This thread is dedicated to the DFA21Ltd. So I think we should explore it further ...
"Oh no, an integrated hood" came to my mind when I saw it and read the specs. And now it's my first such lens - and I really enjoy it.
I have to check how much the built-in hood would restrict filter usage I thought. My M10 filter system doesn't work. Okay, I could DIY something to attach it. But when I tested the coverage of the hood openings it was clear, that it's not that easy and especially rectangle GNDs would be far from the front glass element. Some people say that such filters are obsolete today, since the cameras have such great dynamic range and there are other techniques like HDR to get along. I'll not discuss these things here and go directly to the usage of screw-in filters.
Until now, I didn't own 67mm screw-in filters. Since I want to be able to use a PLC and 10stop filter I ordered these and on top a clear filter for situations where flying sand and/or salt water could be a problem. To prevent from strong IQ degradation I decided to go for very good ones. Read and viewed some internet reviews in addition to my experiences with filters from Hoya and 10stops from Haida until now. The Haida 10stops shows more color shift than I thought.
I read good things about the B&W Master series and similar for the Breakthrough X4. The latter ones were significantly more expensive so I decided to go for the B&W's Master series - no fault!
With PLCs you have to be very careful when working at 21mm @ FF to get no uniformity problems in blue sky, I know. Did some simple tests mainly at different apertures, mainly to see how it works concerning vignetting when stacking the filters and I always was curious if I'd see significant color shift. My results:
- I can stack 2 of the slim B&W Master series filters without any problems - nice!
- When I stack a third filter, I get dark corners
- And with the 10stop color shift seems to be really absent or shows to be marginal - cool
In total I have really no reason to complain.
A test image taken with 2 slim B&W filters:
K-1 | FF mode | DFA21Ltd | B&W Master PLC | B&W Master 10stop | ISO400 | f/16 | 15s
One last thing: since the lens hood has two open areas down to the filter thread, it is very easy to turn the ring of the PLC filter - much easier than if you use a hood with one small window!
Hope this info is helpful.