Monday, December 20, 2010

About photographing oil paintings


I thought I’d share with you how I photograph my oil paintings. Photographing drawings, pastels or watercolors is pretty easy because the surface is flat and diffuse. Taking good photos of oil paintings however is quite challenging, because of the surface texture and glossiness. It seems no matter where the light source(s) are put, there are a lot of bright specular/direct reflections from the canvas which alter the perceived value of the paint. A dark area in a painting appears too bright because of the reflections.

I have tried different approaches (haven’t found the perfect solution yet though), but I’ve narrowed it down to two setups which work for me:

  1. Tilted camera approach
  2. Using cross polarization

 I usually try #1 first, but if there are still too many direct reflections, I’ll use approach #2.


First some general things that are common to both techniques:
I use a single lens reflex camera with a medium telephoto (around 100mm or longer) lens. If the camera is too close to the painting, it will see more direct reflections than if it’s farther away. Also, a wide angle lens typically causes barrel distortion, so a longer lens is a better choice. 

I shoot RAW, so it’s easy to adjust exposure and white balance later.  The camera is on full manual mode, so I can control the aperture and shutter speed. The ISO is kept low (100-200) to keep noise down.

I use a tripod for the camera and a light stand for the external flash unit (strobe). I generally use only one strobe for lighting a small painting and two strobes if it’s a large painting. The strobes are triggered with cheap wireless flash triggers. The flash is placed as far as possible from the painting to ensure even illumination. The angle to the painting is around 30-40°. By keeping the light source angle so small the brush strokes can be seen better because side lighting reveals texture.


1. Tilted camera approach

Normally when photographing artwork, it’s advised to keep the camera centered and parallel to the painting. In this setup, however, the painting is shot from a higher angle, so the camera sees less reflections of the canvas texture and brush strokes. The lens aperture is kept small, around f11 in order to keep the whole painting in focus. See image below.




After the image is taken, there’s going to be vertical perspective distortion. The farther the camera is from the painting, the less perspective distortion there is to correct. I take care of the distortion with Photoshop Elements’ vertical perspective correction tool. Now the image is rectangular, but too short vertically. That’s corrected with selecting the area of the painting and stretching it vertically using Free transform tool until the correct aspect ratio is reached. All this pixel stretching degrades image quality, but it’s not an issue though when posting small images to a blog.

I would much rather use a tilt-shift lens (e.g. Canon TS-E 90mm), but those are pricey. It would allow keeping the camera parallel but off-axis to the painting and no perspective tweaking in post would be necessary.

Tilted camera setup

Pros:   
  • Most reflections are gone
  • Colors look natural.

Cons:     
  • Not possible to remove all reflections.
  • The need to correct perspective and aspect ratio in Photoshop. Image quality drops.


2. Cross polarization

In cross polarization the light from the strobe is polarized by placing a piece of linear polarizing sheet in front of it. A circular polarizer is placed in front of the camera lens. By rotating that filter it is possible to control the amount of direct reflections. I prefer partial polarizing, since the texture looks more natural. I keep the lens aperture around f5.6, which is small enough to get a sharp image but large enough for the flash to be able to produce enough light through the polarizers, which eat light quite much.


Cross polarization setup

Pros:
  • The amount of reflections can be controlled and completely removed if desired.
Cons: 
  • The colors are too saturated and contrast is increased: the dark areas go easily too dark or black, especially if the painting surface is matte.
  • There’s a lot of tweaking in Photoshop when trying to match the colors to the painting.

This image shows the differences between the results of tilted camera and cross polarization techniques:




12 comments:

Jose Romero said...

Hi Arto,
I found very useful a pdf at the Auckland Art Gallery website describing how they copy artwork - check their photoshop technique to minimising surface reflection with superimposed images - it works great!

http://www.aucklandartgallery.com/the-collection/image-capture-process

Erik said...

Very useful article Arto, the first time I've seen a comparison between the cross polarization and the tilted camera setup which I've used until now. Where did you get the polarizing gels for the light? I've been looking for them in the past but couldn't find it then.

Jim Serrett said...

Very interesting information.
I will have to try the tilt.
Thanks for sharing your knowledge.
Happy Holidays

Arto Isotalo said...

Jose:
Thanks for the link, I hadn't seen that before. I have to try that sometime.

Erik:
Thanks! I bought the polarizing sheet from a local small company specializing in optical components. It costs 7.5€/dm².

Jim:
Thanks! I'm happy if I can help fellow artists.

Erik said...

Thanks Arto, I've found a local company which has these gels and ordered one. How do you adjust the polarizer on the camera if you're not using a continuous light source? Do you take a few testshots to get the correct amount of polarization?

Arto Isotalo said...

There's a modeling flash mode on my Speedlite 430 EX II, which gives almost continuous looking bursts of light. I look through the viewfinder while rotating the filter.

Erik said...

Do you have the flash on the camera for that? I have a 580exII, I believe it can only do that on camera (may have to consult the manual on that). Otherwise I'll have to get one of those extension cords for the flash.

Arto Isotalo said...

No, I press the Pilot button for modeling light. First you need to set custom function C.Fn-02 value to 1. Then it should work.

Jesus Estevez said...

Thanks for the information, I was looking for this type of information,
I wish you a prosperous new year, ah I love the two last painting that you post

Arto Isotalo said...

Thanks! I hope you found some useful info. Have a great 2011!

Tracey Frugoli said...

Arto, thanks for the info, Can you tell me how high you have the speedlite in relation to the painting? It looks as if you have to have the painting and camera low. How do you shoot so low? Do you have to lay down?

Arto Isotalo said...

Hi Tracey,

I have the speedlite almost touching the ceiling and the painting is very low. The reason for this is inverse square law: by placing the light source far away from the painting, the upper part of the painting is just somewhat brighter than the lower part (we aim for even illumination). If the light source would be close to the painting, the lower part would be much darker due to rapid light fall off.

About the camera position: I assume you mean the cross-polarization setup. You can use a tripod or lay down.

I hope this helps!