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Author Topic: Cross-polarized light setup for photographing artwork  (Read 22852 times)
BartvanderWolf
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« Reply #80 on: March 18, 2014, 03:30:53 AM »
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Hi Bart,

Thank you for your input. I've read many of your posts on this forum and appreciate you sharing your knowledge and experience. I will also look into the level you have suggested. Smiley

Interesting to think that some of the sensors may not be completely level. Another one of those things that most would assume a given.

Hi Jay,

You're welcome. I've experienced the slight sensor rotation myself when I was experimenting with Flat stitching, i.e shifting the camera on a bar to one side, and the lens to the opposite side, to keep the entrance pupil stationary (only needed for 3D subjects to avoid depth parallax). The left and right images should overlap perfectly because only a shift along the bar cannot change the camera rotation (and the rigid bar did not bend from a few centimeters displacement), yet the left side of the right-hand image and right side of the left-hand image had a vertical offset of a couple of pixels. That's when I stopped obsessing about leveling. An accurate Level is good enough, perfection is a theory.

Cheers,
Bart
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BobDavid
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« Reply #81 on: March 18, 2014, 07:57:03 AM »
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Hi Jay,

You're welcome. I've experienced the slight sensor rotation myself when I was experimenting with Flat stitching, i.e shifting the camera on a bar to one side, and the lens to the opposite side, to keep the entrance pupil stationary (only needed for 3D subjects to avoid depth parallax). The left and right images should overlap perfectly because only a shift along the bar cannot change the camera rotation (and the rigid bar did not bend from a few centimeters displacement), yet the left side of the right-hand image and right side of the left-hand image had a vertical offset of a couple of pixels. That's when I stopped obsessing about leveling. An accurate Level is good enough, perfection is a theory.

Cheers,
Bart
I used jigs to move flat art for stitching while leaving the camera stationary. Even when using a view camera, I found that moving the art worked out better than shifting the rear standard. Using the Hasselblad multi-shot back was great for 2 1/2 D--it had enough acuity to dispense with moving the camera or the art.  
« Last Edit: March 18, 2014, 08:07:42 AM by BobDavid » Logged
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« Reply #82 on: March 18, 2014, 08:09:46 AM »
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Nice little level. No frills. Accurate enough. Fits in pants pocket (Starrett part #135a, 2.5" long).
« Last Edit: March 18, 2014, 08:23:39 AM by BobDavid » Logged
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« Reply #83 on: March 18, 2014, 08:13:41 AM »
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Small business insurance, Zurich North America: https://secure.zurichna.com/small_business_insurance.htm
« Last Edit: March 18, 2014, 08:19:04 AM by BobDavid » Logged
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« Reply #84 on: March 18, 2014, 08:17:29 AM »
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I did not provide canvas stretching services. I had relationships with several framers in town that would do that. I often took in paintings that were on home-made or really old stretcher bars--often warped. Some artists actually make stretcher bars (or their assistants do) from scratch. 
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« Reply #85 on: March 18, 2014, 05:27:45 PM »
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I used jigs to move flat art for stitching while leaving the camera stationary. Even when using a view camera, I found that moving the art worked out better than shifting the rear standard. Using the Hasselblad multi-shot back was great for 2 1/2 D--it had enough acuity to dispense with moving the camera or the art. 
Bob,

Were these jigs you speak of a geared setup for somewhat accurate positioning or were the adjustments coarse?

Cheers,
Jay
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Jason DiMichele
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« Reply #86 on: March 18, 2014, 08:45:07 PM »
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Great thread with a lot of great info. Some of which I was already aware of, some that I've been searching for, and some that never even occurred to me...
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BobDavid
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« Reply #87 on: March 18, 2014, 09:26:53 PM »
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Bob,

Were these jigs you speak of a geared setup for somewhat accurate positioning or were the adjustments coarse?

Cheers,
Jay

Nothing geared. Usually a 48" long metal ruler or a 60" long metal bar with a depth of 3/16". I align and attach the "fence" along a x-axis grid line marked on the copy stand table.  Then for lining everything up I'll use live focus with the in-camera grid activated. I then just slide the art along the fence. This method works well for artwork of any size. It's just a matter of scaling up or scaling down. I have a rig for macro setups too. As long as you keep your work true to the x-axis, and step and repeat in equal increments, stitching is a breeze. You need to be careful that the x-axis marked along the table is exactly parallel to the bottom x-axis of camera sensor.

For art work that is tall and wide, I'd use the above method and then rotate the art 180 degrees and follow the same scheme. You have to be clever about how you go about stitching the elements together. Meaning, you will have to use non-standard procedures in PS. I found that putting big puzzles together, those involving six chunks, are best done manually. It is a bit fussy to do it this way, but after you've done it a few times, it's second-nature. Use the "difference" curve mode when aligning one piece over another. Then set the curve mode back to normal.

