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10/03/2005 03:59:23 PM · #1
I've recently undertook a project to digitally capture paintings of my great uncle. What I have been doing is placing the painting on the ground and the camera on a tripod facing down towards the painting. I angle the painting to be parallel to the angle of the lens. I judge this by looking through the viewfinder and making a spot decision if I need more angle or not. When everything looks square I take my picture. I was wondering if anyone has done this type of work (like a museum photographer) and how it is typically done or if there are some tips that can be had from their experience. Thanks!

Fred
10/03/2005 04:04:52 PM · #2
I've photographed my art + a few other paintings. I did my research prior and the best setup I found was having the artwork on the wall (leveled) and having 2 srtobes with softboxesat 45 degree angles on either side. Ensure you have the correct w/b and try not to shoot below f8 for optimal sharpness.

I always shoot a bit wider to have the room to rotate and crop if need be.

10/03/2005 04:11:13 PM · #3
You have the basic idea, about getting the subject and film/sensor plane parallel and centered.

If you're going to shoot vertically, you might use a plumb-bob to check the centering. There's a device called a copy stand designed for this purpose -- you might see if you can rent one.

Either way, as previously mentioned, you need to have even lighting from at least two (opposite) sides, at between a 30-45 degree angle to the subject, to avoid glare. Shoot a white/gray card under the lights you're using and set a custom white balance for that particular situation, to help maintain color fidelity.
10/04/2005 12:33:22 PM · #4
If you're sure the floor is level or the painting is on the wall, perpendicular to the ground (ie not tilted because of the hanger), use a hot shoe level to insure you don't have keystoneing (trapezoidal distortion.) And if it's on the wall, be sure to keep the lens and the picture exactly parallell (e.g. use a carpenter's square or the 3-4-5 rule to insure that a line from the center of your lens to the center of the picture is at right angles to both the picture and the lens).

Message edited by author 2005-10-04 12:36:31.
10/04/2005 01:21:24 PM · #5
We used to record exhibitions for major museums in California, in San Diego, Los Angeles, and San Francisco. This was back in the 70's. The work was done with large-format cameras on 4x5 film.

The key question here is, "How many of these do you have to do?" In other words, is it worth your while to engineer a setup for repeatable results?

As others have noted in earlier posts, the most important thing is to have the sensor plane (back of the camera, roughly) parallel to the image plane. I'd add to that; the axis of the lens, projected forward, should point to the geometrical center of the painting being reproduced. By doiung these things, you remove distortion from the equation; no "keystoning" in either the vertical or horizontal direction.

The easiest way to accomplish this is to hang the art on a vertical wall and square your tripod up so that the center column is a true vertical. Ideally you'd draw a vertical line on the wall and extend that at right angles on the floor to our past where the tripod will be standing. Then you'd attach a plumb bob to your center column and be sure that the tripod was "directly in front of" the line on the wall. With a dSLR a small horizontal shift will be required if the lens is not aligned with the tripod screw, which they typically are not. If the lens were offset by 3/4 of an inch to the left, then you'd want to plumb to a point 3/4 of an inch to the right of the line on the floor.

Then you'd set the camera up at eye level and measure the height of the optical axis of the lens above the floor. You'd measure up along the line on the wall and mark that height ohnt he wall, and use a level to draw a true horizontal on the wall passing through that point and extending far enough on each side to be wider than the largest painting you will photograph. You'd use a high-quality zoom lens (this would be easiest, for photographing art of wildly varying sizes) and set up so the tripod were at a position to cover the largest painting you're gonna shoot at the wider end of the zoom. For smaller painings, you'd zoom in.

If you need to shoot vertical and horizontal paintings both, it's best to do them as two separate groups, because rotating the tripod head to portrait orientation will move the offset of the lens sufficiently to one side to require repositioning the tripod, plumbing it to a different offset from the line.

Anyway, using this setup you can position paintings on the wall so they are centered on the intersection that defines the projected optical center of the lens, and you never need to adjust the tripod settings, just the zoom. It's also desirable to have a "quick change" system for hanging paintings on the wall. An acceptable approach is to use a true "artist's easel" (the kind with two parallel vertical bars and adjustable "tray" to hold the painting and clamp to snug it in place) as long as the easel can be set up to a true vertical. A better approach would be to replicate the easel directly on the wall, but that's a lot of work.

When photographing exhibitions in museums, we had a system for measuring the degree-off-vertical a painting was hanging at (some leaned out from the wall a tad) and transfering that angular deviation to the fore/aft tilt on the tripod, but this gets complicated.

Your next issue is lighting. It's generally better to shoot art with floodlights than with strobes, because you can more easily see the results you're getting. Your standard setup would be to draw on the floor two lines coming out at 45-degree andles from where the tripod-axis line intersects the wall. You'd position 4 floodlights, one high and one low on each axis, measuring the same distance out from the wall along each axis. You'd then use an incident light meter to measure the light falling at the center and on each corner of the largest painting you had to shoot, and angle your lights so the measured illumination was even across the entire surface of the painting. If it's even on the largest painting, it will be even on any smaller painting subsequently hung in that space.

