Filters

[terry72]

Can I check what is the square filter size for 82mm? currently my square filter size is 84mm x 96mm and there are vignetting when I use the widest aperture. Was wondering is there any filter size larger than my current ones?

 

[Octarine]

Have a look here: https://en.wikipedia.org/wiki/Photographic_filter#Square_filters
But first of all, do verify where the vignetting comes from. Could the the lens (some exhibit quite a strong vignetting by design, for example UWA), could be the filter holder (assuming you use one, based on your posting). Some holders are fixed with three slots, others can be reduced to one slot.
Also, I have seen some people using screw-in CPL and mount the filter holder in front with adapter ring. That;s also a good way to introduce vignetting.

 

[terry72]

I am using the Pentax-D FA 24-70mm lens which is a 82mm filter thread in diameter and the vignetting are around the 4 corners of the frame when using the widest aperture. I have both tried using the 3 slots holder as well as the single slot holder and both are the same.
So is the 84mm x 96mm square filter the standard size or are there larger size filter or is my filter holder the wrong type?

 

[Octarine]

Corner vignetting at widest aperture is pretty common, especially for shorter focal length. First of all, do a controlled comparison, shooting the same image without any filter holder and with filter holder. Then add a slot in filter (ND) and check the results. Compare whether the filter holder really causes the vignetting. If it's caused by the lens you have no choice but to accept it and correct the vignetting in post processing. Usually it only take a few clicks in LR, PS and others.
In case the filter holder causes the vignetting, you could try a 150mm type to see whether that works better. But keep in mind that prices for 150mm filters are significantly higher.