For warped canvases, I've devised a clamping system that grabs each corner along the edges to hold the picture flat. The clamping system is attached to a sled that slides along the above mentioned fence(s). I used to build furniture, so my cabinet-making background is handy. There are many ways to improvise setups for copy work. Necessity is the mother of invention. The only time I required accuracy down to less than half a millimeter was when copying microscope slides--fortunately that account went bye-bye.  

The most difficult repro job that came into my studio was a pile of architectural drawings by Frank Lloyd Wright and his assistants. The drawings were on vellum and on tissue paper. They had been mishandled, neglected, water-damaged, and some even had coffee stains. The tissue paper was crinkled and very fragile. The vellum sheets were ragged too. Some of the drawings were over 50" long. I had to put the art under a 60" X 40" 5/16" sheet of tempered glass to keep them flat. And I had to devise a "sled" to be able to slide the work along an x-axis to stitch the captures. Luckily, that project came in after I painted the ceiling black--otherwise the camera would have picked up reflections from the ceiling off the glass. I had to wrap the camera and the bracket in black velvet to eliminate reflections. It was a good gig, but very fussy. I upped my insurance coverage on that project.

I will try to get around to sending you snaps of my left over canvas stock soon. I've been sidetracked with health, family, real estate, and a few odd photo jobs.


« Last Edit: March 19, 2014, 07:49:25 AM by BobDavid » Logged
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« Reply #88 on: March 19, 2014, 04:41:34 PM »
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I used jigs to move flat art for stitching while leaving the camera stationary. Even when using a view camera, I found that moving the art worked out better than shifting the rear standard. Using the Hasselblad multi-shot back was great for 2 1/2 D--it had enough acuity to dispense with moving the camera or the art.  

I'm currently using a spherical pano head I made if I need really high resolution. I'll position myself far enough from the art that I can use a 200 or 300mm lens to minimize distortion. Works well. I did make a custom adapter for my DSLR on my Cambo monorails (4x5/8x10) but found the depth of the mirror box interfered with the image circle. I have now made a conversion for my Fuji X-E2 (Bayer-less and no anti aliasing filter) and hopefully that will work out better since the camera is much more shallow. I usually have to do very minimal geometrical tweaking. I'd like to say there is no quality loss, but theoretically there probably is.. if it can be seen by the human eye, not sure about that.

I would love to make-up a rig to be able to move the art though. That would be great as I could move the art and remotely trigger the camera and repeat. It would be great as I could then use the 100 macro and with a stepper motor controlled art holder, could make extremely accurate overlaps to maximize resolution and make post processing as efficient as possible.

Cheers,
Jay
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Jason DiMichele
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« Reply #89 on: March 19, 2014, 04:42:15 PM »
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Bob,

Thanks for this info and for the level part number. Smiley

Cheers,
Jay
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Jason DiMichele
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« Reply #90 on: March 19, 2014, 04:56:32 PM »
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Nothing geared. Usually a 48" long metal ruler or a 60" long metal bar with a depth of 3/16". I align and attach the "fence" along a x-axis grid line marked on the copy stand table.  Then for lining everything up I'll use live focus with the in-camera grid activated. I then just slide the art along the fence. This method works well for artwork of any size. It's just a matter of scaling up or scaling down. I have a rig for macro setups too. As long as you keep your work true to the x-axis, and step and repeat in equal increments, stitching is a breeze. You need to be careful that the x-axis marked along the table is exactly parallel to the bottom x-axis of camera sensor.

For art work that is tall and wide, I'd use the above method and then rotate the art 180 degrees and follow the same scheme. You have to be clever about how you go about stitching the elements together. Meaning, you will have to use non-standard procedures in PS. I found that putting big puzzles together, those involving six chunks, are best done manually. It is a bit fussy to do it this way, but after you've done it a few times, it's second-nature. Use the "difference" curve mode when aligning one piece over another. Then set the curve mode back to normal.

For warped canvases, I've devised a clamping system that grabs each corner along the edges to hold the picture flat. The clamping system is attached to a sled that slides along the above mentioned fence(s). I used to build furniture, so my cabinet-making background is handy. There are many ways to improvise setups for copy work. Necessity is the mother of invention. The only time I required accuracy down to less than half a millimeter was when copying microscope slides--fortunately that account went bye-bye.  

