Shooting obsidian - lighting for a barebones setup?

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RoxnDox
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Shooting obsidian - lighting for a barebones setup?

Post by RoxnDox »

Hi folks. Haven't posted here or done much camera work in general for a while - but I just ran into an interesting little issue that got me restarted.

I was given a big (according to my wife) pile of obsidian, agate, and other decorative rocks recently. One of my hobbies is (very) amateur flintknapping, so naturally the obsidian in gonna get broken. I am trying to do some focus-stacking and create a good image that shows the surface in fine detail. The problem is that it's basically volcanic glass with impurities. On a fresh surface, it is highly reflective and may be anywhere from translucent to nearly transparent.

My setup is Pentax K-50, Tamron 90mm SP AF lens, manual focus rail on a good tripod/head. Set to f/2.8, ISO 200, 1/8s. I'm using a tabletop light box, with 2 LED strips at the top somewhat hidden behind diffuser shields, and a single unshielded LED desk light. A quick snapshot from my little Olympus to illustrate:

Image

These are the results of a 25-frame stack (MacOS - Focus Stacker). The chip is about 1.5 inches long, and about 12 inches from the lens to subject.

Image

I did read a rather lengthy thread on microscope reflections on shiny surface, and got a few ideas on diffusing point sources, but any suggestions would be welcomed. And if anyone has references to info on the how-tos of shooting surfaces like this, I would love it. My Google-Fu was defeated by the existence of some program called Obsidian and some photographer using it in his business name. And the paywalls hiding the few relevant journal articles.

Jim
I go by "Jim" in real life, "RoxnDox" on here...

Pau
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Re: Shooting obsidian - lighting for a barebones setup?

Post by Pau »

With all those curved surfaces it is indeed a difficult to illuminate subjet.

My first option would be crosssed polarization
Pau

Lou Jost
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Re: Shooting obsidian - lighting for a barebones setup?

Post by Lou Jost »

Cross polarization is a good idea, but here the interesting wavy surface details are revealed only by the reflections. so I would suggest not crossing the polarizers completely. Or you could add a second small unpolarized key light with adjustable intensity, which could provide the highlights independently of the cross-polarized main light. Youi could turn it down until it gave you the desired effect. A warm colored filter in front of the key light would also be nice I think.

rjlittlefield
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Re: Shooting obsidian - lighting for a barebones setup?

Post by rjlittlefield »

To summarize, I think what you need is a much more effective light box -- more like a light cube, one that provides illumination from such a wide range of angles that almost every part of the mirrorlike surface of the subject reflects some bright part of the box into the camera lens.

Now, trying to explain that recommendation...

I would start by asking, what do you not like about the current photo?

You mentioned that your main interest is to "create a good image that shows the surface in fine detail".

For that goal, what I don't like about the current photo is that I can only see the surface in a few places. Everywhere else, I'm seeing patterns of color in the stone below the surface, with no clue about what the shape of the surface is.

A couple of my own threads from long ago come to mind here. At "The face behind the mask (cricket mandibles", I showed a photo of some cricket mandibles where the surface structure is very evident. That prompted some discussion of how the subject was illuminated, including this exchange:
rjlittlefield wrote:
Fri Dec 21, 2007 10:03 am
cactuspic wrote:My, what big mandibles you have, grandmother....Very interesting story about how curiosity lead to good photography, Rik. On a technical note, I think the glare on the mandible may partially be eliminated by a polarizier.

Irwin
Thanks, Irwin.

As it happens, I worked very hard to get that glare just as it appears here -- three different diffusers and a zillion different light placements got tried and rejected, before I settled on what you see here. :lol:

Look closely, and you'll notice that none of the glare is blown out, while every ridge, valley, pit, bump, and scratch can be clearly seen. Without the glare, most of that info disappears -- all that shows is a dark shape. If I wanted to highlight the color of the material, a polarizer would be a blessing. To highlight the shape, it's a curse. Different tools for different goals... :D

--Rik
rjlittlefield wrote:
Sat Dec 22, 2007 12:23 am
Irwin, the best answers to your questions are visual, but that will have to wait until tomorrow. In the meantime, a few words...
cactuspic wrote:It's my understanding that removing the glare will allow you to see texture and shape better, such as using a polarizer to allow you to see into water better.
Ahh, but suppose what you really want to see is the shape of the water.

