Filtering in Real-Time


 In a perfect world you don’t need a filter. Your lens, even the most basic of kit lenses, comes pre-coated to minimize flare and color aberration. And when not in use, every lens comes with a lens cap that protects the front element of your lens and never ever unknowingly falls off your camera as you stroll down the boulevard. But we don’t live in a perfect world so forget about all of the above. (And by the way, I think you just lost your lens cap)

Unlike film cameras, which are limited to an ever-dwindling choice of Daylight, Tungsten, or B&W film stocks, most all digital cameras can be programmed to a number of (usually) accurate preset color parameters. Custom white balance is a simple, menu-driven chore for most digicams, and there’s no shortage of affordable, easy-to-use white-balancing devices.

And while I’m a big proponent of getting things right the first time, in-camera, it’s still reassuring to know you can tweak your efforts days, weeks, months, or years after the fact in Photoshop, especially if you shoot RAW or better yet, RAW+JPEG. As for color and other ‘creative’ filters, many of these filters can be easily mimicked electronically using any number of digital filter kits we carry at B&H. So the question of the day is, in a digital world, who needs glass filters?The simple answer is … you, me, and everybody else running around with a camera. And the reason we need filters is because most unfiltered images fall short of what they can and should be in terms of clarity, contrast, saturation, and overall detail. But before we get into the details, let’s cover a few of the basics.

Filters 101 - The Basics

Do filters diminish image quality? Anything placed in front of a lens diminishes image quality. The question is to what degree is image quality affected and is it even noticeable? What brand filters are you currently using (if any)? The generic brand or the ‘same’ filter costing several times the price but made by a company whose name you’ve actually heard of? To paraphrase Townsend T. Stith, ‘You get what you pay for’.Filters consist of 2 components – the glass filter itself and the threaded ring that secures the glass filter to the lens. Glass quality varies from brand-to-brand, and usually (but not always) goes up hand-in-hand with the price. Clarity and color neutrality are the basis for determining the quality of a filter. Glass thickness is also a factor. The thicker the glass, the more ‘interference’ the image must traverse before reaching the camera sensor, which means clear, neutral, and thin filters tend to be the best for transmitting a sharp, accurately rendered image to the sensor. (FYI, the thinnest filters are made by Leica) Another aspect of filter-quality has to do with the filter’s coatings. Most filter manufacturers offer their goods in a choice of coatings – single and multi-coated. The differences have to do with cost (single-coated filters are less expensive) and image quality (multi-coated filters deliver cleaner, better-saturated imagery). And if you plan on shooting in extreme climates, you might want to invest in a set of weather-sealed filters such as B+W Kaeseman-series filters, which will not delaminate in the hottest, coldest, or dampest environments.The 2nd component of the filter – the threaded ring – should also be a consideration when purchasing filters. Less expensive filters have aluminum rings, which do the job but tend to jam if you inadvertently screw the filter into the lens flange at a cockeyed angle. Brass rings, aside from being less prone to jamming also offer a greater degree of crash protection if you should accidentally bump the leading edge of your lens into a hard surface (and we’ve all had this happen… haven’t we?) As you might have guessed, brass rings cost more, but again… 

UV, Skylight, & Basic Protection Filters

The most basic of filters addresses the most basic of filter functions (and a function that cannot be performed digitally after the fact), which is to protect the front element of your lens. Though ‘purists’ consider placing a filter in front of a lens an act of blaspheme, watch how fast they crumble into a pool of tears when they inadvertently scratch the front element of their favorite lens.  UV (ultra-violet) filters, sometimes called Protection filters (which may or may not have UV-reduction coatings), perform dual functions.Aside from keeping dust and smudges away from the surface of the front element, UV help eliminate the visual effects of UV radiation, which while invisible to our eyes, degrades distant details and overall image quality when taking photographs outdoors. (Note- ordinary window glass eliminates a great deal of UV radiation. UV filters contain additional coatings designed to finish the job).UV and Skylight filters perform parallel functions and the differences from a digital standpoint are relatively insignificant. In the days of film your choice of UV or Skylight was determined by your preference of film – color or black and white. UV filters, which tend to have a warm cast, were suitable for color or black and white, while pink-tinged Skylight filters were better suited for eliminating the bluish cast that was common to color slide films, especially when shooting landscapes.For shooting in higher altitudes, in snow, or around large bodies of water (which contain higher concentrated levels of UV radiation), stronger UV filters (Haze-UV2A, UV17, etc) are highly recommended for countering the detail-robbing effects of dense atmospheric haze. And for the record, the image-enhancing benefits of shooting through UV and Skylight filters cannot be replicated digitally. UV reduction can only be accomplished in-camera at the time of capture.

