M10 and UV LEDs

[adan]

Advertisement (gone after registration)

Shooting color pix at the gallery, I have run into a problem I haven't seen before.

Put simply, artists and performers are using UV "black light" LED lamps to create effects - and my M10 seems to be far more sensitive to the "raw" black-light that my eyes. In short, apparently the M10 can "see" UV light that I can't. And thus I get surprising results.

It's kinda the inverse of the M8 IR problem - in the sample below, note the "purple blacks" in both the background painting at right (which does have a pure black background - visually), and the woman's black dress. As well as excess "purple-blue stuff" everywhere else (ceiling, walls, skin, carpet, misc. background objects) - even 5m/16 feet away from the light sources. All of which looked black (or ordinary skin/metal-colored) to me at the time.

I swear that this purple light was not visible to my eye, except very, very close (cms/inches) to the light sources, and at the source LEDs themselves.

Before I run out and get a bunch of UV-blocking filters (and there are various types, from the standard "lens-protecting" type to seriously strong filters) I'm looking for some feedback.

- Anyone noticed this before? With any digital camera?

- What were the "special" filters that are more powerful or "scientific" than the basic "available everywhere" UV-haze filters - and do I need those, or are the everyday filters sharp-cutting enough to get rid of this "Purple Haze?"

- I assume old-fashioned tube "black-lights" would do this also (but it's been decades since I've run across those in use) - or there something unique about modern LED UV sources (e.g. wavelengths emitted)?

- Any other feedback?

I'd like to be able to, for example, photograph that backdrop painting and capture the visible day-glo paints - without having the black-painted background turn purple-blue. The artist didn't intend that.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Edited December 17, 2019 by adan

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[TomB_tx]

I saw similar results with my M9 in 2011, shooting a party in a roller skating rink that would at times light the rink with black lights. It made some interesting images, but not what you saw directly.

[Stuart Richardson]

Camera sensors and our eyes have fundamentally different responses to light, so when things start to get "extreme" in either direction (UV or IR), things start to go wrong. I remember a Leica rep telling me that all Leica lens coatings filter UV already, so UV filters were no longer necessary, but that was many years ago, so I cannot verify its veracity. I know that optical brightening agents in papers work by reflecting UV light back into the blue spectrum...perhaps something light that is going on here...the light the camera saw is reflected UV? I think this is a case where the easiest option would be to try a cheap UV filter and see if it actually does anything...

[adan]

Actually, on further consideration, I think I have seen this once before. At this 2014 overnight event where the operators were conscienciously using environmentally-friendly LED floodlights with "mixed" red/green/blue LEDs to nominally add up to visual white light. Which did "look white" - for human vision - but photographed magenta-purple.

A mess to white-balance.

(Incidentally, M9 using Adobe profile)

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

At the time, (again, the first time I'd seen those in action) I thought it was just an LED oddity - the lights were not "full-spectrum white" in the same way that tungsten bulbs are not "full-spectrum white," even though our eyes accomodate for them.

I suspect that the people who make LED light sources specifically for photography/video have tested them for reduced UV output and correct color balance, but those made for "general-purpose illumination" are tested only for visual effect, and just leak more of the "invisible" UV wavelengths.

Anyway, I will try out a standard UV-Haze filter and see what it does.

As to Leica lenses - once upon a time they used Canada Balsam (evergreen-tree sap) as the cement to hold elements together, and that did absorb UV. But I think that was replaced with chemical resins quite a long time ago (1940s). Although - recently I had Leica look at a 1980-ish (Leitz-Canada) lens with element separation, and Leica diagnosed it as "balsam-fraktur."

For that matter, almost all glass blocks or absorbs some UV - a good reason to frame color photos under glass, to prevent UV-fading.

[jaapv]

An interesting problem. Blacklight is not "Real" UV. It is filtered from violet - about 460 nm and peaks in UVB -350-360 nm. So you need a specific filter and lose a bit of the top of the visible spectrum. UVA will run up to an unhealthy  100 nm but is not relevant for this case.
Another approach might be to use Photoshop - LAB, blending layer, "blend as" with split sliders.

Sensors are quite sensitive to UV in general. I have done a bit of UV photography using an M8 and Summarit 50 1.5. and B+W 403 filter. Worked quite well.

BTW, I am not bothered by the result in your OP, The opposite rather, I think it works.

Edited December 17, 2019 by jaapv

[mujk]

I have seen something resembling this with my M10 when shooting our company band performing at a party. They had constantly changing lights of different colours, and there was probably a blacklight as well. However, there were strange results with several different colours, not only this blue. At some point I realised the strange colours and changed WB from auto to something else and I think this reduced the effect somewhat, or at least reduced the variation in colour between pictures.