Some talk about speed and speed

[Eric Hiss]

Time machine can measure flash speed

Hi,
Just jumping in on this thread and am new to OPF as well. I have a little box called the Time Machine which can measure flash duration. This box will control either flash or camera based on sensor input and do a bunch of other cool stuff as well. I think it cost me a few hundred and is made in California by Mumford Electronics. You need their high speed light sensor but it works well.

I'm going to have to measure my profoto flash units to see if they are faster at full power or low power. I do recollect that they are fastest at low power so I would be surprised if the Elinchroms are the opposite but that would be interesting.

I'll have to also check on the Broncolor - that would certainly be a nice feature to be able to adjust flash speed.

Eric

 

[Asher Kelman]

Hi Erik,

Yesl, that's an interesting machine. Can it measure flash duration? I know it can set a timer to make a time delay or a repeated pattern of flashes and shutter triggering.

I can't see it measuring anything? Can you explain, or you made a mistake, LOL!

Asher

 

[Bart_van_der_Wolf]

Google turned up this URL. Point 8 on the specs link is Measure Flash Duration, in millionths of a second.

Bart

 

[Frank Doorhof]

I would love to know the outcome.
The information came directly from Elinchrom.
I have tested it here with both FX and RX units and it's true for those units, on full power they are faster than on low power.

 

[Will_Perlis]

"Mode 8: Measure Flash
This mode uses a high speed photodiode to measure the duration of an electronic flash in millionths of a second. To take high speed photographs, your flash must be faster than the motion you're shooting. But there's no easy way to know the actual duration of an electronic flash. The Time Machine will measure flash duration to a millionth of a second and allow you to know whether or not the flash you're using is fast enough. It also allows you to see how the flash speed changes with adjustments to the intensity.

This mode can also be used to measure the shutter speed of film cameras. You open the camera back and arrange a bright light to shine through the lens. The photodiode is positioned at the film plane and the shutter is tripped. The Time Machine will display the shutter speed in millionths of a second.

Mode 9: Measure Lag
This mode uses a high speed photodiode to measure the time between tripping the shutter and taking a picture. It uses an electric shutter release cable to trip the shutter, and then measures the time until the built-in flash on the camera fires. It can also be used to measure the lag between tripping an electronic flash and getting the light. The time delay is display in millionths of a second."

 

[Eric Hiss]

I'll try to measure my profoto flash speeds this weekend

Looks like you all found the info on the time machine and how it measures the flash speeds. It's really simple so I'll try and measure my Profoto Acute heads with the D4 power pack this weekend and report back. I've also seen a chart that listed the flash speeds at full power and 1/4 power for a lot of the studio flash units...I'll try and dig that up.

Here is what the D4 manual says I should expect:
The flash duration can be shortened by reducing the power output with the Power Dials [13].
The shortest flash duration using a AcuteHead and a D4 1200 generator at lowest energy
is1/7500 sec. To shorten the flash duration at a given setting, use an AcuteTwin head.
In example: If you connect the two plugs of an AcuteTwin to the Lamp Head SocketsA
and B [9] of a D4 1200 generator and use both outlets at 600Ws, the flash duration is just
1/1600s. instead of 1/1000s. at max. power with one AcuteHead.

Flash duration (t 0.5) D4 1200 D4 2400
2400Ws 1/600s. (1/1000s.)
1200Ws 1/1000s. (1/1600s.) 1/1000s. (1/1600s.)
600Ws 1/1600s. (1/2700s.) 1/1600s. (1/2700s.)
300Ws 1/2700s. (1/4500s.) 1/2700s. (1/4500s.)
150Ws 1/4500s. (1/7500s.) 1/4500s.
75Ws 1/7500s. 1/4500s.
37,5Ws 1/7500s. 1/4500s
18,75Ws 1/7500s. 1/4500s.
9Ws 1/7500s.
Times in brackets are valid with Acute/D4 twin.

 

[Frank Doorhof]

I would to see your own outcomes.

 

[Eric Hiss]

I will do this....

Sorry I have lagged on getting the info. I've been busy, obsessed actually, with all my new leica glass and stuff for the DMR/R8 and had temporarily forgotten about timing my flash gear. Now I can also check the duration on my Metz 54-4 flash unit as well. Stay tuned.
Eric

 

[Eric Hiss]

measured some flash units

Hi Frank,
I finally got around to measuring some flash units. So far I have tested the profoto d4 with an older acute head, the canon 580 ex flash, and the metz 54. All of them got slower as power was adjusted up.

