backlit glass with black background?

JCJC Major grinsPosts: 777Registered Users Major grins
edited April 3, 2012 in Technique
I need to get a good shot of some volcanic glass, backlit, to show detail in the glass itself, as well as the detail of the overall shape of the object.

I don't have a light table, so I was quickly experimenting with using my laptop screen, open to a blank text page, and it seemed to work really well. I put a piece of paraffin sheeting over the top to diffuse it slightly. I got some nice clear obsidian on the thin edges, and some deep black in the thick center for contrast.

I'm wondering how to get something backlit, with a dark background though, something like on this page:

http://www.pugetsoundknappers.com/interesting_stuff/jim_miller_art.html (scroll down to see the backlit 'glass')

It looks to me like it really isn't actually backlit, but lit from the side at a small angle, with a black backdrop that isn't illuminated from that angle? Is that correct?
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Comments

  • pathfinderpathfinder Drive By Digital Shooter Posts: 14,027Super Moderators moderator
    edited March 28, 2012
    Most of these shot against a black background are lit with a large light source off to one side or the other, with care that the background is NOT illuminated by the light source. Gives nice specular reflections and sharply delineated images.

    Some of the stone with grass or natural backgrounds may have been shot with just sunlight.

    You need to keep the object a fair distance from the background to light the object and not the background, I think.

    Looks like an interesting group of flint snappers. Lovely workmanship.
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  • OffTopicOffTopic Searching for the light Posts: 501Registered Users Major grins
    edited March 29, 2012
    I don't know the size and shape of the volcanic glass you are shooting, but you might want to try underlighting, it can have beautiful results with glass. Just cut a hole slightly smaller than the base of your object in your black background sweep and place the object directly over the hole with light beneath/behind the hole. I don't think your laptop screen would provide sufficient illumination for this method, but you can always give it a try and experiment, that's half the fun of lighting.
  • JCJC Major grins Posts: 777Registered Users Major grins
    edited April 3, 2012
    pathfinder wrote: »
    lit with a large light source off to one side.

    A large light, thanks, I would have thought a smaller light, I was experimenting with a small tactical flashlight.....
    OffTopic wrote: »
    I don't know the size and shape of the volcanic glass you are shooting,... place the object directly over the hole with light beneath/behind the hole. I don't think your laptop screen would provide sufficient illumination for this method, but you can always give it a try and experiment, that's half the fun of lighting.

    It'll be an arrowhead, I don't know the size yet, probably only an inch or two, the artifacts are hard to locate. I don't know if the museum is going to let us take it out, or if I have to shoot it at the museum. If so, I won't have too much room to play.

    Can anyone recommend a good small portable light box for backlighting? When i try to search I get just as many bulb diffusers and tents as I do the kind of lightboxes I'm looking for.

    I'll be shooting with a 5D and Canon 100mm macro, not the L, unless it seemed worth it to rent an L.
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  • ian408ian408 More wag. Less Bark. Posts: 21,221Administrators moderator
    edited April 3, 2012
    In the example, I would guess the background is black because it's under exposed and that only flash is used to light the subject (no ambient). The light is most likely a speed light in a softbox. There are several different kinds of Speedlight softboxes. Something like this might be enough though a bigger SB would make nicer light. A larger softbox.

    When you are shooting with flash, it's important to remember that the shutter controls ambient light and aperture controls the flash. Set your camera up to produce the ambient exposure you want (with no flash) then add the flash to get the desired side lighting (you're correct about the flash being off to the side. I suspect it's actually off to the left and forward of the piece just a bit (to provide the back light). I am also guessing it is very close-within a foot or two.

    If you're budget minded, you can achieve similar softbox effect using the cheapest white bed sheet--think Wal-Mart cheap--and placing your flash behind it. You'll need to experiment with the distance behind the sheet. The reason you want the cheapest sheet is those typically have a very low thread count meaning it's easier for light to pass through them.
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  • pathfinderpathfinder Drive By Digital Shooter Posts: 14,027Super Moderators moderator
    edited April 3, 2012
    Some of the backgrounds are so evenly black that I think they may have selected them in Photoshop, and adjusted the curve to drive the background to black.

    Another way is to set your flash to high speed synch so that you can use a shorter shutter speed and under expose the ambient lit areas. If you under expose by four stops, then it will appear black.

    A 580ex at distances of less that 18 inches will easily over drive sunlight, let alone indoor ambient light.
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  • JCJC Major grins Posts: 777Registered Users Major grins
    edited April 3, 2012
    Thanks pathfinder and ian.

    I've been playing with museum putty and a dowel, but I'm not sure I'm going to be able get a way for the arrowhead to stand alone to do the sidelit set-up. I don't want an image showing fingers holding the artifact, no matter how well they do at providing scale ;) If I can find the right balance, I'll experiment with the side-lighting, if it doesn't, I'll want to stick with my original idea of backlighting the artifact with a lightbox.

