ND Filters

wavecaller

Hi Moose. I am trying to purchase an ND filter for use in shooting long exposure waterfalls. I bought a Hoya veritable ND filter but it isn't any good - not sharp and exposures are too short. So, I guess I have to shell out some big bucks. So, my question to you is, if you had to buy 1-2 high end ND filters, what brand and "stop" would you recommend?
Thanks, Stephen

bruto

I am a little suprised that a Hoya filter did not work well for you, as Hoya is usually a reliable brand. I wonder if either you got a bad one, a counterfeit one, or perhaps are having an issue with its use.

I read that the usual Hoya variable ND filter goes up to 9 stops when fully darkened, and that should be more than enough. But when darkened to that degree it will also not auto focus correctly. If you are shooting with auto focus enabled, it might be trying to refocus when it should not.

One thing I'd try before giving up on it would be to manually focus, if you can see well enough through it, and if possible to manually focus first before fully darkening it.

Make sure too that you are using a camera setting that maximizes the effect. You should be at the lowest ISO possible, and choose the right aperture. Make sure you have Auto ISO off. On DX you'll get some softening above f/16 or so, and I'd suggest about f/11 for starters. A shutter speed of 1/4 second will be enough to blur moving water some.

Needless to say, if you're shooting at the very slow speeds involved here, you'll have to use a tripod. A wide angle lens with VR can probably go hand held down to 1/4 second or so, but any slower, and you'll get blur.

@Moose might have better suggestions on a specific filter, but generally speaking, a plain non-variable ND filter should not present any sharpness problems, and I would have recommended Hoya as a likely balance between price and quality.

ND filters are numbered in ways that can be confusing, as the numbers do not refer to actual stops, so make sure you know which numbers are being used. So, for example, a filter give a 6 stop reduction might be listed as a 1.8 (optical density, and one set of numbers used), an ND 106, or an ND 64.

Something around 6 to 8 stops should be more than enough for blurry waterfalls or for enhanced depth of field in daylight. If you get standard filters, you can stack them up to a point. You'll get vignetting at picture edges if you stack too many, but a couple should work fine, so you might consider getting one for two or three stops, and another for four, to increase versatility.

Remember that you cannot reliably auto focus with dark filters. You will almost certainly have to put the camera on a tripod, and prefocus. Many people use square filter holders and drop in filters, because that makes focus easier. But if you have a kit lens with a rotating front element, a square holder is a big nuisance, since it will have to be straightened every time you adjust the focus.

Another alternative I've seen recommended is to get a larger square filter and simply hold it in front of the camera. I've even seen some people recommending arc welding filters. That's a drastic darkening, but it's likely to be relatively cheap. Check out the welding section at some place like Tractor Supply.

Moose

@wavecaller - As always, @bruto offered up some invaluable advice. For long exposures during the day, I use a B+W 10 stop ND filter. I have used Hoya filters in the past and still own a couple, however, I prefer the B+W filters...mostly due to their color rendition, sharpness and build quality. The 10 stop ND filter will have no problem smoothing water (and clouds) during a bright sunny day.

One accessory you might think about getting, is the Manfrotto Xume quick release filter adapter. It allows you to snap filters into place using magnets. This is essential when working with a 10 stop ND filter, where you will need to obtain focus and metering before attaching the filter. You can check out my review of the adapter here...



Additionally, I recommend downloading a free ND filter app for your phone. This will allow you to determine the correct exposure, based on the metering done before attaching the ND filter.

All the best!

wavecaller

Thank you! I am really thinking about getting the Manfrotto fume filter kit. It just makes a lot of sense and with my shaky hands I won't be dropping any $100 filters into a ravine!