Polarizing Filters

The effects of Polarizing filters are also all but impossible to emulate post-capture. While many electronic filter kits tout ‘Polarizing’ filters, all they are really doing is buggering color saturation levels to make white clouds seemingly ‘pop’ from darker blue skies and the greens of summer foliage pop from the landscape.  But this is an illusion. What electronic polarizing filters cannot do is eliminate reflections and extraneous glare from shiny surfaces, which is the reason colors pop off the screen when you open the file. Glass Polarizing filters on the other hand, do a swell job at eliminating window reflections and any number of distracting reflections going on in your pictures.Polarizing filters are available in 2 formats – Linear and Circular, which look and function identically but are designed for use with manual lenses (Linear) or autofocus lenses (Circular). And while Circular Polarizers can be used with both AF and non-AF optics, Linear Polarizers can cause false meter readings and/or balky AF operation under certain lighting conditions.Polarizing filters are available in Neutral as well as Warm-toned variations. Designed primarily for film, warm-toned Polarizers come in handy when shooting mid-day during the higher Kelvin-degree days of summer. Warm-toned Polarizers are equally useful when shooting digital as long as you’re not shooting in Auto WB mode.Note – Polarizing filters eat up 3-4 stops of light and as such you should take extra precautions when shooting under lower lighting conditions, especially when using kit lenses and other optics with maximum apertures of f/3.5 or slower.

IR (infrared) Filters

If shooting infrared landscapes is your thing, here too IR blocking glass filters (e.g. 87c) are your only choice. While many digital filter kits showcase ‘IR’ filters, there’s simply no way you can differentiate and record heat waves from JPEG, TIFF, or RAW files. You can fake the look of IR, but you can’t record true IR images after the fact.   

Neutral Density (ND) Filters

ND filters are another class of filtration that cannot be emulated through the use of software-based ‘filter kits’. Neutral Density filters are essentially neutral grey filters that depending on the manufacturer, are available in 1/3, ½, and full-stop increments. ND filters enable you to reduce the amount of light entering the lens opening without affecting the aperture and/or shutter settings, which is useful on several fronts.For studio shooters, ND filters allow you to further reduce the light output of your strobes even after you’ve lowered to power setting to the unit’s minimum output levels. ND filters also allow you to shoot at very low shutter speeds under bright lighting conditions, which can be a challenge if you want to blur the movement of tumbling waterfalls and the lowest ISO setting on your digicam is 200 and the sun is blazing down on you from a cloudless sky.  Conversely, ND filters also allow you to shoot at wider apertures when you want to employ selective focus techniques under bright, sunny lighting conditions.If you plan on shooting video with a VSLR, ND filters enable you to go beyond the limits of aperture and frame-rates in order to shoot at wider apertures under any lighting condition by simply placing more or less ND filtration in front of the lens.Star filters are another type of creative filter that, while possible to emulate electronically via digital filter plug-ins, is more-often-than-not easier to  manipulate on-camera, and in real time. And the same can be said for many electronic filters. If you have the filter, why not get things the way you want them at the time of exposure rather than spend additional time down the line to accomplish the same goal.

 Step-down Rings

If you own more than 1 lens there’s a high probability you own lenses with differing filter sizes. Rather than purchasing multiple filters to satisfy your filter needs, you can save money and storage space by investing in step-down rings. As an example, if you own 3 lenses, each with a different filter thread size - say 72mm, 67mm, and 52mm – you can purchase a 72mm filter and 2 step-down rings, say a 72 to 67mm and a 72 to 52mm (or 67 to 52mm) and your home free with a lighter bag and more money remaining in your bank account.Like filters, step-down rings are available in aluminum and brass, and while the aluminum rings are less expensive, the brass ones are less prone to jam and certainly last longer.

Other Filters

The abovementioned filters represent only a sampling of the various types of filters we sell at B&H.  While I think these filters remain the better option when comparing the advantages of ‘real’ filters to their digital counterparts, there are those who will rail endlessly about the advantages of one approach over the other. And while it’s true many filter choices, i.e., color temperature, primary colors (red, blue, green, etc), warming and cooling filters (80 and 81-series filters) can be dropped in effortlessly in Photoshop and similar photo editing apps; others, such as graduated filters can also be applied post capture, but will need more time and patience on your part.So the question in these cases is, is it worth my time to diddle around later or simply shoot through glass filters at the moment of capture? There is no right or wrong answer here. It’s simply a matter of what works best for you.

Parting Notes

If you wish to retain the color qualities of glass filters, avoid setting your camera to Auto WB, which by design will do everything in its power to neutralize everything in its path. So if you’re shooting in bright sunlight, set the camera to Bright Sunlight. Do the same when photographing in Open Shade, Overcast, or other lighting conditions – match the ambient light to best match a WB setting on your digicam. Optimally you should create a custom WB to most accurately match the ambient light values regardless of your working light source.And one last thing – with the exception of graduated filters, which are often combined to darken the top and bottom of the image separately, never stack filters. Stacking filters almost always degrades image quality and usually causes vignetting at the corners of the image frame. In 2 words, it’s a lose/lose situation. 

Discussion 4

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I love the effects of a polarizing filter but the images that I take with them are never sharp.  I have 2 different filters that I spent about $70 each and as my lenses and cameras got better I felt like my pictures were getting worse.  Is there a significant difference in the optics of different (more expensive) filters?  Are there polarizing filters that photographers recommend?

@Kevin - Sadly, I don't think the star wipe was an option when the film was made...

@AW - Much shorter, but more confusing. It's a trade-off. The runtime actually varies quite a bit based on whether you're watching it a PAL or NTSC version due to the differences in frame rates between the two formats.

Does he also use the Star Wipe?

If you have an affinity for star filters and about 15 hours to kill, make sure to block out some time for Rainer Werner Fassbinder's film adaptation of Berlin Alexanderplatz -- he uses a star filter in practically every shot!