Monday, April 13, 2009
Invariably the store salesman will try to sell you a "protective" filter for your newly purchased lens, and likely your dad always had a UV filter on the lens, so you think why not? It can't hurt anything, right?
Well, besides costing an arm in a leg for high quality filters, or just being overpriced for some others, a digital sensor does not need a UV filter. A UV filter was added to a film camera to prevent hazing of the film in strong UV. A digital camera sensor is not particularly sensitive to UV light, so no UV filter is needed.
Well, if you don't need the filter for UV, what about to protect the front element of the lens from accidental damage? This is up to each individual user, but there are a few points to keep in mind before buying a filter for protection.
A protection filter is a glass (or plastic) element that is added between the image and the sensor. Each air-to-glass or glass-to air surface reduces the light available to the imaging sensor. A cheap uncoated filter could easily cut the available light by roughly 8% (http://www.astrosurf.com/luxorion/reports-coating.htm), and also cause internal reflections that cause a ghosted image to appear on the sensor.
Also, a poorly ground filter could have irregularities in it that defocus light causing soft images. This is especially true in circular polarizers.
So if we buy a multi-coated filter, we can reduce the light loss to a much more reasonable 1 or 2%. This will have minimal impact on image quality, contrast, and sharpness. But at what cost? The B&W and Heliopan filters are very expensive, running from $40-$150 per filter. You almost need a filter protector for your filter protector! These clearly won't help your image quality, but shouldn't hurt it noticeably either.
"What to do? I don't want to damage the front element of my lens". Well, first off, that front element is actually really durable. It will take something harder than the coating to scratch it, like sand, dirt, or a file. Careful cleaning won't harm the front element in the slightest.
Use your lens hood. A lens hood sticks out in front of the lens and helps protect it from getting hit by random objects, and at the same time it prevents stray light from hitting the front element of the lens. This stray light reduces the contrast of your image.
Consider getting insurance for your camera gear. According to Photo.Net it is about $1.50 / $100 of insurance with no deductible, or about $15 for a year for a $1000 lens (http://photo.net/learn/insurance). It would take 4 to 10 years to equal the price of the "protection" filter and it would cover against a lot more than scratches to the lens. Just make sure your plan covers accidental damage, and any other protection you want.
"Well, I didn't use a protection filter, and my lens got a tiny scratch when I was shooting beach volleyball and tried to get a little close to the ground for that great perspective shot when I got stepped on and buried my lens in the sand. What do I do now?"
Don't panic. A scratch on the front element of the lens is not the end of the world. It will only serve to reduce contrast slightly and could possibly cause flare spots when looking into bright lighting conditions. More than likely you will never notice a small scratch on the lens in any of your pictures.
If the scratch is bad enough, the front element of the lens is replaceable. Although this will cost more then the UV filter, it is cheaper than a new lens. Some pro Canon and Nikon lenses even have a built in lens protection element that is designed to go in front of the contoured elements that is relatively cheap to replace.
"Should I use a filter?" That is a question only you can answer. If you are shooting in an unusually harsh environment I would definitely consider it. If you do use a filter, get a quality multi-coated filter. Spending a lot doesn't mean you will get much better image quality, but you do want the coated filter to prevent image quality loss from less light transmission, flare, and ghosting.
A good filter will cost a significant amount of money, so it might be pointless to add one to your kit lens that can be replaced for about the same cost as a good lens filter. Do use your lens hood, and do learn how to clean your lens effectively. I will post a blog post at another date with how to clean a lens effectively and efficiently.
I personally don't use a filter, because they certainly don't help image quality, but I sure like buying used lenses that have always had the filter on. They tend to be spotless underneath, making my job of cleaning them up far easier. No one way is right, but this quickly turns into a holy war on any photo board. Get out there and enjoy your shooting!
See the impact of a scratched lens element at my flickr page.
Posted by Eric Tastad at 9:45 PM