Angles of Incidence and Reflection

Learn how to position your lights right every time.

If you’ve ever struggled to position a light correctly, or wondered how to avoid glaring reflections in an image, this class will answer all of your questions.

Here, Karl breaks down some simple laws of physics to help you get to grips with how reflections work and how you can optimise them in your photography.

After describing the four different types of reflection, Karl goes on to explain the angle of incidence and the angle of reflection. (In the video, the latter is sometimes referred to as the ‘angle of reflectance’.)

Understanding how these angles relate to one another is crucial to capturing successful photographs. Using graphical examples, mirrors, laser pointers, smoke pellets and even a Harley Davidson motorcycle, Karl demonstrates how to put this key aspect of lighting theory into practice.

To wrap up the class, he shares a handy technique for removing glaring reflections from a shot – without having to move your lights.

By the end of the video, you’ll have a deeper understanding of how light works and how to harness and manipulate it for stronger images.

In this photography class:

  • The four types of reflection
  • The angle of incidence
  • The angle of reflection
  • Using polarising filters in photography
  • How to use a laser pointer to position studio lights
  • Adjusting focal length to alter reflections

If you enjoyed this class, check out Understanding Light or Harley Davidson Night Rod Photoshoot.

You may also like to watch How and Why to Polarise Light in Studio Photography, which Karl mentions in the conclusion to this class.

Questions? Please post them in the comments below.

Comments

  1. Hi Karl,
    Kindly disregard my previous comment.
    The family of reflectance angles is inversely proportional to the focal length. The longer the focal length and the narrower the family of reflectance angles. In the examples you demonstrated above the reflectance angles are always shown in instances where the light source is positioned at the side of the camera. Because the field of view spans at 360 degrees this would mean that reflectance angles are also applicable above and below the camera which would mean that direct reflections do also occur if a light source is positioned directly above or below the camera or at any angle around the field of view for that matter. Is this assumption correct?

    Also, if the light source is positioned directly across the camera and shining onto a highly reflective surface where its plane is diagonal to both the light source and the camera (shown at 01:23) how does the family of angles relates to the direct reflection produced even though it is on the opposite side of the camera and should be out of the family of reflectance angles?

    Thank you.

    1. Hi Myles, lets try and break down your questions one at a time.
      Your Q: ‘In the examples you demonstrated above the reflectance angles are always shown in instances where the light source is positioned at the side of the camera’
      My A: Yes as this is the most common lighting position but you can also add lighting from the top and the bottom if you felt it necessary, I usually use a global illumination as my base lighting.
      Your Q: ‘Because the field of view spans at 360 degrees this would mean that reflectance angles …….’
      My A: Yes but the angle of view is much less in the vertical portion of the picture than the horizontal (if the camera is horizontal) and visa versa so you only need to worry about the family of angles that are the most extreme and then the other ones could actually be brought in closer for the shorter side of the camera view. However this is all adjustable by eye as you can see what is happening, as long as you understand why it is happening which you do.
      Your Q: ‘Also, if the light source is positioned directly across the camera and shining…..’
      My A: I’m not really sure what you mean here, it’s obvious from diagram where the light is going to go as it’s a direct reflection as demonstrated with the laser trick with the motorcycle.

      1. Hi Karl,
        In response to the last part of my query: when you look at the diagram shown at 01:23 the reflectance angle is equal to its correspondent incident angle. We know that when those two angles are equal we have a direct reflection (returning polarised or unpolarised) of the light source on the recording medium.
        When the camera is positioned side by side to the light source they are both facing the subject almost from the same viewpoint as they both point to the subject from the same direction thus the concept of focal length impacting family of angles and positioning of the light source inside or outside the family of angles depending on the focal length does make perfect sense to me.
        However, things for me get a little more complicated when I try to apply the same concept of family of angles and focal length in the scenario depicted at 01:23.
        When you apply the bare concept of angle of incidence = angle of reflectance this is easy to understand. If you apply the concept of family of angles I am sorry but I can’t figure it out in that specific application. Regardless of any focal length used even when using a fisheye lens, how can there be a family of angles so wide that would allow to encompass a direct reflection of the light source that is on the most extreme angle past the angle normal of the subject plane.
        The only thing I could think of is that when we go past the angle normal of the subject plane we are kind of “resetting” things optically and the light source is as if it was positioned on the same side of the camera again because we are past the angle normal of the subject plane. I hope I was able to explain the issue a little better this time.
        Thank you for your input.

