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I got into this situation just recently when upgrading my camera body. On my former D40x, I use warming filter almost all the time. I used 52mm Nikon L1BC and 77mm Hoya 81A. More than when cleaning my glasses, I took them off only when I want to put other kind of filters: CPL, ND and diopters. With superior color space of D200, I am no longer seeing a need to warm my shots up with filters. Then I start listening to talks about usage of UV filters both to block UV as well as a mean of protection to expensive lenses. Questions and different opinions (I intentionally use opinions instead of answers) flew around. Why do we need to block UV? Would it negatively affect the images? What brand (and type) to buy?

UV Theory

This is the theory I recalled from my old high-school days. Colors created by light with different wavelength, which is measured in nm (= nanometer = a billionth of one meter). Visible color spectrum spans from red (700nm) to violet (400nm). Red light has the longest wavelength and violet has the shortest. Light with longer wavelength than red (> 700nm) is called infrared, and light which has a shorter wavelength than violet (<400 nm) is called ultra violet or UV. So theoretically UV filters are supposed to block light with < 400nm wavelength.

Why Do We Want to Block UV?

The answer came from the film age. Films have three color sensitive layers, each sensitive to red, green, and blue light. Unfortunately, the blue-sensitive layer does not only sensitive to blue light, but also to UV light. So if there is a lot of UV around the blue sensitive layer gets too much exposure and resulting in bluish image. On the other hand, film’s red-sensitive layer is not sensitive to infrared, so normally infrared blocking filter has never been needed. Digital sensor works the opposite way. It is sensitive to infrared instead, and therefore all digital camera manufacturers include a kind of built-in infrared blocking filter. However, digital sensor is not sensitive to UV.

Furthermore, normally UV presence is very minimum at sea level. There is some - giving you tan skin after beach sunbath - but intensively diffused by the atmosphere. As altitude increase - like going up high mountain - amount of UV increases, under which condition UV filter prevents blue cast in film photographs.

The answer is crystal clear and pretty straightforward: with digital camera, UV blocking is not needed.

Why Do People are Still Using UV-Filters on Digital Camera?

UV-filters look clear and neutral to naked eyes. Therefore, thinking that they would not affect the image, some people use them as a mean of protection to their expensive lenses, leaving UV-filters on the lenses all the time. Others question the wisdom of placing a $20 filter in front of a $1000 lens and potential negative effect to image quality. Both schools of thought have some valid points. Final decision is yours to choose.

I personally think that protection offered by using filters is important. To protect camera from falling against concrete floor, hoods may do better. But what about salty air on the beach, water splash, finger prints, dust, and something alike. Microscopic dust particle may scratch the lens coating when you slide your lens-pen on.

My Experience

UV-filters are the most commonly available type in the market, and the price ranges in very wide range. The largest filter-thread I have is 77mm, and price ranges from as cheap as $20 to around $100. My first UV filter is Kenko 77mm. I felt very lucky to get a couple of 77mm filter, from a middle-board brand, for just about $12. Which immediately means $6 each. But it only took me two weeks to realize significant difference between shots taken with and without the filter. I then compared result with other filters I have which are Hoya 81A, Visico CPL, and Visico ND8. Putting their native effect aside, I noticed significant difference in image quality especially compared to the Hoya one.

As price difference between 52mm and 77mm filters, especially high-quality ones, are quite significant, I decided to go for 52mm first. Researching available option I decided to take Hoya Pro1 Digital MC Protector, which theoretically does not give anything more than protection. That is all I need anyway, digital cameras do not need UV-blocking function. I put the $6 77mm Kenko on my Nikkor 80-200 f/2.8 and $25 52mm Hoya Pro1 Digital Protector on my Nikkor 50mm f/1.4. I have no other reasons for using that configuration than correct filter-thread pairs. Got 20 various shots on each, transfer them into the computers, and … GOT IT.

I believe that I have to throw away my 77mm Kenkos to the better ones. I have just proven that Hoya Pro1 Digital Protector (77mm version costs about $45) is by far superior. But how does it compare to even more expensive (and possibly much better) ones like B+W UV-MRC which costs about double for the same size. I do not want to spend that much of money just out of curious question. I went out with only my 50mm f/1.4 without filter and take 20 similar shots. Back to the computer I compared the results between shots taken with Hoya Pro1 Digital MC Protector and those taken without filter attached. I took every single way I could think of to compare in search of difference. The only difference I barely see is blade on shot taken directly to the sunlight.

Whilst I do believe that UV blocking filter is not needed on my digital camera and I do think that being clear to naked-eyes, UV filters represent a valid mean of protection to extremely expensive lenses, However I also believe that a lens performs at its best being used as it is. Placing an extra glass between the lens and the object will somehow affect the image. The answer to giving reasonable protection my lenses without compromising quality is high quality (read: expensive) filter.

Why did I Choose Hoya Pro1 Digital MC Protector?

The most important is high-quality multi-coating which minimizes reflection down to only as little as 0.3%. Mean that reflection index of normal glass is 9% and high-quality singe-coated glass is 2-3%. Gets more critical as digital sensor is more suspectible to reflection than films. Multi-coating allow us have clearer image and higher contrast by minimizing flare and ghosting created by light reflection. It also save your investment in super-fast lenses. 9% reflection technically cut f-width down by almost one full stop, which immediately means expensive f/2.8 lens works like cheap f/4.0 lens.

Secondly is alloy filter frame instead of brass. Brass is a far more rigid material than either aluminum or the polycarbonates that are being use in today’s lens barrels. This means that, should the front of the lens get hit, the rigid brass filter ring will transfer almost all the force of the shock to the lens barrels and mechanics. An aluminum filter frame will absorb some of the shock by bending and at a certain point the glass will chip or break, which is what the filter is supposed to do, protect the lens. Replacing a filter is always preferable to getting a lens repaired. Black matte satin finish reduce potential reflection from the frame.

Some other reasons includes:

Black rimmed glass to reduce the chance of light reflecting off the edge.
Ultra thin filter frames to help avoid vignetting on super wide angle lenses are also designed to hold a lens cap.
Straight knurling edge for non-slip, easy attachment and removal.
Filter cases are UV protected to further lengthen the life of filters.

Conclusion

Digital cameras do not need UV-blocking filter.
The only benefit of UV-filter for digital camera is protection.
Filters are potentially affecting images negatively.
To get protection without negative affect to the image, high quality filter is essential.

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