Try this little experiment. Make yourself a cup of black coffee or dark tea. While it's brewing, haul out some polarizing sunglasses. Now, pour the coffee into a cup. Position it so you have a nice reflection of some background light area, fairly glancing, say around 30 degrees to the surface. Tap on the side of the cup. Watch the ripples. They're easy to see. Now put on the sunglasses. The reflections will disappear. That's what polarizing sunglasses are supposed to do, and they do it quite well. But when the reflections disappear, the ripples disappear too!

If you want to see through the water, then a polarizing filter is just the ticket because it kills the glare. But if you want to see the shape of the water (the ripples), then killing the glare is just the wrong thing to do, and the polarizing filter works against you.

The cricket mandibles are like the coffee. I want to show the ripples.
...
--Rik
There was a follow-up thread, at "Effect of polarizing filters on the cricket mandibles photo", which shows the disappearance of surface structure when crossed-polarizers were used.

Again, I think you want a light box that has a lot more lighted areas that can provide surface reflections. In other discussions, I've used the analogy that you want the subject to be illuminated as if it were inside a cloud of fog, with light coming in from all angles. It's the same concept in different words.

--Rik

RoxnDox
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Re: Shooting obsidian - lighting for a barebones setup?

Post by RoxnDox »

Much to peruse and ponder... In a way, my goal is to show off the coloration of this piece, but also to display the smooth curves and the very fine detail in the conchoidal fracture patterns. Might be challenging to get both. I do have a circular polarizer I can experiment with. I can also pursue a few thoughts on adding diffuser material to the box to see how it changes things. Thanks, everyone!

Jim
I go by "Jim" in real life, "RoxnDox" on here...

rjlittlefield
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Re: Shooting obsidian - lighting for a barebones setup?

Post by rjlittlefield »

RoxnDox wrote:
Sun Nov 20, 2022 6:03 pm
I can also pursue a few thoughts on adding diffuser material to the box to see how it changes things.
The words "adding diffuser material" always make me nervous, because there are lots of ways to do that which will not help. The only time diffusion material really helps is when it's located far from the light source and relatively close to the subject. The idea there is to get the whole diffuser lighted up, and have the diffuser span a wide angle with respect to the subject. If the sides and top of your box were made of diffusion material, and you were shining lights on all that area from several feet away, that would be great. But most ways of adding diffusion material inside the box are not going to help because they will not have much effect on the directions from which light reaches the subject.

Instead, let me direct your attention to the back of your current box.

It looks to me like the back of the box is covered by dark gray material with no lights shining directly on it. So that area is...dark. But that darkness is also exactly the area that is being reflected by a lot of your stone's surface. This is the reason why most of your stone does not show surface reflections -- those areas are reflecting, they're just reflecting darkness.

So, try sticking a big piece of white paper on the back of your box, and shining a light directly on that white background. That should make a big difference in what you get, which hopefully will give you some new insight about how to further change things to get what you want.
In a way, my goal is to show off the coloration of this piece, but also to display the smooth curves and the very fine detail in the conchoidal fracture patterns. Might be challenging to get both.
It will be more like impossible to get all that in a single picture. Consider instead using at least a couple of pictures, one with lots of surface reflections to show the fracture patterns and another with minimal surface reflections to show the coloration. Cross-polarization with direct illumination would be a good approach for that second part. Bouncing light off big pieces of paper is a good approach for the first part.

By the way, there's another trick that may give some insight in this case. Turn off all your current illumination, get a laser pointer or a flashlight that will throw a narrow bright beam, place it where the lens currently is, point it at the subject, and see what parts of the box light up because of reflections from the stone. Whatever parts of the box light up via reflections of the flashlight, are the same places that need to provide light if you want to see surface reflections when you photograph the stone.

