50D - Camera won't consistently take the shot with Polarizing or ND filter on the lens

[IBaSchmuck]

If I have a polarizing or ND filter attached to a lens, any lens (Canon, Tamron, offbrand)(EF or EF-S)(zoom, fixed or macro), camera set to "Full Auto" (manual modes also), any image stabilization turned off, or on, the lenses will always autofocus, but some times the camera won't take the shot. Some times it will. The camera acts like it would if it were too close to a subject for the installed lens. However, moving further away, or closer, to the subject has no affect on the issue. I can AF the camera, switch the lens to "manual" focus and it will take the shot.

Changing the ISO makes no difference. Changing the AF point/s makes no difference.

At first I thought one of my lenses was the problem, then I tried another one and got the same result.

Is there a setting I may have changed that would cause this? Easy fix? Or am I going to have to send it in to Canon for diagnosis?

[jrhoffman75]

Poloarizing and ND filters reduce the amount of light entering the lens. You may not have enough light for the AF system. Are you sure its reaching focus; is the green dot lighting up?

[RobertTheFat]

I think if your problem were confined to the polarizer, we'd guess that you're using a "linear", rather than "circular", polarizer. So trying to salvage that thought, I wonder if your ND filter is itself acting like a linear polarizer. Try changing its rotational position relative to the lens. And have you experimented with other examples of either type of device?

In any case, it's a good guess that your camera is appearing to complete the AF process but not actually doing so. All of the symptoms you describe point in that direction. Some camera/lens combinations can be told to take the picture even if AF hasn't been achieved. See if you can set yours that way, and try again.

[jrhoffman75]

Thats a good thought Bob.

[IBaSchmuck]

Yes. The green light is on.

Both filters are circular. Sometimes I can hit the shutter three or four times, without moving the camera in or out, and it on the third or fourth attempt it will take the shot. Some times I can hit the shutter 10 times with no response.
With a UV or 81A filter attached I can shoot all day with no issues. It appears only with polarizer or ND. Even if they are backed off to allow the most light in. Filter light allowance positioning doesn't seem to make any difference, with either filter.

I think I have another circular polarizer in with my A-1 stuff. If I have a step up ring I'll give that a try too.

"Some camera/lens combinations can be told to take the picture even if AF hasn't been achieved. See if you can set yours that way, and try again."
I'll give that a try.

[jrhoffman75]

I'm confused. If the green dot lights up camera is in focus - are you saying the light is on but shutter won't fire?

[IBaSchmuck]

That's correct.

[jrhoffman75]

does your camera have LiveView? Can you take a photo using LiveView?

[IBaSchmuck]

It does have Live View. In the two years I've had this camera I've never used it so I'll have to learn how and then go play with that too.

[RobertTheFat]

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@IBaSchmuck wrote:

Yes. The green light is on.

Both filters are circular. Sometimes I can hit the shutter three or four times, without moving the camera in or out, and it on the third or fourth attempt it will take the shot. Some times I can hit the shutter 10 times with no response.
With a UV or 81A filter attached I can shoot all day with no issues. It appears only with polarizer or ND. Even if they are backed off to allow the most light in. Filter light allowance positioning doesn't seem to make any difference, with either filter.

I think I have another circular polarizer in with my A-1 stuff. If I have a step up ring I'll give that a try too.

"Some camera/lens combinations can be told to take the picture even if AF hasn't been achieved. See if you can set yours that way, and try again."
I'll give that a try.

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I apologize if I'm seeing you as more of a newbie than you are, but are you sure you know what "circular" means in this context? A circular ND filter is an oxymoron.

If you're not sure, google "circular polarizer" (which is the only type of polarizer that works with most AF systems).