UV Filters, Polarized Filters

[juzan42]

Does anyone have some good reference/reading material that you can share with me, I would like to experiement with filters. Ive googled some stuff but did not find strong material. 

Any help on this would be greatly appreciated. 

[jrhoffman75]

http://www.all-things-photography.com/photographic-filters/

[ebiggs1]

Did you have any specific questions or are you just fishing for info?

For instance all but just a couple filters are now obsolute.  The useful ones are the ND, polarizer, and protector filters.

[TCampbell]

Many of the filters people used to buy can be simulated in software these days... but a few cannot.  If you need them... you NEED them (you can't use something like Photoshop to make up for the lack of one of these filters.)

Circular Polarizer (CPL)

Polarizers reduce reflectiosn which has the side effect of improving color saturation in your image.  Skies look bluer.  Foliage looks greener.  Etc.  Technically they are really just reducing reflections but you actually do get reflection off the surface of foliate and that makes the foliage look a bit glossy.  Haze in the air creates reflections and that dulls the color of the blue sky.  By eliminating those reflections, everything looks more lush.

And of course it also reduces the sorts of reflections that you think of as reflections.  If you're photographing a car, it cuts the glare of the windows and helps you see into the interior.  You can adjust the tuning of the polarizing effect by rotating the filter.  I sometimes want a little bit of a glossy reflection... I just don't want a STRONG reflection.  So I tune out the reflection and then  rotate back to add in just a hint of it.

Incidentally the type of polarizer you need is called a "circular polarizer".  This type is needed for most modern digital cameras.  A typical linear polarizer (which is what we would have used back in the days of manually focused film cameras that didn't have built-in metering systems) confuses the auto-focus system and also the metering system.  The "circular polarizer" really is just a linear polarizer... except it has an extra layer after the light passes through the polarizing layer.  That extra layer is called a "quarter wave plate" and it alters the light to make work easier for the camera's focus and metering systems.

Neutral Density (ND)

Another type of filter most photographers will buy is one or more Neutral Density filters.  These simply limit the amount of light that can pass through the filter without creating any other effect (no color cast should be produced -- which is why it's "neutral").   The purpose of this filter is to change your shooting circumstances to make it possible to take shots that would otherwise not be possible in your lighting conditions.  

Those photographs of waterfalls... where the water is smooth and creamy so it really looks like it's flowing (rather than droplets frozen in mid-air) are taken with this type of filter.   The photographer wants to extend the amount of time that the shutter is open without over-exposing the image.  But perhaps they've already stopped down the aperture on the lens and they are shooting at lowest possible ISO... and still the shutter speed is too fast.  By blocking some light they can use a longer exposure.   

Also, if you want a shallower depth of field (for a deliberately blurred background) but you need a longer shutter time to imply motion into your shot, the filter allows you to do that too.  

So basically this filter changes your shooting circumstances and allows to you to use exposures that would require less light.  Indoors or at night we can, of course, turn down the lights.  But outside during the day, there's not much we can do about the sun.  These filters let you get rid of some of the light.

They do come in various strengths (density values).  And here's the confusing part... there are at least three different ways that companies descirbe the density of the filter.     On a camera, if you change a shutter speed or aperture value by 1 stop, it means you are exactly halving or doubling (depending on which way you go) the amount of light you can collect.  Neutral density filters are based on "stops" of light.  So reducing light by 1 stop means you allow in 1/2 the light.  2 stops is 1/2 of 1/2 (or 1/4) of the light.  3 stops is 1/2 of 1/2 of 1/2 (or 1/8th) of the light.  etc.

Some manufacturers will label the filter by it's number of stops.  A 3 stop ND means it allows only 1/8th of the light to pass... and 7/8ths is blocked.)

Some manufacturers will label the filter by the percentage of light that can pass.  A 3 stop ND would be called an ND 13.  It's really allowing 12.5% of the light to pass (1/8th) EXCEPT they round the value and instead of calling it an ND 12.5, they call it an ND 13.

Lastly, most manufacturers tend to use the density value system.  In this system each "0.1" worth of "density" is equal to 1/3rd of a stop on the camera.  So 1 full stop would be called an ND 0.3.  A 3 stop filter would be called an ND 0.9.   A 10 stop filter would be called an ND 3.0.

3 stops (ND 0.9) is very common.  

Most manufacturers make a 10-stop filter (which allows only about 1/1000th of the light to pass).  This especially dense filter is so very dark that when you look through to frame and focus your shot, you can't see a thing... it's usually just black.  SO... you frame and focus your camera with the filter removed.  Switch the lens to "manual" focus mode.  Then attach the filter being careful not to change focus as you thread the filter onto the lens.

