Chromatic aberration from U.V. Filters

Discussion in 'Mirrorless Digital Cameras' started by john schroeder, Jun 21, 2004.

  1. "Can U.V. filters cause chromatic aberrations?" a customer asked me
    this weekend. I had to admit that I didn't know, but I feel it is
    possible. A filter is another element added to the front of the
    lens. If it isn't made perfectly flat or smooth couldn't it cause
    chromatic aberration? In the camera store we are always selling
    U.V. filters as protection for lenses. We sell Hoya and B+W. We
    always offer the better filters first except for the cheaper kit
    lenses. With film I have never seen any difference in image quality
    with either brand. Digital SLR's are much more sensitive. Has
    anyone done a test?
     
  2. This question may keep many people busy for hours :) . How can one answer to such a general question? A filter is an additional glas with two glas/air surfaces. We all know that this will certainly not improve the lens and that indeed it ->can<- cause all sorts of optical problems, but may not. I think it is very unlikely that these possible problems can be nailed down to specific "aberrations". I would primarily be concerned about increased risk of flare and loss of contrast. So I think there is a short and a long answer. The short one is : If you need a filter , use the best one you can afford for the occasion, If you do not need one - do not use one. You might "need " one not only for filtering but also for protection of the lens. A broken front lens has a pretty large "chromatic aberration".

    The long answer is in studying MFT curves and test results, considering differences between wide angle lenes and telefoto and .... and of course philosophy : can we be sure to exclude this :) - Looking forward to a long discussion on pro/con use of filters. cheers Walter
     
  3. No, it wont.
    What it will potentially cause is ghosting/flare/loss of contrast. Light that takes on different visible colours is actually composed of different wavelengths of energy. A wavelength is a unit of measurement, with blue light being much shorter than red light. Light can be bent using different shapes of glass, which is what happens in camera lenses. Since different colours actually differ in size, when they are bent, they bend at different speeds in whatever is bending them. This causes chromatic abberation, which is a separation of colours.
    So basically, only transparent articles that bend the light can induce chromatic abberation. This additional plane(the filter), that you question to cause the abberation, might cause the problem called ghosting, which is an overlay of an additional copy of the image.
    If you require a more scientifically technical reason for what I have said, I suggest that you do some research on a phenomenon called "Red/Blue Shift".
     
  4. To try to answer my own question I did a test today. The results are the not what I expected. My image quality was worse with no filter, better with the Hoya filter and best with the B+W filter. The lens was a Nikkor 60mm micro. The camera was set for best quality JPG, manual exposure, auto white ballance, and manual focus. The distance from the subject to the lens/filter was about three inches. The camera was fixed to a tripod and was not moved. Being so close to the light source I was surprised that no ghosting occured. Neither the Hoya nor the B+W advertise multi-coating on their packaging. I feel this is a good (apple to apple to apple) test.
    008cFm-18469184.jpg
     
  5. A quick check of Hoya's and B+W's websites indicates that both filters are single coated on both surfaces.
     
  6. Just press P.....
     

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