I had a focus problem with my camera when it had a polarizer on it, it was on a 28-300 zoom with my digital rebel, all my pics were out of focus, and didnot auto-focus correctly but when i took the polarizer off, it focused fine... i dont get it, it was like the central part of the pic was in focus, but the outer part was out of focus...

You are using the wrong type of polarizer. You must be using a Linear or regular polarizer, what you need is a Circular Polarizer. The camera's autofocus system uses a polarization trick to focus, so the linear polarizer confuses the AF system. A circular one uses a slightly different method and spins the light waves after polarizing them. By circular I don't mean a round filter, both types are round; it refers to how it polarizes the light. Getting a C-PL or Circular Polarizer should solve your problem.

no i just checked, it is a circular polarizer

Hmmm...I use a C-PL and have no problems focusing with my Fuji S5000. Maybe the filter is scratched and causing the focus to fall short.

Ya, i suspected that too, but there are no scratches. i did notice though when i had it on full auto mode with the polarizer turned to make the sky look darker, and i was outside in bright sun light, i noticed that the flash came up and it did its flickering as though there was not enough light to focus... maybe that has something to do with it.

Yeah, I think that’s it. The maximum aperture of the lens is like 4-5.6, and the polarizer reduces the light by 1.5 to 2 full stops. The AF system is not sensitive enough on the digital rebel to focus in that sort of low light situation. That’s why its firing the AF assist light (the flash bursts).

ok, do you know of a way that i could circumvent this issue, should i use a different lense, ie one besides the 28-300 zoom? mabe the one that came with it?

Well, use the lens with the largest minimum aperture. The 18-55 that comes with the digital rebels has a min aperture of 3.5-5.6, so it's hit or miss. Try it though, if it still doesn’t work, you need to either get a lens with a larger minimum aperture, a body with a more sensitive AF system, or manually focus. Lenses with polarizer focus best if they are around f/2.8 or larger.

Unfortunately there is not a way to circumvent the problem. The AF sensors in the camera require a certain amount of light, and if they don’t get the right amount, they fail to do their job properly.

hmm, well i think i forgot to mention that i had it on infinity focus mode...

That would also do it! Was the samera in Servo or One Shot mode? If it's in One Shot, still having focus problems but taking pictures, then I'd suspect hardware problems.

not sure what servo mode is, it was in infinity focus mode... (the mountains dial) so it should have set the aperture.... umm when i take the polarizer off, it focused fine...

I would recommend using Tv, Av, P, or M modes. You will get much nicer results with a bit of practice. The full auto modes have rarely produced acceptable results on any camera of mine!

As I had mentioned, the 28-300 is not a fixed minimum aperture lens (which really surprises me, as the better L-series zooms maintain f/2.8 or f/4 throughout the entire zoom range.)

If you recall, the 28-300 is f/3.5-5.6. If you are at 300mm (f/5.6), a polarizer will reduce the light by two stops, making it like an f/8 lens. None of Canon’s DSLRs except the 1 series (1D, 1DMKII, 1Ds) will autofocus with f/8 or smaller. Even at 28mm (f/3.5) the polarizer brings it to f/7.1, making it almost impossible for the autofocus system to work. (Try it at 28mm though, it may work)

Hopefully my explanation makes some sense!

Unfortunately, due to the limitations of that lens, you can’t use a polarizer and have autofocus on a Digital Rebel. Manually focusing is your best bet.

Will.

thanks, i understand now!!!