I have other K+F filters for other lenses and they have been exceptional. I ordered this duo for the Sigma APS-C 18-50mm F2.8 zoom I use on my Sony A6000. When I stack both filters together, there are severe black corners. When I zoom from 18 mm to 19.5 mm, they are gone. If I use one filter at a time, no problem. So I decided to leave the polarizer on for the summer and reinstall the UV in the fall. Unless I plan to shoot 20-50mm on a given day. These filter rims are so thin that I don't think there is anything on the market that could improve this situation. I have put K&F on other lenses with no problems. Must be just this Sigma lens design.

As a non-electronic alternative to the much more expensive Sigma MC-21 adapter, this is great. I also have an MC-21 and the build quality seems to be comparable - it's sturdy and well made. Note that this is entirely non-electronic, so is only useful with fully manual lenses. It does not support camera controls (iris/auto focus). So don't expect to use it with anything that requires it.

ATTENTION! This filter is not compatible with wide-angle lenses.
On my Sigma 16mm it produces a blue X when set to ND1000.
The manufacturer was very nice and offered me a replacement filter.

WARNING! This filter is not compatible with wide-angle lenses.
On my Sigma 16mm it creates this blue X when set to ND1000.
The manufacturer was very nice and offered me a replacement filter.

ATTENTION! This filter is not compatible with wide-angle lenses.
On my Sigma 16mm it produces a blue X when set to ND1000.
The manufacturer was very nice and offered me a replacement filter.

WARNING! This filter is not compatible with wide-angle lenses.
On my Sigma 16 mm it produces this blue X when set to ND1000.
The manufacturer was very kind and offered me a replacement filter.

Bought for a Sigma Art Sony 24-70 and the Sony 28-135 (with Step Down), it is now permanently on my lenses. Additionally, having an ND and a polarizer on the same filter is a really nice surprise, especially at this diameter. For video recording and holding at 1/50 or 1/100 in broad daylight, this is best. A highly recommended essential.

Bought for a Sigma Art Sony 24-70 and the Sony 28-135 (with Step Down), it's now permanently on my lenses. In addition, having an ND and a polarizer on the same filter is a really nice surprise, especially at this diameter. For video recording and keeping at 1/50 or 1/100 in broad daylight, this is the best.
A highly recommended essential.

The way I use this filter is by combining it with a fast lens like the sigma 18-35mm f1.8 art. I use this filter in combination with the fast apertures to blur out the backgrounds in broad daylight without letting too much light into the picture. If I want to make it lighter or darker all I have to do is turn a ring at the edge of the filter.

The only thing that gets me is when I turn it too much and it ends up unscrewing the whole filter out of the threading a little bit. But that's not a bad thing, its just a part of the experience.

I bought it 8 months ago. This has been, thus far, an excellent purchase.

A very good filter. It’s very smooth and has a stopping point. I used this on my sigma art lens for a shoot. No vignetting!