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Some talk about speed and speed

A lot of people ask me questions about freezing action like I use in my jump photography and I find out that there is a lot of unknown base knowledge on flash equiptment so I will try to make some things clear in this little tech talk.

1.
Shutter speed vs flashspeed.
When we photograph we work with two speeds together, the first is the flash duration and the second is the shutter speed.
Normally in the studio we use a shutter speed that is arround 1/80 and 1/125th of a second.
The reason is that that is the speed on which the shutter and the shuttercurtains operate, meaning going higher you will see abnomalies in the shot like one dark side.

The second is the flash duration, this is what actually makes the shot, and this is also what a lot of people don't know.

The speed of the flash (flash duration) is even often not quoted by the manufacturer. The higher the flashspeed the more you will freeze the action, the lower the more motion blur.
A lot of cheap flashes will have speeds arround 1/500 - 1/800 while topbrands will be arround 1/1500-1/3000's

Most of the time they are mentioned in two, one fast one slow.
This is normal, normally when you open up your flash the flashduration will go up, for example 1/1000's on the lowest setting it will be faster for example 1/1800's, again this is normal because a flash will vary the output by longer or shorter discharges.

2.
Playing with them.
In practice this knowledge is a superb tool.
Let's say we let a model jump and we want to freeze her in the air, we will often work with a flash unit on the lowest setting, meaning a very fast flashduration.

When we want a little bit of movement for example in the hairs or arms/feet we will raise the flash output and extending the flashduration.

Learn your flashheads and you will have gained a creative tool.

Any questions, feel free to ask.

Greetings,
Frank
 

Nill Toulme

New member
Interesting Frank, thanks. I had a notion about flash duration determining the exposure, but I had no idea about output varying the duration for a given exposure.

Nill
~~
www.toulme.net
 

Stan Jirman

New member
Flash ratio also influences the "stopping" of action. When I take pictures of my little one, I have the camera often set to 1/60s @ f2.8 @ 400, and the rest is flash. With that exposure, there will be still a lot of blurring when she moves, simply because the flash makes out only a fraction of the light. It's a balance between a "flash look" and stopping action.
 
Totally correct in the normal enviroment where you work with ambiant light and flash you can use all kind of neat tricks.
For example photograph a rally car with second curtain flash and you will have a wonderful trail of light coming from the back.

But you can indeed also balance the flash to give just enough for fill in, not freezing too much.
For sports flash can be wonderful but often it's best to shoot with only fill in flash, because otherwise there will be too much frozen.

Greetings,
Frank
 

Sid Jervis

pro member
Playing with them.
In practice this knowledge is a superb tool.
Let's say we let a model jump and we want to freeze her in the air, we will often work with a flash unit on the lowest setting, meaning a very fast flashduration.

When we want a little bit of movement for example in the hairs or arms/feet we will raise the flash output and extending the flashduration.

Learn your flashheads and you will have gained a creative tool.
I understand what you have described, I have two questions: Other than using the flash heads at various power levels, to get the right shot, is there a way to measure the speed of the flash at differing levels of output?
Do flash heads respond in a linear way plotting speed / output.
Thanks
 
Don't know about that, I know it can be measured because otherwise the manufactorer would not know it :D

I don't know if the speed is linear.
For more light the tube stays on longer, for less power the tube stays on shorter, so I THINK you can assume it's more a curve than linear to get twice the ammount of light you will need alot more power than twice the power, but again I would not really take my word for it.

Greetings,
Frank
 

Tony Field

New member
Frank Doorhof said:
The speed of the flash (flash duration) is even often not quoted by the manufacturer. The higher the flashspeed the more you will freeze the action, the lower the more motion blur.
A lot of cheap flashes will have speeds arround 1/500 - 1/800 while topbrands will be arround 1/1500-1/3000's

I wonder if this is for manufacturing reasons? Years ago, when I bought my Norman 1200 flash and film was the only game in town, you WANTED a slow flash in the order of 1/1000 second or even longer. In those ancient days, reciprosity failure was a serious concern for both long exposure and short exposures. In colour images, there could be colour shifts because of differential sensitivites of the colour layers, and in B&W you could have a decrease in sensitivity. Expensive flashes were longer duration and sometimes engineered to have the same exposure duration at different power levels. The cheap units were often much faster.

