Thanks for the sanity check, scr4. I see now I forgot to factor in the 1/125th second exposure time.
But I’m getting tired of the anti-factual bias in this discussion.
Somebody else please take over.
OK, I’m going to depart from the “hard science” focus and mention a few “practical” reasons that flash photography isn’t a good idea, or even necessary, in museums.
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Most of the things displayed in museums don’t move by themselves, so, if the ambient light is low, a photographer can take a timed-exposure to get the shot without a flash. That is, assuming that the museum wants to let you take any photograph… some museums don’t allow sketching. (Hey, perhaps the “scientific” answer is really to just make the ordinary snapshot schmoes shut up and put their disposable cameras away until they get to Disneyland…)
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Depending on your subject, a flash will ruin your photograph. This doesn’t seem to stop people from taking photos of the Hope Diamond or other exhibits behind glass (which will give you a nice picture of your flash). This doesn’t keep people from taking flash photographs of fireworks, either.
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Highly varnished canvases, and watercolors, prints, and photographs which are framed under glass all provide reflective surfaces that will give you another really good picture of your flash.
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It’s very annoying for the rest of the museum patrons to have flashes going off left, right, behind, and in front of us.
Enjoyable though the above calculations are, I am sure they miss the point completely. I have seen similar restrictions on photography in many places, not just art galleries, and in places where it was hard to see extra light as a problem.
What you need to do is consider the bureaucratic mind. Forbidding photography is a good idea if you are making a major income out of selling postcards/photographs, but it does require some investment in notices/guards and possibly somewhere to check cameras, and may put off tourists.
You might therefore be prepared to allow amateur photographs – they will probably want a postcard anyway, or spend money in the snack bar – but professional high-quality studies are a different matter; you will want to charge a lot for those, and sign a copyright/marketing rights agreement. Now, how do you differentiate?
These rules are generally about 10 years old, and 10 years ago any high-quality photograph involved a lighting set-up. Voila! Just ban photo-floods (and flash) and you have the rule you need to stop professionals. They might sneak a picture, but you will be well placed in any court case which may follow. Gluteus Maximus has already pointed out that objects are often positioned to make it hard to take a professional photograph – for the same reason.
Of course, these rules were established long before the advent of small pop cameras with built-in flashguns, and I’ve been to places where no-one minds you taking pictures with these, but will jump on you if you try to set up a tripod and flash. Now there’s another rule I’ve seen – No Tripods – again obviously aimed at the professional photographer.
Cheap little cameras have had flashes for a long time. The first Kodak Brownie with a flash was 1940. Then came cubes and flip flashes. Electronic flashes came out in the late '70s, and they quickly took over.
So you have about 60 years with non-professional flash cameras.
If you are a pro, not only do you want a tripod, but if you aren’t using natural light (or even if you are), you’ll want reflectors and and least a couple of flashes. If you want a straight-on shot of a painting, you’ll need a either the camera high enough or the painting low enough so that the camera is level and shooting at the middle of the painting. This won’t happen without cooperation of the museum. You can’t setup the shot in 10 seconds.
I’m not a pro, but I have a studio tripod that would do the trick - max height is about 8 feet. It’s a bear to carry, and if you extended it fully, the legs would stick out about 4 feet in each direction.
If you just want a nice picture to take home, a postcard is probably better, but if you insist on taking the picture yourself, use high speed film, turn off the flash, and, if you can, take in a monopod to help steady the camera. Most places don’t care about monopods - think of them as a walking stick or cane that happens to have a tripod screw-mount on the top. If not, there are other tricks to steady a camera (place on ledge and use self-timer, lean against a wall, sit down, step on strap from bottom of camera to floor, wrap your left arm around your right and hold your right shoulder, breathe out, etc).
They were out by the late 50’s to my certain knowledge.
However, they required a lead-acid battery hip-pack about twice the size of a notebook computer, so they weren’t exactly in the consumer-snap market.
There was also Polaroid’s “Wink-light”. I have no idea what that tech. was.
You cut out the first sentence in the paragraph: Cheap little cameras. Electronic flashes hit the instamatic crowd in the late '70s.
