1Ds MarkII AF system: Confused

[valo_soul]

Hello everyone. I know I must be a moron for asking this but I'm just so

confused. So it has 45 AF points which is phenomenal, but, they are basically

all lumped into the centre! I don't understand how you can autofocus on

something at the frame edge or even close to it. Something like the 350D with

7 points that spread far out, almost to the edge, make it quite simple. I

just don't know how it would be possible to use large apertures creating a

shallow DOF, and nail your focus where you want it with AF unless it's

practically in the very centre of the frame. Seems illogical that an $8000+

DSLR would be so impractically designed so there must be something I'm missing.

[bobatkins]

"I don't understand how you can autofocus on something at the frame edge or even close to it"

 

That's because you can't. You can't with any DSLR that I know of.

 

That's why you sometimes have to focus first, then recompose, or even focus manually.

[valo_soul]

Reeeally. :S So you have to manually focus a nearly 10 thousand dollar camera if you want to focus on anything besides the center of the frame. Seems like a pretty wretched quality. Why wouldn't any company incorporate this? Like I said though, with the 350D it is MUCH better (almost to the edge) so it allows more possibility. I just fail to understand why the more high-end cameras would just basically have one large, hyperactive centerpoint. And Bob, that's why I mentioned the ultra large aperture shooting; focus/recompose is not an efficient way of nailing focus like this. I would rather manually select a focus point which falls over my subject. So I suppose manual focus is the only option. That's pitiful.

[kenny_c]

Thats because the centre portions of the lens area is the most accurate and sharp for focusing, regardless of lens, once you start using edges with poor grade lenses you're going to start having people complain about focusing otherwise.

[valo_soul]

Kenny, that's why i don't use low grade lenses, believe me every lens I own is pretty darn good. This just doesn't make sense that there is NO option to autofocus anywhere but the centre. lol it's absolutely laughable. You mean to tell me that Canon is saying "We will definitely have to limit the photographer's creativity by only allowing him/her to autofocus in the very centre of an image." It just doesn't add up that after years and years of innovations and technological advancements in photography, you would be limited by the very BASIC of ideas; to only be able to shoot one way. You could have literally 5 million AF point in that little crammed in centre area and it wouldn't do a thing for me. Why not just put even ONE at each side. There must be a way around this is just doesn't make sense.

[steve_dunn2]

<p>In most (though admittedly not all) compositions, the subject is somewhere in the middle part of the frame. The AF system on the 1Ds covers almost a quarter of the entire frame; I don't think you'll find any cameras with greater coverage. Yes, the outermost points on the 350D are farther out than on the 1Ds, but to say they're "almost to the edge" is stretching it a bit, and there are huge gaps between AF points, so in total the AF points only cover a few percent of the frame.</p>

 

<p>Anyway, as others have pointed out, that's the way it is. Different cameras have different numbers of AF points, in different layouts, covering different parts of the frame, and all of them have more AF points towards the centre of the frame than towards the edges.</p>

[jim_larson1]

James;

 

You spend how much on this camera . . . without understand some of the basics of the AF system?

 

The 1 series AF system is a totally different animal than the 7 and 9 point AF systems in the cheap stuff.

 

The cheap stuff is designed with drunk bozos (like me) in mind -> for use with F5.6 lenses. In this application. . .the idea is to try and find something nice and contrasty to focus on. . and rely on the relatively large DOF of the lens to ensure everything is in focus. The target audience for this AF system are those that may not realize that you should put the AF sensor ON THE SUBJECT to ensure focus. The AF sensors are therefore WIDELY SPACED. . and cover a large area.

 

The 1 series AF system is designed with lenses like the 85/1.2 and 200/1.8 in mind. Applications where DOF is so tight that your subjects left eye will be in focus, but the right eye will not be in focus. Applications where parrallax is an important factor (do a search on "why focus recompose sucks") and focus-recompose is *not* an acceptable option.

 

In the 1 series AF systems. . . certain sensors (8 I believe) are high precision. . .with three times the focus precision of the 350D sensors. Not only that. . .but the sensors cover a smaller area. Put the huge high precision sensor of a 30D or 400D on a subject. . .and that sensor may pickup EITHER the eye or the tip of the nose. The 1 series sensors are more likely to pickup the part of the face you are intending to focus upon.

