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Thread: Specular reflection and family of angles

  1. #1

    Default Specular reflection and family of angles

    Hi lighting gurus,

    I'm currently reading the book on light science magic. Very deep. Hoping it'll give me a better understanding about light.

    I have a question. In chapter 3 it is explained that direct reflection(specular reflection) causes specular highlights (eg brigh hotspots on the forehead and nose of the subject, assuming of course that this is not due to oils etc). And this specular highlight is only visible when the camera is positioned in the family of angles (angle of incidence = reflection)

    So my question is, if I were to position the camera out of the family of angles, I won't get the (often unflattering) specular highlights and only enjoy the nice and preferred diffuses reflections?

    Am I on the right track?

  2. #2
    Moderator Octarine's Avatar
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    Default Re: Specular reflection and family of angles

    One of the many 'standard' setups for portrait is to have one or two flashes in an angel of 45 degrees from the face whereas the camera looks straight at the person. Compare.
    EOS

  3. #3

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    Quote Originally Posted by Octarine View Post
    One of the many 'standard' setups for portrait is to have one or two flashes in an angel of 45 degrees from the face whereas the camera looks straight at the person. Compare.
    Hi Octarine. Thanks for your response. I have actually tried that set up many times. I do remember specular highlights being present. That's what is causing me confusion. Nevertheless I shall go and experiment again to put this to the test.

    But to your knowledge, am I understanding the principal of specular reflections and family of angles correctly?
    Last edited by NormanSelvaraju; 11th January 2015 at 09:37 AM.

  4. #4
    Moderator Octarine's Avatar
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    Default Re: Specular reflection and family of angles

    Quote Originally Posted by NormanSelvaraju View Post
    Hi Octarine. Thanks for your response. I have actually tried that set up many times. I do remember specular highlights being present. That's what is causing me confusion. Nevertheless I shall go and experiment again to put this to the test.
    The Laws of Physics are as what is written in your book. But no face is a flat surface. Therefore, wherever you put your flash lights in relation to the camera there are will always be areas of the face that will have the right angle to flash and camera and will create highlights. Therefore, countering this requires more than just a different angle. Diffusers, distance, multiple lights and last but not least: make up can help here.

    Quote Originally Posted by NormanSelvaraju View Post
    But to your knowledge, am I understanding the principal of specular reflections and family of angles correctly?
    I would say so. To me, this would come under 'good to know'.
    EOS

  5. #5

    Default Re: Specular reflection and family of angles

    Actually hot spots are most often the result of facial oils, most evident in the T zone. Or some people have naturally shiny skin. It's more obvious in dark skinned people because there is greater contrast between the hotspots and the rest of the skin. You can try to combat this by using a diffuse light source eg, a lightbox, but generally that means a larger, less intense hotspot.

    Changing the angle of your lights? Nah, as Octarine has said, the face is too complex a shape. That only works with simple shapes with 1 or a few facets. Incidentally, at times we WANT (controlled) specular reflections eg. jewellery and glass.

    Your best bet if you aren't going full makeup -- a little bit of powder. I think Guardian or Watson sells this 'powder paper' (sorry I don't know what it's actually called) that you can use to dab away the shine. Comes in convenient tear-away pack, like some lens cleaning paper.

  6. #6
    Moderator catchlights's Avatar
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    Default Re: Specular reflection and family of angles

    Quote Originally Posted by Edwin Francis View Post
    Actually hot spots are most often the result of facial oils, most evident in the T zone. Or some people have naturally shiny skin. It's more obvious in dark skinned people because there is greater contrast between the hotspots and the rest of the skin. You can try to combat this by using a diffuse light source eg, a lightbox, but generally that means a larger, less intense hotspot.

    Changing the angle of your lights? Nah, as Octarine has said, the face is too complex a shape. That only works with simple shapes with 1 or a few facets. Incidentally, at times we WANT (controlled) specular reflections eg. jewellery and glass.

    Your best bet if you aren't going full makeup -- a little bit of powder. I think Guardian or Watson sells this 'powder paper' (sorry I don't know what it's actually called) that you can use to dab away the shine. Comes in convenient tear-away pack, like some lens cleaning paper.
    That is call facial blotter. :-)
    Shoot to Live, Live to Shoot
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  7. #7
    Moderator catchlights's Avatar
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    Default Re: Specular reflection and family of angles

    to create shape of a human face on a 2D photos you will need to use highlights and shadows, else everything will just look flat.
    what you don't want is to have specular highlights on your subject's face, there are many ways to lessen this issue.
    the proper way is to understand your lighting, use the correct light modifier, for each types of light modifiers have a optimal placement distance, according to the size of the light modifiers.
    take softbox as an example, to get the right amount of softness, the size of softbox is the same size as the area you want to light, if you want take a half length portrait of an individual, you should use a 3 feet softbox,
    so where to place your light? if you place your light correctly, you can see the skin texture on the highlight area, not a blot of specular highlight.
    you can do some test, taking some photos of the light place at different distance from your subject, than look at these photos, you will know where is sweet spot, where is the right distance.
    Shoot to Live, Live to Shoot
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  8. #8
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    Default Re: Specular reflection and family of angles

    Just to share my usual standard is a 3 light setup for studio work as it's main purpose is to accentuate
    the makeup and hair styling thus producing minimum hotspots on the face. The main light is a 100 x 100cm
    softbox using a white bed sheet for diffusion and at it's highest angle. A side light bounced thru white
    umbrella for high lights and a left frontal light for fill. To me it's just clean lighting and may appear
    to be flat but it worked well for me.Of course the makeup also play an important and crucial role.