Not a flash. A regular 12 volt light bulb that gets a momentary shot of 48V. Required 3000 (yes, three thousand) ASA film.
Permit me to simplify.
A fair number of (crude) consumer cameras have a fixed aperture and shutter speed. As they can work indoors (with a flash) and outdoors, we can assume that the flash is calibrated to put out an amount of light roughly comparable to daylight. Furthermore, the color temperature will be comparable to daylight as well, since the same film will be used indoors or out. (Yes, I know that indoor film exists, but it typically isn’t used with flashes. And there are also parts of the spectrum that film doesn’t react to that could be considered. Sue me.)
Now then. Assume the flash goes off for 1/2000 of a second. That’s actually a fairly long-duration flash, but what the heck. I’ll assume 1 flash every 10 seconds, which is also a lot. (We’ll ignore icons such as the Mona Lisa, whose venues would probably resemble a discotheque if flash photography were permitted).
That works out to 2880 flashes for an 8 hour day for a total of 1.44 seconds of artificial daylight per day.
Let’s round up again to 1 and 1/2 seconds, in order to err on the side of overestimation.
If we allow 5 holidays during the year, that works out to 540 seconds=9 minutes per year of direct sunlight on canvas or whatever.
Over 500 years, that would be about 3 days of direct sunlight.
This seems small -heck 30 days over 500 years seems small- but I’m not a conservator.
I must add though that I like the prohibition, for the reasons discussed by gluteus maximus and Mogadon.
Permit me to simplify.
A fair number of (crude) consumer cameras have a fixed aperture and shutter speed. As they can work indoors (with a flash) and outdoors, we can assume that the flash is calibrated to put out an amount of light roughly comparable to daylight. Furthermore, the color temperature will be comparable to daylight as well, since the same film will be used indoors or out. (Yes, I know that indoor film exists, but it typically isn’t used with flashes. And there are also parts of the spectrum that film doesn’t react to that could be considered. Sue me.)
Now then. Assume the flash goes off for 1/2000 of a second. That’s actually a fairly long-duration flash, but what the heck. I’ll assume 1 flash every 10 seconds, which is also a lot. (We’ll ignore icons such as the Mona Lisa, whose venues would probably resemble a discotheque if flash photography were permitted).
That works out to 2880 flashes for an 8 hour day for a total of 1.44 seconds of artificial daylight per day.
Let’s round up again to 1 and 1/2 seconds, in order to err on the side of overestimation.
If we allow 5 holidays during the year, that works out to 540 seconds=9 minutes per year of direct sunlight on canvas or whatever.
Over 500 years, that would be about 3 days of direct sunlight.
This seems small -heck 30 days over 500 years seems small- but I’m not a conservator.
I must add though that I like the prohibition, for the reasons discussed by gluteus maximus and Mogadon.
Or flash photographs of Barry Bonds hitting a home run, from 300 feet away in the stands.
I realize that grg88 has bowed out of this thread, but his point relates to my previous post, so I thought that I’d quote him anyway.
With ASA 125 film, you would be lucky to be able to take a picture indoors at 1/15th of a second at f/2.
1/15 is 8x that of 1/125th
f/2 lets in 2^6= 64 times the amount of light as f16.
64x8=512, the approximate amount by which indoors is dimmer than outdoors. 1/512=.002, which is an order of magnitude less than 4%.*
Anyway, multiply .002 times the number of seconds in an 8 hour day gives the “daylight equivalent” of typical indoor lighting - I get about 1 minute. This is greater that 1.5 seconds (see my previous post), but by only 1 order of magnitude or so.
Also, I’ve assumed that flash color temperature is equivalent to daylight. And I’ve ignored the fact that museum (or nonmuseum) glass will filter out additional UV/IR rays: my “1 minute” figure is probably an overestimate.
Finally, light intensity varies with the square of the distance: in practice, the bulk of the damage suffered might be done by (ignorant) amateurs taking flash pictures from less than 3 feet or so.
So in case it wasn’t clear, I’m backing away from yesterday’s conclusions: the marginal effects of amateur flash photography may be small but non-trivial.