 

You are going to have some interesting times with this camera.

[chrisjb]

Hi, I`m just a little confused by your confusion, for my money the 1Ds2 is basically a highend digi replacement for my Hassy gear, designed for studio, commercial and landscape.

 

In the studio its use is portraiture, product photography and similar, nearly all portraits fill most of the frames so a centre focus point nearly always used, unless your main subject part is an ear.

 

In product work most clients want all their items sharp so smaller apertures are used for DOF, therefore a little focus / recompose is aceptable, otherwise a TS lense used.

 

In landscape most good landscape artist use Hyperfocal techniques so the AF not needed anyways.

 

Could you shed some light on the times that you would need to focus on the very edge of your frame. as said this AF system is so much more accurate then the consumer market bodies, if not, they would not sell.

 

thanx

[mark u]

You might not be so scathing if you actually tried using the 45 point AF system and a 100% view full frame viewfinder, especially in more challenging focus situations. Bear in mind that for small angles of pitch or yaw, focus and recompose is not going to introduce a significant focus error - macro work aside - at anything other than closer distances and only when using fast apertures (you'd need to use a ~1.6x faster aperture on your 350D to get the same narrow depth of field). Given that the frame edge is about 10mm away from the AF area (which is 15x8mm), the approximate angle you have to turn the camera is 10/43rds of the diagonal angle of view of the lens - and the resulting focus error is very small with telephoto lenses.

 

You should also recognise that your 350D only gives about 90% linear, 80% area view of what is captured by the sensor, so the AF points appear closer to the edge of the frame than they truly are. Moreover, the view is darker (because it has a higher magnification and because there is more light loss in the pentamirror than in a pentaprism), and still smaller - all combining to make manual focus adjustment very difficult which is not the case for a full frame 1 series viewfinder - especially with the appropriate interchangeable focus screen.

 

There are various technical reasons to do with optics why AF sensors that are more distant from the optical axis of the lens are less sensitive and less accurate, not to mention difficult to accomodate in the mirror chamber. The 45 point AF system offers some central sensors that will focus 3 times as accurately as the 350D sensors, and the centre sensor allows AF with an f/8 lens. To gain some insight into these and related issues read these articles:

 

http://www.canon.com/technology/canon_tech/explanation/area_af.html

 

http://doug.kerr.home.att.net/pumpkin/Split_Prism.pdf

[frank_skomial]

"how you can autofocus on something at the frame edge or even close to it" - That's because you can't. You can't with any DSLR that I know of." - not with Canon expensive cameras.

 

For this you would need to borrow a Nikon DSRL inexpensive camera, then select a focusing point that is at the edge, then focus using it, - very simple.

[bloosqr]

I have to admit when i first picked up an eos 3 used (as an upgrade from the elan 7e) the

exact same thing went through my mind .. its a bit of an optical illusion actually..

[pbizarro]

Canon recommends using the 45 AF points when trying to track a moving subject, with servo-AF.

 

You would be better off reading their documentation, instead of spreading more BS and ignorance in the internet.

[valo_soul]

Frank, could you elaborate on that Nikon bit?

 

As for an example of when I would want to focus at or near the edge of the frame; even this included image would not be possible as far as I can see. If I wanted to focus on this person's left eye (their left) there would be no AF point covering it. Perhaps I miss the shot for lack of time to manual focus. I would also be using the 85mm f/1.2L so, as I said, focus/recompose will most likely blow it. So, what do I do? :S

 

This is even a modest example as there will be shots requiring focus even more towards to edge. (Image credit to Henrike Scholl)

[valo_soul]

Well, Paulo, that was a rude comment. I'm not spreading "BS" or ignorance whatsoever. For the record, Canon does not "recommend" it for moving subjects using AI-servo, but they say it would work especially well for situations like that. Of course it would. That doesn't make it a sports/action camera my friend. It can be used for portraiture too and sometimes in portraiture, you want to do what I'm talking about in this thread.

[hash]

I am with you James. Expensive top end cameras should be able to autofocus anywhere in the frame, and not be making excuses about what it was designed to shoot.