I guess there is no concern for this problem now for digital (except for many very long exposures and the possible noise associated with digital sensors). I wonder if there is still a concern for film?
 
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I don't think noise is an issue with the 1/125th shuttertime and the ultra short flash duration.

I only know from the newer brands but I love a fast flash system it gives the images just that more, how do you call it, crisp quality ?

It's really weird to talk about it, I shot a long time with Jinbei and the pictures always lacked some crisp, the day I switched to Elinchrom it was there from the first shot I took, the pictures just had the dimension and crisp I always thought was there :D

Some will claim it to the reflectors or softboxes but to be honest I strongly believe it has something to do with the flash duration.

Would love to hear some other views on this subject, it has become my favorite over the last few months. I have been working alot with different powerlevels on the FX400 set and I just love the all the way down setting for jump photography freeze, and the middle position for the little movement in the arms and legs.

Greetings,
Frank
 

Will_Perlis

New member
"...is there a way to measure the speed of the flash at differing levels of output?"

If you have access to an oscilloscope and a sensor it's easy. If those words didn't make sense it's difficult. The problem is more in determining the points where you say "It's on" and "It's off" 'cause the light output isn't a nice steep square curve. The light builds up quickly and decays more gradually.

See here for the curve of a small flash unit:

http://www.chem.helsinki.fi/~toomas/photo/flash-discharge.html

Rather than give you the curves, some studio flash companies give you the time to 1/10 the max light output and the time to 1/2 the max light output. Those are shown as "0.1t" and "0.5t". Sometimes they give you a few more data points but usually not many.

In any event, you can get shorter durations for the same amount of light by dumping the power from two studio packs set at half the desired power into two flash heads or using a "bi-tube" head. You can do the same with shoe mounted flashes if your camera system can control more than one. And so forth.

I don't know about Frank's Elinchroms but I can tell you that the Visatec monolights have a relatively long duration flash even at their lowest setting. It's too long to play with bouncing balls and splashes, for example.
 

Sid Jervis

pro member
Thanks for the link to Toomas's Photo Website.

Yes I know how to use an oscilloscope, I checked out the Tektronix Optical / Electrical Converter, all I need to do now is consider if paying $200 for the sensor is a sensible use of cash :)

Looking at Toomas's Photo Website, I was intrigued at the behaviour of the Canon flash in high-speed synchro mode. As he says, a clever device.
I am happy that I do not have to deal with that 40,000 Hz HSS burst from studio strobes.

Rather than give you the curves, some studio flash companies give you the time to 1/10 the max light output and the time to 1/2 the max light output. Those are shown as "0.1t" and "0.5t".
OK, before I buy an OE sensor I think it's time to email Elinchrom support.

Thanks
 

Will_Perlis

New member
"...all I need to do now is consider if paying $200 for the sensor is a sensible use of cash..."

I think, for studio flash units, which aren't what I'd call "fast" even at their fastest, you could use a photovoltaic cell from Radio Shack or Fry's costing a few bucks at most. Or, a whole flash meter can be gotten for much less and scavanged for the parts or even the signal.

I used those and a flashlight to send music across rooms back in high school decades ago so the response time would be adequate to give you a good idea of what the flash unit is doing. Finding out what shoe-mount flash in HSS mode or at 1/128 power is doing might need something better.

And I think I saw the .1t and .5t figures on the Elincrom site in the product specs section. I'm not sure what use the .5t figure is since that's only one stop down. I could be wrong about that, the caffiene has barely started to take effect. (Later: It's caffeine, not caffiene. One needs some to notice the difference)
 
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Sid Jervis

pro member
Frank Doorhof said:
The elinchrom FX400 are fast enough for wind and jump photography.
If you are in doubt buy the one class above those are faster.
I will accept that, thanks. I have images to capture, a far better job than pawing over a 'scope :)
 

Tony Field

New member
Frank Doorhof said:
It's really weird to talk about it, I shot a long time with Jinbei and the pictures always lacked some crisp, the day I switched to Elinchrom it was there from the first shot I took, the pictures just had the dimension and crisp I always thought was there :D

Some will claim it to the reflectors or softboxes but to be honest I strongly believe it has something to do with the flash duration.

