The Shady Truth behind ND Filters

Neutral Density Filters, are nothing more than a tinted pane of plastic, glass or sometime resin but what do they do?

There not complicated regardless of what some people say, just think of them as sunglasses for your Camera. The tinted glass simply reduces the amount of light getting to the lens and then the sensor. Which means you can do two things, one use a slower shutter speed and two shoot at a smaller F-Stop,

Practical Example !

Your off walking in the Yorkshire Dales (or what ever your preferred national park is) and  you across a beautiful scene of a lake with the sun just dropping between two hilly peaks. There is a gentle breeze rippling across the lake you decided that you want to blur the water using a slow shutter speed.

Unpacking the camera you dial in the settings F10 and ISO 50 which gives you a shutter speed of 1/4th slow but not slow enough. . . . . . . . Digging around in your bag you find your ND 0.3 Filter that gives you a exposure of half a second, slow but not slow enough, you dig around in you bag a bit more (its a big bag) and find your ND 0.6 that gives you a 1 second Shutter Speed, which you decided is enough to give you the look you wanted and you click away.

So instead of shooting at f20 to get a 1 second exposure and having to deal with all the nasty Dust spots, chromatic abrasions and the such like you have been able to shoot at f10 and still get the shutter speed that you wanted.

Strengths of tint

There are about 4 common strengths of ND Filters however you can get them up to and beyond 10 stops. Working out which filter you need is pretty simple as Neutral Density filters come in 1 stop differences.

ND 0.3 –  1 Stop Darker

ND 0.6  - 2 Stops Darker

ND 0.9 – 3 Stops Darker

ND 1.2 – 4 Stops Darker

And so on, so going back to the Practical example earlier if you want to loose 2 stops of shutter speed you’d use a 0.6 Neutral Density Filter. If you wanted to loose 4 stops you could use a nd 0.6 and a 0.3 together, it’s really that simple!

One Step Beyond

Neutral Density Filters don’t just come in solid tints they also come in what’s called a Graduated ND Filter these are Tinted at one end and not at the other with a gradual fade between the two. They allow you to do one brilliant thing and thats lower the exposure of the sky while keeping the correct exposure on the ground. giving you big fluffy clouds and plenty of detail in the shadow areas.

The above shows how the three different ND Grads Effect the exposure, In conditions like this I would look at using a ND 0.3 just to under expose the sky a little and make it a nice deep blue.  However if you were wanting to go about it properly and not just gestimate like me the trick is to zoom into the foreground so it fills the frame and take a meter reading then zoom in on the sky so it fills the frame and take another reading, work out how many stops difference that is then select the most suitable filter(s), (you can also do the same by spot metering if you have this function available). Again I just gestimate where to position the filter but if you want to be exact about it. frame up the shot, slide the filter in step the lens all the way down using the DOF preview button, this will make the difference between the top and bottom of the filter very clear then slide the filter up and down till its spot on.

What to buy

Like everything in the world its very much a case of the more you spend the better quality product you get. Most filter company’s produce ND and ND grad filters but I’m a big Fan of the Lee Filters by far the best quality set up that I’ve used, however you do pay a premium for them. The other brand I would look at are the Hitech set ups however they can have a purple tint which is annoying to say the least.

Polyester or Resin

Again how much money do you have to spend, I don’t see the point of having £1,000+ lenses then putting sub quality filters on the front just to save 20 quid or so. Resin is best but Polyester will work if your on a budget. Be warned though the Resin can be brittle

Screw in or square Filters

Neutral Density Filters come I both square and Screw in, some people prefer Screw in and other prefer square, I prefer square for two reasons.

1. You only have to buy one to fit all your lenses

2. For the big filter sizes they work out cheeper.

Grads

Graduated Neutral Density filters on the other hand only come in rectangular  as you need to be able to slide them up or down to get the tint over the right part of the frame.

If you go for Square filters your going to need more than just the filters, your also going to need the required adapters to fit your lenses and also a filter holder .

Bellow is a list of what you’d need from lee (why aren’t these guys paying me?)  to get started.

The Foundation Kit

The Suitable Adaptor Rings

Although the filters come in a protective wallet I can’t recommend the Multi Filter Pouch enough,

and then what ever filters you want.

This entry was posted on Thursday, May 6th, 2010 at 5:03 pm. It is filed under Tutorials and tagged with Filters, Lee, Tutorials. You can follow any responses to this entry through the RSS 2.0 feed.