Sunday, 27 February 2011

Using protective filters on lenses

A topic of much debate is whether or not to use clear glass filters on the front of lenses, for protection. Some would argue that putting on a clear filter protects the lens against objects touching it, and against water, dust, and so on. If something hits the front of the lens, they would say, it breaks the filter and not the lens itself.

Others argue that the front lens element typically is strong, and does not need extra protection. Some would even say that adding a filter may be negative, that it breaks more easily, and that the glass shards could add more to the damage of the front lens element.

Another argument is that an extra glass filter deteriorates the optical properties of the lens.

Now, I wouldn't want to drop my lens on the pavement to examine if using a filter helps protect it or not. Besides, as all lens accidents are different, one drop would not prove much anyway.

But to look at the resulting images when using a filter, as opposed to not using a filter, is possible. To examine the effect of using a clear glass protective filter, I took the same picture with and without a filter.

Example @ 200mm

Here is an example picture taken using the Panasonic GH2 with the Lumix G 45-200mm f/4-5.6 lens at 200mm f/5.6.



without filter
with filter

This is an image with fairly low contrast, and on first glance, the two images are pretty similar. Let's look at an enlargement:



So is there any difference? Not really, I would say. Perhaps one could say that there is a tad bit more contrast in the left image, without the filter.

Example @ 14mm

Another example taken using the Panasonic GH2 with the Lumix G 14mm f/2.5 lens at f/5.6.



without filter
with filter

In this case, we barely need to look at an enlargement to see the differences. Clearly, there is more flare when using a filter. The right image also has some odd "phantom lights" in the frame, from light reflections between the filter and the lens. Here is one example in the centre of the frame:



Beyond the flare, it's hard to argue that the right image is worse in terms of sharpness, for example.

Example @ 45mm

Finally an example picture taken using the Panasonic GH2 with the Lumix G 45-200mm f/4-5.6 lens at 45mm f/4.



without filter
with filter

In this case, it is very clear that the presence of the filter deteriorates the image. Not only is there much more flare, there is also a severe reduction in the contrast and sharpness across the whole frame.

Here is an enlargement which demonstrates this:



Conclusion

In low contrast situations, it is hard to find much evidence of negative impact from using a filter. However, when there is more contrast, e.g., a strong light source in front of the camera, the presence of a filter generates significantly more flare, and potentially also less contrast.

People who are proponents of using clear protective filters may still not agree with me. They could argue that if I had used higher quality multi coated filters, I would not have gotten these negative impacts. And perhaps they are right.

Since I don't believe in using filters for protection myself, I haven't invested in the most expensive filters. So it could be that higher quality filters would have reduced the deterioration.

Still, I believe it is fair to say that adding a filter will generate some deterioration of the image quality. But if using a protective filter gives you more peace of mind when using your expensive lens, perhaps that is an acceptable cost to you.

Personally, I prefer using hoods for basic protection of the front lens element.

Appendix

The filters used were: "Kenko Digital Filter UV" (52mm) for the Lumix G 45-200mm f/4-5.6 lens, and "Green Digital Filter UV" (46mm) for the Lumix G 14mm f/2.5 lens. Both filters are littered with terms like "High Quality" and "Premium Quality", but I would take that with a grain of salt.

11 comments:

  1. Your findings are exactly such as my own experience from the past. I stopped using protective filter several years ago and only lately I have invested again in Cokin system which I found very helpful in landscape photography (ND gradual filters). The other useful filter I use is Circular polariser and when using high quality one the results can be spectacular.
    In my research I found that the front glass element is very very cheap when it eventually has to be replaced in service. So in my opinion there is no sense to use protective filters as You have found by yourself.

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  2. Yes, I can understand using ND filters or polarizer filters for the effects. That makes sense to me.

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  3. Nice posting. I've also gone to not using filters other than ND and polarizer. Partially also because I use a polarizer a lot and putting it on-off is easier than switching filters.

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  4. Thanks for the information.

    I still prefer a filter.

    Wide angle lenes require removal when the image has a strong light source.

    But I am hard on cameras, exposed to sand, snow, rain etc and removal of grit is a less stressfull exercise with a protective filter. I have tried going naked a few times and have always regretted it.

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  5. Yes, I figure a lot of people still like to use protective filters. And if it gives you peace of mind, and enables you to take your lenses to more hazardous conditions, then I think that is all well.

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  6. thanks alot!
    it helped me!!

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  7. I used to have Green and Massa UV filter but changed to Hoya HMC to fix the flare problem

    Checkout Lentip's UV group test for some interesting result
    http://www.lenstip.com/113.1-article-UV_filters_test_Introduction.html

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  8. I think the reason you are seeing flare in these shots is because the filters are cheapies with poor coatings. I use B+W MRC UV filters for protection and have no issues with flare. They are multi-coated to resist flare.

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  10. I use to agree with you, until I had kids. When you pick up the camera and look through the lens, and you see what looks like peanut butter on the front element, you then are happy with a UV filter. But if I didn't have kids; I would just use a lens hood.

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