- Admittedly my numbers feel excessively diminutive. Corrections are welcome. I confess that I’m at a loss to explain the Cornell figures.
To point out how rediculous this is:
Most point-and-shoot cameras have a flash with a guide number of around 30, a maximum aperature of somewhere around f4 (wide angle) to f11 (fully zoomed in), and are typically loaded with ISO 100 to ISO 800 film.
Plug these numbers into the formula (guide number * sqrt(ISO speed / 100) / aperature) and you get the following ranges:
ISO 100 film: wide angle 7.5 feet, telephoto 3 feet
ISO 800 film: wide angle 21 feet, telephoto 7.5 feet
In other words, assuming you are using the telephoto setting on your lens (hey, you’re aiming at something 300 feet away), the flash will light up the head of the person in front of you, or maybe a couple of rows down.
It is possible to hit something with a flash 300 feet away. One of the flashes I have has a guide number of 180 (at 105mm setting). Combine that with an f2.8 telephoto lens and 3200 speed film (or 800 or 1600 speed that is pushed) and you can light up a subject 360 feet away. Mind you this combination is bulky and very expensive ($400 flash, $700 - $6000 lens, $300 - $2000 body), you’ll need to feed it 4 AA batteries with every roll, and when you push film or use very high speed film you should get it professionally processed (i.e. don’t take it to Walmart).
Why would Barry Bonds hit a homerun in a museum?
Another superb example of hopeless flash photography was when Nixon was flying back from China. They got a big crowd at the airport, kept about 400 feet back in bleachers.
When Nixon came down the steps of the plane, it seemed EVERYBODY in the stands took a flash photo of the event. I suppose if 1000 of them did it at the same instant it might have worked. But that probably was’nt their plan.
It may be that many of the folks taking flash pictures of things like Nixon disembarking or Barry slugging didn’t mean to use the flash. On many consumer cameras, the default flash setting is “automatic”, meaning that the camera decides for itself whether to use the flash, based on the ambient light level. The camera doesn’t know that the thing you’re interested in is behind glass or a hundred meters away; it just knows that it’s kinda dim out. In order to turn the flash off, you have to hit a little tiny button that you can just barely press with your thumbnail, twice (once to switch to “Flash on”, and again to switch to “Flash off”). That’s a good bit of trouble, especially when you’re trying to get a picture of something transient like a home run, and you’re not sure whether it’s even dim enough to need to in the first place.
Another factor is that on some snapshot cameras, turning the flash on will also automatically give you a larger aperature (the reasoning being that if it’s dark enough to want the flash, it’s also dark enough to want large aperature). In that case, turning the flash on will help even if your subject is far away.
It’s the ones who use a flash to capture movie screens that drive me to dispair.
Yeah, it’s so tricky to time the flash just right. 
Far worse, surely, are the people who use a flash from the inside of a tour bus. I mean, what happens when they get home and get their photos processed? “Here’s one of the Eiffel Tower, you can just see it through the glare here … I think this one is supposed to be the Arc de Triomphe…” Don’t they ever learn?
Let me start off saying that I agree with those saying the physical effect of the flash is much smaller than almost any amount of solar light, and that the reasoning is more social than physical. (Flashes are annoying, the rules probably pre-exist air conditioning and the masses attending art museums.) However, I do seem to recall going to a museum that displayed some textile piece that had been subjected to flash photography. The physical deterioration was obvious.
Nonetheless, it is the UV that is the greater threat. grg88 and Measure for Measure just assume that the color balancing applied to the filter also filters out the uv. A, ahem, clear counter example is just any untreated window. It does filter uv, and reflect IR, fairly effectively, but its transperancy to visible light is a window’s raison d’tre. Without knowledge to the contrary, I think a safer approximation is that the uv is not filtered at all. It is probably also safe to assume that very little solar uv hits any painting. As stated above, museums go to great length to assure that uv is filtered. Therefore, flash photography might be a significant source of uv.
Picasso he likes to swing for Da Vincis.
(Because he like to swing for the fences. Get it?) <sigh>
RR
Tortured, RiverRunner, but cute.