SimpleJack wrote in post #10672472
I just bought a Marumi DHG Super Polarizer Filter yesterday, but for a different reason from this one.
Can I add 2 filters on my camera? (Just wondering if the option to do that is there)
How do I know which ND filter I need to get? since I would only like to buy one ND filter and be good.
I don't wanna spend more then like $60 online price for a lens filter if possible.
You shouldn't have a problem at all with using two filters (CPL + ND) in combination, provided they are both quality filters (these two are basically a must for waterfall photography). Look for a polarizer that doesn't leave a color cast, such as a B+W Kaesemann. Some (such as Marumi) leave an obvious blue cast, which becomes a PITA in post. Also, due to their nature, very strong ND filters, such as the B+W 10-stop, will oftentimes leave a magenta cast due to IR comtamination. This is pretty common with strong ND filters, and gets worse as the filter quality gets lower...all the more reason to use quality filters. Beyond that, the only thing to watch out for when stacking filters is vignetting, which will be dependent on the focal length of the lens.
To get the silky water effect, you'll need to get your shutter speed down to at least the 1/2-second range, and usually slower. The strength of the ND is dependent upon the ambient light at the time, so its very difficult to recommend a single filter. But as an example, suppose you meter a scene at f/16 and 1/250-sec. To reach the 1-second shutter speed, you'd need 8 stops of ND filtration (125-60-30-15-8-4-2-1). If you have a good polarizer, that should account for 2-stops, so you'd need a 6-stop ND filter to make up the difference. In not-as-bright light, you'd need less ND...it just all depends. With that being said, in addition to a good polarizer, I'd recommend carrying two ND filters, a 3-stop and a 6-stop. Considering your location, these should cover you for most situations. A 2-stop ND wouldn't be necessary since the CPL would do double duty.
Also, when you start getting into even longer exposures (60-seconds or so), its best to use your hat or something else to cover the VF during the exposure...this will keep stray light from entering and 'clouding' the image.