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Author Topic: art repro: minimum o.k. distance between painting & lights for even coverage?  (Read 2329 times)
markwilliam
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« on: August 08, 2013, 02:08:49 AM »
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Scenario: one painting hanging on a wall, one 10x36-inch stripbox at 45 degrees to the left of the painting's left edge, one 10x36-inch stripbox at 45 degrees to the right of the painting's right edge.

I know this is matter of continuum, and that the answer is a range, not a single number, but, to put the question differently:

If x = (painting length) and y = (distance between stripbox & painting edge,) then y/x ≦ ?

(What is the maximum acceptable value of y/x?)

Or: What is the maximum acceptable ratio of (painting length) to (distance between a stripbox and the painting's nearest edge) in order to cover the painting evenly?

I notice that Sheldan Collins, in his book "How to Photograph Works of Art," seems to imply a ratio of 3 to 8 as just barely acceptable. But I'm not sure this is what he means, since it's not his primary point in that sentence.

Another way of putting the question: what multiple of a painting's width should be the distance from painting edge to closest light? (3 to 8 ratio = 2.67 multiple, but of course all we need is a ballpark figure.)

In my experience, a ratio of 3 to 8 still requires significant compensation in post; a ratio of 1 to 10 requires hardly any. I sometimes have to settle for a ratio of approximately 2 to 1 if the painting takes up half the length of the wall in an on-location shoot, of course. What does your experience tell you?

Also: if z = (painting height) and y = (distance bet. stripbox & ptg. edge,) then y/z ≦ ?

Thanks!
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Ellis Vener
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« Reply #1 on: August 08, 2013, 01:04:52 PM »
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Why strip lights?

The further back you can get the lights the more even the fall off; that's just simple physics. You can help yourself by aiming the left side light at the right edge of the painting and vice-versa.
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Ellis Vener
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Creating photographs for advertising, corporate and industrial clients since 1984.
markwilliam
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« Reply #2 on: August 08, 2013, 06:45:28 PM »
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Why strip lights?
Hi Ellis. Thank you for your help on this. I don't always use stripboxes, but when I do, it's because I like the way they seem to reduce hot spots and spill--and to spread the light vertically but not horizontally. I do pretty much all of my just-for-money photo work on location in art galleries and in artist's studios, so the walls are usually white and any light spilling out away from the paintings gets bounced around the room unless I work hard to control it. Also, to be honest, one reason I use stripboxes is because some of the people who seem to do this kind of work best use them and recommend them. I'm not at all arguing that this is how one should proceed--just confessing my reasons. But I'd like to learn why you advise against using them, if you do. Not in order to debate it, but because I really would like to keep learning from you and others. (I don't mean to imply that you seek a debate, of course!)
The further back you can get the lights the more even the fall off; that's just simple physics.
Yes, of course. I think my question takes that as its starting point.
You can help yourself by aiming the left side light at the right edge of the painting and vice-versa.
Yes, I do this. Thanks again.

Humbly,

Mark
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BartvanderWolf
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« Reply #3 on: August 09, 2013, 05:10:46 AM »
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I don't always use stripboxes, but when I do, it's because I like the way they seem to reduce hot spots and spill--and to spread the light vertically but not horizontally.

Hi Mark,

But they do create more specular highlight reflections of of glossy uneven surfaces! They also have more light fall-off with distance, so you may need to use a larger distance to compensate for that, or get less oblique which again increase the reflection risk.

As long as your inside edge of a larger e.g. soft box is not too close to the optical axis, it won't make any difference as far as reflection risk is concerned, but they will create less specular reflections and less light fall-off. Of course with the use of polarizing filters on lights and camera, the reflection issues become almost trivial.

Depending on the allowable shooting distances, longer means less light fall-off, and a longer focal length allows to bring in the lights closer to the optical axis, it may be useful to test on a uniform surface (a back wall, or a blank canvas of the appropriate size) with light from one side, and see how much light fall-off that creates.

Next, you may test by alternating left and right illumination of an artwork, and compare in Photoshop (e.g. in darker blending mode) if blending two separate exposures (exposed for the darker/further end) will get rid of the reflections.

Cheers,
Bart
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Ellis Vener
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« Reply #4 on: August 09, 2013, 11:35:20 AM »
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Hi Mark,

"I do pretty much all of my just-for-money photo work on location in art galleries and in artist's studios, so the walls are usually white and any light spilling out away from the paintings gets bounced around the room unless I work hard to control it. "

I think grids, like those from Lighttools = http://www.lighttools.com/ - on standard light banks  might work better for you . They will limit the spill and even  out your horizontal illumination distribution. However they are not cheep. If yo uuse Chimera they make barndoors  that fit their   Lightbanks http://www.chimeralighting.com/Products/Light-Modifiers/Barn-Doors

"lso, to be honest, one reason I use stripboxes is because some of the people who seem to do this kind of work best use them and recommend them."

