December 2007 HelpLine
• Step Up To A Larger Filter
• Switching To A D-SLR
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Step Up To A Larger Filter
Q) I'm about to purchase a 28-75mm lens for use with my digital SLR. It has a 67mm diameter lens; however, I have a 77mm circular polarizer that I would like to use with the new lens. I also plan to purchase a 67-77mm step-up adapter so that I can use these larger filters on the smaller lens. My question is, how will the quality of the image be affected by not using the exact size filter required, i.e., a 67mm polarizer on a 67mm lens?
Ron S. Surprise
A) Before I get to your step-up question, I want to clear up a common mistake when dealing with lens specifications. When you see a spec like 28-75mm, 10-22mm or 18-200mm, the measurements listed refer to the focal length of the lens.
If you ask me what size filter you should purchase to use with these lenses, I can't give you an answer. (Well, I might be able to guess based on which manufacturers build zoom lenses with those focal lengths, but it would just be a guess.) The focal length of a lens doesn't tell you anything about the filter size you need.
From your question, however, it's obvious you know what size filter to use-you probably looked at the markings on the front of the lens. But I'd like to correct your terminology. When you mention you're considering a 67mm diameter lens, that really isn't accurate, although I understand what you're saying. While there may (or may not) be an element in the lens that's 67mm, the marking you see on the front of the lens indicates a filter diameter of 67mm. The Ã¸ symbol normally on the front of the lens next to the measurement indicates diameter.
Now back to whether there will be a problem using a different-sized filter. As long as you use a filter that requires a step-up adapter and not a step-down ring, you shouldn't have a problem. I say "shouldn't" because with some very wide-angle lenses, the step-up adapter may cause vignetting or darkening of the edges of your picture. In some extreme cases, this won't be subtle. When you use a step-down ring for a smaller filter, the edges of the filter may appear in your image, depending on where you are in the zoom range of your lens.
The only other problem you might face is that your lens shade and lens cap won't fit the larger filter. If you have the filter for use on a different lens, you can probably use that lens cap. Lens shades are designed for specific lenses, though, so you probably won't be able to use a different lens shade on the new lens.