Purple flare: Causes and remedies

Started Mar 1, 2013 | Discussions
Anders W
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Purple flare: Causes and remedies
Mar 1, 2013

There have been quite a bit of discussion here over the last half a year or so about the fact that the E-M5 (and possibly some other MFT cameras too) tend to produce purple flare in certain situations. The problem is particularly noticeable with the Panasonic 7-14 but that is, in all likelihood, merely a consequence of the fact that the 7-14, like other UWAs, is more prone to flare in general than other lenses. The tendency for the flare to go purple is there with any lens, not just the 7-14.

Ever since the first major thread on the subject about half a year ago (see here) I have been trying to figure out exactly what is going on here. Why is the flare, which is neutral white/gray with other cameras (e.g., the G1) going purple on the E-M5 (and perhaps some other MFT bodies as well)?

I have had what I consider to be reasonably promising ideas about that for a while now but I have been waiting for some key equipment that would allow me to test my ideas to a somewhat greater extent before spelling them out. That equipment finally arrived so here goes.

As a testing stage, I chose my kitchen ceiling with associated spotlights. As previously observed, strong lights just outside the frame is one of several conditions that might cause the dreaded purple flare to appear and as shown by the first of the three images posted below (with the spotlights just outside the top of the frame), I had no difficulties reproducing the problem with the 45/1.8 on the E-M5.

What we see here, by the way, is in all likelihood the same phenomenon that has received so much attention with regard to the iPhone 5. Just google the phrase "purple flare" without specification, e.g., by means of this link and you will see what I mean.

Apple's official explanation (see here) is the following:

"Most small cameras, including those in every generation of iPhone, may exhibit some form of flare at the edge of the frame when capturing an image with out-of-scene light sources. This can happen when a light source is positioned at an angle (usually just outside the field of view) so that it causes a reflection off the surfaces inside the camera module and onto the camera sensor. Moving the camera slightly to change the position at which the bright light is entering the lens, or shielding the lens with your hand, should minimize or eliminate the effect."

Well, so far so good, but we all kind of knew that already. The key question is why the flare now goes purple whereas it previously stayed neutrally colored (white/gray) and, as far as I can tell, not much of a convincing answer has been provided yet, by Apple or anyone else. As you can see here, DPR, in their "quick review", suggest a lot of potential explanations but reject most of them and in the end have little more to offer than speculations about the new saphire glass in front of the lens and the lens coatings.

So what's really going on here? In the second and third image posted below, the flare and/or its purpleness has been vastly reduced. So what did I do to achieve that?

No, I didn't change the light, the camera position, the framing, the lens, the focus or the aperture. The light remained unchanged and the camera was firmly fixed on a tripod. All images were shot with the E-M5 and the 45/1.8 at f/1.8 and 1/5 s. And no, I didn't do anything to reduce the flare or its purpleness in PP. What I did to reduce it was done at the time of shooting. So what did I do? Two different solutions were tried, one for image two and another for image three.



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ryan2007
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Simple,

Don't shoot directly into any light source, move camera position so you do not see direct light, tilt camera toward the ground and zoom in if you have to, crop purple issues in post editing, change to a different lens. Just skip the shot, or don't buy the lens.

I use this lens all the time and never get any purple flare.

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noirdesir
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Anders W wrote:

No, I didn't change the light, the camera position, the framing, the lens, the focus or the aperture. The light remained unchanged and the camera was firmly fixed on a tripod. All images were shot with the E-M5 and the 45/1.8 at f/1.8 and 1/5 s. And no, I didn't do anything to reduce the flare or its purpleness in PP. What I did to reduce it was done at the time of shooting. So what did I do? Two different solutions were tried, one for image two and another for image three

IR or UV cut-off filter?

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Anders W
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Re: Purple flare: Causes and remedies
In reply to noirdesir, Mar 1, 2013

noirdesir wrote:

Anders W wrote:

No, I didn't change the light, the camera position, the framing, the lens, the focus or the aperture. The light remained unchanged and the camera was firmly fixed on a tripod. All images were shot with the E-M5 and the 45/1.8 at f/1.8 and 1/5 s. And no, I didn't do anything to reduce the flare or its purpleness in PP. What I did to reduce it was done at the time of shooting. So what did I do? Two different solutions were tried, one for image two and another for image three

IR or UV cut-off filter?

I see your idea. But, nope.

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richarddd
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

I'd note that there are two issues, flare and purple. Purple is relatively easy to deal with in post processing (if you have the right tools). Flare is a much more difficult task in post.

The usual remedy for flare is to avoid bright lights, especially point sources.

I look forward to seeing your technique.

I notice you didn't include EXIF data. Does that provide a clue to your technique?

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kenw
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Well, just to potentially eliminate the obvious since you didn't mention it explicitly...

Did you shade the lens front element from the ceiling lights?  They are notably outside the image so you could have done that...

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Macx
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Well, I suppose it isn't a lens hood. Pol-filter perhaps?

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Dr_Jon
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Aperture? Narrower beam of light so less possible reflections.