    [IMG][/IMG]

    [IMG][/IMG]

    Some samples




    Last edited by Zeisser; 12th January 2015 at 09:55 AM.
    5D/5D3/Zeiss/28-85/100 F2/200 F4/50 F1.4/70-200/24-85/85 F1.4
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    Moderator daredevil123's Avatar
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    Default

    All i can say is... shadows is your friend. No shadows means flat.

  10. #10

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    Quote Originally Posted by Octarine View Post
    The Laws of Physics are as what is written in your book. But no face is a flat surface. Therefore, wherever you put your flash lights in relation to the camera there are will always be areas of the face that will have the right angle to flash and camera and will create highlights. Therefore, countering this requires more than just a different angle. Diffusers, distance, multiple lights and last but not least: make up can help here. I would say so. To me, this would come under 'good to know'.
    Yeah. I re read that part in the book. The wok was talking about a regular shaped object. And not a face. Hence, you are absolutely right. The angles are gonna fall in the family of angles of reflection no matter what.

    And here I thought I had found the answer to my problems. Haha.

    Thanks Octarine.

  11. #11

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    Quote Originally Posted by Edwin Francis View Post
    Actually hot spots are most often the result of facial oils, most evident in the T zone. Or some people have naturally shiny skin. It's more obvious in dark skinned people because there is greater contrast between the hotspots and the rest of the skin. You can try to combat this by using a diffuse light source eg, a lightbox, but generally that means a larger, less intense hotspot. Changing the angle of your lights? Nah, as Octarine has said, the face is too complex a shape. That only works with simple shapes with 1 or a few facets. Incidentally, at times we WANT (controlled) specular reflections eg. jewellery and glass. Your best bet if you aren't going full makeup -- a little bit of powder. I think Guardian or Watson sells this 'powder paper' (sorry I don't know what it's actually called) that you can use to dab away the shine. Comes in convenient tear-away pack, like some lens cleaning paper.
    Quote Originally Posted by catchlights View Post
    That is call facial blotter. :-)
    Haha. Yeah. You are right. That blotter does work wonders. I have in in my bag at all times.

  12. #12
    Moderator Octarine's Avatar
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    Default Re: Specular reflection and family of angles

    Quote Originally Posted by NormanSelvaraju View Post
    The wok was talking about a regular shaped object.
    What's going on in your kitchen? Or is this your 'beauty dish'?
    EOS

  13. #13

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    Quote Originally Posted by catchlights View Post
    to create shape of a human face on a 2D photos you will need to use highlights and shadows, else everything will just look flat. what you don't want is to have specular highlights on your subject's face, there are many ways to lessen this issue. the proper way is to understand your lighting, use the correct light modifier, for each types of light modifiers have a optimal placement distance, according to the size of the light modifiers. take softbox as an example, to get the right amount of softness, the size of softbox is the same size as the area you want to light, if you want take a half length portrait of an individual, you should use a 3 feet softbox, so where to place your light? if you place your light correctly, you can see the skin texture on the highlight area, not a blot of specular highlight. you can do some test, taking some photos of the light place at different distance from your subject, than look at these photos, you will know where is sweet spot, where is the right distance.
    Thanks for the reminder Catchlights, of the basic principal that I seem to have forgotten. That the size of the light is relative to the distance from the object. Just because I have a large diffuser, it doesn't mean that I can pull it way back from the subject, increase the power of the output to compensate for distance (using the inverse square rule) and then expect soft light. My bad.

    I guess to answer your question, if you have a 3 foot softbox and want to light half a body, the softbox has to be pretty close to the subject to be able to deliver a good sized light to cover the seated height of the subject(3ft). Hope I'm right.

  14. #14
    Moderator catchlights's Avatar
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    Default Re: Specular reflection and family of angles

    Quote Originally Posted by NormanSelvaraju View Post
    Thanks for the reminder Catchlights, of the basic principal that I seem to have forgotten. That the size of the light is relative to the distance from the object. Just because I have a large diffuser, it doesn't mean that I can pull it way back from the subject, increase the power of the output to compensate for distance (using the inverse square rule) and then expect soft light. My bad.

    I guess to answer your question, if you have a 3 foot softbox and want to light half a body, the softbox has to be pretty close to the subject to be able to deliver a good sized light to cover the seated height of the subject(3ft). Hope I'm right.
    it is not about able to cover the subject, is getting to optimal soft lights, and nice fall off.
    Shoot to Live, Live to Shoot
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  15. #15

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    Thanks catch lights. I think I have not experimented enough. When the shot looks good on cam and I get a few more safety shots, I move on. I should take some time to experiment instead.

    Sage advice. Appreciate it.

  16. #16

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    Quote Originally Posted by daredevil123 View Post
    All i can say is... shadows is your friend. No shadows means flat.
    Noted! Thanks DD123. Can always count on you for guidance.

    Btw, I would like to say thanks again to you and CS for the mentorship. If there is anything I can do to give back, lemme know. Would love to contribute.

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