ND Filters - What Are They? What Do They Do? Do I Need One?
ND stands for neutral density. A neutral density filter reduces the amount of light that passes through the lens to the camera sensor. This gives the photographer more control over the camera settings that he or she can use, whilst still getting a correct exposure in a variety of lighting conditions. ND filters can be used in very bright conditions to help get the correct exposure or to reduce the depth of field. ND filters allow photographers to use longer shutter speeds in conventional lighting situations for creative reasons, such as to blur water, clouds or anything moving in the photo.
ND filters are basically sunglasses for cameras. And a very cool tool that I love to use!
Hi and welcome to Episode 133 of the Photography Explained podcast.
I’m your host Rick, and in each episode I will try to explain one photographic thing to you in plain English in less than 10 minutes (ish) without the irrelevant details. What I tell you is based on my lifetime of photographic experience. And not Google. Definitely no Google in this episode.
You can listen to the episode here
Or you can read on - it’s entirely up you!
How do ND filters work?
They simply reduce the amount of light that gets through to the camera sensor. That is all they do.
How do I get the filter onto my lens?
There are two types. Ones that screw into the filter thread on the front of your lens, and ones that slide into a holder which screws into the filter thread. That is what I use, and I will tell you why shortly.
Can I get them for my phone?
Yes, of course you can. I have never tried them myself, that is why I have an actual camera, to do stuff like this.
How much light do they stop?
Well, there are two main ways of describing ND filters and the amount of light that they block.
Numbers of stops. The way that I understand them.
A 6-stop ND filter reduces the amount of light that gets through to the sensor by, well 6 stops.
And a 10-stop filter reduces the amount of light that gets through to the camera lens by 10 stops.
And a 15-stop filter reduces the amount of light that gets through to the camera lens by 15 stops.
OK – that makes sense – but what does this actually mean?
If you are taking a photo with a shutter speed of 1/125th second without an ND filter, this is what the shutter speed is with an ND filter
6 stop – ½ second
10 stop – 8 seconds
15 stops – 4 minutes
Yep. I know. Amazing.
They are also known by how much the light is reduced
ND2, or 2x,– this reduces the amount of light by a half, or one stop.
ND4 – this reduces the amount of light to a quarter, or two stops
ND8 – this reduces the amount of light to 1/8th, or 3 stops.
I was happy with a 2 stop ND filter giving me 2 stops. ND4 does not help me as a term.
Do they stop a fixed amount of light?
Yes. Unless you get a variable ND filter that is.
You can get variable ND filters that give you all sorts of ranges, 1.5/ 2 – 8/10 stops. So you can please yourself, which is nice.
Which ND filter should I buy?
Well, that is up to you. If I were new to this I would try a single, variable ND filter just to give it a go. Sure the quality won’t be great but it will give you a flavour of what they can do for you, and if this is something that you might get into you can then buy the best filter that you can.
My ND filter costs a lot of money, circa £200, but that was many, many years ago, and I still use the same filter and holder now.
OK – how do I work out the exposure?
Get an app. Nice and simple. There are loads of them. I mean, you could work it out yourself, but why would you when there are free apps out there that can do this for you?
And if you get a variable ND filter then the app is even more useful – you can decide what shutter speed you want and then let the app give the correct exposure.
And do I need to do anything different when taking a photo with an ND filter?
Yes, well maybe. Depending on the strength of the filter. If you have, say a 10 stop ND filter you might not be able to see what you are taking a photo of, so you have to compose, focus, get the exposure right and then add the filter and take the photo, adjusting the exposure of course.
If you get one with a holder this helps, as with a screw in one you erm have to screw it onto the lens. And that sounds like a bit of a pain to me. This is why I use the holder with my 10 stop ND filter.
Is there anything else that I need to know?
You can get a colour cast when you take photos using an ND filter. With the one that I have, I sometimes get a blue colour cast, but I can fix this in Lightroom with no problem.