Although it seems counter-intuitive to me I will try that approach. Thank you for recommending it.
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Ellis Vener
http://www.ellisvener.com
Creating photographs for advertising, corporate and industrial clients since 1984.
markwilliam
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« Reply #5 on: August 10, 2013, 01:19:09 AM »
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I think grids, like those from Lighttools = http://www.lighttools.com/ - on standard light banks  might work better for you . They will limit the spill and even  out your horizontal illumination distribution. However they are not cheep. If yo uuse Chimera they make barndoors  that fit their   Lightbanks http://www.chimeralighting.com/Products/Light-Modifiers/Barn-Doors

Thank you for this tip. I think that grids and barn doors on my stripboxes might make them even better suited for the white rooms I so often shoot in. As for using them on standard light banks (shaped more like squares and less like strips), this approach is counter-intuitive for me (you can read why, below) but I will experiment with it if I can afford to buy or borrow banks and grids and barn doors of that kind.

Although it seems counter-intuitive to me I will try that approach. Thank you for recommending it.

You're welcome; if this turns out to work for you, then the credit should go not to me but to others who have recommended it to me (like someone I quote below, and whose explanation might make this approach seem less counter-intuitive).
I have found that a member of another forum is especially helpful and convincing on this topic (he documents large and small flat art all day long for a museum in a high-end studio--at the museum--designed and equipped specifically for this task):

http://www.dpreview.com/forums/post/42063556

kb2zuz
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Lighting-Strip Boxes for 2D work
In reply to pilgrimage6
17, Jul 19, 2012
"One other thing that came up in the conversation was the use of softboxes. Using 2meter x 2 meter softboxes can be problematic when reproducing paintings. I prefer to use strip softboxes. We have 12" x 50" (30.5 x 127cm) Westcott softboxes. The reason I like using the strips is ideally when lighting paintings and other 2D works, you want the lights at 45 degrees. The problem with having a very wide softbox (like a 2m x 2m) the problem is the center of the soft box may be at 45 degrees, but depending on how close they are to the painting, the one side of the soft box might be [at] 30 and the other side might be [at] 60. If you had a smaller work of art and got the softboxes very close, the one edge might be [at] 90 and the other might be [at] 180. The reason you want 45 degrees is to reduce the amount of specular highlights (as the saying goes "angle in = angle out"). As the angle gets closer to 90 degrees (directly where the camera is) the amount of reflection coming back is greatly increased so you get a lot more specular highlights. Now if your light source is closer to 180 degree you end up with the problem that you get more raking light and the edges will be noticeably brighter than the center."

"Ok[:] so you want a small light right at 45 degrees... well[,] not quite[:] a pin-point light will cause harsh shadows on any texture or impasto, [so] you want a broader source. Also if you have 2 pin point lights right level with the camera at 45 degrees[, then] the top and bottom of the object will be darker than the center. So if we use vertical strips it makes the light a little softer and keeps the illumination more even from top to bottom, but it doesn't create the extra specular highlights that a square light source would cause."

"Also it's possible to get rolls of 12" or 18" polarizing material which you can use to make frames to go infront of the strip boxes. This will help if you need to cross polarize.-- ~K"

I (Mark) quote K here not only because he can explain it better than I can but also because he's one of the people I mention above who seem to be especially good at doing this kind of work, and who knows better than I do what he's talking about. Though I have found so far that his advice on strip boxes for this application seems to hold true.
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BobDavid
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« Reply #6 on: August 10, 2013, 01:26:12 PM »
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Here is a large canvas that I copied. http://www.topdogimaging.net/about/fine-art-reproduction.html The reproduction is true, very true, to the original. I used two Elinchrom RX1200 heads with wide angle modifiers and polarizing gels, and placed a polarizing filter over the camera lens. The lights were angled at about 45 degrees from the artwork. I took two photos and stitched them together. My camera, monitor, and ICC profiles were carefully calibrated. I am not a fan of soft boxes for repro work. If you know what you are doing and employ a little science and art, it's possible to make exquisite reproductions of flat art. There are workarounds for photographing paintings with metal-based paints and gold leaf. There are also workarounds for photographing impasto and other high-relief media without shadows. I think a lot of people under estimate the learning curve involved with capturing and printing paintings.

Another solution is to source out the digital capture to a company that has a Cruse scanner or similar piece of equipment. A good scan, not color-corrected, shouldn't cost more than $45-$75.

Incidentally, I now only service one corporate client and consult on occasion. I did not post the link to my website to sell repro services. I cannot overstate enough that the learning curve is steep with regards to operating a profitable and sustainable fine art repro business. My advice to anyone out there that is thinking about going down this road is to stay away from servicing amateur artists. Savvy professional artists and corporate clientele will pay your overhead and provide a realistic profit margin. In my experience, most amateur artists are terrible clients. They complain about cost and tend not to understand that the color gamut of a painting does not always fit within the parameters of pigment inks, canvases, and papers. The tricky part of making a decent giclee is being able to work in Profoto and LAB while using a top-quality sRGB monitor. That is where the art, science, and learning curve come into play.  
« Last Edit: August 10, 2013, 01:45:34 PM by BobDavid » Logged
markwilliam
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« Reply #7 on: August 13, 2013, 08:08:51 AM »
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Thank you for your thoughts BobDavid. I appreciate your expertise and input. --Mark
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