case), (2) the mass of the reflex mirror is lower and therefore it's easier to move rapidly and possibly (3) the mass of the shutter blades is lower and they don't have to move as far.

Of these I suspect that #2 may be the most important since higher processing power and a faster and larger buffer and memeory card can deal with #1 and I doubt that #3 is much of a factor at DSLR frame rates (10 fps).

Banging a honking great mirror up and down 10 times a second isn't easy if you want 150,000 or 300,000 cycle reliability. It has to be decelerated both on the upstroke and downstoke so it doesn't crash into the stops and not only the reflex mirror has to move, but the AF sub mirror has to do so also - and stay within a few microns of alignment to ensure accurate AS. I'm sure faster frame rates would be possible if the mirror(s) just stayed up and all frames were shot with the same focus and exposure. In fact HD video comes close to doing that already at 30fps!

[whizkid]

I own both a 7D and 5DMk2 and have not had any focus issues with the 5D Mk2 in the year plus I have owned it. If you are looking to the 5DMk2 for a lot of continuos shooting as in sports, it is not by design how Canon expected this model to be used. I've used it in a mild continous shooting venues such as a wedding, without a wimper. For the fast and furious you have the 7D and the IDMk4.

[Roxie2401]

If there is another thread that has discussed crop vs full frame that I should be looking at, please let me know.

I have a friend who is now on the second 5D MK II body and still can't achieve AF very well.  The discards outnumber the keepers.  The "action shots" are of small children (babies) and I would think the 5D2 should be able to capture focus - this isn't soccer or hockey.  This person is using the same lens complement as before (and that was a Rebel), specifically, the Canon EF 70-200 f/4 IS and the Canon 100mm macro.  I know the macro is tack sharp and the AF on the 5d2 is driving us nuts.

I would love to get a 5d2 myself but keep wondering about Canon AF issues.

Maybe we should be looking at AF "One Shot," "AI Servo," "AI Focus" that we are not fully understanding and its more of an operator error than camera body issue.

The fps was not an issue - its just the AF on the two bodies that was of interest, along with IQ - which I would think the 5d2 would be superior.

Bob, I know you are still working the 7D review and am looking forward to seeing how the new AF performs.  That being said, and its a fluid environment, I wonder if we will see the 7D AF design come out in a Full Frame body in the next 12-18 months, along with flash control, etc.?

[Bob Atkins]

I suspect that the 5D MkIII may incorporate some of the features we're seeing in the 7D, but that's probbaly a couple of years away. There's really no room for a full frame body priced between the 7D and 5D MkII and if you want the ultimate in AF and high speed you'll be looking at a more expensive body, i.e. the 1d MkIV which should hit the streets by the end of the year and cost $5000.

This article http://www.bobatkins.com/photography/digital/full_frame_vs_aps-c.html has some discussion of APS-C vs full frame issues.

[Roxie2401]

Bob,

Thanks for the link.

Could it be that the 5D2 has only the center AF point as a cross-type and the 7D has all 19 AF point that are cross-type?  I keep seeing posts that reflect an AF issue with the 5d2.  Do the cross-type really make a big difference?  If only the center point is a cross-type, what are the other eight?

I'm still using my trusty 40D and haven't seen a focus issue - maybe I was lucky - looks like all the AF points are cross-type.

Thanks so much.

[whizkid]

The center AF point in the 5D Mk 2 is how I use it and that point is not alone. Unseen are 6 others that detect motion in the center circle and how they function is based on other settings that pertain to whether the subject was  moving to start with or still before moving.

[Roxie2401]

Guess I'm really confused.  On the 5d2, for the visible sensors, the center AF is cross-type, the one above and below are sensitive to vertical and the other six on the sides are sensitive to horizontal.  As you pointed out, the six hidden only function in AF servo mode.

Sure is a mixed bag.  Maybe that's why the outer points seem to have issues when you get out of the center point area?

But on the 40D all nine visible sensors are of the cross-type, which I take to mean sensitive to both horizontal & vertical lines for focusing, plus the center point is a diagonal cross point.

Wonder why Canon mixed the sensors so much on the 5d2 and used all the same on the 40D?

It just seems like I'm getting better AF on the crop sensor vs. the FF.  But is all this because of the type of AF sensors used and have nothing to do with the image sensor size?