1dmkIII vs 5D focusing question

I have an XT that focuses extremely fast with all of my lenses except my 100 f/2.8 macro. I am thinking of getting another body and I have narrowed it down to either the 5D or 1dmkIII. How much faster (and more accurately) will each of these bodies focus with the 100 f/2.8 macro than my current XT body??

did you move the focus limiter switch to the 48 position ?

Focus on both cameras will be significantly more accurate that your XT. Focus speed probably won't be a terribly noticeable difference, unless you're shooting in low light a lot.

silvex wrote in post #6095996
did you move the focus limiter switch to the 48 position ?

This may be a dumb question, but what is the focus limiter switch?

PictureDisk wrote in post #6097278
This may be a dumb question, but what is the focus limiter switch?

Not dumb at all. It limits the range the lens will try to gain focus. Slide it to 48 from the 31 and the lens should focus much faster for normal use.

Thanks silvex ... I hadn't thought of that.
Normally I only use the other switch to turn off AF when I'm doing really close work (1:1). I'll give it a try to see how much faster it focuses, and whether it hunts excessively.

PictureDisk wrote in post #6095951
I am thinking of getting another body and I have narrowed it down to either the 5D or 1dmkIII. How much faster (and more accurately) will each of these bodies focus with the 100 f/2.8 macro than my current XT body??

I would think the 1dmkIII would be much more accurate and better then both the XT and the 5D. Better AF is one of the main reasons im looking at buying a 1D MkIII as my main body and using the 5D for landscapes etc, unless the 5D mkII whenever it is that comes out has a much more accurate AF system.

On the XT I think we are talking 8 AF points (I think only 1 is cross-type) vs what im fairly sure is 19 cross-type AF points (plus 26 Assist AF points) on the 1D MkIII for a total of 45 AF points, no contest.

That's about correct, even if it's seven or nine focus points in the 300D - 450D range. But AF speed is not only the number of focus points, it's also a question about which lens you use and how focusing is calculated in the unit.

Having many focus points active increases the chance that one of them find anything to focus on, but also increases the workload on the focusing processor to figure out which to use.

on the XT/350D there are no cross points I believe. And there are 7 points not 8. Just thought I'd give the forum the info.

There is really no comparison in terms of AF between the xt/5d/mkIII

The MkIII has a separate processor dedicated to AF. It has 19 cross sensitive points for f2.8 lenses. The 5D is similar to the 30D in terms of AF; except that it has 6 assist points that can't selected around the centre that will aid in tracking.

Both the 5D and MkIII and faster, if not considerably faster than the XT, but you can't just look at AF of these two cameras when you are looking to upgrade. Both cameras offer some really sweet newer features over the XT and will both give incredible IQ.

hope that helps,
Nelson

when it comes to AF - xxD < 5D < 40D < Mark III. I found the 100 macro to be slow to AF with any camera body. But thats the nature of a macro lens. Is there a particular challenge you are having with your lens/kit right now?

Any difference in AF speed would be slight, but the improvements will be there. The problem is with the 100 macro lens. It's a lens with slow AF speed.

As far as accuracy is concerned, yes, the MKIII's AF system is more robust so you should see some improvement.

What do you typically shoot?

PictureDisk wrote in post #6095951
I have an XT that focuses extremely fast with all of my lenses except my 100 f/2.8 macro. I am thinking of getting another body and I have narrowed it down to either the 5D or 1dmkIII. How much faster (and more accurately) will each of these bodies focus with the 100 f/2.8 macro than my current XT body??

nicksan wrote in post #6100253
Any difference in AF speed would be slight, but the improvements will be there. The problem is with the 100 macro lens. It's a lens with slow AF speed.

As far as accuracy is concerned, yes, the MKIII's AF system is more robust so you should see some improvement.

What do you typically shoot?

Actually, depending on the lens the improvement may be drastic. With a long telephoto or something with IS, the 1dmkiii has more voltage to run the focus drive than the XT. With a 70-200IS with IS on, you'll see the viewfinder dim in the XT as the power goes dangerously low (when battery charge is lower). Not so on a 1d. With something like 100 macro, nick is completely right, not going to get any faster, just more accurate.
If you have good lenses, the 1d will show a bigger improvement than the 5d would. But at current 5d prices, if you really need something better, 5d is pretty damn nice to have.

10fps and fast AF is why i like the mkiii

You'll see improved IQ with either the 5D or Mark III with less noise at high ISO's and shadow areas. But the Mark III autofocus will be much better than either the XT or 5D,especially with moving objects, in low light or with low contrast objects. Besides having 45 focus points you can customize the number of focus points in play as well as their helpers.

I've done quite well tracking moving objects with the Rebel SLR as well as a 30D so it's really a matter of how good do you really need your autofocus to be.

There are differing opinions on the 45 focus points.

Personally, I never use all of them (Ring of Fire) at once. Also there are 19 user selectable AF points (which is still tons better than 9!) and 29 assist points. I typically select 1 AF point and have the surrounding assist points enabled.

I agree that it's much more flexible and robust than that of the 5D.

In fact the 40D's AF system is better than the 5D, especially on non-center points. It's just quicker and more accurate.

The MKIII ups the ante quite a bit...

Jon_Doh wrote in post #6101449
You'll see improved IQ with either the 5D or Mark III with less noise at high ISO's and shadow areas. But the Mark III autofocus will be much better than either the XT or 5D,especially with moving objects, in low light or with low contrast objects. Besides having 45 focus points you can customize the number of focus points in play as well as their helpers.

I've done quite well tracking moving objects with the Rebel SLR as well as a 30D so it's really a matter of how good do you really need your autofocus to be.