p.3 #2 · Why is the 5D3's AF system so sensitive to the lens you use?
Sadly, because I have no life, I've been looking into this quite a bit.
One point that explains some of the 'not in the right group' is that the Macro lenses have higher-than-listed f-stops when used at macro distances. So the f/2.8 macros are really f/3.5 or even f/4 working at 1:1.
The great mystery to me is why the 24-70 f/2.8 is a group B lens but the 24-70 f/2.8 II is a Group A. I wonder if perhaps it's because the Mk I is actually a T3.4, perhaps?
p.3 #3 · Why is the 5D3's AF system so sensitive to the lens you use?
I also believe it is dependent on the lens transmission of light and possibly also related to the amount of vignetting. I am one of the most cynical people around, and I do not see any conspiracy here. Some very affordable lenses are in Group A, like the EF50mm 1.8, EF50mm 1.8 II, EF85mm 1.8, and EF100mm 2.0. How to explain that other than the transmission characteristics?
To those who think it's not much of an upgrade over the 5D2, you should try it before you settle on that conclusion. I have found that even the normal f/5.6 cross sensors in the middle group and the outer f/4.0 cross sensors of the side groups on the 5D3 are at least as accurate as the center cross point on most cameras I have used.
I have been very happy with the AF performance of these two lenses, so I'll list them as examples of what points are available on the 5D3.
The EF40mm 2.8 STM is a group D lens. 61 points total, 31 cross points. 21 cross points in the middle group, with the center dual cross, and 5 cross points on each side group.
The EF70-200mm 4.0 L IS is a group C lens. 61 points total, 41 cross points. 21 cross points in the middle group, and 10 cross points on each side group.
p.3 #4 · Why is the 5D3's AF system so sensitive to the lens you use?
Roger - thanks for your input here. Very interesting - I did not know the macros dropped to f/3.5 +! I had also noticed the 24-70 discrepency. Is there a simple way to test your theory about the 24-70's? Maybe check the shutter speed at f/2.8 for both lenses and see if the II is letting in an extra stop of light?
Have you done any testing, found anything interesting about outer points performance on the 5D3? I think I am mostly running up against your earlier conclusions about the older type of lenses having basically same performance on 5D3 as they did on 5D2 (in terms of accuracy). I need to go read that article again...
I wish I had an Imatest setup to play with, you lucky dog.
p.3 #5 · Why is the 5D3's AF system so sensitive to the lens you use?
I'm not sure of the 1DX metering, but if the 1DX can do spot metering on every focus point, this would be easy to test on a grey surface. Change the focus points, or distance, and see if the metering changes. That would give some idea of the 'equivalent' wide open aperture at each point. (I assume the 1DX groups are the same.)
p.3 #6 · Why is the 5D3's AF system so sensitive to the lens you use?
Schlotkins wrote:
I'm not sure of the 1DX metering, but if the 1DX can do spot metering on every focus point, this would be easy to test on a grey surface. Change the focus points, or distance, and see if the metering changes. That would give some idea of the 'equivalent' wide open aperture at each point. (I assume the 1DX groups are the same.)
Chris
I did try my 100L w/ spot metering on 5D2 (center point) - I tested against a well lit white wall. Definitely saw shutter speed drop as I went into macro distance (light was directional and I did not create any shadow as I got close to the wall).
Tangentially, 5D2 managed to lock on just fine pointed at the small texture detail of my white wall, despite it's poor reputation for being able to focus.
p.3 #7 · Why is the 5D3's AF system so sensitive to the lens you use?
mco_970 wrote:
Tangentially, 5D2 managed to lock on just fine pointed at the small texture detail of my white wall, despite it's poor reputation for being able to focus.
The center AF point locks focus just fine. It's the outer (linear) AF points which struggle.
p.3 #9 · Why is the 5D3's AF system so sensitive to the lens you use?
mco_970 wrote:
...(like male drivers )...
Oh, that hurts. I haven't gotten lost in days.
Anecdotally, I just got back from a week in Costa Rica - heavy overcast, rain, dark foliage. Traded my 100-400 back and forth between the 7D and 5D2. In those difficult conditions the 5D's center point was quicker and surer to lock than the 7D with less hunting. Used the 100L on the 5D2 for butterflies quite a bit and it locked very reliably if I could hold the focus point steady. This without using the limiters and one shot, center point only. My hope is the 5D3's outer points will be as good as the 5D2's center point which seems better than the 7D points. Sadly we didn't see as many flying Macaws so I didn't get to exercise AI focus much.
p.3 #10 · Why is the 5D3's AF system so sensitive to the lens you use?
Jeff Nolten wrote:
Oh, that hurts. I haven't gotten lost in days.
I am just mad about someone telling me you don't have to be a woman to be a woman driver. That joke still burns!!
Jeff Nolten wrote:
Anecdotally, I just got back from a week in Costa Rica - heavy overcast, rain, dark foliage. Traded my 100-400 back and forth between the 7D and 5D2. In those difficult conditions the 5D's center point was quicker and surer to lock than the 7D with less hunting. Used the 100L on the 5D2 for butterflies quite a bit and it locked very reliably if I could hold the focus point steady. This without using the limiters and one shot, center point only. My hope is the 5D3's outer points will be as good as the 5D2's center point which seems better than the 7D points. Sadly we didn't see as many flying Macaws so I didn't get to exercise AI focus much....Show more →
Sounds like 5D3 will be a very good fit for you... So what are you waiting for?
p.3 #11 · Why is the 5D3's AF system so sensitive to the lens you use?
mco_970 wrote:
Sounds like 5D3 will be a very good fit for you... So what are you waiting for?
Cheers,
Michelle
Well, the short answer is the f8 update, but the slightly longer answer is that we've done our traveling until at least spring. Since I have a 5D2 + 7D, trading a 7D for a 5D3 is a marginal improvement right now. The real benefit will be traveling with one body that can do it all, carrying a .5 lb 1.4x instead of a 2 lb 7D. My experiments with the 5D2 + 1.4x + 100-400 indicate that the IQ and reach is very close to the 7D + 100-400 and the 5D2 + 100-400 beats the 7D when not reach limited. I'll probably sell the 7D and keep the 5D2 as a 2nd body. I'll lose 2 fps and outer cross points with the 100-400 but gain in most other ways. So the hard part, the decision, has been made.
Funny, a year a go I thought I was done buying gear and then Canon released the G1X and announced the 35 f2 IS and f8 for the 5D3 and I'm rethinking my whole travel kit. Fortunately I have a very tolerant wife and travel is our only real extravagance. See, I have another man trait women like to make fun of, I never grew up! Cheers!
Two Toed Sloth eating a carrot I'd just given it. Peace Lodge, Costa Rica
Cheers!