You now have a geometrically consistent setup and a constant light level across the entire working space. All you have to do is move art on and off the wall, shooting each piece as you go. Use a cable release, and ideally mirror lockup as well. You should also photograph a "color target" (available at camera stores and online) under your controlled setup. You will process the color target image to eliminate any color cast and add slight exposure corrections needed, and then set up an action you can use to batch process all the other images to correct color balance and exposure.

That, in a nutshell, is a bare-bones "professional" approach to copying largish art that's too big to fit within the confines of a copy stand.

Robt.
10/04/2005 01:57:30 PM · #6
If you have a tripod with a reversing column and the piece you are photographing can fit underneath your setup here's what I do. First pick a focal length that will work within your setup limits by hand-holding the camera above the piece; note roughly the elevation and adjust your inverted column to suit. Next get yourself a line level and allign the back of your camera about two axis-left to right and front to back; on the 300D I place the level on the LCD screen (I'm making the assumption that it is parallel to the CMOS - I think that for these purposes it's parallel enough - I'm also assuming that my levels are accurate). You may find that you need to reverse your quick release plate to get your camera levelled depending on your setup. Level your piece in the same manner with a larger level (be careful that no sharp edges scratch the surface) and orient the piece to suit. Set your camera at f8 or close and let the camera determine the shutter speed. If you have reflections due to acyrlic or oil paints a polarizer may help. A room with lots of natural light works best but you may find that you have to block or diffuse some of the light to make it even across the piece. Keep your ISO low and don't be alarmed if the camera sets a shutter speed in seconds range.
02/13/2011 06:14:27 PM · #7
The previous posts refer to using a telephoto lens. I would naturally think that using a 35mm on a camera with a 1.5 crop factor thus rendering an approximate 50mm, would be the best to eliminate barrel or pincushion distortion. However, in actuality, I have to be at about 20mm (effectively 30 including crop factor) to get the sides of the painting to be straight. More than that, they swoop in in the middle, less that that...even 18mm, the lines bulge. Can anyone explain to me why this is the case when we all know that 50mm is "normal"? Thanks!
02/13/2011 07:44:46 PM · #8
I've begun doing a similar project as a small side job for a guy I work with. He contracts oil paintings to use for covers on old books that he republishes (Bruin Books). He gives me the paintings, and I provide him with a digital image of that painting to use in his cover designs. It was just going to be a couple paintings at first, but he was thrilled with the results and the work keeps coming. The process is starting to go much more smoothly for me, but there's still not so much demand that I need to create a contraption, nor do I have the space.

I use mostly natural dawn or dusk sunlight. I'm lucky enough to have two huge windows in my apartment; one faces East, the other West. I just tape the painting to the wall with blue painters' tape and shoot it with my 50mm on a tripod. Depending on what time of the day it is or how cloudy it is sometimes I'll pop a flash off the ceiling/walls. Whatever it takes to lessen the little thread shadows from angled light. I don't bother perfectly leveling or straightening the painting physically, I just line it up in the viewfinder by tilting the camera. After that I process it on the computer with usually just slight cropping, contrast, and levels adjustments. I've had to use Lens Correction on a couple, but just very slightly.

At full size the thread shadowing/highlighting still needs work. For our purpose though it's fine, since the image is downsized and put on a paperback book. He's completely happy with the results, but I'm still secretly working on improving it even if no one will ever see it but me. Here's a 100% crop of the one I completed for him last weekend.

Copyrighted_Image_Reuse_Prohibited_935563.jpg

Message edited by author 2011-02-13 19:53:06.
02/13/2011 07:52:58 PM · #9
Originally posted by tjandjwsmith:

The previous posts refer to using a telephoto lens. I would naturally think that using a 35mm on a camera with a 1.5 crop factor thus rendering an approximate 50mm, would be the best to eliminate barrel or pincushion distortion. However, in actuality, I have to be at about 20mm (effectively 30 including crop factor) to get the sides of the painting to be straight. More than that, they swoop in in the middle, less that that...even 18mm, the lines bulge. Can anyone explain to me why this is the case when we all know that 50mm is "normal"? Thanks!


This has nothing to do with "normal", it's a function of the quality of the optics of the given lens. If you can get far enough back to use one, your best flat-copy lens is actually a macro, they are designed for this kind of work and should be distortion free.

However, pincushion and barrel distortion can easily be corrected in post: you can right a macro for it in photoshop. For a given lens, at a given focal length, the distortion will be constant. Better, of course, not to have it in the first place.

R.
02/13/2011 08:11:43 PM · #10
Ive gotten damn good results with a prime and bounce flash. Minor adjustments and i saw what I expected.
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