Only one filter may be attached?

[SPL Tech1]

The manual for my stock EF28 - 135 mm lens that came with my Canon 40D says I can only use one filter at a time. Well I regularly use a polarizer and a UV filter at the same time. Is that a problem? Why does it say I can only use one at a time?

 

[potownrob]

According to the following article, "Adding another element degrades image quality due to aberration and flare."

http://en.wikipedia.org/wiki/Photographic_filter

 

[Alex_B]

Well I regularly use a polarizer and a UV filter at the same time.

Why would you do that? The UV will not help your images at all.

I accidentally stacked polariser and UV recently, and of course in the ultra wide angel range I got strong corner shading since the filters rings added together were too thick.

However, this would not affect you at 28mm on a crop frame like yours though. So if you use excellent filter glass, you'd probably fine with a UV and a polariser stacked together. With cheap glass, flare and other effects might occur though.

Also, there are cases where you would need to stack filters, just your case is useless.

 

[TamiyaGuy]

I think it's so Canon don't get a ton of complaints that people stacked 4 filters on top of each other, then found that they got vignetting at 28mm . Basically, so long as you don't get vignetting yourself (or you want that effect), and the image quality degradation doesn't bother you, you will be fine.