Lighting issue - Profoto B1 off-camera flash kit – sequence of photos, movement

Discussion in 'Lighting and Hardware' started by gosia1234, Oct 31, 2015.

  1. gosia1234

    gosia1234 TPF Noob!

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    I'm going to be photographing a footballer doing a trick with a ball (called around the world, ref: https://www.youtube.com/watch?v=6V1l1nfKK5M) and I need to photograph a sequence, of about 5 images while he's doing that. I'm using a Nikon D700, I was advised to photograph using a shutter of about 1/1000 sec and using Profoto B1 off-camera flash kit (http://www.bhphotovideo.com/c/product/1009783-REG/profoto_901094_b1_500_airttl_monolight.html).


    The trouble I'm having is the flashes do not recycle fast enough, so when shooting a fast sequence the lights are uneven, or don't fire. I found that you can use the flashes in a Quick Burst Mode, which means the following: When the output is set to three stops below full power, you will empty 1/8 of the tank with every flash, which means that you can flash eight consecutive times with almost no delay in between.


    When setting the camera to the flash/bracketing option of 1/135 which allows me to photograph on any chosen shutter speed with flash, and shooting on a range between 1/500-1000 sec, the flashes lock to the range 8-10 (10 is max) and I can't reduce them any more than two stops, the Air TTL-N remote switches into the high sync mode - and still flashes don't recycle fast enough and are uneven if I attempt to shoot a sequence.


    I'm really struggling to find a solution to this, so I would appreciate any advise on the above and how I can improve the situation and the set up to get this right. The location of the photoshoot means I won't be able to plug into the mains.


     
  2. Derrel

    Derrel Mr. Rain Cloud

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    There is some bad advice being dished out to you from somewhere.The camera's shutter speed of 1/1000 second is a puzzling suggestion to me! The FLASH pops are what will freeze the movement of the athlete and the ball! The FLASH is of very brief duration...the shutter speed could be 1/125 or 1/160 or 1/200 or 1/250, and the FLASH exposure will be identical.

    High-speed synch flash is often just verrrrrrry high-frequency, repeating flash micro-pulses, which cover fast shutter speeds by firing for, a relatively lengthy period of time; this tends to produce BLURRED motion on fast action, but is very useful for static poses in bright sunlight with wide lens apertures and fast shutter speeds, such as say fashion models or portraiture done in bright light at say f/2.8 at 1/8000 second, and using high speed synch flash to fill-in shadows, and NOT to stp motion.

    High Speed Synch does a crappy job of freezing motion!!! It is NOT designed to freeze fast movements.

    You want to shoot this with flash? Set the ISO somewhat higher than normal, say ISO 400. Set the flash relatively close to the player. Set the shutter to 1/200 second, and the camera on its fastest continuous advance mode. You will get 8 flash images per second, which ought to allow you to shoot the move. Shoot repeated sequences.

    Shoot in raw capture mode, and adjust the exposures in post to even out any unevenness the flash pops might have.
     
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  3. gosia1234

    gosia1234 TPF Noob!

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    Hi there,

    Thank you very much - I appreciate a swift reply. I've been browsing around and both Profoto company and some other sources recommended the high-speed sync for freezing action shoots, that's also the advice I got from a technician who's recommended the equipment.

    I'll definitely try the set up you suggested at 1/200 sec and higher ISO, this will allow me to two turn the flashes down 3 stops, hopefully this will work.

    Again - thank you for the advise,

    Thanks, Gosia
     
  4. gosia1234

    gosia1234 TPF Noob!

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    Just one more thing, I've just tested few things, and the profoto flashes indeed have the capacity to recycle faster, if not used on the full power, and not in the High speed sync mode. 1/250s - with a fast recycle worked, which is great. However in terms of ambient light and potential bleed (which happens if there is too much ei. daylight) and as there is a possibility of the shoot happening outdoors, during the day - I may encounter too much of the ambient light, which will create a blur - based on the test shoots around the white ball. This is where the high speed sync would come in handy - because that would reduce the ambient light, but again, the flash wouldn't recycle in this setting to photograph the sequence. Any ideas or recommendations on how to solve this? If I turn the aperture up, this might help, but means I have to use flashes on the higher power, which depending on the conditions and how much I need to increase the flash may bring me back down to the situation where the flash power is too high to recycle fast enough. I need as little ambient light as possible, any ideas on perhaps how to block it/go about this in an outdoor setting?

