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Author Topic: Copy work: glossy painting on canvas problem  (Read 6529 times)

ComputerDork

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Copy work: glossy painting on canvas problem
« on: September 12, 2015, 01:56:10 am »

I'm trying to figure out the best way to photograph a painting on canvas that is painted with some very glossy acrylic paint. The problem is that the glossy rounded threads of the canvas are always going to have specular highlights even with the lights at very indirect angles.

I'm using two strobes with soft boxes, but I've got limited space to work in. I am using a cpl filter.

On most parts of the painting this isn't too much of a problem since viewers don't necessarily mind seeing the canvas texture, but it becomes a problem in lighter areas where subtle color variations tend to get washed out by it. This can be compensated for to some extent with digital manipulation but it takes extra time so the more of that I can avoid in the future the better.

Is there anything else anyone can think of that would reduce the glare? I'm working in a confined copy work area so I can't relocate to a white room with light bounced off all the walls or something.
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pfigen

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Re: Copy work: glossy painting on canvas problem
« Reply #1 on: September 12, 2015, 02:58:57 am »

Have you tried polarizing the lights as well? You normally need both the lights and lens polarized to completely get rid of those types of reflections. And then you also might need to make multiple exposures while moving lights around to move the reflections around, and just use the parts you need.
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Rob C

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Re: Copy work: glossy painting on canvas problem
« Reply #2 on: September 12, 2015, 04:06:30 am »

Some assignments are better than others, some best passed!

;-)

Rob C

John Nollendorfs

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Re: Copy work: glossy painting on canvas problem
« Reply #3 on: September 12, 2015, 11:07:12 am »

Best avoid large light sources like light boxes when copying! Your best bet is small strobe reflectors with polarizers as far from the art as possible. Also try a shallower angle, instead of 45 degree. And of course polarizer on the lens. Test to make sure it is cross-polarzing !
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JoeKitchen

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Re: Copy work: glossy painting on canvas problem
« Reply #4 on: September 12, 2015, 11:36:25 am »

+2 for cross polarizing.  My fiancĂ©'s uses cross polarization for images with drinks and bottles all of the time and it works wonders.  No glares or reflections what so ever.  Only problem is doing so eats up 3 stops of light, so you will need 8 times more power then you normally would.

PS. Polarizing gel is expensive, enough for two soft boxes is going to cost you at least $150, and it is a special order item.  (We buy all of our gels from a theatrical supply, which at any one time has 95% of the entire Lee and Rosco catalog is stock; they never have polarizing gel in stock.)  Also, it starts to loose its property once the gel becomes creased or warped, so treat it with care.   
« Last Edit: September 12, 2015, 11:46:44 am by JoeKitchen »
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ComputerDork

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Re: Copy work: glossy painting on canvas problem
« Reply #5 on: September 12, 2015, 09:04:48 pm »

Best avoid large light sources like light boxes when copying! Your best bet is small strobe reflectors with polarizers as far from the art as possible. Also try a shallower angle, instead of 45 degree. And of course polarizer on the lens. Test to make sure it is cross-polarzing !

I'm working in a very confined area, about 10' by 10'. The shop I work for had to move into a smaller building a few years ago and space is quite tight. (They used to have a larger room for this purpose. Now they have a 10x10' corner of a larger room. At least the studio area is painted black and there's a bit of a partition.)

When I was hired they seemed to be using narrow tall soft boxes all the time, but they have umbrellas and small parabolic reflectors. I figured the sort boxes must be better for avoiding falloff and hotspots at short distances. Are parabolics going to work at distances of 6'? And if I need an angle of less than 45 degrees then the max distance I can move the lights away is going to be less than 5 feet.

So I have two major restrictions: space and this isn't a very leisurely work environment so I don't have much time to experiment with stuff. To give you some idea, this is a general purpose imaging and digital printing shop that tries to do it all, so the photographic copy work is just one small part of the main business.

I'll have to search around to see if they have any polarizing gel. (The previous guy quit before I got there and everyone else there seems rather unfamiliar with what photo accessories they have and where.)
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pfigen

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Re: Copy work: glossy painting on canvas problem
« Reply #6 on: September 13, 2015, 02:26:54 am »

I get the polarizing gels in rolls from Birns and Sawyer in L.A. You can probably any size you need from them. They cater to the film industry.
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Wayne Fox

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Re: Copy work: glossy painting on canvas problem
« Reply #7 on: September 24, 2015, 10:50:35 am »

Another technique which often offers good results if you can't polarize the light source is after setting up the two lights take two exposures with one light at a time. Stack and align the images in Photoshop and then use a blend mode to combine them. (I think difference mode is the one that works). Doesn't always work but often it works really well.
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Bart_van_der_Wolf

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Re: Copy work: glossy painting on canvas problem
« Reply #8 on: September 24, 2015, 11:05:02 am »

Another technique which often offers good results if you can't polarize the light source is after setting up the two lights take two exposures with one light at a time. Stack and align the images in Photoshop and then use a blend mode to combine them. (I think difference mode is the one that works). Doesn't always work but often it works really well.

Correct, I use 'Darken' blending mode, and expose the individual images for the Whites at the darker side of the uneven exposures.

Cheers,
Bart
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LKaven

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Re: Copy work: glossy painting on canvas problem
« Reply #9 on: October 02, 2015, 07:52:59 am »

Rosco Cinegel polarizing filter, 17x20, $50.

http://www.bhphotovideo.com/c/product/45130-REG/Rosco_101073001720_Polarizing_7300_Filter.html

You can use strobes with bowl reflectors, and an approx 8x10 sheet over each one, oriented the same direction.  Use a circular polarizer on the camera lens.  If the bowl reflectors are decent at all, they will cover half of a good sized canvas (40x60") evenly.  You need enough distance to get the spread.  It doesn't take much though. 

Equally as important is the choice of lens.  If you're using a Nikon, the 60mm/AF-S G Micro is a sharp lens with virtually zero distortion that is clean across the frame.  My other choice would be an 85mm/1.8g, which is clean, sharp, and has very little distortion.  Stop down to f/5.6 or f/8, and adjust the strobe power accordingly.

Kill the room lights to the maximum extent possible.  They will only pollute the image.

Note: It is a very good idea to do some color profiling, since the polarizer may introduce some color shift.  A QP-card is a good and inexpensive color reference.
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