The most difficult repro job that came into my studio was a pile of architectural drawings by Frank Lloyd Wright and his assistants. The drawings were on vellum and on tissue paper. They had been mishandled, neglected, water-damaged, and some even had coffee stains. The tissue paper was crinkled and very fragile. The vellum sheets were ragged too. Some of the drawings were over 50" long. I had to put the art under a 60" X 40" 5/16" sheet of tempered glass to keep them flat. And I had to devise a "sled" to be able to slide the work along an x-axis to stitch the captures. Luckily, that project came in after I painted the ceiling black--otherwise the camera would have picked up reflections from the ceiling off the glass. I had to wrap the camera and the bracket in black velvet to eliminate reflections. It was a good gig, but very fussy. I upped my insurance coverage on that project.

I will try to get around to sending you snaps of my left over canvas stock soon. I've been sidetracked with health, family, real estate, and a few odd photo jobs.




Bob,

I think I'm going to mull over this concept and figure out the best way to make it work vertically as I'm not using a copy stand. This definitely seems less complicated and costly than a stepper motor system. I don't need more complexity than I need if you know what I mean. Smiley  I had to re-read the x-axis alignment information you wrote a couple of times but I think I've got it. I'll know when I try it. lol.

For stitching I'm using Autopano Giga which, in my experience, is superior to PS image stitching. Especially with non-orthographic stitching. I haven't done any orthographic stitching with it yet but it supports almost every projection type.

That's insane about the clamping system. At this point I kind of hope that I don't acquire clients with that type of art issues. Unless the price is right of course. Smiley Copying microscope slides.. I'm thinking that would get kind of old in the tooth very quickly?

That Frank Lloyd Wright job definitely sounds like an experience. It blows my mind that there can be such carelessness with such important documents. Certainly more value now but they must have still been important for obvious reasons during the day?

Thanks about the canvas inventory. I look forward to it but understand that life has other priorities. Smiley

Cheers,
Jay

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Jason DiMichele
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« Reply #91 on: March 19, 2014, 09:09:06 PM »
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Jay, I think you can rig up something for the wall. I'd think about using a ledge for the x-axis. Attach tape measure to the ledge. Rig a clamping device along the top to keep the art from tipping over. Really, my solutions are usually inexpensive, repeatable, and fast to set up. I'd nix the motion control idea for now, unless you are passionate about experimenting with it. And if you truly are passionate, go for it.
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« Reply #92 on: March 19, 2014, 11:26:25 PM »
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Jay, I think you can rig up something for the wall. I'd think about using a ledge for the x-axis. Attach tape measure to the ledge. Rig a clamping device along the top to keep the art from tipping over. Really, my solutions are usually inexpensive, repeatable, and fast to set up. I'd nix the motion control idea for now, unless you are passionate about experimenting with it. And if you truly are passionate, go for it.

Bob,

Ok that sounds great. I'm going to see what I can come up with. I'm neither here nor there about the motorized control. What I am passionate about is doing the best that I can and being able to continually provide top-notch service/product to clients. Sometimes it's nice to have someone else assist with the balance of not going over the top and creating a solution to a problem that can just as effectively be resolved with a simpler approach. Wink

Cheers,
Jay
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Jason DiMichele
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« Reply #93 on: April 08, 2014, 10:08:01 PM »
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I thought I'd come back and post my results with the polarizing setup for documenting my daughter's paintings. She works mostly in oil but occasionally with a background of acrylic when she wants a flat, featureless background. Her work is extremely finely detailed and she is extremely particular in documenting her work for her own use as well as catalogs and website that there be no artifacts visible.

For oil paintings the two big flaws are often little points of light reflecting in a specular fashion that are never noticed when in the gallery with broad diffuse lighting and glare: large areas of specular reflection. Lastly non-uniform illumination which usually shows as a gradient.

In the past we've used flashes and big umbrellas but it was always a struggle to get something passable. The results took hours of retouch time in Photoshop which could be much better spent doing compositions for new work.

This thread came at a perfect time as it allowed me to rework our lighting. We just finished shooting the last two works of this series which will be on display at her opening this weekend. Down to the wire!

The results were nothing short of excellent!! She will have zero retouch time on the works shot with the polarizer setup. The setup wasn't cheap but it is an easy one year payback so it's a no brainer investment. She's one happy artist!

We used two Profoto D1 1000w/s lights with 6ftx1ft softboxes covered with polarizing film. The D300 camera used a 77mm Nikon circular polarizer (CP).

Some learnings:
Spend time with the circular polarizer and the polarizing film to find the point at which light is maximally attenuated and somehow mark that point on the CP. On our polarizer that point turns out to be conveniently the "C" in circular polarizer printed on the unit. When aligned upwards the output of the lights was maximally attenuated.

