Filters (Circ-Pol + ND)

[Shadowness]

This tutorial will cover two main types of filters: Circular Polarizers and Neutral Density (ND).

Before I begin, I will start by saying that these are luxary items, and are not necessary to take great photos. They are tools to help improve photos, or provide new ways to take photos (more on this later).

So first up: Circular Polarizers.

The main use for these, and forgive my unscientific answer, is to make photos prettier.
Circular polarizers:
- darken the sky
- improve the contrast between the sky and clouds (pics below)
- remove glare from water surfaces ie. sea and lakes etc.
- generally increase the saturation of all colours in the photo

Enough talk, lets see some pics:

Photo 1: Photo taken under normal conditions with no filters.
Photo 2: Photo taken with circular polarizer (correctly set <-- more on this later)
Photo 3: Photo taken with circular polarizer and NDx8 filter <-- more on this later.

The visual differences between photos 1 and 2 are very obvious. The sky is a much darker and richer colour, and the contrast has been improved. Also, the very ligh clouds at the top of the frame are much more obvious in photo 2.
Photo 3 is slightly different from photo 2, the colour cast is different, and the sky has lost the rich blue colour. On the negative side, note how the clouds are slightly over exposed.

Unlike most filters, the circular polarizer can be adjusted by rotating it. So care must be taken to correctly set the polarizer before taking the photo. You will see as you rotate the polarizer as the sky becomes darker - that is when the polarizer is at maximum effect.

Left: Polarizer incorrectly set
Right: Polarizer correctly set.

Another BIG use for circular polarizers (CPLs) is in motorsport. If you want to seriously get into this type of photography, then a CPL is a MUST.......NO QUESTION!!

The biggest effect thats noticable is that it removes the glare from the windscreen, so you can see that driver, see these two pics:

The glare is so bad that you can only just make out the driver's helmet.


The CPL has completely removed the horrible glare, and now we can see the driver

Again, to create this effect, the CPL has to be correctly set. My tip is to find some other car/ambulance to use, and then rotate the CPL until the glare has been removed.
NOTE: If you change position, remember to re-set the CPL.

TIP: To see if your CPL is working correctly, remove it from the camera, hold it up to a LCD/TFT monitor, look through it with your eyes and rotate it - see what happens


Well, that's CPLs covered. Now lets talk about Neutral density (ND)filters.

NDs are a lot more basic, they just attach onto the lens, and that's it, no adjustments to make. Basically, the job on an ND is to block light - that's it.

This may sound dull, but it can be VERY useful. Common applications of it are shooting waterfalls. Classic waterfall shots show a lot of movement:

The classic style waterfall shot, the low shutter speed (3 seconds!) creates the smooth flowing effect.

To create this effect, you need a low(ish) shutter speed, and on a bright sunny day and at f/32 you may not be able to go low enough. So this is where an ND filter is essential. The ND blocks light, allowing you to use a much lower shutter speed.

Other very common applications are when using automotive rig shots. The cars are driving (usually psuhed!) very slowly, so to create the sense of movement, a ND is needed to drop the shutter speed right down.

Here, an ND helped me to use a shutter speed (0.5 sec) slow enough
to create the sense of movement needed. Without one, it would have been impossible.

NDs also have an effect on landscape photography:

The ND has darkened the sky, but the contrast is still
very similar. The clouds are a little darker, showing a little more detail.

NDs come in various ratings ie. x4, x8. The higher the number, the more light it blocks.


Well I hope that's helped some people, like I said before - these are luxary items, but they're worth every penny. They can be quite expensive depending on the size you require. I've found some bargains on eBay (reputable dealers!!!).
Any questions, feel free to ask. I'm sure ive forgot some things, but hopefully the pics say more than words ever could!
Dan

[jimmymac]

great stuff, really interested in the use of the polariser, very early days for me in photography and to be fair i hadnt even thought to think of rotating the polariser, silly really when i know full well what things like polarising sunglasses do. Hoping to do work with motorsports so this will be really useful, cheers

[jayhawk]

I have a Hoya CPL that is used whenever there is adequate light. Probably worth it's weight in gold, photography wise.

To make sure it is in the correct position, I point the camera at grass on a sunny day and adjust until the glare is gone. Or, if you are in a car, put a piece of white paper on the dash, and adjust until the papers reflection in the glass vanishes. Bought the filter here: http://www.2filter.com/

[damnhawk]

damn....so is the ND filter that necessary for rig shooting? I never thought about how to get that low of a shutter speed in bright light. I bet a 77mm one is on the expensive side of things...

[Shadowness]

Originally Posted by damnhawk

damn....so is the ND filter that necessary for rig shooting? I never thought about how to get that low of a shutter speed in bright light. I bet a 77mm one is on the expensive side of things...

I got my 77mm off eBay for about £30 inc shipping. In the UK they are WAY more than that.

