T3 with 18-55 doesn't recognize AF switch is on?

Sometimes, when I turn my T3 on and then flip the AF switch on the lens, it doesn't acknowledge that AF is on. In live view, I can just hit the live view button twice and it starts focusing (I use the pentamirror to focus for live view, very rarely) but I always shoot from the viewfinder and it doesn't work until I leave the AF switch on, shut the camera off, and turn it back on. Does anybody know what might be going on? Is it a lens or a camera problem? Thanks in advance!

Paul

I came up with a hypothesis, actually. I think I may have worn out the AF switch on the lens. I have a habit of shutting it off and resetting the lens to its "shortest" mode (focus barrel all the way in, lens about 2/3 of the way between 24 and 35mm marks) before I pack it up, and most of the time switch it off before shutting it off. Then, of course, most of the time I switch it back on when I turn the camera on, sometimes a few times in a row. I tried pushing in on the button while flipping it on with the camera already on, and it seems to work just fine.

Bump

I didn't think the AF switch on a lens was an "on - off" switch that needed to be actuated with the turning on or off of the camera's power.

I thought it was essentially there for the purpose of allowing you to manually focus the lens - and stop the AF from "trying" such as in low light settings or total darkness (moonlight) where the lens will just keep trying to focus and "hunt" for it.

Hadn't ever even considered turning this on and off each time I powered up or shut down my cameras.

Could you explain exactly what is the advantage of doing this?

Hillbille

Hillbille wrote in post #17287474
Hadn't ever even considered turning this on and off each time I powered up or shut down my cameras.

Could you explain exactly what is the advantage of doing this?

He said he was doing it to adjust the lens so it was at its shortest length when he packed it away, so I assume he is just wanting to save space in his bag. I do the same when I put mine away, but don't need to flick the AF switch as all mine are USM lenses so I can just turn the barrel whilst in AF.

The advantage of flipping the switch is that it is possible to damage, or even strip, the gears if you adjust focus manually, whilst the AF switch is at "AF", even when the camera is powered off. This doesn't apply to USM lenses etc., as they have no gears to strip

So - if I understand what you are saying - you believe the lenses are receiving power to it's gear train even when the camera is off - and the gear train inside can be "stripped" by manually moving the barrel without having that switch in it's "off" position?

Right?

Hillbille

No because the AF/MF switch throws the motor clutch in and out of engaement even with the lens unmounted. I should add that the gear system on non-USM lenses is not up to turning even the unpowered motor.

Alan

Hillbille wrote in post #17287972
So - if I understand what you are saying - you believe the lenses are receiving power to it's gear train even when the camera is off - and the gear train inside can be "stripped" by manually moving the barrel without having that switch in it's "off" position?

Right?

Hillbille

No, I never said they were receiving power.

When the switch is set to AF the gears are engaged, and if you try and turn the barrel you are fighting against the gears locked in place by the motor, even when unpowered. It's probably much the same as trying to push a non-running car that is in gear, you are trying to turn the whole motor. Whether the lens is powered up or not, you are putting a lot of strain on the gears and can damage them.

A guy at my camera club bought a 55-250 and complained about the AF packing up after he had only used it 3 times. Turned out he had been using the focus ring whilst in AF and wrecked the gears.

While you are correct that your particular lens should be turned off before manually focusing it, I think if you do this a lot you are going to be wearing the AF/MF switch out pretty fast... maybe you already have.

Instead, to accomplish the same result you can simply leave the AF turned on and point your camera and lens toward a distant object and activate AF by half-pressing the shutter release button. That will set the focus to infinity, which will also make the lens physically the shortest possible for storage. Same result without having to flip that switch so often.

Live View focusing isn't something I do enough to be able to advise about it.

One note of clarification: you are using what Canon calls "Quick Mode" or something like that, in Live View, where it momentarily drops down the camera's mirror, focuses, then raises the mirror again for Live View to be active.

That is not the "pentamirror" being dropped down and raised for Quick Mode. The pentamirror is part of the viewfinder assembly, above the mirror that you see inside the camera when the lens is removed, above the focus screen, inside the "hump" on the top of the camera. Rebel series cameras use a pentamirror (to save weight and cost) to reflect the image in the viewfinder, while the more advanced Canon cameras use a true pentaprism.

This is a relatively minor thing, but could cause confusion while discussing and trying to solve your problem.