Red Spots When Photographing Christmas Lights

<p>Why is it that whenever I photograph Christmas lights I get these red spots all over the place? I've included a sample photo of a baby (zoom in to see them especially on her face and there are some on the backdrop as well) and also a screen shot of my histogram with some of my camera data. <br /> <img src="http://www.karenmorelandphotography.com/img/s6/v135/p1768013325-4.jpg" alt="" /><img src="http://www.karenmorelandphotography.com/img/s9/v95/p1721242133-11.jpg" alt="" /></p>

<p>What you're seeing are reflections, within the lens, of the point-source lights in the shot. Your lens is made of multiple pieces of glass, and each may or may not have different coatings to help control lens flare and similar artifacts. Those coatings can defeat some frequencies better than others. In your case, the lower frequencies (the red end of the visible spectrum) is being bounced around between those layers of glass before escaping out the back of that stack of lens elements and making it to the camera's sensor to be recorded as part of the image. If you were to put up that string of lights against a simple, non-busy background, you'd see that the pattern of those red dots corresponds directly to the pattern of the lights in the frame. <br /><br />There's really nothing you can do about this, as it's a function of the lens design. I notice that you shot at exactly 50mm, so I'm guessing this is a 50mm prime lens (not a zoom). Zoom lenses are optically more complex, and will often exhibit more (or more complicated-looking) examples of this behavior. In very general terms, the more expensive the lens, the better the quality of the glass and the lens coatings, and the better this is usually controlled. <br /><br />If you get a shot that's a real keeper, the good news is that small points like this are very easily cleaned up with a few mouse clicks in a decent photo editing program. </p>

<p>Hi Matt, thank you for the detailed response. It has been so hard to find answers about this stuff online in a simple search! Yes, my lens is a Canon 50mm f/1.4 prime. I love the lens and never usually have any issues with it except if I'm in low lighting with these Christmas lights and if I don't have other lighting. I had the same red spots issue last year and I think I used a 35mm prime and then also a zoom lens, and the zoom WAS worse with the spots, as you indicated. This year I've got mostly artificial lighting so I haven't run into this problem except with this shot yesterday when I turned off all the studio lights and bumped up the ISO to capture this shot. It's too bad though that there's not much that can be done about it. I don't plan to do many of these types of shots so hopefully the editing of the spots will be kept to a minimum. </p>

<p>Hi<br>

If you have one of those UV filters or "lens protection" filters mounted on your lens, try removing it. They often make things much worse.</p>

<p>Cheers,</p>

<p>Yes I do have one on all my lenses, so thanks. I will try that!</p>

Hi, like Frode says. These filters are usually the main cause of ghost reflections. If there are no bright light sources in the scene, then

usually no problem with the filters.

<p>+1 to a filter being the culprit. I keep UV filters on most of my lenses, but unscrew them for taking unless there's a good reason to leave in place - like at high altitude or dust, rain, sea spray or mist in the air.</p>

<p>I once came across a webpage offering a very good illustrated explanation of exactly how and why such "echoes" of bright lights in the subject were caused by a filter. Of course I can't find it again now! Anyhow, IIRC the article showed how bright spots are reflected from the digital sensor back into the lens, then reflected back from the plane surface of the filter to be focused by the lens onto the sensor again, but in a displaced position. Removing the filter gives the reflected light no plane surface to directly bounce off.</p>

<p>Wow!! Thanks everyone for the research. I'm definitely going to try this again soon without my filter. I always used filters as a glass protection and nothing more, really. I guess they are causing the problem. </p>

<p>Just wanted to report back that I took the filter off my lens and voila! No more red spots!! Can't believe it was that easy! Thanks again! </p>

<p>Thanks for reporting back!</p>

<p>;-)</p>

<p>Is it more obvious being red?</p>

<p>An uncoated lens will generate white spots. </p>

<p>Last year I got my first pair of glasses with antireflection coating. It works very well, but the remaining reflection is bright purple. Much more noticeable than a white, but brighter reflection. </p>

<p>A single coating has one wavelength that minimizes the reflection, normally in the middle of the visible spectrum. With more coating layers, you can generate more minima in the reflection vs. wavelength graph.</p>