[watto]

I love my CPL, it's a great thing. I described it to my girlfriend as simply as I could by just saying "it's like putting sunglasses on the lens. Creates more contrast and reduces glare"

[flamingice]

Since I've had my new lens, I've been going without a CPL... but with doing a lot of landscape photography, I ordered one of E-Bay a few days ago. Including shipping, it came out to less than half the price I could find it for in the stores here!

Dan, a question about that last comparison shot... if it's a ND, not a GND, how does it have an effect on a landscape photo?

Thanks for the writeup!

[Shadowness]

A graduated ND probably would be better, but I just wanted to show the effect a normal ND has. You can see a difference, but for landscape photography - its probalby not as useful.

[flamingice]

Yup, understood... I can see the difference between the two photos, but was just wondering if you happen to know why it makes a difference? My understanding was that it was just a darkened piece of glass... so to get the correct exposure, you'd just have a longer shutter speed, but the resulting photo would be the same?

[mautzel]

First - thanks fpr the tutorial.

I got a specific question regarding CPL's. I got a cheap CPL off ebay for my f 4.0-5.6 70-300mm telelens. Could it be that CPL's have an impact on sharpness as my camera doesn't seem to be able to focus properly the longer the focal lenghth is when the filter's put on? Also, could it be that the effect is much more noticeable through the view-finder than on a PC monitor?

[Shadowness]

Regarding the quality issue - to a certain extent, filters do affect the quality of images, as the light has to travel through more glass, but it's very small and hardly noticable. I imagine it will start to have a big effect if you stack loads of filters.
As for focusing, CPLs shouldnt affect focusing at all on modern cameras.

[mautzel]

Seems like there's something wrong with my filter, then.

[flamingice]

Originally Posted by mautzel

First - thanks fpr the tutorial.

I got a specific question regarding CPL's. I got a cheap CPL off ebay for my f 4.0-5.6 70-300mm telelens. Could it be that CPL's have an impact on sharpness as my camera doesn't seem to be able to focus properly the longer the focal lenghth is when the filter's put on? Also, could it be that the effect is much more noticeable through the view-finder than on a PC monitor?

I've seen filters that have significantly decreased the quality of an image. You don't need to buy a super fancy one, but try to get something that's at least decent... I figure it's worth paying a bit more for the extra quality.

Regarding focusing, as Shadowness said a CPL shouldn't really affect it, although I think linear polarizers can cause problems with automatic focusing/metering on some cameras.

Another possibility is that you might not be getting enough light through the lens. In low light situations, a lens with a larger apeture will be able to focus better than one with a smaller apeture. Your camera will always use the widest apeture possible for focusing. The lens you're using has a pretty small apeture to begin with, putting on a polarizing filter will reduce the amount of light even further. If you're trying to shoot in conditions with a bit less light, that could be the problem.

[BerserkerCatSplat]

Originally Posted by flamingice

Another possibility is that you might not be getting enough light through the lens. In low light situations, a lens with a larger apeture will be able to focus better than one with a smaller apeture. Your camera will always use the widest apeture possible for focusing. The lens you're using has a pretty small apeture to begin with, putting on a polarizing filter will reduce the amount of light even further. If you're trying to shoot in conditions with a bit less light, that could be the problem.

That's his problem, pretty much guaranteed. The 75-300 is f/5.6 at the long end, and sticking a CP on the end further restricts the light getting to the AF system.

[burnsy]

i've got a question about my new Promaster CPL.
i'm an old school film SLR guy, as i can't afford a nice DSLR. just bought a CPL, as this tutorial will help with my pictures, but, it would be the first time i would have it. my Vivitar v3800N with 28-70mm and 70-210mm is a manual focus. would i need to adjust the CPL every time i focus either lens? or just adjust once no matter the focus?

[flamingice]

As long as the camera is pointing in the same general direction, the CPL should stay set at the same angle for the best results. So, if you change the zoom, or refocus, you shouldn't have to change the CPL.

UNLESS... you have a lens where the front rotates when you focus or zoom. In that case you would need to readjust the polarizer.

[burnsy]

Originally Posted by flamingice

As long as the camera is pointing in the same general direction, the CPL should stay set at the same angle for the best results. So, if you change the zoom, or refocus, you shouldn't have to change the CPL.

UNLESS... you have a lens where the front rotates when you focus or zoom. In that case you would need to readjust the polarizer.

yes, the whole lens rotates when focusing. do i need to get a different kind of polarizer for my lens?

[flamingice]

Nope, it'll just be a bit of a pain, because you'll have to readjust it after every shot.

[MXM]

And it's not something you can fix by getting another filter. All polarizers are direction-dependent, as you can probably tell from this tutorial

[DoN]

If I may add some little info about graduated ND filters:

they are usually square/rectangle that is darkened on top and 100% transparent on bottom - which darkens the sky while leaves the landscape without effect. I believe they use this filter a lot in TopGear.



and here actual comparsion without/with the filter:

they are usually more usefull in cloudy weather, when the sky would be overexposed without filter...when its sunny like this, its just to create some "cool" effect with almost black sky on top - which not everyone might like.