PetaPixel

Are the Mirrors Inside DSLR Cameras Ever-So-Slightly Green?

You know the infinitely long tunnel that appears when you look into two mirrors that are pointed at one another? Have you ever noticed that the tunnel becomes more and more green, the deeper you go?

YouTube personality Vsauce has a fascinating new video titled “What Color Is A Mirror?”. In it, Mr. Sauce explains that this is due to the fact that there is no such thing as a perfect mirror (i.e. a mirror that perfectly reflects 100% of light). The fact is, a typical mirror best reflects light in the 510nm range, which we perceive as green light.

Each mirror is a tiny, tiny, tiny bit green — a tint so insignificant that we don’t notice it. However, when you point two mirrors at one another and have them reflect light back and forth, this green tint is magnified until it becomes very noticeable.

Here’s the video in which Vsauce explains the phenomenon (among other things):

This raises the question: doesn’t that mean the mirrors inside DSLR cameras are every-so-slightly green? In other words, objects in the mirror are be less-green than they appear…

Luckily for DSLR users, shots are framed through a couple of mirrors rather than in a mirror tunnel.

(via Doobybrain)


Update: The paper that Vsauce references deals entirely with mirror tunnels and mirror color. You can read it here (warning: it’s pretty technical).


Image credit: mirrors06.jpg by joshstaiger, Mirror mirror 3 by Michael D. Dunn


 
  • http://tambnguyen.com/ Tam Nguyen Photography

    Well… technically, the pentaprism means it’s a 5-time mirror.

  • http://www.petapixel.com Michael Zhang

    Thanks for pointing that out Tam :)

  • http://tambnguyen.com/ Tam Nguyen Photography

    Whoops, sorry, I forgot to drop a smiley face at the end of my comment, which was meant to be sarcastic/funny, not a smartass :)

  • adnrew

    I’m not so sure how scientific this video is. wouldn’t taking a photo of a mirror with a traditional camera sensor. that has 2 green to each red and blue pixel emphasize the green reflected. as well as the lighting around the mirror. ie. fluorescent lights would diminish to a more green tone then say halogen?

  • hansmast

    You do realize that a DSLR doesn’t take pictures using the mirror; the mirror is just for the viewfinder.

  • nickg

    While I can’t argue with the 510 nanometer peak of reflection (although the material doing the reflecting wasn’t specified), Mr Sauce makes a false leap of logic when translating this to his tunnels of mirrors, which the author happily repeats. Mirrors in cameras are front-surfaced; that is, the aluminium (or whatever is used) is on the face of the mirror that the light hits. Large mirrors such as you might see in the ‘tunnel’ photos have the silver coating on the back of the glass – so the light reaching your eye as a reflection has passed through a sheet of glass somewhere between 3 and 10mm thick – twice (incident and reflected rays). Most float or plate glass has a distinctly green tinge. It’s this green tinge which is multiplied by the multiple reflections, rather than the ‘green-ness’ of the 510nm peak in reflected radiation. (“Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt% produce a green tint which can be viewed in thick pieces…” from Wikipedia)

    I’d like to know what the vertical scale of the 510nm-peak-indicating graph is. I’m willing to bet that the actual amount of that peak over the average across the range of visible light is not discernible to human vision.

  • jack

    Is’nt this topic ever-so-slightly unrelated and even ever-so-slightly wrong to begin with?

  • Benjamin

    I agree. If you look into the side edge of a pane of glass it’s usually green – it’s explained by the absorbtion spectrum of the glass, not the mirror.

  • http://www.facebook.com/brian.poulsen.33 Brian Poulsen

    Light is only reflected two times in a pentaprism…

  • bruce b

    Its true that soda lime float glass looks green, and is the cause of most of the green tint in mirrors (the glass protects the coating, front surface mirrors are extremely delicate) but there is a peak transmission for mirrors, but it has to do with not only the coating (Alum vs gold vs platnium, they all have different transmission and reflection characteristics) but also due to the AR coating that is applied. Most AR coatings are applied at 550nm because the 1/4 wavelength covers most of the visible spectrum before it turns to a 1/2 wavelength retarder and becomes ineffective. (coatings need to be 1/4 as thick as the wavelength they are meant to enhance, so that the incident and reflected waves are 1/2 wavelength different and cause destructive interference. )

    How about That for some optical nerdiness

  • http://www.facebook.com/DanielGBallard Dan Ballard

    I think if front side mirrors had been used the green would be gone, no?

  • wickerprints

    Why be concerned with the color of the viewfinder mirror, which as has been pointed out, isn’t even in the optical pathway during the exposure? Furthermore, what do you think the lens itself is made of? The elements of a lens, depending on desired refractive index and dispersion, are made of various materials. These elements, taken on their own, are not necessarily color-neutral. To compensate, pigmented coatings may be applied to the surface, which improves color rendition at the expense of overall transmission.

  • Iris

    “Mr Sauce makes a false leap of logic when translating this to his tunnels of mirrors, which the author happily repeats.”

    I thought it was obvious the video was referring to mirrors as in the common mirror which compose of both the glass panel and the silver lining. Whether it was the panel or the lining that contributed to the green tint was never discussed but the conclusion is that the mirror as a whole does have a green tint to it.

  • michael roberts

    doesn’t the mirror flip out of the way during the exposure? henceforth the name reflex….duh

  • Mark

    As with the blueness which deepens as you look at hills receding into the distance, the colour tint comes from the medium light is passing through, in this case air, or in the case of a mirror, glass – and we all agree you can see a green tinge in glass. I think the multiplication of the “green” effect can be calculated by the number of iterations in the example pictures. For example, if the mirror used is 5 mm thick, and you can see ten iterations getting greener and greener, then the tenth iteration would look like a piece of the same glass which is 50mm thick.

  • kendon

    it is called reflex because the mirror reflects the light. not because it swings out of the way. duh.