I used my time machine to do the testing, and I am not certain whether it measures the entire duration or the duration at half intensity like the flash manufacturers use. I measured these with the flash head very close to the sensor. I noticed that the times got shorter if I pulled the flash back away from the sensor which is more realistic use. For about 3 feet away you can divide the numbers by 2, bounced or much farther away, you can divide the time by 4.

The metz and 580 were similar turning in about 1/3500 at lowest power settings (1/256 for metz, 1/128 for canon) and similar times for full power ... about 1/60.

The profoto d4/acute flash head did 1/500 at 8w/s and 1/50 at 1200 w/s. Like above if you move back to 3 ft the times were cut in half, further away or bounced you can divide the times by 4.

What surprised me is that none of these units including the camera mounted flash units are really very fast at full power.

Notes: The profoto unit repeated nearly exactly the same numbers (out to 5 decimal places) from flash to flash. The canon 580 was prety sloppy, bouncing around by 10-15% from flash to flash (I'm measuring only time not intensity) and the metz was more consistent than the canon but still varied by about 5%.

I'd like to test my D4 pac with my d4 head, but I left the head in the studio. rats.

I understand that the profoto 7 series are much faster - I'd be happy to test them but don't have any.
Looking at the numbers, it doesn't seem like any of these would freeze motion well even at only half power, but they do so I'm guessing the time machine measures the entire flash duration, but the bulk of the inensity would be only a portion of that. That also makes sense since the times I measured were a lot slower than the manufacturers quoted times.


Eric

 

[Frank Doorhof]

I would love to see some REAL studio strobes tested.
I know from the standard flashes and the old battery powered ones that they get slower with full power.

But the newer ones like the Elinchrom FX/BX/RX and profoto should be faster on full power than on low power.
Or at least that is my experience with jump photography and what Elinchrom tells me.

 

[Eric Hiss]

profoto D4 isn't real?

Hey Frank,
Not sure where you have been getting the idea that full power is going to be faster, but if you want to send me up some 'real' strobes to SF, I'd be happy to test them. I doubt very much that any strobes are going to be faster at full power but am willing to believe it if you can show me some data. You can download specs from most of the manufacturers. Take a look. It certainly isn't true for any of the strobes Profoto makes and I consider the D4 pack to be about as real as it gets. It might be that with a 7 series or the d4 flash head I will get faster overall times, but I can tell you that the full power is going to be longer than the lower settings. There are some newer strobes that do allow one to dial in the flash speed but I doubt that at full power you can get a faster speed than at low power. Actually I challenge you to find just one real strobe that advertises a faster flash at full power than low power. Even a spec sheet will do.
Eric

 

[Frank Doorhof]

Why the doubt if I tested it ??

This is a direct answer from the technical department from Elinchrom

Style RX for example:
At full power the flashduration is 1/2625 s
At half power the flashduration is 1/1870 s
At minimum power the flashduration is 1/1380 s

Style FX:
At full power the flashduration is 1/900 s
At minimum power the flashduration is about 1/600 s


Profoto :
http://www.profoto-usa.com/products/pro-7/pro7b2.asp faster full power
http://www.profoto-usa.com/products/pro-7/pro7b.asp faster low power

 

[Ray West]

Hi Frank and Eric,

I should know something about capacitors and flashes, etc. Here is a link that can explain why it can be confusing - http://www.scantips.com/speed2.html

I suspect the newer studio flash units switch off the capacitor discharge circuit before it is discharged fully, the improvements in electronics allowing this to be cheaply done these days. It is interesting how the flash duration becomes meaningless (if considered as being the 50% of total max. power. Very poor definitions, manufacturers hyping performance etc., customers not knowing nor bothering to ask the right questions nor manufacturers understanding what they are doing, (present company excluded, of course).

Best wishes,
Ray

 

[Frank Doorhof]

I know the engineer from Elinchrom was very clear and also stated that some large manufactorers quoted it wrong on their website because it was for some sales persons very confusing.

My experience at the moment is that with my ultra cheap backup set the flashduration drops with output, the FX/RX/Dlites rise with the increased power.

 

[Asher Kelman]

Hi Frank et al,

Wouldnt it be better to just have the graph of the flash duration to look at? How easy is that to get?

Asher

 

[Frank Doorhof]

Don't know how easy that is to get.
I try with jump photography and look what setting freezes the most

 

[Eric Hiss]

Frank,
I think the link to the profoto b2 you listed with a faster max has the times mixed up as I've seen the data compared elsewhere on profoto's site where the list all the models together for purchasing decisions. I am 99% positive that all their flash pacs are slower at max power.