    Here is an example: The top image is a VERY quick and dirty test with a piece of obsidian i had and my laptop screen. Nothing is in focus because I was handholding the camera, just a very quick and dirty test. The bottom image is a reflected light image of the piece the museum sent us.

    i-L5HpsHn-M.jpg

    I'm not sure what power lightbox I"d need, I see several on adorama, and there a couple for sale on craigslist, but I'm not sure what meets my needs. If the museum lets us take the piece, I have access to a bunch of drafting tables I could add a second light source to brighten them up, although the color would be off, but if we have to shoot at the museum I'll need a portable lightbox.

    I'm taking this to illustrate an article about the obsidian, so I want the artifact backlit fairly strongly to show up the internal detail in the glass. I'll want a moderate amount of surficial side-light to show up the physical detail of the artifact's shape. Hopefully we'd get the cover too with a good enough image.
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  • pathfinderpathfinder Drive By Digital Shooter Posts: 14,027Super Moderators moderator
    edited April 3, 2012
    As an example, this is an arrow head I shot in a display case at the Cahokia Mounds State Historic Site just east of St Louis Missouri. Shot in dim tungsten light, inside a plastic display case, at ISO 1600. I selected the arrowhead with the Quick Select tool, copied onto a new layer, and painted the lower layer absolute black with the Brush tool, and reduced the file size to allow uploading to dgrin as an attachment.

    SO while it is great to do this in-camera, in less than five minutes I have accomplished the following. Is this kind of what you had in mind? You can see the nylon retaining thread that was holding the arrowhead on the previously brown background.

    Obviously, with a transparent background, you could even back light an arrowhead, and then remove the background and drive it to black. I think this is how the shot of the Green Imperial Jasper arrowhead and the Knife River Flint blades you linked to above, were done, actually.

    I tend to like a black to white gradient for lots of images, like this
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  • pathfinderpathfinder Drive By Digital Shooter Posts: 14,027Super Moderators moderator
    edited April 3, 2012
    kolibri wrote: »
    Thanks pathfinder and ian.

    I've been playing with museum putty and a dowel, but I'm not sure I'm going to be able get a way for the arrowhead to stand alone to do the sidelit set-up. I don't want an image showing fingers holding the artifact, no matter how well they do at providing scale ;) If I can find the right balance, I'll experiment with the side-lighting, if it doesn't, I'll want to stick with my original idea of backlighting the artifact with a lightbox.

    Here is an example: The top image is a VERY quick and dirty test with a piece of obsidian i had and my laptop screen. Nothing is in focus because I was handholding the camera, just a very quick and dirty test. The bottom image is a reflected light image of the piece the museum sent us.

    i-L5HpsHn-M.jpg

    I'm not sure what power lightbox I"d need, I see several on adorama, and there a couple for sale on craigslist, but I'm not sure what meets my needs. If the museum lets us take the piece, I have access to a bunch of drafting tables I could add a second light source to brighten them up, although the color would be off, but if we have to shoot at the museum I'll need a portable lightbox.

    I'm taking this to illustrate an article about the obsidian, so I want the artifact backlit fairly strongly to show up the internal detail in the glass. I'll want a moderate amount of surficial side-light to show up the physical detail of the artifact's shape. Hopefully we'd get the cover too with a good enough image.


    For close up shots you may not really need a real soft box, but just a sheet of white 8x11 vellum paper taped into the top and bottom of your flash head, so that you have a much larger diffuser over the output tube. At a distance of 12-18 inches this is a very large, and very powerful light source, that will give a soft light appearance to your subject. A second flash behind you subject can back light it as well.

    I think the images you posted here are under exposed by at least 1 stop also.
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    Moderator of the Technique Forum and Finishing School on Dgrin
  • JCJC Major grins Posts: 777Registered Users Major grins
    edited April 3, 2012
    first off, I want to thank everyone for helping. I don't think I'm explaining very well what I need.
    I'd like something like this- where you can see the detail within the glass.

    i-D5X4LCW-X2.jpg


    But, without the putty. I took this outside backlit by the sun.

    I haven't figured out a good way to suspend, prop the artifact though, so I was thinking of laying it ontop of a lightbox, the kind with a lightbulb inside under a glass sheet you lay objects on.
    Kind of like this ghetto version made with my lamp.
    i-FD72QDx-XL.jpg

    The artifact will have the advantage over this piece, of not having such a razor thin edge, so hopefully I could delineate the edge more. I haven't actually seen it though, the picture above was sent to us by the museum.

    I think you guys have helped me enough to try to do the sidelighting, if I can find a way to prop the arrowhead up at some distance from a backdrop, but I'd like to see if I can do it with a lighttable style lightbox. I think I need a small amount of light coming in the from the front/side.
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  • DeVermDeVerm Major grins Posts: 405Registered Users Major grins
    edited April 3, 2012
    How about putting a speedlite on the table pointing straight up with diffuser attached and put the arrowhead on top of that? Camera straight above it, pointing down.
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