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UV lens reflection and purple light in photo (2 images)
I just got a new 50mm f/1.4 lens and Canon UV lens filter for my Canon XTi. Today I was trying them out and got some undesirable effects in my photos. The first:.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Shutter-Priority AE 1/320 1.4 EC: +1 2/3 ISO 200 AWB, picture cropped and resized.

The UV lens seems to be catching a reflection somehow. Is there something I can do to avoid this, or is it something that will always happen when using the UV lens inside?.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Shutter-Priority AE 1/100 1.6 EC: 0 ISO 200 AWB, picture cropped but not resized.

Why am I getting this purple light? What's it called? Is it because my camera or lens is cheap?.

Thanks guys...

Comments (9)

There's a short, but decent Wikipedia article on this. It's an effect called "purple fringing".

Http://en.wikipedia.org/wiki/Purple_fringing.

In short, it's a form of chromatic aberation, and most of it comes from the lens. From the reviews I've read of your lens, this is not atypical of it's performance in the situation you're putting it in..

Stopping the lens down to f/2 or smaller will help noticably. It's just not practical to use a lens like this wide open in such a high contrast situation. The light source comming straight at the lens is also exacerbating the problem. Finally, if you intend to post process these images anyway, you're better off underexposing the highlights a tad...

Comment #1

Actually, the jury is still out on the exact cause of purple fringing..

What I should have said is that:- in my opinion- in this particular case.

Most of the fringing is caused by the combination of the lens itself and the settings chosen for the given shot...

Comment #2

Mrkristopher wrote:.

I just got a new 50mm f/1.4 lens and Canon UV lens filter for myCanon XTi. Today I was trying them out and got some undesirableeffects in my photos. The first:.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Shutter-Priority AE 1/320 1.4 EC: +1 2/3 ISO 200 AWB, picture croppedand resized.

The UV lens seems to be catching a reflection somehow. Is theresomething I can do to avoid this, or is it something that will alwayshappen when using the UV lens inside?.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Shutter-Priority AE 1/100 1.6 EC: 0 ISO 200 AWB, picture cropped butnot resized.

Why am I getting this purple light? What's it called? Is it becausemy camera or lens is cheap?.

Thanks guys..

MrK,.

Were you shooting in RAW ? .

If so, you might download the new version of Canon's DPP (DPP 3.2) and try using it's Lens Aberation correction tool to reduce that "colour-blur" (the name Canon use for "the blue or red blur which sometimes occurs at the edge of the highlighted area of an image")..

Obviously you should keep all lens and filter surfaces clean and free from grease and fingerprints etc but - unless you're very clumsy - there's little point in using a UV filter indoors. Although it didn't cause this problem (try shooting a pair of shots, with and without it, to prove that to yourself once and forever!), it can give flare and ghosting under some coditions..

Peter.

Peter - on the green island of Ischiahttp://www.pbase.com/isolaverde..

Comment #3

Most lenses are a compromise in many ways - it laws of optics..

A good raw converter like DxO will automatically remove this because many lenses have been tested with DxO Analyzer and this is built into the program. Sure, you can do it manually with some software, but what a pain..

Peter.

Persuasive Marketing Systems -inc Copywriting, Design & Photography..

Comment #4

Is caused by your filter. Cheap filter, toss it. If your at all careful with your camera just run bare and keep the lens hood on it. That's what I do unless I'm headed into an environment where blowing sand or water is a problem and then I use a filter, easier to clean.If you must use a filter get a good multicoated one from Hoya, B+W, or Heliopan..

Everyone else has commented on the purple fringing, that's a function of the lens and certain lighting situations. Either learn to avoid them (the lighting situations) or learn to PP them away or buy a better lens.A member of the rabble in good standing..

Comment #5

I wasn't shooting in RAW for these pics, I had just taken the new lens out of the box and was shooting random pics from my computer desk with no real purpose in mind. I don't actually know how to use RAW effectively yet. And to be honest, I'm still learning about aperature and shutter speed too, as you can tell by my purple-fringing. .

I do have a lens hood with the new lens, so I will just use that. It's a shame the UV filter does that. It wasn't smudged or anything, I had just taken it out of the box..

I'll keep your tips in mind when shooting next time. This lens is a great improvement over the kit lens and I'm having a lot of fun...

Comment #6

Mrkristopher wrote:.

I do have a lens hood with the new lens, so I will just use that.It's a shame the UV filter does that. It wasn't smudged or anything,I had just taken it out of the box..

This is why I, and many other people, don't routinely use UV filters on our lenses. UV filters can't help the image, but they can sure hurt it in certain cases like this..

What's happening is that some of the bright light from the window is bouncing off the reflective front surface of the sensor, back out through the lens, and hitting the flat rear surface of the filter. Multi-coated filters won't reflect much, but inexpensive uncoated filters will re-reflect a good part of that light straight back into the lens and back to the sensor..

(The rear surface of the front lens element is also flat on most lenses but is almost always multicoated to reduce reflection. Still, one does occasionally see this kind of "ghosting" when no filter was being used at all.).

As for the fringing, I disagree with the suggestions that it's due to chromatic aberration (CA). This is a result of an out-of-focus edge between dark and blown-out bright areas. A similar effect is often seen when shooting foliage such as trees against a blue sky: you get blue fringing around the foliage if you don't have it in focus and the sky is blown out...

Comment #7

Mrkristopher wrote:.

I just got a new 50mm f/1.4 lens and Canon UV lens filter for myCanon XTi. Today I was trying them out and got some undesirableeffects in my photos. The first:.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Shutter-Priority AE 1/320 1.4 EC: +1 2/3 ISO 200 AWB, picture croppedand resized.

The UV lens seems to be catching a reflection somehow. Is theresomething I can do to avoid this, or is it something that will alwayshappen when using the UV lens inside?.

Remove the filter or buy a really good (multicoated = expensive) one..

Why am I getting this purple light?.

It indicates the presence of evil forces! Be very afraid....

What's it called?.

It's called an "aura" and all pictures taken this time of year have them..

Is it because my camera or lens is cheap?.

Yes...Canon only makes cheap stuff..

Thanks guys..

Sure, my pleasure. .

Actually, "purple fringing" is a mystery, but all digital cameras do it to varying degrees. It seems most obvious on cameras with more pixels than God intended a camera to have. It can appear anywhere on the picture..

In contrast, classic chromatic aberation (CA) appears mostly in the corners and is two colors. Most people notice it mostly in landscape shots taken with low-cost zoom lenses at the full WA position. There will be a tree in the upper left corner and one side of the small branches/leaves will be red and the other side will be cyan. Blue/yellow is also common..

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #8

Doug Pardee wrote:.

As for the fringing, I disagree with the suggestions that it's due tochromatic aberration (CA)..

I agree. That is to say, I disagree. What I mean is, I agree that it's not CA..

But I also don't think it's flare of the usual kind - it looks like some sort of blooming to me. Not digital sensor blooming, but the sort of blooming that can occur when a lens or filter is misted over. Such as can happen when a brand new camera, lens and filter sits in a cold depot or a cold vehicle all night, then is eagerly unpacked and used in a warm, humid environment while still cold..

But there is also a ghostly reflection in the picture - presumably it was taken through glass? That won't help either..

With all these different problems and alleged problems, I would just delete it and move on!..

Comment #9

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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