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Flash duration?


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#1 SMY

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Posted 13 August 2017 - 03:26 AM

I have questions for the Pros:

- how long takes a flash ignition normally?
- I read in the web different meanings about the power of flashes: on one side it is stated, that a flash ignits always with the same power when using different power levels, it just differs, how long the flash ignits. On the other side it is stated, that the the power is modified and not the time....whats correct?Whats the best book orwebsite to learn more about flashes UW.....in use with ambient light?

Best regards, Sascha

#2 Pavel Kolpakov

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Posted 13 August 2017 - 11:01 AM

Xenon tube in uw strobe works at the constant voltage, control is only in flash duration. More duration, - more energy in flash.  User controls duration manually or by TTL.

Linear shape tubes max flash duration - 1...4 ms (full energy), round shape tubes max flash duration - 8...25 ms, depending on the size. For example, Inon Z-240 full flash duration is 3.2 ms,  Sea&Sea YS-250 full flash duration is 23 ms.


Edited by Pavel Kolpakov, 14 August 2017 - 04:19 AM.


#3 SMY

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Posted 13 August 2017 - 11:52 AM

Thanks Pavel for the fast response! So this means e.g. YS-D2 (which I formerly used) have longest ca. 1/250? Can this be the reason for sharp images with nikon D810 on 1/125 because flash freezes the picture? No with my new Seacam 60 I have to be more careful because it has round shape tube? Better go there to 1/250 on camera when full power on flash?......Or am I completely on the wrong track?

Best regards, Sascha

Edited by SMY, 13 August 2017 - 11:53 AM.


#4 SMY

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Posted 13 August 2017 - 11:57 AM

on the other side: what does a long flash duration of 23ms bring if shutter speed of camera is set to 1/125, which means 8ms??

#5 SMY

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Posted 13 August 2017 - 12:04 PM

on the other side: what does a long flash duration of 23ms bring if speed of camera is set to 1/125? Silly question?

Edited by SMY, 13 August 2017 - 12:05 PM.


#6 Pavel Kolpakov

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Posted 13 August 2017 - 04:05 PM

YS-D2 full flash duration - 4.2 ms. You can use full energy at shutter speed slower than 1/250.

YS-D250 full flash duration - 23 ms. You can use full flash energy at shutter speed slower than 1/50.  

But how often do you need full energy? - very rare. In many cases we use only a small part of it, and there is no problem to set more fast shutter speeds (up to Nikon's max synch speed 1/250).

Sorry, I don't know Seaflash-60 flash duration. There is a round tube inside, but tube's diameter and thickness are small. I can suppose duration about 5...8 ms. 

 

Underwater objects move rather slowly because of the water, flash freezes them fine, independently of strobe type and duration. There is no need to specifically take care of this.


Edited by Pavel Kolpakov, 14 August 2017 - 02:00 AM.


#7 SMY

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Posted 14 August 2017 - 02:36 AM

Hi Pavel,

as always, thanks a lot for your very helpful information! Nobody has explained it so far to me in so easy and understandeable words!

Best regards, Sascha

#8 rwe

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Posted 14 August 2017 - 12:52 PM

YS-D2 full flash duration - 4.2 ms. You can use full energy at shutter speed slower than 1/250.

YS-D250 full flash duration - 23 ms. You can use full flash energy at shutter speed slower than 1/50.  

But how often do you need full energy? - very rare. In many cases we use only a small part of it, and there is no problem to set more fast shutter speeds (up to Nikon's max synch speed 1/250).

Sorry, I don't know Seaflash-60 flash duration. There is a round tube inside, but tube's diameter and thickness are small. I can suppose duration about 5...8 ms. 

 

Underwater objects move rather slowly because of the water, flash freezes them fine, independently of strobe type and duration. There is no need to specifically take care of this.

 

 

 

Not all underwater objects move slowly as can be seen by the blurred critters in this photo taken on a night dive with an Inon Z-240 (shutter at 1/125): 

Attached Images

  • DSC00766a-1000kb.jpg

Edited by rwe, 14 August 2017 - 12:54 PM.

Sony NEX-5N,10Bar Housing, Olympus C-8080, PT-023 (broken port tabs, of course), single Inon Z-240, flickr site: https://www.flickr.c...9071@N08/albums


#9 Pavel Kolpakov

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Posted 14 August 2017 - 03:38 PM

Not all underwater objects move slowly 

Not all, but most of those that we shoot.


Edited by Pavel Kolpakov, 14 August 2017 - 04:06 PM.


#10 bvanant

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Posted Yesterday, 05:38 PM

Pavel: did you make those measurements yourself? In my hands at least the flash durations are much shorter (measured via oscilloscope and pin photodiode). 23 ms seems to me way too long, more like 2.3 in my hands. 

 

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#11 Pavel Kolpakov

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Posted Today, 12:46 AM

Pavel: did you make those measurements yourself? In my hands at least the flash durations are much shorter (measured via oscilloscope and pin photodiode). 23 ms seems to me way too long, more like 2.3 in my hands. 

 

Bill

Hello Bill,

 

I measure all values by myself. This is related to my work.

23 ms - this is full duration for YS-250 ring tube. For comparison, Z240 linear tube has 3.2 ms duration.  Full duration, - from flash beginning to zero level at the end. Pay attention, that ending of flash has low level but rather long time.

For photoflash measurements i use special optoelectronic receiver and logic analyzer. Flash duration measurement accuracy is 0.00025 ms in that system.

Almost the same durations i get by digital oscilloscope and the same receiver, but with less accuracy.

 

I don't know you measurement details, but i can suppose that you see only the main part of flash curve (high power part). May be because of your sensor. Or may be any other measurement error.

Light measurements are highly dependent on equipment and measurement techniques


Edited by Pavel Kolpakov, Today, 02:44 AM.