Gradient Neutral Density (GND or ND-Grad)

This is a special version of the ND filter used most commonly for landscape photography.  In fact I would venture to see that probably most stunning art photography involving landscapes... probably used one of these filters even if you didn't realize it.

These filters are clear on one half... and tinted on the other half.  The filters are usulally not round.

The filter is typically a rectangular filter.  Mine are 4" x 6" (100mm x 150mm).  Since they aren't round, you can' screw them onto the filter threads.  Instead you attach a filter bracket.  The bracket has slots on it and you slide the filters into those slots.  The reason for the slots and slide-in design is because it allows you to decide where the tinting starts in your image

When you take a landsape near sunrise or sunset (one of the best times), you face a problem wherein the sky usually still has plenty of light in it... but the landscape below -- the foreground -- is getting dark.  If you expose for the sky, the land looks horribly underexposed and in shadows and you can't see much.  If you expose for the landscape below, then the sky is over-exposed and blown out. 

By using a part clear / part tint filter... you can insert the filter so that the land is visible through the "clear" part of the filter and the sky is in the "tinted" part of the filter.  You end up with a result where overall everything looks excellent.

These are made in various strengths (just like regular ND filters) but they also come in "soft edge" and "hard edge" versions.  This refers to how quickly they fade from clear to tint.  A "hard" edge filter transitions fairly quickly and are best used for situations where there's a strong and abrupt light change between land and sky.  A "soft" edge changes very gradually.  If you have a landscape that doesn't have a strong "line" separating land and sky then a hard-edge filter would look strange.  The soft edge version changes so slowly that people looking at the photograph really can't tell where the tinting is occuring.

Other Comments

Everyone should probably own a circular polarizer (CPL).  This will improve the look of outdoor photography.

Assuming you've learned the fundamentals of "exposure" and how you can change aperture, shutter, and ISO to alter the look of an image... depth of field, background blur, freezing action, deliberately blurring motion, etc. then you'll start to run into situations where you wished you had a neutral density filter when working outside.   I suggest a 3 stop ND filter as a first filter (you can stack them ... stacking a 3 stop ND with a CPL (which usually has nearly 2 stops on it's own) would net out to about 5 stops of ND.   

I ALWAYS buy filters with anti-reflective coatings.  Flat filters can and will produce reflections which appear as "ghosting"... if you don't have good filters, you'll start to wonder if there was a ghost in your photo... or a UFO in the sky... when really it was just a poor quality filter.  This is especially imporant if you have to "stack" filters.

If you like to shoot photos that have flowing water (rivers, waterfalls, oceans, etc.) then you will probably eventually want a 10 stop filter.

If you like to shoot a lot of landscapes, you might want to start collecting GND filters (you can spend a lot of money on these things.)

There are effects filters that aren't nearly as common anymore.  I do still use a 4 point "cross screen" filter (causes any well-defined point of light... such as candles, holiday lights, etc. to throw "diffraction spikes" so they look like 4 point stars.)  You can do this with software.   But I find the software rendered version doesn't look as good.

There are colored filters used when shooting with Black & White film but these aren't really needed anymore in the age of digital photography.  Those effects are easily applied by processing software.

[ebiggs1]

"I would like to experiement with filters ..."

I will add to Tim Campbell's indepth reply about filters, that even the polarizer, ND and the gradient filter can be largely done away with, also.  If you are willing to do these two things that is.  Shoot all your images in RAW and learn Photoshop throughly.

You may say the actual use of the specific filter yields a better result but guys learned in PS can do amazing things and come as close as anybody would ever need.  On most photos I would challenge anyone to tell the difference.

But this leaves us with only one filter that is still viable. The protector filter. Even it gets severe debated questions as to its usefulness.

I am going to stick with my assertation that filters are virtually obsolete.  IMHO, of course.

[RobertTheFat]

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@ebiggs1 wrote:

"I would like to experiement with filters ..."

I will add to Tim Campbell's indepth reply about filters, that even the polarizer, ND and the gradient filter can be largely done away with, also.  If you are willing to do these two things that is.  Shoot all your images in RAW and learn Photoshop throughly.

You may say the actual use of the specific filter yields a better result but guys learned in PS can do amazing things and come as close as anybody would ever need.  On most photos I would challenge anyone to tell the difference.

But this leaves us with only one filter that is still viable. The protector filter. Even it gets severe debated questions as to its usefulness.

I am going to stick with my assertation that filters are virtually obsolete.  IMHO, of course.

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Though not a Photoshop user, I'm usually willing to accept your paeans to PS at face value. But PS won't replace a polarizing filter until it can let you see into a sunlit pond. And I flatly don't believe it can do that.

As for the "protector" (née, "ultraviolet") filter: If you're in a situation where you actually need one of those, you should definitely be using your backup camera (i.e., the one you're not afraid to take out on the beach).

