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Lens Flare What is it?
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PostPosted: Sat Mar 31, 2007 9:33 pm    Post subject: Lens Flare What is it? Reply with quote
I know what I mean by ‘Flare’ and it isn’t the bright streaks / shapes and lines you see when pointing your lens into the sun. That is in fact ‘Diffraction’ caused by excessive lens flare. To help explain I looked it up on some web sites and here is a summery of the loads of information on flare.
Lens flare appears as a haze / glow / sparkle caused by internal reflection inside a lens. It can result in washed out images, reduction of contrast and loss of sharpness. It can also result in ‘Diffraction’.
Many mistake ‘Diffraction’ for flare. Diffraction artefacts from bright light sources often seen as star shapes or shapes representative of the aperture blade shape. Although strong direct lens flare also creates this diffraction, lower intensity flare doesn’t and will show only as soft hazy highlights a loss of contrast and loss of sharpness. Highlights are often blown by flare. This effect is often reproduced for portrait / glamour work by soft focus filters or simply inducing flare by breathing on the lens front element / filter. Many less well made lenses suffer from this type of flare due to a number of reasons. The most common is a proper lack of light baffling within the lens which causes internal reflections; other causes can be uncoated lens elements, strong direct light sources and in some cases overexposure. Any and all can cause flare or add to the problem.
All lenses have some degree of flare. For good optical systems, flare is a secondary effect that is widely distributed across the image and not visible. But when an image includes a very bright light source, flare generated can have enough intensity to become visible. This can result in ‘Diffraction’ the common, but not the only visible effect of flare. The flare produced by some lenses is often looked on as a good effect. Often described as ‘Pleasing bokeh’ ‘A nice glow’ ‘Soft colours’and is often a good attribute to have with a portrait lens. Such lenses often control the flare very well with little real degrading of the image and good distribution of the effect others are not so clever and such flare is much more noticiable with highlights, often resulting in them being blown out.


PostPosted: Sat Mar 31, 2007 10:06 pm    Post subject: Re: Lens Flare What is it? Reply with quote
Rob Leslie wrote:
I know what I mean by ‘Flare’ and it isn’t the bright streaks / shapes and lines you see when pointing your lens into the sun. That is in fact ‘Diffraction’ caused by excessive lens flare. To help explain I looked it up on some web sites and here is a summery of the loads of information on flare.
Lens flare appears as a haze / glow / sparkle caused by internal reflection inside a lens. It can result in washed out images, reduction of contrast and loss of sharpness. It can also result in ‘Diffraction’.
Many mistake ‘Diffraction’ for flare. Diffraction artefacts from bright light sources often seen as star shapes or shapes representative of the aperture blade shape.


Yes, flare typically shows itself with the hazey effect - the blades images and such are instead commonly refered to as ghosts. Of course ghosts originate from internal reflections also, and can therefore, at least theorically, be regarded as a part of the consequence of flaring.

Rob Leslie wrote:
All lenses have some degree of flare. For good optical systems, flare is a secondary effect that is widely distributed across the image and not visible. But when an image includes a very bright light source, flare generated can have enough intensity to become visible. This can result in ‘Diffraction’ the common, but not the only visible effect of flare. The flare produced by some lenses is often looked on as a good effect. Often described as ‘Pleasing bokeh’ ‘A nice glow’ ‘Soft colours’and is often a good attribute to have with a portrait lens. Such lenses often control the flare very well with little real degrading of the image and good distribution of the effect others are not so clever and such flare is much more noticiable with highlights, often resulting in them being blown out.


I do not agree at all with the second part of this resume. It seems to imply that a pleasing bokeh is caused by the flare, although controlled. I don't think it's true.

Firstly, it seems to me that the source of information is confusing the glow with the bokeh. They are not necessarily related and they can exist completely independently from each other. There are lenses that do fantastic bokeh without a single trace of glow. The Zeiss Distagon 35mm of which I posted the images yesterday is a perfect example. The glow is completely absent from that lens, even wide open. Yet, it has a bokeh that is a total cream. So, if good bokeh comes from glow/flare, where would it come from for the Distagon 35mm, which has neither? (flare nor glow)

Secondly, the bokeh is an independent optical effect, caused by the distance from the ideal focal plane, and has no relation with the flare which originates from reflections and develops as a physically different phenomenon.
How can these two things be possibly confused and mixed in a theory? I don't understand.

The assumption that a good bokeh depends from the flare is in my opinion very debatable. There are lenses such as Carl Zeiss that are the fruit of researches done on some of the most advanced lens laboratories in the world, display absolutely NO flare, and yet, they are notorious for the most gorgeous bokeh around.


PostPosted: Sat Mar 31, 2007 11:38 pm    Post subject: Reply with quote
Oro I agree with you.
When I wrote 'The flare produced by some lenses is often looked on as a good effect. Often described as ‘Pleasing bokeh’ ‘A nice glow’ ‘Soft colours’and is often a good attribute to have with a portrait lens.' I meant it as 'Often looked on.' Not meaning that it was. Although Flared background detail is often described as Bokeh, by some. If you follow my meaning. Or another way of looking at is a good bokeh often means different attributes to different people. A 'Nice smooth creamy background' is nice and may not be anything to do with flare, yet some may see a flared background as creamy!
This is one of the reasons I posted something about flare. First there seem to be too any people who only see flare as diffraction and don't see glowing edges, glowing highlights as anything to do with flare.
I will also add again that soemtimes a little flare is not always a bad thing. A modern very good lens can almost be too perfect with no character and nothing to add to an image except stark detail and contrast While a nice old one can add that certain quality that many of us find good. However when the flair does start to degrade the image for example a telephoto lens that very often flairs the highlights or edges or a lens that shows flair only in the centre then things get a bit bad.


PostPosted: Sat Mar 31, 2007 11:45 pm    Post subject: Reply with quote
Rob Leslie wrote:
A modern very good lens can almost be too perfect with no character and nothing to add to an image except stark detail and contrast While a nice old one can add that certain quality that many of us find good. However when the flair does start to degrade the image for example a telephoto lens that very often flairs the highlights or edges or a lens that shows flair only in the centre then things get a bit bad.


I think that the most common consequence of flare when it's not devastating (that is when it does not completely ruin an image), is the loss of contrast.
Loss of contrast, along with true chromatic aberration, is one of the few phenomena that can be effectively corrected in Photoshop.
The really bad flare in my opinion is the one that does not happen homogeneously on the image. This will not let you fix it by adjusting the black point.
Another bad consequence of flare is when it mixes with the chromatic aberration. CA alone can be easily corrected in photoshop. When flare gets in the way, it create those fringes that are nearly impossible to remove, because usually CA removal filters look for neat edges.


PostPosted: Sun Apr 01, 2007 10:59 pm    Post subject: Reply with quote
Take a look at this Orio
http://forum.manualfocus.org/viewtopic.php?id=5832
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