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Reflection angle

TonyTony Member
edited March 2011 in flash & lighting
Hi Neil,

I have been reading your *outstanding* site for a couple of weeks now and am starting to think one of my basic preconceptions about light may be wrong.

I had always assumed that light hitting a surface would be reflected off that surface at an equal and opposite angle, i.e light hits a wall at 45˚ from the left, and (most, but not all) of the light leaves at 45˚ to the right. Much like a pool ball hitting a cushion.

Therefore, I had also assumed that unless your subject is within this angle to receive 'most' of the light, you would get inconsistent results and be wasting a large amount of power.

However, given the example shots you've posted, and particularly the pull back shots you include, I'm starting to think that these assumptions are completely wrong?

Can you please put me out of my misery and explain, what will no doubt be, 'the bleeding obvious' to me?

Thanks in advance, and many many thanks for your openness and generosity that is, neilnv.com.

Cheers
Tony

Comments

  • Correct! For a mirror! But walls are rough surfaces and simply light up like a skylight or diffuser screen. If the wall were VERY smooth (like metal), the result would be different.
  • TonyTony Member
    Funnily enough, It was this pull back shot in particular that started me wondering...

    http://neilvn.com/tangents/2009/09/19/workshop-view-jersey-city-nj-2/

  • Light coming from a flash isn't a narrow beam (as you might see in a physics experiment), so you get a lot of light scattering when it hits the bounce surface. There is going to be enough light there for you.

    Bounce flash is a waste of power, but the TTL system is smart enough to know that it is bouncing flash and adjust subject exposure accordingly (within a certain range). That is how the exposure is somewhat consistent (for consistent, repeatable flash exposure, you have to use manual flash).

    Page 96 of Neil's on-camera flash shows two pictures where he is bouncing light of a surface that is approximately equidistant to a group of people that are not lined up in a row. The result is fairly even lighting.

    Lastly, you can easily test this yourself with your on-camera flash and a subject. Bounce off a surface at 45-degrees and check the results.
  • Neil vNNeil vN Administrator
    Tony ... I most often bounce the light from my flash towards the direction that I want the light to return from.

    It's not an efficient way of bouncing flash, but the light that returns looks very good.

    You can think of bouncing flash as a game of billiards .. angle of incidence = angle of reflectance ... but the light also scatters quite broadly.
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