Shadows in corner and dark pictures-stuck filter

Question

I have a Canon Rebel EOS T3. Great camera but some problems of late. I put a polarizing filter on it. Not sure if this is where my problems began but some pictures in normal outdoor light have black corners on the top left and right. Secondly indoor pictures with flash are noticeably darker.

Of course the simple answer is to try and remove filter but it is on real tight and am afraid to force it- ant thoughts-suggestions? not to sound like a complete moron but clockwise or counter clockwise to remove?

Answer 1

A filter which is too thick will cause vignetting. This will usually be seen only at wide-angle but that depends on the lens. Now filters are symetric so you should see all corners being dark if this is the case.

Since you only see two dark corners and your filter is stuck, I am guessing you have crossed the threads and your filter is not parallel to the lens, meaning the top is slightly forward. If you take it off, see this question, and mount it properly back, you may not see dark corners.

The other reason to have some dark corners is that the lens hood is tilted. Check that too.

Answer 2

It sounds like vignetting. This can happen with filters because they extend out from the front of the lens and obstruct some of the light coming in from the sides. This is particularly noticeable in the corners and is probably why you are seeing the darkening. If you can't remove the filter, you could try putting on another and see if it makes the problem worse, if so, then that's certainly the problem. You can also check by seeing if the the problem become less pronounced as you use the telephoto side of the lens' range, but there are some other possible causes there too.

As for the interior lighting, a polarizing filter generally does reduce the amount of light to make it through by a decent amount, particularly with cheaper filters, so that's also not unexpected.

Answer 3

To remove the filter it needs to be turned counterclockwise when you are facing the front of the lens. You need to grip the base of the filter, rather than the ring on the front that rotates to adjust the angular direction of the polarization. A filter wrench should help. They are available in a variety of sizes.

Depending on the filter, a polarizer will normally reduce the light entering the lens by around 2/3 stop to as high as 2 full stops. When used on a wide angle lens a normal thickness filter will cause vignetting because the ring the filter is mounted on will shade the parts of the lens that transmit most of the light that falls on the corners of the image sensor. This will be most noticeable at larger apertures and shorter focal lengths.