Coincidental colour?

[pgk]

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Looking through some image files I came across this one from a 35mm pre-aspheric Summilux (not as per exif) on my M9. The bit that intrigues me is the flare which is of a similar colour to the dreaded purple fringe. Now I'm well used to this lens flaring and it has very characteristic flare patterns but not in this case. And FWIW wide open it has all sorts of interesting optical problems but, I can't find an image with that harsh, severe purple tinge that I can sometimes get from other (later lenses) wide open (and obviously I can't show something I don't get). This shot though was well stopped down. Any comments (I'm sure that there will be;))?

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[adan]

Well, again, purple/violet is the most energetic part of the visible spectrum (cf. "sunburn" and "skin cancer"), so it will usually be the most obvious.

 

However, flare is generally cause by internal lens reflections, and the colors of the lens coatings come into play. Look inside your 35 from the front, and you'll notice the internal reflections are generally purplish (with perhaps some blue and/or yellow or even green - depends on how the manufacturer thinks the reflections should be suppressed).

 

BTW - modern lens coatings are not actually colored. They are colorless compounds vapor-deposited on the glass in ultra-thin layers. They suppress reflections through destructive interference - reflections from the coating, and from the glass underneath, come out 1/2 wavelength out of phase, and cancel each other out (less net light reflected). But since a given wavelength is a given color, they usually leak a bit in some part of the spectrum, giving them their color tint.

 

Basically the same effect that gives oil patches on wet pavement their colorful patterns - nanometer-scale changes in the thickness of the oil cause different colors to be suppressed, or to dominate.

 

https://40.media.tumblr.com/73f07c9376504192ef7a92a4b6480d3b/tumblr_nb777c0Emq1tan5dpo1_500.jpg

[pgk]

Andy

 

I have no issue with your post. My point here is that an area of extreme overexposure is creating an 'unusual' 'flare' patch (the 35 pre-aspheric Summilux has characteristic flare of which this is not an example) of similar colour to that of extreme overexposure which leads to vivid and distinctively heavy 'purple fringing'. I simply wonder if there is a link and if so what it is?

[CheshireCat]

There is no link to the CA purple fringing.

Like Andy has explained, the color is determined by the lens coating.

[wda]

Paul, the first thing that strikes me is the strength of that bright reflection of the sun in one window. Although there will be a little attenuation and filtering caused by the window glass, you could just as well have been pointing the lens directly at the sun. That cause alone would give rise to internal reflections in your lens - any lens - which overlay the optical image.

[adan]

Well I see 3 (at least) different violet patches - a faint cloud around the highlight. that fades to violet. most notably top left of the blown reflection; a violet crescent on the balcony; and a violet patch under the balcony. And maybe a green/cyan patch (in the full image) above the arched window recess - too small to be certain.

 

I'd count the last 2 (or 3) as simple lens-reflection flare spots. Colored by the coatings on whichever elements are doing the reflecting.

 

The violet edge to the flare cloud around the highlight itself, I'd suggest, is just powerful violet being "the last wavelength standing" as the cloud of (white, full-spectrum sun) light fades away at the edges.

 

[Edit- however, two other possibilities occur to me. The reflecting window glass may be refracting the reflected light as does a prism or a raindrop, with violet to the outside. OR it may simply be another lens-reflection violet arc, superimposed on the edge of the white flare cloud.]

 

But perhaps I am still misunderstanding your question.

[CheshireCat]

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And maybe a green/cyan patch (in the full image) above the arched window recess

 

I see that too. That is symmetrical to the saturated white sun spot with respect to the center of the image, therefore I believe it is light reflected by the sensor bouncing back into the sensor again from the rear element (or lens filter, if in use).

[pgk]

When I can find it I'll post a 'normal' shot showing typical flare from this lens. As you might have guessed, flare and other characteristics of lenses intrigue me;).

[CheshireCat]

When I can find it I'll post a 'normal' shot showing typical flare from this lens. As you might have guessed, flare and other characteristics of lenses intrigue me;).

 

Indeed, flares are quite interesting and can be used artistically.

BTW: Do you use a filter on that lens ?