Just one to be aware of.
The talky bit
Sunglasses for camera lenses – I love that.
I use a 10 stop ND filter, which has a holder which screws onto the lens. I attach the holder to the lens, get the composition and all that good stuff, and when I am ready slide the filter into the holder and take the photo, having sorted the camera settings out for the revised exposure that is.
And 10 stops give me crazy long shutter speeds. Let me give you another example.
If I am taking a photo, and the correct exposure is 1/60th second at F8. If I use my 10 stop ND filter the correct exposure with this massive reduction in the amount of light getting through to the camera sensor is this.
15 seconds at F8.
Yes, a 15-second long exposure. Let’s think about that….. I can take a photo with a 15-second exposure when, without the filter, I would be using a shutter speed of 1/60th second.
I can take a photo with a 15-second shutter speed in daylight conditions.
So what?
Well here are things that I have taken photos of with my ND filter.
Any water anywhere.
I love flattening the sea with a long exposure. Before I had an ND filter I could only do this in low light, but now I can do this any time of the day which is a wonderful thing.
I am talking about the sea here, I love to take seascapes with a super flat sea, it is one of my things. And I am so glad that I have written this episode as it has got me excited again about playing around with my ND filter.
Rivers, waterfalls, the sea, lakes – anything with water can be transformed with an ND filter.
I would like to go back to a previous episode, episode 132, Do I Need New Photography Gear? My Common Sense Check That Says Probably Not.
See, an ND filter helps me do things that I cannot do without one, so falls into my legitimate gear category.
And what about my commercial photography work?
Not to be overused, you wouldn’t use an ND filter on every shoot now, that would be weird. Or would it? Hmmm, that has got me thinking. Sorry one for another time.
I used it to get a photo from a shoot where the moving sky was blurred, giving a dreamy, surreal effect. This is not for real estate photography, no, those clients would quite rightly look at me and say, really? Not that I have ever done this. No.
But for architectural photography, this is something that I do sometimes when there is an opportunity to give my clients something different. And I am going to have a play with this on an upcoming trip. I can’t wait now to get out there and do something different.
What else can you use an ND filter for?
Well, anything that moves you can blur. Think of a busy street, with lots of people moving around. Cars, buses, all sorts going on. Take a photo with your camera on a tripod and a long exposure and all the people and things that move become blurry, but the stuff that is fixed, the buildings, road, you know. They will all be sharp.
Yes, you will need a tripod for long exposures, as you want still stuff sharp and the moving stuff blurry. If everything is blurry in a photo you just have a blurry photo, which is no use to anyone.
Do you need one?
Hopefully, you do. So get thinking about this and if this is for you get an ND filter and get out there and give it a go.
And if you do let me know how you get on. Send me your photos – I would love to see them.
One last thing. 10 stops might be a bit extreme I have to say, so if you are getting started in this you might want something a bit less than 10 stops. I love my 10 stop filter and am happy to just have the one but like I say you might want to go a bit less, in the 3-5 stop range to get you started.
What do I do?
I use a 10 stop ND filter with my camera on a tripod to blur water and clouds. And I love it. ND filters give me creative opportunities that I would not have had without them. And I use my ND filter to create striking, stylish, and a little bit different, photos.
Which all has to be good right? We need to be able to do something a bit different.
Next episode
Photography Explained Podcast Episode 135 – Polarizing Filters - What Are They? What Do They Do? Do I Need One?
Yes, the other filter that I use with my photography. There are no more – that is it! 2 filters.
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This episode was powered by, wait for it, a cheese sandwich and a bag of salt and vinegar crisps. Yes, I am back to my old faithful snackage, washed down with an ice-cold Diet Pepsi, sitting here in my overly warm, homemade, acoustically cushioned recording emporium.
I’ve been Rick McEvoy, thanks again very much for listening to my small but perfectly formed podcast (it says here), and for giving me 10 (ish) minutes of your valuable time.
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Cheers from me Rick