The cross polarizers attenuate anything specular. The painting surface actually has a slight diffusion property which scrambles the polarization and that passes thru the CP in opposite polarity. The specular light from the same surface is often seen as glare and is very difficult to edit out later. The CP when properly aligned with the polarizing film on the softboxes completely eliminated this from all of our shots. Also no little light nits were visible.

We initially started with 4ftx1ft softboxes and found them insufficient to evenly illuminate her 4ftx6ft works. There were gradients top and bottom as a result. The 6ftx1ft boxes completely eliminated the gradients.

I was very glad I got the 1000w/s lights. It made it possible to move the softboxes back to 10ft and still shoot at ISO200 f/8. Softboxes and polarizers eat a lot of light.

The polarizing film is 17.25" wide and is sold by the foot. I got a 4x8ft sheet of 4mm black coroplast and made a frame 3" wide window frame to fit around the edge of each softbox. To that is attached the polarizing film with binder clips. That allows me to roll up the polarizing film for safe keeping and makes it easy to transport.

I bought and used a simple Sekonic 308 to ensure uniform illumination of four corners and center of artwork. Easy.

Big thanks to Jason DiMichele who provided lots of help in getting this done!

Here's a link to her upcoming show:

http://www.connersmith.us.com/exhibitions/katie-miller-enduring-solo-agniet-snoep-alive-and-present-solo/

Jim Miller
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framah
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« Reply #94 on: April 18, 2014, 08:38:34 AM »
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Here's what I use to shoot art. A movable wall that is perpendicular to the camera and rolls on PVC pipe and skateboard wheels. Then the camera on the stand is also on PVC pipe and wheels so it can move toward or away from the wall and still be perpendicular to it.

The whole idea is to not have to keep aligning the camera and the art or move the lights. By moving the camera but NOT the lights, each section won't be lighted equally. There is also a bit of software out there that allows you to even the light out over the piece. When lighting anything, you will always get a hot spot in the middle where the 2 lights overlap and then get falloff toward the edges with the most at the corners. This software reads the difference and adjusts the file so it is even over the entire piece.
http://www.rmimaging.com/equalight.html

You're better off using continuous lighting rather than strobes.
I use polarizing inserts into my lights and a filter on the camera lens to allow me to adjust the amount of polarizing I need.









« Last Edit: April 18, 2014, 08:40:39 AM by framah » Logged

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« Reply #95 on: April 18, 2014, 08:57:04 AM »
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One more thing...

The wall has 1/8th" holes drilled in it on 1" centers the area of a sheet of mat board.. 32x40.. and it has a small shop vac hooked up to it to create a vacuum wall allowing me to hold flat art on the wall without any clamps. For stretched canvas, I use bungie cords across the top so it holds it onto the aluminum angle ledge that it sits upon.
This setup has allowed me to hold flat, a 4x5 ft piece of 1/8th inch luan that an artist painted on so I could shoot it. all large work is shot in sections and then merged back together.

My system for shooting is the Betterlight system in a Cambo 4x5 view camera.

Setup is everything. For shooting multiple small pieces of paper, I close off any unneeded holes using wide painters tape. Then what is left is the size of the paper pieces and I can shoot and swap multiple pieces of the same size very quickly.

I once shot a 2x8 foot rug hanging it on carpet tack strips and just moving the wall for each section of the rug.  As no fibers were moved, all of the shots realigned perfectly when merged.




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BobDavid
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« Reply #96 on: April 20, 2014, 12:21:07 AM »
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Nice/clever Betterlight setup. What model are you using? I'm surprised you're working in a room with white surfaces instead of black.
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« Reply #97 on: April 22, 2014, 09:01:17 AM »
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It's the Super 8K-HS. 549MB in 24 bit RGB.

The walls in the room aren't much if any of an influence on the art as it is far enough away from the art and the art is on the black wall which is the most important area where it needs to be black. I also turn the ceiling lights off  when shooting because they WILL contaminate the light on the art. With 2  900 Watt lights cooking, I really don't need any more light to see in the room.  Grin


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« Reply #98 on: April 24, 2014, 08:31:36 AM »
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This is our setup (http://www.pbase.com/tojo123/image/155269267/original)

Folding panels allow for different lighting s lighting setups to include single lighting, dual direct non polar, dual direct polar & various indirect lighting.  We mainly use strobes but have a P1 scan back that we use infrequently that require continuous lighting.

The wall easel will slide 40"  left/right of center for stitch shots.  This setup has been very flexible to use with the many different art mediums that come to our studio.
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« Reply #99 on: April 24, 2014, 09:18:02 PM »
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A beautiful set-up, to be sure. But how can you have such beautiful floors in a
working studio?  Do you require clients to take off their shoes? 
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