--Rik

Lou Jost
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Re: Shooting obsidian - lighting for a barebones setup?

Post by Lou Jost »

I think you can do what you want in a single picture, using cross-polarized light and an unpolarized adjustable-intensity light for highlights. You'll have independent control of the reflections and the main light.

rjlittlefield
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Re: Shooting obsidian - lighting for a barebones setup?

Post by rjlittlefield »

Lou Jost wrote:
Sun Nov 20, 2022 8:39 pm
I think you can do what you want in a single picture, using cross-polarized light and an unpolarized adjustable-intensity light for highlights. You'll have independent control of the reflections and the main light.
I'm guessing there's some difference of ideas about what's wanted.

My claim is that you cannot have simultaneously, at the same place on the subject, both surface reflections and non-degraded color. I agree that you can tune the relative intensities to get less degraded color with less intense reflections. Or you can arrange to have some portions of the subject with surface reflections and degraded color, while other portions of the subject have no reflections and clean color.

All this is part of a range of compromises. If there's a limitation of one still photo, then you can tune the tradeoff between two competing effects, or you can render different parts of the subject to show both aspects. Or if you're permitted two photos, you can do the whole subject two ways. Or if video is permitted, then you can move the lights and/or the subject to give an even better total impression from the sequence. Lots of options.

--Rik

Lou Jost
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Re: Shooting obsidian - lighting for a barebones setup?

Post by Lou Jost »

I don't have any idea what the poster wanted, whether it is one photo, two photos, or a video.. I just said that IF a single picture was wanted, a cross polarized main light and unpolarized highlighti illuminant gives exact control. You can choose the position and intensity (and color) of the highlights. without the sort of overall glare that comes with uncontrolled highlights produced by the main lights.

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Re: Shooting obsidian - lighting for a barebones setup?

Post by ray_parkhurst »

Your dilemma is similar to mine when I shoot new coins. They are very reflective, often very colorful (the ones I prefer anyway), and have interesting characteristics at the device level and on the surface, such as luster and scratches that are important to show. I have never found light boxes of any type to be useful for coins, as the highly diffuse and side-lighting they offer eliminates the subtle color and shadow details.

I use two solutions that give relatively similar results:

- variable height (I use a vertical setup) masked ringlight. The centers of the unmasked areas are orthogonal in order to maximize luster and surface detail presentation. I use as high an angle as I can to minimize the reflections from the sides of the devices, while still showing luster. It is always a compromise.

- fixed-position lens-mounted diffuser with a pair of LEDs such as Jansjos or Quans. This solution gives more flexibility since you can move the LEDs to different heights from the diffuser, changing the effective amount of diffusion. You can also move the lights to different clock positions to direct the light for optimizing shadow details. Depending on the need, the diameter of the diffuser "hole" can be adjusted to vary the maximum angle of the lighting.

Here is a piece of obsidian shot with the masked ringlight. Not as pretty as your example. 36 shot stack. The 3D renderings show you the shape so you can see how the shadows and highlights render the topography. Would have looked nicer without the background, or maybe by putting the piece on a spacer to push the background out of focus.
22-11-21_134319_M=B_R=8_S=4_3.JPG
2022_11_21_134610_3.JPG
2022_11_21_134653_3.JPG
Edited to add: here is the same specimen using the lens-attached diffuser method.
22-11-21_143311_M=B_R=8_S=4_4.JPG

soldevilla
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Re: Shooting obsidian - lighting for a barebones setup?

Post by soldevilla »

For my work I have had to photograph a large number of archaeological flint pieces (very similar to obsidian, although somewhat less brilliant). The best solution that I have found is to combine two photographs, a photograph with almost axial light or with a ring light, which shows the reliefs; and another with a very diffuse lateral light that shows the colors and sometimes the transparency of the edges.

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