 

But I don't think Nikon is any better in this respect. I use a D70 and the AF sux majorly. Only 5 AF points, out of which only one really works. I used to have an EOS 300 film camera before and even that had 7 points, most of which seemed to actually work. I never really had to manually choose the AF point.I went to Nikon only because Canon crippled their DSLR offering at the time - the 300D - just to protect the 10D.

[ci_p]

"I know I must be a moron for asking this but I'm just so confused."

 

Not as much a moron as I feel. I've used this camera since it came out and never even noticed being severly impacted by this serious design error.

[dcheung]

I'm with James as well.

 

If you want to compose the subject at the 1/3 point of the frame, it would be out of reach of the Autofocus system and that's just ridiculous.

[valo_soul]

Thank you, Hashim and Weiyang. That's exactly what you hear; excuses. People trying to defend the camera because it's their brand or just because it's the "flagship" model. That doesn't negate the fact the the system is limited. Any photographer who says they wouldn't even like the OPTION of being able to AF on any area of the frame is lying. Even if you never used the ability (although I wouldn't understand why), the fact that it is there would be a huge plus. Like, would you rather have a DSLR capable of 1 FPS or 8? Even if you don't shoot action, knowing the option is there is a bonus. It just simply makes for a nicer camera. I've got to say I'm very dissapointed.

[mark u]

So have you actually USED a camera with the 45 point system and big, bright viewfinder and compared it with a 350D for AF and MF? I can't recall anyone previously who has claiming that they would prefer to use the 350D for its "extra" focus capability.

[ci_p]

What would you pay for this?

[valo_soul]

CI, what would who pay for what?

 

Mark U, that's the thing. Like you, nobody who spends this much on a camera of this caliber likes to admit that it is missing something so basic. I don't care how big and bright the viewfinder is because the AF system is so limited. The 350D is far from perfect as well. Even a combination of the two cameras would be an improvement. Like using a large center area with, say, 40 points and then 2 more on each far side and one at the top and one at the bottom. I guess the thing is: me talking about it won't change reality and the reality is that the AF system is limited and incomplete. Like I said in my last response, if you say you wouldn't want the OPTION to AF anywhere in the frame you're lying. Why would anybody WANT their photography to have any limits whatsoever?..especially something so simple.

[jim_simon3]

James,

You misunderstand the setup of the digital cameras. In the cameras that have a crop feature they import the focus points of the film camera and viola, the focus points get very close to the edges. I have the 45 point system in a 1DMkII and with the 1.3 crop factor the elipse covers a huge area. It is exactly the same as the full frame but the edges are cropped out. With the 1.6 crop of the 350 the points can appear spread out, but it is a relative matter.

[musubi1000]

I hear ya james for the exact same reason I'm not going to buy a Mc Laren race car. For that much money it should have a cup holder. I won't buy a car unless it has a cup holder. If I were a Professional race car driver a cup holder would be the farthest thing from my mind. it is a convienence afforded to the regular driver not to a professional.

[hash]

That's silly. A cup holder doesn't help the driving in any way, but a better AF system does help a photographer. And I don't see why it should cost significantly more to have the AF points spread out. And no one seems to point out any ADVANTAGE of having them all in the middle anyway, other than a bit of cost saving for the manufacturer by retaining component compatibility with a cropped sensor model.

[chrisjb]

Hi, just finished printing last nights work and ask a couple of other pros about their nikons, they seem to be in the same boat. So what AF system alows a focal point on the edge of the frame. I`m not a lens tester but I think most lenses are sharp in the middle and the worst towards the edge, common sense says not to go there. The 45 pt AF are smaller sensors so focus on finer details than the larger and quite often misaligned point on consumer bodies. the x1.6 body would never use the outer edge on the lens mentioned so it doesn`t matter as it is only using the centre portion of the lens.Most times focussing on the most contrast quite often the part you don`t want.

 

What would be interesting is tio hear from a 5D + this lens user on the feelings they have on so few focal pts.I feel that a fairer comparison than a 350D. Yeh would love to have all options but that only goes with demand.

 

I`ve seen many similar shots as your sample, nearly all are corrected with some manual aid, AFAIK AF only has to be within the DOF so even with such a large aperture that is still a large margin for error. Is there a focus system that is closer? my Nikonian friends don`t think so. I really feel that the outer most focal would still allow recom ok with the final adjust manually if necesary

 

Have fun