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Thread: Dark-Field Glass

  1. #1

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    Dark-Field Glass

    This will be my last exercise for awhile from the book, Light: Science & Magic, pages 165 - 169.

    The purpose is to photograph clear glass using the dark-field method. The procedure is very similar to the bright-field method that was my previous exercise explained at Bright-Field Decanter. The primary difference in setting up the shot is that, rather than back lighting the subject with light shining through translucent material, the back lighting is blocked with opaque material to ensure that the light falls only on the edges of the glass.

    The dark-field process poses problems that make it a lot more difficult (time-consuming) than bright-field photography at least in the early stage of learning how to do it and dealing with the comparatively complex setup itself. As an example, unwanted reflections from anything and everything in the room can ruin the image. I knew this a long time ago when I first decided to learn how to photograph glass, so the walls of my makeshift studio (situated in a small storage room) are hanging black fabric. I also covered the floor with black carpet and I built a black false ceiling that can be lowered using pulleys whenever I need to isolate the rafters and everything being stored in them from the glass being photographed. I even isolated the camera from the glass by cutting a hole the same size as my lens in black poster paper. I hang the paper on my lens to prevent the camera from being reflected in the glass.

    The other problem is that this method of lighting creates a huge amount of flare. For the purpose of conducting this exercise, I eliminated the flare coming from the left and right but didn't take the time to set up stuff to eliminate it also from the top and bottom. I dealt with the flare in those areas during post-processing, which is not ideal.

    Notice in the image shown below that the top of the glass is not clearly defined. In fact, the top left part of the glass completely disappears. Though I don't know why that happened, this exercise certainly served its purpose and I look forward to improving my skill. EDIT: Now that I have thought about this some more, I think the problem is caused by the way I positioned the light source.

    The two soft bands of light were added to the middle of the glass to help display the shape of the glass and to simulate the third dimension. That was done by "painting" the glass with a reflection of white tracing paper.

    I made a much more refined image of the same subject positioned on the same piece of clear glass using the bright-field process. It can be seen at Tallest in the house

    Dark-Field Glass
    Last edited by Mike Buckley; 30th August 2012 at 12:31 PM.

  2. #2

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    Re: Dark-Field Glass

    Nice shot and thanks for the explanation.

    I am going to get the book and try some of these things for myself. I have a project in mind that involves fish and coral in tanks. The last time the results seemed ok but with a bit of lighting assistance they could have been quite good.

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    Re: Dark-Field Glass

    It's interesting that you mention fish tanks. I've read portions of the book several times and I've assembled copious notes in a Word file, yet I don't remember any mention of photographing them. I also don't see anything about that listed in the index.

    My understanding is that the basic setup involves using an off-camera flash positioned at about a 45-degree angle to the glass while placing the camera at a 90-degree angle to the glass. Now that I understand the concept of the family of angles and how to use it to prevent the camera from "seeing" the direct, polarized reflection, this makes sense.
    Last edited by Mike Buckley; 30th August 2012 at 01:23 PM.

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    Re: Dark-Field Glass

    LOL, that is exactly what I did. Off camera flash to my right or left but pointed to wall for bounce and camera pointing straight or slightly angled. Hmmmmm.

    The shots were posted here Fish. Light from camera right which is pretty obvious. Wonder what could have been done to balance both sides? Two light sources?

    This is getting to be interesting....
    Last edited by Bobobird; 30th August 2012 at 04:33 PM.

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    Re: Dark-Field Glass

    This composition has a sense of elegance that appeals to me.

    Karm

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    Re: Dark-Field Glass

    Wonderful
    i am not sure whether i have to take that a creative dissolution of the glass at the top left into darkness, or something needs correction

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    Re: Dark-Field Glass

    Welcome to the forum, Wavelength. You might want to edit your profile to include at least your first name in the "Real Name" text field. Once you do, it will be displayed along with your screen name.

