Hi, we checked the sigma art 24-35mm f2 lens size is 82mm, please reconfirm it , if the lens size is 82mm, this square filter holder system kit can fit it ,thanks. 

I use one on a Pentax 24-70mm filter size 82mm. Just make sure you buy the right size for your lens. I have the nd1000, and I am very happy with result. They also sell adaptor step down for your other lens. 

Yes. I have the same lens and adaptor on my Sony a7ll and it works beautifully. The m42 is also known as the 'universal' mount as other 3rd party camera and lenses also used it. I own 6 other K&F e-mount adaptors to different lens makers (ltm, MD, CF/CD, Nikon) and they all are well built with a nice snug fit. Highly recommended. 

I actually have not received this adapter yet. It's shipping from China. Don't think that was disclosed in the ad. However, I do not believe this is for the Pentax Q body rather for digital and film cameras that take the Pentax K mount in its many variations. So I'm expecting to be able to mount my Leica M mount lenses on my digital and film Pentax K mount cameras, no autofocus or relay of exposure information, only to be used with manual focus and exposure. 

1. Adapting APS-frame lens to full-frame camera, it may generate vignetting, some cameras could correct it by adjust APSC, please contact us and provide your lens&camera model to check the way to correct it.
2. Adapting full-frame lens to APS-frame camera (i.e: large format to medium format, medium format to 35mm, 35mm to micro 4/3) provides excellent edge-to-edge sharpness. The smaller image field helps minimize the effects of lens distortion and aberration by using the 'sweet spot' or center of the larger lens image circle. and it will magnify the focal length by 1.6 on Canon, 1.5 on Nikon and Sony，2.0 on M4/3 camera.