Another theory might be applicable... My good friend Ivan Karabobaliev (good stuff on: http://members.shaw.ca/ivansphotography ) shoots Elinchrom. He received a guift of some ancient Ascor lights that did not match the light "quality" of the Elinchrom. He tracked down a USA flash tube wizzard and had replacement tubes for the Ascors made with the same GAS COMBINATION as the Elinchrom. They turned out to be a perfect match.

Apparently, each manufacturer has it's own concept of how the gas in the tubes should be mixed. Ivan's taste seems to match Franks - Elinchrom seems the best.
 
I have to change the story.
When filming the instructional DVD I found out that with the new flashsystems like the Elinchroms it works different.

The HIGHEST flashouput setting has the FASTEST flashduration, so freezing action.
The LOWEST flashouput setting has the SLOWEST flashduration, keeping motion.

I have talked about this with the designers at Elinchrom and this is correct.

It's totally different from what I've learned but in practice it also seems to be correct.

So sorry :(
And changed by this post :D
 

Will_Perlis

New member
"The HIGHEST flashouput setting has the FASTEST flashduration, so freezing action.
The LOWEST flashouput setting has the SLOWEST flashduration, keeping motion."

Frank,

Did they explain how they managed that trick? I can't find anything about it on the Elincrom site.

Will
 
Stan Jirman said:
Flash ratio also influences the "stopping" of action. When I take pictures of my little one, I have the camera often set to 1/60s @ f2.8 @ 400, and the rest is flash. With that exposure, there will be still a lot of blurring when she moves, simply because the flash makes out only a fraction of the light. It's a balance between a "flash look" and stopping action.

Stan,

The term for this technique is dragging the shutter (first tier search term) and I am fond of it. It works great in horrible lighting by stopping action with the flash and then capturing the ambient light to get a more natural look. I am fond of using 1/8-1/20 second with aperture and ISO set to get fill from the ambient light. Albeit, I get a lot of culls at those shutter speeds too.

enjoy,

Sean
 
Home solution.

Will_Perlis said:
"...is there a way to measure the speed of the flash at differing levels of output?"

If you have access to an oscilloscope and a sensor it's easy. If those words didn't make sense it's difficult.

Take a fan of known RPM (inside your computer case) and shoot a shot of it with the flash where the ambient light is at least 4 stops below the flash to minimize its effect (at low power bring the unit in close to increase intensity). By measuring the angle of blur you should be able to determine the exposure time. You may have to experiment to find a fan of appropriate speed (5000+ RPM chipset fan, 2300 RPM case fan, lower RPM 120 mm case fan, ...). You can often get readings on the fan RPMs via software.

You still have the issue of at what point is the flash over, but now you are judinging it with your eyes so your taste in sharpness will filter the answer for your needs.

While this solution may not terribly precise, it should be reasonably accurate for the needs expressed here. And buying a few case fans and plugging them into a motherboard header is far less expensive than an oscilloscope. On a PC you can use a program called Speedfan (its free) to monitor fan speeds and in some cases you can control them with it.

enjoy,

Sean
 
@Will,
I have to translate something very technical to English (not my native tongue) so excuse if I do it wrong.

To get stable power and digital correctness over the whole range the flash manufactorers use more than one capacator, often 4-6 in packs.
When a flash is set at the lowest setting this is done by lowering something after the capacators meaning they have to lower the output.
When using a flash at full power all the power is released at once and so getting the fastest speed.

When I filmed the instructional DVD I asked arround to people who in my opinion could answer this, and I researched the internet for this and found that almost everyone claims the opposite, meaning lower flash settings equals faster flash, and higher meaning slower flashspeed.

BUT this seem to work only for one capacitor units or tricolistors ??? which are used in speedlights like the 580EX.

Because I use mainly jump photography it's very very hard to really see what happens, most of the time I use the middle setting for just a little bit of movement.
When I filmed the DVD I experimented with the settings and to my eyes the highest setting yielded the slowest flashduration, in opposite to the lowest setting.
HOWEVER every jump is different.

I now did the same test with my own hand, and Elinchrom is 100% right, on the highest setting the flash duration is SHORT, on the lowest setting, it's longer.

MEANING:
Freezing action full power.
Motion blur lowest setting.
 

