# high speed photography - synchronisation of 2 speedlites?



## sulla (Mar 27, 2015)

Dear all!

My problem: I want to capture tiny tiny droplets (a few dozens micrometers) of a fluid which are moving quite fast. I know this will be a difficult task, this will be at the limit of the resolution of the lens and the sensor, The droplets could turn out as small as a few pixels in diameter, but I would like to get a rough measure of their size.

My setup: For this I shall take my macro lens (EF-S 60 or MP-E 65, not sure yet) and a 600 speedlite set to 1/128 power in a backlight setup. This will give me roughly a flash duration of 1/40.000 of a second or 25 microseconds. Motion blur should then be limited to some 10-30 pixels (at 1:1 magnification) on the sensor of an EOS 60D. (I expect to get motion-blurred streaks of droplets, then.)

Question: I expect the lighting to be quite weak. If I were to use both of my 600 speedlites via the ST-E3-RT trigger, do you think they would fire in synchronisation? i.e. they would have to fire within some 10 microseconds of one another. Do you think this kind of sync is possible? If they don't, I would get double-images of my droplets.

I fear the sync will not be of the required precision.

thanx for your help and judgement,
Sulla


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## kirispupis (Mar 27, 2015)

This speed is beyond the ST-E3-RT trigger. You need to use something like StopShot to do the actual synchronization. In terms of the lighting, I have found that Einstein gives me a fast enough flash duration (I think it is around 1/16000). I use two of them - one for foreground and one for background + 2 580EX speedlights from underneath.

The drops I am doing are considerably larger than yours, so I am not sure if this flash duration will be enough for your purposes. You can attach multiple speedlights to achieve this, but you'll need far more than two. My guess is you'll need at least 8. Cognisys has equipment that will enable you to synchronize a lot more speedlights. You may also want to look at a high speed flash such as this one - http://www.highspeedflash.com/#!flash-units/c1kgp that can go over 1/100,000s.

1:1 magnification is not overly difficult for catching waterdrops, but be aware if you are looking for this tiny then you'll probably want to go over that - which will magnify your lighting and DOF concerns. I have done a few water drops with my MP-E 65, but it is quite a struggle (I am building a new rig that should fix that though).

Here is an example of a water drop I did with my setup.



Sunrise Dreams by CalevPhoto, on Flickr


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## sulla (Mar 27, 2015)

Ah, thanks for your help! Relly impressive, those 3 pillars of water.

I want to capture the droplets from an airbrush right at the nozzle. The image quality does not need to be excessively good, it is really just more of a technical documentation: I want to roughly measure, or better: estimate, their size. (you normally use a laser interferometer for this, but I don't have one. However, I have photography gear.)

Thanks for the link to the Cognisys system. I've not been aware of this. The µFLASH Ultra looks really cool. Let's see where the 600RT speedlight takes me and then perhaps I can move on.


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## privatebydesign (Mar 27, 2015)

kirispupis,

Fantastic reply and great image.


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