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Photo Forum / Digital Photography / Digital Photo / November 2007Taking photos of strobe
Hi, I'm wondering if anyone may be able to help me. I am wanting to photograph the airflow over a turbine blade being tested in a wind tunnel, via the attachment of small cotton threads to its surface. The only way to isolate the blade is to use a stroboscope and I would like to then take a photo of this, so I have a record of the direction the cotton threads are being blown in. I tried today without the strobe, and just using my flash gun. It wasn't too bad, but a little blurred still from the slow shutter speed. I've tried also using the bulb setting and letting the strobe pulse a few times hoping there would be enough light, but this wasn't very successful either. If anyway has ever photographed this sort of thing and has some clues on what I should do, I would be very grateful. Thanks in advance. > Hi, > [quoted text clipped - 13 lines] > If anyway has ever photographed this sort of thing and has some clues > on what I should do, I would be very grateful. Which camera, and which flash gun? > > Hi, > [quoted text clipped - 15 lines] > > Which camera, and which flash gun? Hi, I'm using a Nikon D70 with an SB600 flash gun. > I'm using a Nikon D70 with an SB600 flash gun. If I remember correctly, the D70 can sync up to 1/500" speeds. Put your camera into Manual mode (M), push the speed to 1/500" and open the aperture as much as needed. Keep your ISO sensitivity as low as possible. In order to make the flash the exclusive light source, you must record as less of the ambient lights are possible (here, the high shutter speed of the camera means that the ambient light is less recorded into the final image). You may want to use an grey ND 'neutral density' filter, in order to lower even more the ambient light. If you cannot close all ambient light sources, you will have to raise the shutter speed and put your flash in High-Speed flash mode (this usually means lower range, though). Put your SB600 into Manual mode and select, say, 1/4 of power with an aperture of 5.6 (don't know how large is your engine, but let's start with these numbers, raise the power progressively up to 1/1 if the reach isn't enough). Hope this will give you 'good enough' photos. Please tell us back if the results were good (upload some samples to Imageshack or another site, if you wish, for some more ideas). Cheers, N.F. > > I'm using a Nikon D70 with an SB600 flash gun. > > If I remember correctly, the D70 can sync up to 1/500" speeds. it can sync at any speed with non-nikon flashes. nikon flashes (including the sb-600) will limit it to 1/500, but that is trivially overidden. >Hi, > [quoted text clipped - 15 lines] > >Thanks in advance. You need to extinguish all ambient light and use the light of the flash alone. Also, if using automatic flash that might be depending on thyristor circuitry, it will help to be as close to the subject as possible. The closer you are, the less flash that is needed, and the shorter will be the duration of that flash. Flash output levels are controlled by its duration rather than luminosity (in most instances, because that is easier to control.) If you don't extinguish all ambient light and depend on flash alone, then the very slow speed of any dSLR's focal-plane shutter will also use the ambient light to expose those threads. Causing blurring, as you have seen. If you have access to a high-quality P&S camera instead, whose flash-sync isn't limited to last-century's focal-plane speeds, that will also help. One of my P&S cameras, for example, allows use of its flash up to its highest shutter speed of 1/2400 (some others go higher than this), in perfect sync with full-frame illumination. If you use a P&S that can do this then you don't need to find ways to extinguish the ambient lights, which in some/many situations is impossible. >> Hi, >> [quoted text clipped - 25 lines] > If you use a P&S that can do this then you don't need to find ways to extinguish > the ambient lights, which in some/many situations is impossible. Here's another piece of advice. Ignore trolls like this gentleman, and google the term "high-speed flash sync." Most DSLR/flash combinations will give you the ability to use flash at any shutter speed now, and the information in the paragraph above is simply false. >>> Hi, >>> [quoted text clipped - 30 lines] >will give you the ability to use flash at any shutter speed now, and the >information in the paragraph above is simply false. Please feel free to list all these "MOST DSLR/flash combinations" that allow this. It will save everyone the bother of trying to hunt down the one that does it. And does it poorly at that, by trying to emulate high-speed sync using cheap gimmicks. > On Mon, 26 Nov 2007 09:04:20 -0500, Cynicor > <j...tru.p..in@sp.eake.a.sy.net> [quoted text clipped - 54 lines] > cheap > gimmicks. Anyone who knows anything about Flash Photography, knows that the Camera Shutter Speed, (any Camera), is irrelevant to correct exposure when Flash is the predominant light source. Except of course for those people who leave the Camera on any kind of "Auto" setting. The effective exposure time becomes the duration of the Flash Burn time, and one 64thousands of a second is quite common for a flash gun set to " low power ". Ambient light might cause problems, by allowing some image recording, (Blur), outside of the