Originally posted by aaacb I often stack ND and CPL filters for long exposure. Provided you're using reasonable quality filters, vignetting is the main concern.
And
ghosting. If you take photographs with strong light sources - the sun, a bright moon, streetlamps, neon shop signs, indoor overhead lamps, car headlights etc. - in (or even close to) the frame, there's a significant risk of ghosting with
any filter (yes, even the good, multi-coated ones), and stacking them increases the chances and cumulative effect of that ghosting.
I'm not saying the OP shouldn't stack filters... only that they should know the risks, and if they decide to go ahead, be ready to shoot around them or accept the potential consequences. I have a whole shoot from a few years back where everything looked fine until I imported my photos to Lightroom, and found half the photos were affected by ghosting - and roughly half of those were unrecoverable. That was with a single (good quality) filter on the lens - and the kicker is, it was just a UV filter... and I was
indoors, so the lens didn't even need protecting