5

I recently took this picture and was frustrated by the white glow coming from the man's shirt. I realize it's a high contrast scene, but I don't understand the science behind why the shirt appears to be glowing. I'm not interested in re-touching it to eliminate the photo -- I'd rather learn what the problem is so that retouching isn't necessary!

The picture was shot with a Canon 6D and a Canon EF 24-105mm f/4 L lens.

Is there some way I can adjust my technique to eliminate this glow?

enter image description here

  • 6
    Do you have a filter on this lens? It looks like the problem may be caused by a cheap un-coated filter. – Mike Sowsun Jul 17 '15 at 13:00
  • Yes -- there's a UV filter on this lens. I definitely feel it's something more than just being overexposed because the blooming seems a bit crazy to me. What happens in an uncoated filter to make this happen? Likewise, why would a dirty lens cause this? Wouldn't everything be smeared, not just the highlights? – aardvarkk Jul 17 '15 at 13:08
  • You know, I think it's a combination of what both of you guys are saying. I shoot in RAW, and this is a high-quality CMOS sensor, so I think this blooming effect is not due to something as simple as a high contrast scene. I can understand it being blown out, but not blooming like this. I'm not sure of the quality of the UV filter since it came with the lens, and upon close inspection there was a fair amount of grime that was visible when I held the lens up to the light. If either of you guys wants to submit an answer, I'll accept it. – aardvarkk Jul 17 '15 at 14:43
  • 2
    A fogged lens/filter can also cause this. If you recently went from a cooler room/car to a humid outdoors it's really easy to get a foggy lens. – Wayne Werner Jul 17 '15 at 15:08
7

This looks to me like a badly smeared lens, I have taken loads of photos with this much contrast and never seen blooming like this, but dirty lenses (or damaged coatings on my cheaper old film cameras) give exactly this effect.

As Mike Sowsun said in the comments, a cheap or dirty filter could also have this effect.

The effect will in fact be consistent across the image; it's just the case that it will show up more in the brighter areas.

This is how starburst filters work; all light is affected by the filter to the same degree, but only the highlights will have visible stars as they have such high contrast compared to the rest of the scene.

Here is a good read on flare: https://photographylife.com/what-is-ghosting-and-flare (far too long to copy I'm afraid, consider it background reading :)

Re: coatings and flare not related to dirt, I'm no physicist, but as far as I can tell, flare is caused by internal reflections within the lens - causing light to fall on the sensor from unwanted directions. Coatings are designed to be specific thicknesses near the wavelength of light that causes destructive interference that eliminates these.

The light reflected by the coating surface and that reflected by the lens surface have a phase difference of twice the coating thickness. If the thickness of the coating is one quarter of the wavelength of the light to be suppressed, light of that wavelength reflected by the coating surface and light reflected by the lens surface will cancel each other out. This reduces the overall amount of light reflected. In short, coatings make use of light wave interference phenomena to eliminate reflections.

From: http://www.canon.com/technology/s_labo/light/003/03.html

Also: https://en.wikipedia.org/wiki/Anti-reflective_coating

In short, it's likely cheaper lenses/filters have coatings that do not have sufficient tolerances to work effectively at reducing flare.

It might be worth noting that I've only seen flaring this bad on either a very badly smeared lens, a lens with a damaged coating, or a lens with no coating.

Also, any filter will tend to increase flare because the more glass surfaces you add, the more opportunity for internal reflection.

5

The shirt is extremely overexposed. As a consequence, the sensor pixels start to leak charge to the surrounding pixels, which leads to the glow.

Short of controlling the lighting of the scene to reduce contrast, you can only avoid that by reducing exposure, which will leave the engine underexposed. You could shoot two pictures and combine them in post (HDR/tone-mapping), or ask the person to step back for a sec. :)

  • So the glow is a function of the sensor pixels leaking into one another due to overexposure? – aardvarkk Jul 17 '15 at 11:00
  • exactly. it's called "blooming", i've seen since. – ths Jul 17 '15 at 11:52
  • 6
    That's too much to be only "blooming". Clean both ends of the lens? – Jim Garrison Jul 17 '15 at 14:15
  • @JimGarrison I think you're correct. I think the combination of a dirty lens filter and it possibly being uncoated are both contributing. Since I'm just now noticing the blooming, I'm guessing it just got dirty without me really noticing. I'm waiting for an answer to this end and I'll accept it. – aardvarkk Jul 17 '15 at 14:45
0

If it helps, I've been struggling with a similar (although not as pronounced) issue with a Nikon 400mm f2.8 lens.

You can see a selection of photos showing this same issue here: https://www.flickr.com/photos/simonawest/albums/72157660943127566

Look at the points where an in-focus white shirt is on an out of focus dark background.

I started (as suggested above) by cleaning the front and rear of the lens.

I've been through all sorts of stuff to try and fix this and ruled out camera body and settings (not ADL, Sharpening nor any other camera setting) by trying three different Nikon bodies with different settings.

Finally a professional suggested Nikon clan the lens and told me how to check the internal elements of the lens using a bright light and looking through the lens (holding the aperture open) to let light fall progressively on different lens elements.

With a 5Kg lens this took a bit of doing!

Anyway, I finally found out that one of the internal elements appears to have something on it. As I bought the lens second hand, I'm guessing that the previous owner (pro) got some water in the lens that has affected one of the elements.

It's currently on it's way back to Nikon for cleaning and service. Hopefully that will sort the issue...

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.