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Prokyon
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013
Anders W wrote:

...but I have been waiting for some key equipment that would allow me to test my ideas to a somewhat greater extent before spelling them out.

Minus Violett-Filter ?

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Anders W
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Re: Purple flare: Causes and remedies
In reply to richarddd, Mar 1, 2013

richarddd wrote:

I'd note that there are two issues, flare and purple. Purple is relatively easy to deal with in post processing (if you have the right tools). Flare is a much more difficult task in post.

Yes, but the purpleness is not always that easy to get rid off, depending on how much of it and where it is. I can't remember seeing any complaints about flare with the 7-14 before that flare started to become purple. The reason, of course, is that before that it was hardly visible since it merely implied a slight loss of contrast, although it was certainly present.

The usual remedy for flare is to avoid bright lights, especially point sources.

Yes, but there are quite a few scenes where this is more or less impossible.

I look forward to seeing your technique.

I hope I won't make you too disappointed. But I should mention in advance that I think my main contribution (if any) will be toward a better understanding of the causes. Not that the solutions are bogus but they do have their downsides.

I notice you didn't include EXIF data. Does that provide a clue to your technique?

They might, yes, at least in one case and perhaps indirectly in the other. So I removed them in order to make the quiz a bit more challenging.

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Anders W
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Re: Purple flare: Causes and remedies
In reply to kenw, Mar 1, 2013

kenw wrote:

Well, just to potentially eliminate the obvious since you didn't mention it explicitly...

Did you shade the lens front element from the ceiling lights? They are notably outside the image so you could have done that...

Hi Ken,

No I didn't shield. That would have been cheating in my book.

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Anders W
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Re: Purple flare: Causes and remedies
In reply to Dr_Jon, Mar 1, 2013

Dr_Jon wrote:

Aperture? Narrower beam of light so less possible reflections.

Nope. I said I didn't change the aperture.

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Anders W
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Re: Purple flare: Causes and remedies
In reply to Prokyon, Mar 1, 2013

Prokyon wrote:

Anders W wrote:

...but I have been waiting for some key equipment that would allow me to test my ideas to a somewhat greater extent before spelling them out.

Minus Violett-Filter ?

You mean a green filter (to eliminate purple)? If so, no.

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Anders W
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Re: Purple flare: Causes and remedies
In reply to Macx, Mar 1, 2013

Macx wrote:

Well, I suppose it isn't a lens hood.

No.

Pol-filter perhaps?

Yes, in one case. Which? And for what reason can a polarizer remove lens flare and/or its purpleness?

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Prokyon
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

they are used in astronomy to reduce purple halo

http://cs.astronomy.com/asy/equipment/f/12/t/36802.aspx

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richarddd
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Anders W wrote:

richarddd wrote:

I'd note that there are two issues, flare and purple. Purple is relatively easy to deal with in post processing (if you have the right tools). Flare is a much more difficult task in post.

Yes, but the purpleness is not always that easy to get rid off, depending on how much of it and where it is. I can't remember seeing any complaints about flare with the 7-14 before that flare started to become purple. The reason, of course, is that before that it was hardly visible since it merely implied a slight loss of contrast, although it was certainly present.

Perhaps because people are generally used to flare, especially with an UWA lens, while purple flare is much more unusual.

The usual remedy for flare is to avoid bright lights, especially point sources.

Yes, but there are quite a few scenes where this is more or less impossible.

Yes, alas.

I look forward to seeing your technique.

I hope I won't make you too disappointed. But I should mention in advance that I think my main contribution (if any) will be toward a better understanding of the causes. Not that the solutions are bogus but they do have their downsides.

I notice you didn't include EXIF data. Does that provide a clue to your technique?

They might, yes, at least in one case and perhaps indirectly in the other. So I removed them in order to make the quiz a bit more challenging.

If it's in the EXIF data and it's not aperture, that leaves shutter speed and ISO, neither of which I'd have thought would have any effect on flare, purple or otherwise.

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MAubrey
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Anders W wrote:

Macx wrote:

Well, I suppose it isn't a lens hood.

Pol-filter perhaps?

Yes, in one case. Which? And for what reason can a polarizer remove lens flare and/or its purpleness?

Hmmm. So at least one answer is DIY filters for the 7-14mm...

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Anders W
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Re: Purple flare: Causes and remedies
In reply to Prokyon, Mar 1, 2013

Prokyon wrote:

they are used in astronomy to reduce purple halo

http://cs.astronomy.com/asy/equipment/f/12/t/36802.aspx

OK. I have yet to try my old green filter. But, given my ideas of what the cause of the purpleness is, I have little reason to think it would work in this case.

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Macx
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Anders W wrote:

Macx wrote:

Well, I suppose it isn't a lens hood.

No.

Pol-filter perhaps?

Yes, in one case. Which? And for what reason can a polarizer remove lens flare and/or its purpleness?

2nd one? Well, the flare is a reflection and as such polarised light? *guessing*

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Erick L
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Re: Purple flare: Causes and remedies
In reply to Anders W, Mar 1, 2013

Anders W wrote:

 So what did I do? Two different solutions were tried, one for image two and another for image three.

So, what did you do?

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