Digital GND's work very well. I don't like to put extra glass in front of the lens if I don't have to. I know photoshop has a GND filter but as I remember, it is somewhat "cumbersome". NIK has a good one in its filter set. You can set individual amounts off top and bottom, set a break line and set a "blend" or feathering number.
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It's a tough job living in Hawaii but somebody's got to do it.
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Digital GND doesn't improve the DR though. I mean recovering too far blown highlights. For that you need to bracket. Looking at recent Sony/Nikon sensors you can do a lot with them (as they are Bayer sensors), but I don't like the look if the photos. Looks fake like bad HDR. See tulip and horse photo in the Sony 7 II preview.
As to putting glas in front of a lens, I don't worry about that. I don't see the point of putting glass to protect the lens, but for effects, why not.
That a bit of glas could in theory make some degradation of the IQ is based mostly on old or cheap filters. Just see how you do not notice any specs of dust on the front lens in your photos.
I'm more concerned with how software deteriorates image quality.
I think I'll look into Cokins S series or similar.
Thanks all!
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Lightwriting with Sigma dp2Q for stills and Blackmagic Pocket Cinema Camera for video