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Author Topic: Freezing motion help!  (Read 8086 times)

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« on: October 09, 2010, 12:34 »
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Hi All

A while ago I posted about whether to buy some lights or a 5dmk2, thanks for the advice and I went for the lights. I bought a pair of elinchrom dlite 4, (400watt) with softboxes, these have proved to be great and opened up a world of photography that previously just wasn't hitting the mark. However I've since got more ambitious and want to freeze motion but it seems that my lights wont cut the mustard. For instance anything over 1/200 power at f8 and i can see the shutter.

I've tried playing with my settings on camera and lights and cant get close to freezing motion, I have been trying to capture pouring chocolate which isnt the fastest of things either! I often see shots of people jumping in the air, how is that done???! Someone here directed me to strobist which has been a great source but is all based on speedlights, do I need to get myself a speedlight set up for anything fast? Any help hugely appreciated, (by the way I shoot on a canon 450d)

Jo


« Reply #1 on: October 09, 2010, 13:45 »
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On the AlienBees site, I believe there is a fairly in depth text about the new Einstein lights and how the tail of the flash helps freeze motion.  See if you can find and read that.  I also have an old thread on IS about freezing motion with strobes.

« Reply #2 on: October 09, 2010, 14:02 »
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The motion is frozen by the strobes themselves and not the shutter speed. The flash of light from a strobe only lasts about 1/1000th sec. When you shoot with strobes to freeze motion just make sure that there's not much ambient light in the room and have a small-ish aperture, say f11 or above. That way the sensor will only 'see' the light from the strobes.

If I was shooting something pouring I'd set the camera to M, aperture to f13 and shutter speed to 1/160. That's pretty much my standard set-up anyway and I use the D-Lite 4's too. I usually only use one light for the subject, at an angle of about 45' in both planes, with a reflector on the opposite side. The light is set to a power of 4.6 (out of 6.0) and is as close to the subject as I can get it without it getting my way __ something like 2-3 feet from the subject.
« Last Edit: October 09, 2010, 14:09 by gostwyck »

« Reply #3 on: October 09, 2010, 14:40 »
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Just found this http://www.scantips.com/speed.html.  The 2nd page explains why studio lights are slower. 

« Reply #4 on: October 09, 2010, 14:43 »
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Your elinchrom dlite 4 flash duration specs at 400 watts are 1/800 sec measured at t.05 effective flash duration, so your effective t.01 flash duration would be approx three times longer or 1/266 second.

You can try to lower your power settings.  Some monolight have shorter flash duration at lower settings. However depending on the manufacture many momolights actually have shorter t.01 flash durations at the highest power settings.

More info about t.05 and t.01 Flash Duration measurements.

When the capacitors in an electronic flash unit discharge through the tube, the light output varies with time. At the beginning, the capacitors are fully charged, and the flash quickly reaches its peak. After this, the power decreases gradually as the capacitors are emptied, and the flash power dies away slowly, so much so that it is difficult to say exactly when the flash output stops completely. For this reason, manufacturers have decided to define the flash duration as the time during which the flash intensity exceeds 50% of the peak value. This is known as the t 0.5 value also called effective flash duration  Because the t.05 value is shorter most use t.05 values in their specs.  However this is misleading if you want to stop action.

Flash Duration t 0.1 versus t 0.5
When you want to freeze motion with a particular flash unit t 0.5 shouldnt be taken as a guide to do so. Even after the flash intensity has dropped to half the peak value, it is still producing light that can expose the sensor, and blur rapid motion. For this reason the standards offer a second definitiontotal flash duration as the time the flash output exceeds 10% of the peak value also known as t 0.1. This time tends to be about three times as long as the t 0.5 figure, and is a much more meaningful measure of a flash units ability to freeze motion.Thus, whilst a manufacturer quotes a t 0.5 flash duration of 1/1,500 second, the total flash duration is more like 1/500 second.