        1. Hi Myles, I’m sorry but I’m struggling to understand what the end necessity for you is here? What are you trying to achieve as it sounds like you understand the family of angles and that a light within them will cause a direct reflection, a light that is outside of the family of angles won’t cause a direct reflection? The concepts of this video are really only useful for two things 1. knowing where to put a light so that it reflects off of the subject surface into camera (laser demonstrations with motorbike) and 2. knowing where to put a light so that it doesn’t reflect off of the subject surface (photographing painting examples). Outside of that what other information is needed with the exception of keeping a direct reflection and de-polarising it?

          1. I greatly appreciate your consistent and professional support, Karl. I, perhaps, sometimes delve too deep into the aspects of physics and forget about the creative side of photography! Thanks.

  2. Hi Karl, I have a quick question. The range of angles that light bounces off a surface is narrower when the camera lens is longer. In your examples, the light always comes from the side of the camera. Since the camera can see all around (360 degrees), reflections can also happen above and below the camera. This means that reflections can occur if the light is above, below, or at any angle around the camera. Is this correct? Also, in the example at 01:23, if the light is directly across from the camera and hits a very reflective surface at an angle, how does the field of view and focal length affect the angles of reflection, causing a direct reflection even though it’s on the opposite side of the camera?

    Thank you.

  7. ppgoesbig

    Hello! Amazing class. The focal length vs reflection area point blew my mind.

    This is a bit off topic, but I can’t get over it. Regarding the tiles – to me it would seem much easier to shoot them lying on a flat surface rather than go through the hassle of mounting them on a wall. Was there a benefit to shooting them vertically other than it being more clearly viewable for the video? Thank you!

    1. Hi and thank you. Mostly so the lesson was more clear in the video. The other advantage is not having to climb up a ladder to look through the camera or adjust the position of your lights.

  10. Hello Karl,

    It’s me again. For product photography, we often use more than one light. How do we set up different lightings correctly when the camera is only pointing at one position on the product but we have 3 or 4 lights set up at different locations? How do we calculate the angle of incidence and reflection?

    1. Hi, you test each one individually. But remember you should only be adding more lights for a specific reason. Some product shots are done with just one light, each light has to have a purpose and reason for it to be there.

  11. This is the best video I have ever watched on this subject. The illustrations and actual live shooting were very helpful in explaining something that is very difficult for a lot of people who don’t understand the physics. Thank you Karl.

  12. Hello Karl,
    watching this a couple of times truly shed more light on angles of incidence/reflectance concepts, no pun intended. I have a question though regarding the last part of this class which is the focal length and positioning of the camera/focal plane in relation to the angle of incidence of the light. My first query would be as it follows:

    Do we change the focal length as a consequence of moving the camera so that narrowing the angle of view allows filling the frame and achieve the same results in terms of perspective or is it the focal length in itself that allows avoiding the unwanted glare? I mean let us say that we do not care about filling the frame therefore changing the focal length of the lens… Would moving the camera further away from the subject alone without changing the lens suffice to kill the glare on the subject surface?

    Also, would the use of a tilt/shift lens aid in this scenario so that no repositioning of the camera focal plane were necessary to achieve the same results?

    Thank you so much.

    1. Hi Thanks and I’m glad you enjoyed the class. Yes we change the focal length because the camera has been moved further back, we do this to make sure the subject still fills the frame and in increasing the focal length we reduce the angle of the family of angles. Moving the camera further away alone but without changing the focal length will actually make it worse as the area of the family of angles actually increases. Cheers Karl.

  14. Micah Cox

    Karl, beautiful breakdown of angles of reflectance and I believe it fully gave an answer to my confusion of light height placement. In the scenario of your motorbike shot, the light you diffused by bouncing off your infinity wall – it could have also been shot through a giant scrim or a massive octa/box? I must ask as well did you have the foresight to know you wanted to bounce the gas tank light off a wall like that and that is why you chose that exact spot in your studio? Incredible either way. It seems as if you have to treat every angular surface of a product as needing its own light source. The example in my head would be shooting a car head on you may need separate light sources for the hood, roof, sides and very front headlight area.

    1. Hi, thanks. Yes I often know where the light needs to go just from experience and looking at the angle and imagining where it would end up. I only use the laser if I need to check precisely. For what you mention on a car front on we have a class that covers exactly what you describe in our automotive section.

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