That said I don't know anything about Elinchrom so it could be. I still doubt it though. The reason is because if they are using the same set of caps for each power setting the rate at which the caps can discharge is similar and will take longer for more power. Yes its true that the engineers could switch off power when they want but why then wouldn't they switch the lower power off as soon as possible yielding a faster flash? Seems to me they would always make it as fast as they could.

Anyhow for now I'll have to believe what you wrote but if I ever get a chance to test one I will.

Asher,
All of the curves I have seen approximate a gausian with time on the x axis and light intensity, flash voltage or power on the Y axis. I think that's the reason why most manufactures measure the time at half the peak amplitude is that it fairly well represents the bulk of the output since the long tails may be many times longer but only total about 15% of the light. If you knew the curve you could do the math and calculate the area under the curve for the time from Y1=.5maxY back to Y2=.5maxY and subtract it from the whole area.... I suspect if the engineers are turning off the current to the flash bulb then they would still be doing this at roughly those points to be efficient.


Regards,
Eric

 

[Ardaly Prawito]

uhmmm

sorry to disturb you guys, I wonder how to setup highspeed sync for Profoto B2 and Nikon D3?
do you guys have any idea? is it possible? or impossible?
is there any way to setup Nikon's CLS on this strobe?

 

[Rachel Foster]

Oh, boy! Is this thread for me!

 

[Frank Doorhof]

Hi,
Highspeed sync only works with system flashes not with studio strobes.
There is one solution, using leaf shutter lenses but that's only possible in the MF systems.

 

[Ardaly Prawito]

thanks frank.
I was keep thinking how to do it~
Nikon D70 is able to flash-sync to 1/500
somehow only that DSLR that able to do that... I wonder why nikon didn't create that on D3.
I'm pretty new for studio strobes, I just got it today~ I guess I gonna post some question often here ^_^;

 

[Frank Doorhof]

I don't know if that also works for studio strobes, I think/believe that will stop at app 1/200 for crops and 1/125 for FF cameras.
But I could be wrong, I know that for the 5D/1DsIII it stops at 1/125 anything above and you get a very faint black line (shuttercurtain).

 

[Doug Kerr]

Hi,

thanks frank.
I was keep thinking how to do it~
Nikon D70 is able to flash-sync to 1/500
somehow only that DSLR that able to do that... I wonder why nikon didn't create that on D3.

Achieving a higher "X-sync" shutter speed limit requires a faster travel of the shutter blades, which places various serious demands on the shutter design. So it's not so easily done.

I'm not sure of all the reasons the maximum X-sync speed recommendation is slower for large "studio flash" units, but my guess is that they may have a slower "rise time" than typical on-camera flash units. Thus we have to have delay the closing of the second curtain a little bit - a shutter speed a bit slower than the maximum X-sync speed - to embrace the majority of the luminous output of such a flash unit.

 

[Will Thompson]

I'm not sure of all the reasons the maximum X-sync speed recommendation is slower for large "studio flash" units

As the power output goes up past a certain point the arc time gets longer similar to having a longer shutter open time. This is due to the fact that the flash tube has a constant impedance once the the arc has started and to increase the power output the flash unit increases the the capacitor size thus it takes longer to discharge the larger capacitor and the flash duration increases. some manufactures vary the voltage also to get a fine tuned out put level that is adjustable to 1/10 stop.

 

[Erie Patsellis]

Speaking as an EE in a past life, I think both sides are right, and I'll explain why:

On older studio packs, power was switched, typicallly in 1 stop intervals by disconnnecting capacitor banks, so the instantaneous current available is less, as Will noted once the arc fires, it's a constant impedence until it reaches the extinguishing voltage (typically much lower than the arc start voltage). the more current available, the longer the flash duration. By using a bi-tube head on a single pack, you halve the impedence of the arc discharge path, hence halve the duration (not quite half, but fo rthe purposes of explanation, half will suffice).

As noted previously, the manufacturers of electronically controlled packs can vary voltage and at the same time use a thyristor circuit (just a larger version of what the more advanced portable automatic strobes use, a la the ubiquitous Vivtar 283/285) to quench or disconnect the tube when the specified current has discharged. With the microcontrolled packs of today, it's trivial to adjust charge voltage and current required, much like an engine ECU, you can map the voltage and current for each discrete power setting, in 1/10 stops if desired. (and some seem to)

So, you can have the same duration for all power settings, and by default color temperature (within reason) and by mapping color temp vs voltage/current settings, make a change across the entire scale upward or downward as desired.

Just my opinion, for what it's worth.

erie