    It's understandable that you might not have read my lengthy explanation in the first post, which indicates that the invisible glass in the top left area is no attempt at creativity. Instead, it's a recognized problem.

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    Re: Dark-Field Glass

    Thanks for the nod, Karm.

    I would actually use the term, "elegant," to describe the bright-field version of this glass, which is linked in my first post, not this dark-field version. I think of this dark-field version more as in-your-face and dramatic. The nuances of adjectives mean different things to different people, so I suppose your impression and my impression are not mutually exclusive. Either way, I'm glad the image appeals to you and look forward to doing a better job of executing the style in the future.

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    Re: Dark-Field Glass

    Quote Originally Posted by Bobobird View Post
    Wonder what could have been done to balance both sides? Two light sources?
    This is getting to be interesting....
    Interesting indeed, Bobo! It just now occurred to me that photographing a fish tank that is made of flat glass poses the exact same situation as doing "copy photography," photographing paper documents, paintings, photographs, etc. In lighting-speak, you need to place the light sources outside the family of angles to avoid photographing any direct reflection. Unlike the subjects of copy photography, that's the only kind of reflection produced by untreated flat glass. You did that even though you probably didn't know you were doing that. (I wouldn't have known either until reading the book.) To light the scene evenly, you would light it from both sides ensuring that both lights are outside the family of angles. That's exactly what happens when doing traditional copy work.

    You'll be glad to know that the book delves into this very extensively and fairly early on, which is especially helpful because the information further demonstrates the difference between dealing with diffuse reflections and direct reflections. It even explains what to do when the subject is so close to a wall on the left or right that the space is so restrictive that any light placed on that side will be inside the family of angles. Hint: the solution has to do with the physical relationship between a polarizer on the lens and a polarizer on the light.

    I have to tell you that I'm rather pleased with myself for recognizing the similarity between photographing a piece of art hanging on the wall and a fish tank. The authors (it only took three of them to write the book!) make a point in the beginning that once you learn why a particular lighting setup works or doesn't work in one situation, you can then know whether to apply it in a seemingly completely different situation. Ironically, it's the physics of light that are the same in the two situations that otherwise might seem very different, such as when photographing a work of art or a fish tank.

    It's time for you to get out your credit card and click "send."
    Last edited by Mike Buckley; 30th August 2012 at 08:49 PM.

  10. #10

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    Re: Dark-Field Glass

    By the way, Bobo, I just realized that I could have been accidentally misleading when mentioning the placement of the light at a 45-degree angle to the glass. When given sufficient room to the left and right of the camera, when placing the camera reasonably close to the glass and when using a reasonably short focal length, doing so places the light outside the family of angles. However, if you don't have sufficient room on the left and the right, you can solve the problem by using a longer focal length and positioning the camera further away from the glass. That allows you to place the light closer to a 90-angle to the glass while still keeping the light outside the family of angles. As you are probably beginning to imagine, the Angle Family is highly influential.

  11. #11

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    Re: Dark-Field Glass

    Thanks Mike, very informative last 2 posts.

    Do I need to get the book when we have some resident experts???

    About the book - a friend has it and will gift it to me. He used to photograph extensively but recent health issues caused him to give it up.

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    Re: Dark-Field Glass

    I'm going thru it as well. Slowing as I seem to have a different learning style. It is excellent, so far. Thanks to those who recommended it here on CIC!

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    Re: Dark-Field Glass

    Quote Originally Posted by Mike Buckley View Post
    Welcome to the forum, Wavelength. You might want to edit your profile to include at least your first name in the "Real Name" text field. Once you do, it will be displayed along with your screen name.

    It's understandable that you might not have read my lengthy explanation in the first post, which indicates that the invisible glass in the top left area is no attempt at creativity. Instead, it's a recognized problem.
    Thank you sir; i will do that; i put that comment after reading your posting completely; even then i felt it could given a creative interpretation like that, hmm, like great paintings interpreted by viewers differently

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