    Thanks again, Gosia
     
  5. Derrel

    Derrel Mr. Rain Cloud

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    A three-stop difference between the ambient lighting level and the flash power as measured at the subject ought to stop most blurring. Have you considered that having the ball a **slight** bit blurred might actually look better than a stop-motion ball?

    Again,. high-speed flash synchronization is basically stroboscopic pulsing of micro-bursts of flash...it is NOT one, single, discrete flash pop! but is instead something like 50-80 hertz pulsing of the flash. And that might be okay...it can add motion to things like bird wings as bird come into or leave a perch...but it is not stop-motion.

    I would suggest that the easiest thing to do would be to use a fairly narrow-angle parabolic reflector and not a softbox or umbrella, to constrict the light to the player AND more-critically, to elevate the flash Guide Number much higher than it would be with a wider beam spread. Use the zoom reflector at its most narrow-angle, OR where you can get the highest Guide Number at a distance that will cover your subject...you do not want or need to illuminate a wide swath of the playing field, just enough to cover the footballer and perhaps a bit more. You might want to know, for certain, what exactly the power options will yield in terms of f/stop at ISO 100; do tests beforehand.

    Estimate via Sunny 16 Rule that the bright sun exposure of the daylight areas would be f/16 at 1/100 second at ISO 100, or as f/16 at 1/200 second at ISO 200. That is the daylight exposure. Then, figure out how far away the flash needs to be to give an exposure that makes the FLASH at the player's position be three EV brighter. That should make the daylight appear very dark behind the player in areas that are NOT lighted by the flash's beam.

    As far as high speed synchronization, I would look into the full technical specifications for your flash and flash head, and see how many hertz the flash might fire at different power levels. Again, something like say 80 hertz might give a nice, very subtle blurring on the fastest-moving elements of the shot, and the high speed synch would allow you to darken the background a good amount by elevating the shutter speed quite a bit.

    I'm REALLY not sure why you want to light this with flash: for creative reasons or aesthetic? This could be done with reflector fill in sunlight....and a fast shutter speed, or ANY shutter speed combo you want to use...
     
  6. gosia1234

    gosia1234 TPF Noob!

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    Hi there, thank you for a fast reply.

    A three-stop difference between the ambient lighting level and the flash power - what method should I use to measure this, is there anything you could recommend? The narrow angle reflector for the flash is a really good idea, this will defuse less light, which means I can turn the aperture up to eliminate more ambient light, but hopefully use the flash more efficiently, on a still slightly lower power.

    Would you be able to advice where I should head to read up on the flash exposure vs daylight and how to calculate it to be three stops brighter? What is the rule? I'm not sure I really understand how to go about this.

    In terms of the day light - I'm not expecting this to be a full bright sunlight, as we're based in the UK, this time of the year, it's mostly cloudy, but that's still quite a bit more light coming in, than indoors. This is also why I think I will struggle to freeze movement without using any flash at all. What shutter speed would you recommend to use in daylight with a reflector fill, to freeze movement?
     
  7. Derrel

    Derrel Mr. Rain Cloud

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    Measure the ambient light with the in-camera meter and a test shot. Under cloudy skies, or wintery skies, the flash from close distances OUGHT TO be at least 3 EV more-powerful/brighter than the sunlight, especially with a narrow-angle parabolic type metal reflector shaping the light. On a gloomy day, the flash might easily be 10 EV brighter than ambient light encountered on a dark, stormy day. Do a test exposure and see for yourself what the effective flash power is for the light; set the light up at 10 feet, and with the camera a ISO 100, do a series of test shots of a person at different f/stop values....see what the proper f/stop is by choosing a good exposure from the resulting series of test exposures.

    The proper exposure at 10 feet, at ISO 100 allows you to computer the flash GN, Guide Number. Multiply the proper or best exposure's f/stop setting by 10, which gives the GN, in Feet, at ISO. You can figure this GN out ahead of time....this is the easiest way to determine how powerful a flash is when set up with a specific modifier. I am going to GUESS (no stats whatsoever) that at 1/8 power but with the right metal reflector, the GN will be 150 or so at ISO 100.

    If at 10 feet the proper f/stop is 13, then the Guide Number (flash power index, so to speak) of the flash would be 130, in Feet, at ISO 100. That is a two-stop specification: meaning in FEET, not meters,and computed for ISO 100.
     

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