Roger Lambert

New member
May I ask a few esoteric questions which are tangentially on topic? :D


I recently purchased a small 400W (120 volt) Speedtronic lighting set up from a friend. (I am a neophyte to studio lighting). I would love to be able to use this equipment to shoot sports in dark venues like gymnasiums using remote triggers.

Looking through an abreviated B&H catalog, I noticed that battery-powered portable lights can switch out their bulbs to higher-powered versions.

I was wondering if replacing a studio bulb, made for the 400W system and for typical studio purposes, with a 1600W bulb ( and a focusing reflector) would produce a shorter, more intense output.

You can tell I am a fan of science fiction, trying to squeeze a diamond from a lump of coal, I think?

I have a very strong suspicion that 400W is 400W, and that it would take a very special filament indeed to push that 400W out four times faster than it would through its usual bulb?

Would this make a difference in the actual light output? Photographically speaking, is having a much "brighter" light, albeit for a shorter time, a more efficient strategy for a *digital sensor*, if one is trying merely to freeze action and throw enough light downfield to make a good exposure?

I have a feeling that the only way a 400W condensor can give more than 400W of light is if some bulbs have much higher efficiency in converting power into light. Do such magic bulbs exist ? ( Or are they in the same universe as a Canon DSLR body with a dedicated MLU button?) :D

Thank you in advance should anyone tackle these questions. :)
 
Roger Lambert said:
Would this make a difference in the actual light output?

If it works at all (underpowered as the circuits may not deliver the right amount of juice), then I suspect you would get color temperature drift which may be potentially undesirable. Albeit, this is all supposition on my part.
 

Will_Perlis

New member
"I was wondering if replacing a studio bulb, made for the 400W system and for typical studio purposes, with a 1600W bulb ( and a focusing reflector) would produce a shorter, more intense output."

Roger,

We're talking about electronic flash, right? Those ratings on the power packs and the heads are all maximum ratings. So, as you mentioned, 400 W/s is 400 W/s. Connecting a head capable of handing more won't get you more. Changing reflectors can change the distribution of what's available, tho'.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Bring the light in. Halving the distance to the subject will give you the same exposure at the subject as have in 1600 W/s power set up replacing your 400 W/s gear.

Asher
 

Roger Lambert

New member
Will_Perlis said:
"I was wondering if replacing a studio bulb, made for the 400W system and for typical studio purposes, with a 1600W bulb ( and a focusing reflector) would produce a shorter, more intense output."

Roger,

We're talking about electronic flash, right? Those ratings on the power packs and the heads are all maximum ratings. So, as you mentioned, 400 W/s is 400 W/s. Connecting a head capable of handing more won't get you more. Changing reflectors can change the distribution of what's available, tho'.

How depressing. I just knew folks around here were too rational to give me much hope! :D

Where is Scotty from the USS Enterprise when you need him? Scotty would have a solution .

My Speedtron lighting set up is ancient. It is as old as the flashlights that took 4 big D batteries and threw a paltry glow. Nowadays we have halogen and LCD flashlights that are much brighter and require much less juice.

So, how come some huge transformer you plug into the wall can't put out a billion candlepower with a the right bulb? Its the 21st century! :D
 

Asher Kelman

OPF Owner/Editor-in-Chief
Roger,

What's wrong with the solution offered? It uses the inverse square law, is free and depends on the fact that light reaching any object increases by the square of the factor by which the distance to the light source is decreased. All lights work this way!

So cutting the distance in

1/2 gives 4 times the light on the subject

1/3 gives 9 times the light on the subject

1/4 gives 16 times the light on the subject

So why can't you use this?

400 W/sec is a good start for most portraits.

Add in a white (black/gold/silver etc) board/ sheet/reflector/wall on the other side and a reflector below at 45 degrees below you have a pretty good light set up

Asher
 

Will_Perlis

New member
"Scotty would have a solution."

Sure he would. All he ever needed was more dilithium, a by-pass around the safety gear, and a few extra minutes.

The basic problem you face is that the max amount of light available is limited by the max amount of power storable in your power pack. There's no getting around that without some as yet to be discovered way of greatly increasing the efficiency of flash tubes.

Otherwise, the answer is (as usual) the application of more money. ;)
 

Asher Kelman

OPF Owner/Editor-in-Chief
Roger needs this for sports shoots where he's not allowed to get closer. That's a different need than studio!

So what is the most economical portable flash for this available used?

asher
 
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