Help on what strength nd to get

[belial]

So my knowledge is progressing but I still don't think in terms of stops when it comes to aperture. I need an nd that can get me f/1.8 and f/2.0 on sunny days and not give me too slow of shutter on overcast days. My shutter maxes on 1/4000. Hitting semi close to Max on sunny days isn't a worry but a little headroom would be nice

 

[tirediron]

Assuming you're shooting on bright, sunny days, and invoking the "Sunny 16" rule, you'd be shooting at f16, so, 1 stop of ND would get you to f11, two to f8, three to f5.6... and so on. I have found that the most useful implementation of ND & G-ND filters is as a set of three in 1, 2, and 3 stops so that you can get, if necessary, up to six stops of reduction. VERY rarely will you need more than that.

 

[480sparky43 43]

Two downsides to stacking ND filters: Vignetting and image quality dropping.

 

[Buckster]

There's also the option of variable ND filters.

As with all ND filters, the more expensive ones from reputable manufacturers will give the best performance, while the cheaper ones will likely give you a color cast and possibly even lower IQ. That said, I've seen the variable NDs priced anywhere from as low as about $50 up to about $300 for the Singh-Ray. There's even the option of DIY'ing two regular circular polarizers to make a variable ND:

[video=vimeo;15313082]http://vimeo.com/15313082[/video]

 

[Buckster]

Two downsides to stacking ND filters: Vignetting and image quality dropping.

If larger than lens square/rectangle style drop-in type filters are used, no vignetting problem. A little planning during the shoot so that a bit of a crop can be employed in post can resolve it as well.

IQ is always a consideration when putting anything in front of the lens, but I think it's an acceptable tradeoff, even when stacking filters. I've stacked as many as 4 or 5 filters at a time to get a particular look, back when I did all my effects at the lens, rather than later in Photoshop. Here's an example:

That's a graduated blue, graduated sunset, mauve and an ND all stacked in front of the lens, and every one of them was an inexpensive Cokin resin filter. I got the look I wanted and the IQ was acceptable.

 

[Village Idiot]

Even expensive ND's can give you a color cast. My 6 stop B+W that I paid over $100 for gives me a magenta cast.