Autofocus?

I have not used the autofocusing of the Rebel XT since I bought it two months ago, but recently I have discovered street photography and tested out the possibility of using autofocus in some of my exposures to compare it to zone focused shots. I believe there is a problem with my autofocus, for when i press the shutter it either autofocuses and then locks, and does not allow the exposure to be taken, or it focuses, takes an exposure, but then refuses to allow me to take any further exposures. And sometimes it does not even focus when I press the shutter halfway. Is this something I should send in for service, or is this something on my behalf? Please enlighten me

First thigs first:


What lens are you using? Did you have AF switched on?

How far away is the subject?

What settings are you using, ie. AF setting:
-one shot?
-AI focus?
-AI servo?
---> (one of those 3)

In the bottom right corner of the LDC, what is showing? A single rectangle, 3 rectangles (stacked) or a 'stopwatch' symbol?


Andrew.

Also, do you get the green confirmation dot in your viewfinder to show that autofocus has a lock? If there is a flashing green dot it means that AF can't find a target and it won't allow you to take a picture.

That's if the 350D is the same as the 20D in this respect - I figure so...

++ Oh, and AF requires some contrast in the subject to get a lock - if you try and focus on a white, blank wall or say the sky with no clouds it likely won't be able to tell where to focus.

Jim G wrote in post #2278584
That's if the 350D is the same as the 20D in this respect - I figure so...

It is the same.

Andrew.

Seems like your camera knows you don't like auto focus and is just messin' with you.

canonphotog wrote in post #2278728
Seems like your camera knows you don't like auto focus and is just messin' with you.

Haha, that's it, and my camera knows I want good pictures and refuses to comply!

The AF was switched on, and I am using the kit lens at the moment, planning on converting to a manual prime FD lens in the near future, but using an autofocus seemed like a decent idea for working the streets until then. AI Focus Mode. I get a red dot when I depress the shutter halfway to focus and check metering.

You get a red dot in the focussing screen - but how about a green dot at the bottom, alongside the shutter and aperture displays?

OBTW - without a major operation an FD lens won't fit on an EOS and give you infinity focus with rated focal length. Tehre are adapters, but they either cost you infinity focus or incorporate a 1.25x or so TC in the works and aside from the very scarce and expensive Canon model made for only a few lenses the optical ones are fairly bad IQ-wise.

Even when my exposure is perfect autofocus does not work, even with an identifiable subject. As for the lens...I do not care if its an FD or a newer lens, I just need something that allows me to zone focus, all of these new AF lenses seem to lack a nice graduated manual focus with focus distances marked. And even the ones that do have markings, they are usually too close together, and often times only have up to three feet away marked as focus distances, if you get what I am saying.

ChristopherJohn wrote in post #2287044
Even when my exposure is perfect autofocus does not work, even with an identifiable subject. As for the lens...I do not care if its an FD or a newer lens, I just need something that allows me to zone focus, all of these new AF lenses seem to lack a nice graduated manual focus with focus distances marked. And even the ones that do have markings, they are usually too close together, and often times only have up to three feet away marked as focus distances, if you get what I am saying.

When you say identifiable subject do you have the focus point over a high contrast area (like say the edge of a building and the sky)?

Oddly enough, you would probably have better luck with non-Canon manual lenses than FD ones. I know that there are relatively cheap adapters you can get for both Nikon and Pentax manual lenses but you obviously need to use stop down metering (you would have had to with the FD lense anyways).

e-k

Jon wrote in post #2286243
You get a red dot in the focussing screen - but how about a green dot at the bottom, alongside the shutter and aperture displays?

Green dot only lights up in One Shot AF.
Blinking green dot means 'AF not possible'.

@ ChristopherJohn: On AI Servo AF: You are aware that the camera wil keep focussing right up till you take the picture? So focus-recompose is not possible? (unless you use CFn4)

Some examples would be real helpfull.