Camera, lens or operator?

Please don't groan! I know it's been done to death, but I think I have an issue with auto-focus that possibly is not me. I shot this on a table with a set of batteries spaced out about 50mm each. I locked up the mirror and used a remote shutter release. The Canon software tells me where I focussed (centre focus only). I use cf4-1 to lock the focus independently.

So, it doesn't seem repeatable and varies depending on the distance away from the object.

Is the focus purely down to the lens or the camera (10d), or a combination?

I do have trouble with focus with all my lenses, but this test seems to be the easiest way to rule me out of the equasion. Some lenses seem better than others, but I could test at every possible permutation of distance, f-stop etc and I would be doing it forever.

If a lens problem, do Canon UK charge for checking it does anyone know? (it's second hand).

Thanks in advance and sorry to drag this up again

Graham

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From what I've read about Canon's auto focus, is that the focus sensor is larger than the red square. I'm not sure if this is what's happening on your end. Here's a link that explains alot about the Auto Focus. It may have an answer for you.
http://www.fredmiranda​.com/forum/topic/24152​4

if it is happening on all your lenses then it must be the camera I would think but lenses can also be out and need calaberating but if they are all diong it it should be your camera.

raven7 wrote:
From what I've read about Canon's auto focus, is that the focus sensor is larger than the red square. I'm not sure if this is what's happening on your end. Here's a link that explains alot about the Auto Focus. It may have an answer for you.
http://www.fredmiranda​.com/forum/topic/24152​4

Thanks for the response raven7, but it hasn't pulled focus on anything within (or even around) the focus point. I don't think that it is a lack of contrast as there seems to be plenty for it to grab. Nor has it focussed on infinity or the back of the kitchen at any rate. It does seem as if it thinks it's focussed, as the rear battery seems to be in focus. This was at f1.4, so the depth of field should be very small (probably smaller than the difference between the battery I was focussing on and the rear most one (about three inches behind). It's a bit surprising - and if I can sort it out, I will instantly become a much better photographer!

Graham

Sadly, it's not a consistent thing. My 85mm f1.8 seems pretty good. The 135mm seems reasonable too. The 17-40, seems not so good, but that is more understandable as it's wide angle. The trouble is, If you can't trust it to focus where you point the focus point, it rather defeats the object of auto focus. I wear glasses, so manual focus is not so easy.

Graham

Here's a good focus chart to print that should give you a better idea where your problem could be, or not be. The download for the chart is towards the bottom of the article.
http://md.co.za/d70/ch​art.html

raven7 wrote:
Here's a good focus chart to print that should give you a better idea where your problem could be, or not be. The download for the chart is towards the bottom of the article.
http://md.co.za/d70/ch​art.html

Do you see a flaw in my trial methods? I tend to think that the point of focus is so large, that it could justifiably pick any point in the red square and it would have done it's job. In the test as I have done, it doesn't have anywhere else to pick to focus on. If it can't focus on the battery in clinical conditions, what are the chances of it operating in the field?

My real question (as it clearly has not focussed on the focus point) is whether it is a function of the lens, camera of indeed both.

Graham

Sounds very much like the camera to me too but just for curiosity sake the closest battery was not closer than the minimum focusing distance was it?.. Do you have any friends or relatives who use an EF camera to test the lens out on?...

The camera beeped to signify it had locked focus. It is a 50mm f1.4 and should focus much less than 4.5ft.

Oh, no friends

Graham

With the focus chart, you would know if your camera was front/rear focusing. I would try manual focus at the same settings to be sure the lens is capable of being tack sharp. Keep us posted as to what you come up with.

Is in not clearly back focussing? I wear glasses, so manual focussing is not that easy, nor what I bought the camera for.

Graham

Can't remember where I read it, but I read something about Canon's AF system can be off by up to 10% for any particular shot.

Also I found that with my 10D it would miss focus about 1 in 4 shots. My 1DsMkII seems to miss focus about 1 in 10. By miss focus I mean more then an inch at 10feet, which means something I want in focus isn't.

Also lenses with a wider aperture (such as 50/1.4 and 85/1.2) tend to do better then those with smaller max aperture.

However, if you are getting multiple misses in the same direction by the same amount, from multiple lenses then your camera is probably out of calibration. If possible I would send camera and your worst lens together to Canon to get calibrated. And then when you get it back see if the other lenses still show the problem (presuming they fixed it). Before sending it in I do recommend using the one of the lens test charts to double check and make sure you take multiple shots each time. Me I use a ruler to prove to myself it was my imagination with all but one lens.

Just my experience and memory,

Thanks for your support. This was a 50mm 1.4, so it's not looking good.

It's only a hobby for me, so nothing more than my pride at stake. I am just grateful I am not a professional. How do you guys cope?

Graham

Just curious because I have not tried it but with cf4-1 will it focus if using a cable release?
Why don't you use centre point focus instead.

Dan

The only think I'd do is spread those batteries out a bit more to make SURE that there's no mistaking which one will be selected by the AF point. But on the surface, it looks like backfocusing.

If your other lenses are doing OK, then I would say that the camera is OK, and that the lens needs adjustment.

My default with all my images has become to blame myself first, and then go on to prove my theory. So far, I've been right nearly 100% of the time. But equipment does fail, and can need adjustment. I had a Tokina zoom for 2 days that refused to focus anywhere near what I was pointing it at. Given that it was new, I sent it back - but, it probably would have been appropriate to have it calibrated.