[ebiggs1]

Bob from Boston said,

"But PS won't replace a polarizing filter until it can let you see into a sunlit pond."

All I can say is Bob, just don't bet your life on it.  I will also say Ben Wilmore.  Check him out some time.  I have grown very fond of him and he is a guy that is willing to help you.

[TCampbell]

Photoshop really can't get around the need for a polarizer when you're fighting reflections.  The pixels will expose the reflection... not the subject behind the reflection.  There's no way to magically eliminate the reflection and reveal the data that was hiding behind the reflection.  Once the chance to capture that data is lost... it's lost.  

There are "polarization" effects for Photoshop.  These are fake polarization effects that try to simulate the "look" that a polarizing filter has a color by trying to saturate some of the colors and also exaggerate the contrast.  But what they can't do... is eliminate reflections.  To do that, you need the real filter on the lens when you capture the shot.

And the same is true of neutral density filters.  Last year I was doing some outdoor photography.  My subjects were in shade.  My background was in sun.  I needed to bring the lighting on my subjects up to within about 2/3rds of a stop of the background to improve the balance (so I don't have an over-exposed background and under-exposed subject.)  So... I use flash to light my subject.  But as soon as you switch on the flash, you are limited to the flash sync speed (in my case 1/200th -- unless you use high-speed sync mode.  But high-speed sync mode limits the power and may not be adequate).  

I know the background needs a sunny 16 exposure... it's mid-day and it's sunny.  I wanted a shallow depth of field...about f/4.  That's 4 stops faster than f/16.  I do get to increase the shutter speed from 1/100th to 1/200th... so that's 1 stop.  But I have 3 more stops to go.  I can't shoot at f/4 ... with flash ... outdoors ... with a sunny 16 background light and get a good exposure.  

But if I slip a 3 stop ND onto the lens then, as they say "I can have my cake and eat it too!"   Now I'm shooting outdoors with the shallow DoF that I want, filling in my foreground subject (in shadows) using flash and without over-exposing the background.

I wouldn't be able to pull that off without the physical filter.

That's why I say that while there are many filters that are no longer essential... the polarizers and neutral desnity filters are still on my list of things that every serious photography (professional or passionate amatuer) should own.  If you like to shoot landscape... add gradient neutral density filters to that list.

Here's such a shot.  I was shooting at Greenfield Village (an outdoor museum created by Henry Ford) and this actor happened to resting under the shade of a tree.   I wanted the civil war era tents in the background and a low camera angle... but that meant I had to shoot the background in the sun and the foreground in the shade.  So now I need flash and THAT means I'm up against the flash sync speed limits (1/200th for my camera).

This is ISO 200, f/7.1, and 1/200th sec.  But you can see the full-sun in the background and to get that right, I'd need a Sunny 16 exposure.  You can see I used ISO 200 and 1/200th ... so that part is right.  But for that to work, I'd need to be at f/16.  I'm not at f/16... I'm two and a third stops faster.     SO... I think i probably threaded on my 2 stop ND filter (I have 2, 3, and 10 stop filters which live in my bag) and I use the flash (but I don't want it to "look" like I used a flash.  Most people probably would look at this and assume it was shot with available light -- but this shot would be extremely difficult to capture without a flash.

[ebiggs1]

I am going to say this again, "All I can say is Bob Tim, just don't bet your life on it."

You may not be able to eliminate certain filters 100% of the time but you can certainly make them mostly insignificant.

You may not be able to have a facimile of the photo you shot because of reflection but you can make a very convincing attempt.

In your exposure example, multi-exposures and PS could likely have done a better job more easily. Its all about layers and masks.   I wasn't there so I am just guessing on that one.

The other polarizing effects depend on the user.  Some are real and some are not. Some folks are good at PS and some are not.

I have a couple filters that sit on the shelf, all kinds and I have stopped carrying them altogether.

[RobertTheFat]

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@ebiggs1 wrote:

I am going to say this again, "All I can say is Bob Tim, just don't bet your life on it."

You may not be able to eliminate certain filters 100% of the time but you can certainly make them mostly insignificant.

You may not be able to have a facimile of the photo you shot because of reflection but you can make a very convincing attempt.

In your exposure example, multi-exposures and PS could likely have done a better job more easily. Its all about layers and masks.   I wasn't there so I am just guessing on that one.

The other polarizing effects depend on the user.  Some are real and some are not. Some folks are good at PS and some are not.

I have a couple filters that sit on the shelf, all kinds and I have stopped carrying them altogether.

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There are those (and I guess I'm one of them) who surmise that if Ansel Adams were alive and practicing today, he would have made himself one of the world's foremost Photoshop experts. But I believe it's equally probable that Adams, who consulted extensively for Polaroid, would not set foot outdoors on a sunny day without at least one circular polarizer.