Flash Burn Time but only if it is fairly high compared to the Flash output. The kind of camera used, and its sync speed, is entirely irrelevant, but the more powerful the Flash Gun, the better. Roy G >> On Mon, 26 Nov 2007 09:04:20 -0500, Cynicor >> <j...tru.p..in@sp.eake.a.sy.net> [quoted text clipped - 74 lines] > >Roy G Thanks, for your extremely inexperienced opinion in these matters. You've made your experience level perfectly clear. >>> On Mon, 26 Nov 2007 09:04:20 -0500, Cynicor >>> <j...tru.p..in@sp.eake.a.sy.net> [quoted text clipped - 86 lines] > made > your experience level perfectly clear. OK Moron- Now is your chance to explain to everyone exactly what is incorrect about my explanation. Go on tell us just what you do know about Flash Photography. Roy G >>Anyone who knows anything about Flash Photography, knows that the Camera >>Shutter Speed, (any Camera), is irrelevant to correct exposure when Flash is [quoted text clipped - 16 lines] >Thanks, for your extremely inexperienced opinion in these matters. You've made >your experience level perfectly clear. As a "rebuttal" that was childish, asinine, and dishonest. Run along, a.shole - you've been spanked.  SignatureRay Fischer rfischer@sonic.net > Ambient light might cause problems, by allowing some image recording, > (Blur), outside of the Flash Burn Time but only if it is fairly high > compared to the Flash output. > > The kind of camera used, and its sync speed, is entirely irrelevant, but the > more powerful the Flash Gun, the better. I couldn't resist peeking at the nymshifter's reply to this. He really is losing it, I can see the facial tics from all the way over here. SignatureChris Savage Kiss me. Or would you rather live in a Gateshead, UK land where the soap won't lather? - Billy Bragg > >> Hi, > [quoted text clipped - 32 lines] > > - Show quoted text - Cynicor is basically right, at least with Canon gear. Get a Canon EX550 or 580 and put it in high-speed sync mode. Then put your camera to 1/4000 or so and it'll sync. You'll need all outside light extinguished and you'll need to be pretty close, but it'll work. The second option is to get an external strobe (hey, if you're testing jet engines you'll have some resources). Get a strobe that is bright and quick. Put the camera in bulb mode and flash the strobe once. That'll work but you'll have to play with your aperature to get the right exposure. > >> Hi, > [quoted text clipped - 30 lines] > will give you the ability to use flash at any shutter speed now, and the > information in the paragraph above is simply false. If the admonition to exclude ambient light is followed, the flash time is what counts- the shutter speed is unimportant. Only while the flash lasts is there light for the exposure, and the flash is much shorter than the shutter speed. >Here's another piece of advice. Ignore trolls like this gentleman, and >google the term "high-speed flash sync." Most DSLR/flash combinations >will give you the ability to use flash at any shutter speed now, and the >information in the paragraph above is simply false. But find out how the "high speed flash sync" actually works before buying the camera/flash combination. If it keeps the focal plane shutter slit small, but simply fires the flash multiple times during the curtain travel, you actually get many short exposures, and the image of your streaming trailers will actually be a composite from many different times. If the camera does high-speed flash sync by actually using a slow mechanical shutter (so the sensor is fully uncovered) plus a fast electronic shutter (to ignore light that leaks through when the mechanical shutter is open) and a single pulse of light from the flash, then you should be OK. Dave >You need to extinguish all ambient light and use the light of the flash alone. >Also, if using automatic flash that might be depending on thyristor circuitry, >it will help to be as close to the subject as possible. The closer you are, the >less flash that is needed, and the shorter will be the duration of that flash. >Flash output levels are controlled by its duration rather than luminosity (in >most instances, because that is easier to control.) Some flashes have a manual mode that lets you set the light output. This is generally done by reducing duration, so selecting 1/16 power will get you a much shorter flash pulse than full power. The other option is to use flashes that are designed for particularly short pulses, from the scientific world instead of consumer photography. Dave First, can you adjust the strobe light flash rate to sync with the turbine blades? If so, use only the strobe light. Use an F stop that allows you to focus on only the area of interest. I have no idea of the light level produced by the strobe, so I cannot say what you should set for in terms of shutter speed. and ISO. Manual focus, F stop, and shutter speed is required. We used to do this quite regularly about 35 years ago using film and high speed cameras that used spinning slit shutters, as well as conventional 35mm SLR cameras with a "prefog" light. (Pictures of moving parts in electrical devices such as relays.) A small amount of ambient light may actually help. > >You need to extinguish all ambient light and use the light of the flash alone. > >Also, if using automatic flash that might be depending on thyristor circuitry, [quoted text clipped - 12 lines] > > Dave |
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