There’s a lot of bad advice about lens filters. I’ll answer two big questions for you:
- Do I need a lens filter?
- If I get one, what kind should I get?
Real fast, let’s go over what a lens filter is. Almost all modern lenses have a set of screw threads around the front of the lens. A lens filter is just a piece of glass that can screw onto the front of your lens. By using different kinds of materials, a lens filter can modify the way light goes through the lens – changing your picture.
Do I need a lens filter?
No. You don’t NEED a lens filter. But the right kind, used in the right circumstance, can help you create great images.
But they protect the lens, right?
This seems to make sense, until you actually try to figure out how strong the front of a lens is:
And keep in mind, that’s basically Canon’s cheapest lens. Unless you’re dealing with really extreme environments (sand, those paint festivals with dust, the apocalypse), the basic lens filter isn’t giving you that much protection.
Oh, and if the front of your lens does get a little scratch? Don’t worry. Lens scratches actually don’t affect the image that much.
But doesn't it improve image quality?
Yes and no, but mostly no.
Here’s the thing: Anything extra you add in front of your lens makes the image worse. It’s one more piece of glass to collect dust, one more thing to have scratches. It’s one more source of imperfections. Adding a filter will always make images less sharp. But good filters have such a small effect that you won’t mind.
Also, remember that glass reflects light. Your computer monitor or television can be hard to see with bright light around it. Adding more glass on your lens allows that light to bounce around between the lens and filter, which can cause “ghosts.”
But filters can help, too. What matters is the kind of image you create. A filter will change the image, making it slightly less sharp, but also altering the way that colors are reproduced. It can increase contrast, change how much light gets through, allow different shutter speeds, and more – depending on what kind of filter you are using.
A filter changes your image. It’s just a matter of whether the changes you want can be helped by a filter.
Then what’s the point?
By changing the amount or type of light, you can change the image.
Let’s look at a couple examples. Below are the three most common types of filters:
UV Filters (Ultraviolet Filters)
UV filters are the most common. They’re typically recommended as an add-on when you buy the camera – and often claim to offer protection. I explained above why I don’t think that’s true.
Typically, I’d recommend the beginner avoid UV filters. While they had some uses for film photography, they simply aren’t as relevant anymore with digital photography.
Now we’re getting somewhere! Polarized filters look dark, like sunglasses. They work just like polarized sunglasses do. Things are a little darker, but colors are more vibrant. Importantly, many reflections are reduced or eliminated. If you’re taking pictures in bright sunlight and you’re worried about reflections, a polarizer is an excellent choice to improve the image.
I think a polarized filter is a great and inexpensive thing to have in your photo kit. Get one and learn to use it!
A couple notes – probably won’t do anything for you indoors, unless you’re really doing something special.
Many polarized filters are circular polarized filters. This means that the glass will rotate freely around the lens. When you’re taking the shot, you should rotate the polarizer. Stop whenever the image looks best. That’s the nice thing about a DSLR – you’re looking right through the lens!
You will want to rotate the filter if you’re flipping back and forth between taking landscape or portrait pictures. If you’re only doing one, then you can probably keep it as is – but spin it around every once in a while to make sure you’re getting the right look.
ND Filters (Neutral Density Filters)
Neutral density filters are really simple – they just make things darker. It’s called “neutral density” because there is a neutral effect on the type of light – it’s just the amount of light that changes. Neutral density filters are generally sold in “stops.” Each stop allows half as much light.
- One stop: Half as much light.
- Two stops: One quarter as much light.
- Three stops: One eight as much light
- Four stops: 1/16th as much light.
- Five stops: 1/32nd as much light.
- Etc. etc.
So why would you want to reduce the amount of light?
A couple good uses:
- Longer shutter speeds in daylight. Without a ND filter, it would be pretty much impossible to have a 15 second exposure in broad daylight.
- Wider apertures in bright situations. I love this look – use a wide angle prime lens, shoot wide open in daylight, and you get this great subject separation that you can’t get any other way!
Maybe it’s just me, but that subject separation and narrow depth of field on a wide-angle lens just looks really cool. You can’t really get it in broad daylight, because even at the best camera settings (low ISO, fast shutter speed) most cameras would be badly over-exposed.
Neutral Density Filters (ND Filters) are great, but you have to have a specific reason to use them. Unless you want to do one of the below, you don’t need one.
- Use a wide open aperture in daylight.
- Take much longer exposures (long shutter speed).
- Shoot at higher ISO. (I have no idea why you’d want to do this, but theoretically a ND filter would help you.)