Monday, August 18, 2008

Image Problem Resolved

I noticed after buying the Sigma f/1.4 30mm lens a few weeks ago that while I was shooting night or low light shots with a strong light source, that I had a problem. I noticed that each one had an extra image of the light source in it. In the night shot at La Fete de Marquette there was an extra moon (quite clear, which was kind of neat). In the fire-spinning shots last week, there was a smear of light somewhere in the photo that didn't belong. In this image, it is right above the subject's head.

Katie Spinning Fire
Undesirable Light Image

I was hoping that it was not a function of the lens. I had read a lot of reviews of Sigma lenses before I bought, and for every good review there was a bad one. It seemed like it was something of a crap shoot when you buy a Sigma, and the recommendation was to Try Before You Buy. Strangely, or tellingly, there are no Sigma dealers in Madison. There are three large photographic supply stores plus the usual big-box guys, yet no one carries Sigma. Why? I ended up ordering the lens from Amazon (great price, by the way). At first all was well, though my shots were all daytime initially. A mentor of sorts had suggested putting a UV filter on every lens. His reasoning is that it is inexpensive protection for an expensive lens, so I had done that with this Sigma. Was the reflected light caused by some bounce between the filter and the lens? I had not encountered that with my Nikon lenses, but this was a significantly larger piece of glass (62mm rather that 52mm for the Nikon lenses).

This weekend I had an opportunity to take some low light shots of the sort that would cause the reflection problem. I took two, and sure enough, there was a ghost of light that could not be edited out post camera. I unscrewed the prophylactic UV lens and re-shot the same image. Voila!

Tiki Smoke
Tiki Smoke

I got a nice, clean image of the tiki torch flame and wisps of smoke with no trace of relected light spoiling it. It seems the Sigma is fine - very fine - and I simply need to remember to take off the UV filter when I'm shooting in low light. I will have to pay attention to see if the same problem occurs during daytime hours when the UV filter would be desirable, but is causing a light problem at the same time. Regardless, I am relieved that the issue is so simple to resolve. I am sure I will forget to remove the filter now and then, but I think I am getting a large enough base of practical experience that this will be simply one of those things that I check automatically. There is so much to learn!

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  1. Hello, I like this blog.
    Sorry not write more, but my English is not good.
    A hug from Portugal

  2. Obrigado, Anastacio! Your English is much better than my Portuguese. Eu sou ignorante. Eu abraço-o igualmente.

  3. You might try a clear glass "filter" - I use Nikon NC or equivalent for lens protection. UV and haze aren't really issues with digital in my experience, since you can remove whatever you want with a color level adjustment.
    Good Luck!
    - Mick


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