Luminous Landscape Forum

Equipment & Techniques => Lighting => Topic started by: sharperstill on December 17, 2018, 04:02:03 am

Title: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: sharperstill on December 17, 2018, 04:02:03 am
Hi all,
I've been aware of the practise of cross or double polarisation in doing reproduction of artworks but have never actually put it into practise myself.

I have opportunity next year to take over the role of photographing some very very shiny artworks.
I hav ordered myself some polaroid film but in the meantime am trying to massage my expectations.
The works I'll be shooting are usually about 2m x 2m and are predominantly works in varnish and resin on an acrylic base. They are often topped with Liquid Glass.
I understand cross (or double) polarisation will enable me to virtually remove any reflections of the light sources themselves but am unable to get a handle on how much, if any, reflection will remain of what the surface itself can 'see' (including myself).

Additionally, the room is barely long enough to swing a 90mm tilt shift - it depends on how much other art is being stored in there.
There is at my disposal a 3m x 5m white-ish (stretched canvas) screen which has been used by the incumbent, who shot the works in 'available light' (diffuse room light that falls surprisingly uniformly across the area where the art is hung).
It is possible to position the screen in front of the art and use lateral shift to centre the work in the frame, although I'm keen to find a better way to tackle the issue as the space is sometimes too crowded.

Would love to hear some thoughts and experiences while I await my materials to do some tests with.

Jon
Title: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: ynp on December 17, 2018, 07:40:26 am
Hi,


I use the Polaroid sheet polarizing film on both of my 30x180 softboxes, for 2 by 2 meters artworks a smaller softbox will be adequate. I use strobes.

The cross polarization will work and it will kill virtually all reflections from the painting. I would have preferred to check how the your  lighting works for your particular artwork, it might make the painting look totally wrong /dull if you kill off the specular reflections.

Usually I like to shoot several shots with different levels of polarization, and several exposures without any cross polarization and work / mix them in post production to make the image look right. Sometimes I also add an exposure, shot with only one light at an oblique angle to expose the structure of paint on the picture.
If you decide to keep some of your specular reflections, your white canvas can be used to place it in front of your artwork and shoot through it. Itís how we shoot the Orthodox icons and metallic acrylic paints.

There is no rules, as far as I know. An available light is very nice for copying work and you can make a White Shading shot / LCC shot to make the light from the window even.
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: petermfiore on December 17, 2018, 08:09:31 am
I have used cross polarization for paintings...works to absolutely eliminate all glare. However, my paintings are quite textural. So I need to be very carful not to over use the polarization, It will flatten all color and ruin the dimension of the paint...For certain paintings, it's the only way to go.

Peter

www.peterfiore.com
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: MichaelEzra on February 11, 2019, 01:53:30 pm
There is a way to do this without polarization. I had to photograph extremely shiny acrylics and after some experimentation, arrived to this method.

Take two shots of the artwork. For the second shot:
 - rotate artwork upside down, do not move the camera and do not change the lighting
 - take care in replacing the artwork in the same plane/place where it was.

Process raw images applying lens distortion corrections. In photoshop place both shots as layers, do auto-align. Nudge the top layer to align it perfectly with the bottom.

Switch the top layer to DARKEN blend mode. Reflections will be GONE;)
Adjust opacity to taste to restore 3D look of the texture.

I was not able to achieve a similar control over reflections using polarization techniques. This method is a life saver.
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: Martin Kristiansen on February 12, 2019, 11:10:01 am
There is a way to do this without polarization. I had to photograph extremely shiny acrylics and after some experimentation, arrived to this method.

Take two shots of the artwork. For the second shot:
 - rotate artwork upside down, do not move the camera and do not change the lighting
 - take care in replacing the artwork in the same plane/place where it was.

Process raw images applying lens distortion corrections. In photoshop place both shots as layers, do auto-align. Nudge the top layer to align it perfectly with the bottom.

Switch the top layer to DARKEN blend mode. Reflections will be GONE;)
Adjust opacity to taste to restore 3D look of the texture.

I was not able to achieve a similar control over reflections using polarization techniques. This method is a life saver.

Thanks for that. Very clever.
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: petermfiore on February 13, 2019, 09:15:01 am
There is a way to do this without polarization. I had to photograph extremely shiny acrylics and after some experimentation, arrived to this method.

Take two shots of the artwork. For the second shot:
 - rotate artwork upside down, do not move the camera and do not change the lighting
 - take care in replacing the artwork in the same plane/place where it was.

Process raw images applying lens distortion corrections. In photoshop place both shots as layers, do auto-align. Nudge the top layer to align it perfectly with the bottom.

Switch the top layer to DARKEN blend mode. Reflections will be GONE;)
Adjust opacity to taste to restore 3D look of the texture.

I was not able to achieve a similar control over reflections using polarization techniques. This method is a life saver.



Hi Michael, 
Sounds like a very cool solution. Have you tried this on large paintings? By large I'm saying 6 feet and larger? Smaller paintings will me much easier to align
when inverted to photograph.

Peter
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: MichaelEzra on February 13, 2019, 09:35:40 am
Hi Peter,

Yes, I used this for a painting 9ft wide. It is impossible to align actual paintings infront of the camera to pixel-level accuracy, so that precision has to be attained otherwise.
What is important is that lens exhibits minimum distortion and is symmetrical. I used 645z and 120 A Macro lens, it worked well.
Also, I was able to do a 4-image stitch to get a higher resolution capture and then blend that with the flipped version for a spectacular reflection-free 160 MP file.
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: petermfiore on February 13, 2019, 09:53:07 am
Hi Peter,

Yes, I used this for a painting 9ft wide. It is impossible to align actual paintings infront of the camera to pixel-level accuracy, so that precision has to be attained otherwise.
What is important is that lens exhibits minimum distortion and is symmetrical. I used 645z and 120 A Macro lens, it worked well.
Also, I was able to do a 4-image stitch to get a higher resolution capture and then blend that with the flipped version for a spectacular reflection-free 160 MP file.
Michael,
I shall Give it a try...I see your located I my former home town. I do get back to New York every week to teach painting at SVA. I have been doing that now for thirty years. Thanks again for post.

Peter

Peter
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: MichaelEzra on February 13, 2019, 10:28:33 am
Hi Peter, let's get together for a NY cup of coffee then:)!
Title: Re: Exactly how magical is cross polarisation? (polarization for the Americanos)
Post by: Bart_van_der_Wolf on February 14, 2019, 08:17:20 am
There is a way to do this without polarization. I had to photograph extremely shiny acrylics and after some experimentation, arrived to this method.

Take two shots of the artwork. For the second shot:
 - rotate artwork upside down, do not move the camera and do not change the lighting
 - take care in replacing the artwork in the same plane/place where it was.

Process raw images applying lens distortion corrections. In photoshop place both shots as layers, do auto-align. Nudge the top layer to align it perfectly with the bottom.

Switch the top layer to DARKEN blend mode. Reflections will be GONE;)
Adjust opacity to taste to restore 3D look of the texture.

I was not able to achieve a similar control over reflections using polarization techniques. This method is a life saver.

+1

I use panorama stitching software (PTGUI) to do the alignment, and it can also be used to do geometrical lens distortion correction. The high quality resampling algorithms retain resolution very well, despite the resampling/warping used for distortion correction.

Cheers,
Bart