« Reply #5 on: October 09, 2010, 15:11 »
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[youtube]http://www.youtube.com/watch?v=n6Er4W-gfwU&feature=player_embedded[/youtube]

jbarber873

« Reply #6 on: October 09, 2010, 16:08 »
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 The strobes you have won't work for this application. To shoot high speed with an off the shelf studio strobe, you need to shorten the flash duration ( very effectively described above). One way to do it with the kind of strobe that has a separate power pack and heads is to plug in heads to all the outlets, which shares to power across all 4 heads. the flash duration is 1/4 of the duration from 1 head. If i need a faster flash, the next best way is to use pocket strobes instead. They have an extremely short flash duration if you have them close enough to the set. Anything falling that is shot with a strobe will have a "decay trail" below it, which makes it look like the object is falling up, which is weird. Some strobes are known for their short flash duration, elinchrome being one of them, but only particular models. The really high speed strobes are more in the area of scientific research, such as the ones eggerton invented, which are not going to be cost effective for microstock. (but they are cool!)
  If you do get into this more, you might also want to look into a "beam trigger" which fires the camera when an object crosses an infrared beam. I can't tell how impossible it is to try to time something falling or moving by eye and hand ( at least for me ). I've had something for years called the "dale beam" which does this. I don't know if it's still on the market.
  I don't know where you are located, but if you are near new york, you can rent these strobes at either Flash Clinic or Fotocare and try them out for a day or 2. It's worth pursuing because it's a great technique to be familiar with.
  When i was an assistant ( along time ago) I worked for a fashion photographer who used to always finish his shoots by having the subject jump. He would shoot the way i described ( 4 heads per pack) and the shots were tack sharp. They had a great way of getting a completely different expression out of the model.
Another trick he used was , when using a fan to blow the models hair, he would have an assistant spray a mist sprayer ( spritzer in NY terms) into the fan. When the cold water hit the model, he would shoot. He got some great shots this way.
   Another thought is that the closer the light is to the subject, the less light you need, so you can dial down your heads and get a shorter duration ( maybe- I don't have these strobes, but it's worth a try). Light falls off by 1/4 for every unit you move a light away, so the closer the better.

« Reply #7 on: October 10, 2010, 01:18 »
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Are you trying to freeze high speed motion, or are just seeing the shutters at 1/200s ? 
I'm using Elinchrom strobes too, combined with a 5DII, and I trigger them wireless.  The transceivers have a sync speed that is slower than the sync speed of the 5DII, which causes shutter shadows on the bottom of the images if I go faster than 1/125s.  So before you start spending money, just try lowering your shutterspeed to 1/125 or 1/100.

« Reply #8 on: October 10, 2010, 07:17 »
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Thanks all for your help, it seems then that I might be able to get some better results than I'm getting by trying out those techniques (thanks gostwyck) also sjlocke I found your IS thread and it never seemed to be totally resolved in terms of shooting people and capturing them mid air, what did you do in the end?

Digging around the internet last night Ive found that to really capture pin sharp 'Big motion' I might need some really expensive gear and knowledge to accompany it! I found a guy shooting amazing hurdlers pin sharp in studio and his lighting gear was tens of thousands of pounds. Also some of the points pasted here are a bit above my head to be honest so Ive lots to learn which is all good....Mmmmmmm!

So for me I think I will invest in the strobist kit of a couple of speedlights and stands etc which is coming in at about $500 so not too bad (maybe santa will bring me some!)... if I cant resolve my issues. For me I want to shoot pouring chocolate (slowish) but would like to try things splashing in water and some other classic studio stuff which I assume is faster and therefore more of a challenge to my studio lights, Ive found lots on you tube about splashes of water and they all use speedlights. Hey will let you know how I get on anyway, and big thanks!

RacePhoto

« Reply #9 on: October 10, 2010, 14:14 »
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Real basic but once you get the exposure right for the strobe and the camera isn't exposing to ambient light (2x less than the flash exposure is fine) The strobe is exposing the subject and the shutter speed is irrelevant!

Here it is: You get the same contribution to exposure from the flash regardless of shutter speed. Only the distance, aperture and ISO affect it.

The only reason shutter speed means anything is ambient light!

jbarber873

« Reply #10 on: October 10, 2010, 15:51 »
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Real basic but once you get the exposure right for the strobe and the camera isn't exposing to ambient light (2x less than the flash exposure is fine) The strobe is exposing the subject and the shutter speed is irrelevant!

Here it is: You get the same contribution to exposure from the flash regardless of shutter speed. Only the distance, aperture and ISO affect it.

The only reason shutter speed means anything is ambient light!

That's right. You should have as little ambient light as possible - just enough to see what you are doing. Check for how much ambient light is contributing to the exposure by taking a shot without the strobe and see if there is any image. If there is, that can contribute to ghosting.


 

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