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Strobe "Shutter speed"


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#1 bobanderson

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Posted 06 October 2013 - 11:43 AM

I am having problems understanding this picture of the tentacles of a common urchin. Now, its not the best picture in the world so I'm not looking for critique but rather for help with the technicalities.

 

1376479_10151952099139260_428214526_n.jp

 

It is taken on a D200 and 60mm with a 36(?I think)mm extension tube. It is a 1 sec exposure at f32 at 100iso.

 

I shot f32 to get dof. I shot 100 to get best quality. I shot 1 sec to get green background.

 

The strobe (both) was a subtronic with dial set to 4 (1/4?) and as the tentacles were moving, it has done quite a good job of "freezing the action" and giving me sharp tentacles (things that are in focus are not blurred, ya catcha ma drift?)

 

My understaning is that one can use strobes as a shutter to freeze action: what are the numbers here? ie at full splat, how long is the light lit in shutter speed terms? is there an equivalency or is it just super fast? How far can you go in freezing stuff that is really small? What use is this idea in a wider context?

 

I guess I am just asking for help with the situation: if anyone could point me in the right direction, I would be chuffed to bits.

 

Many thanks

 

Bob

 

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#2 tdpriest

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Posted 06 October 2013 - 02:00 PM

The strobe is so fast that it really doesn't matter how fast it is.

 

Motion blur comes from those parts of the image that are lit by the ambient light, and you can see ghostly blurring: with moving objects it's the principle underlying the use of rear-curtain synchronisation, creating an impression of movement.

 

A Subtronic strobe is a big, expensive beast with which to learn the basics...



#3 eric black

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Posted 06 October 2013 - 04:56 PM

I seem to recall hearing somewhere that strobes fire a flash of light that is ~1/1000th second long



#4 bobanderson

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Posted 07 October 2013 - 12:36 PM

thanks for your posts guys, input appreciated.

 

However, you seem to contradict each other as a strobe "lit" duration of 1/1000 puts it within the shutter speed range? Am I right in thinking my fastest shutter is 1/8000? How do the "lit" durations vary with light emitted strength, ie is 1/64 as marked on strobe equal to 1/1000sec "lit" for eg? Wrong words but you get the drift!

 

I think in this photo nothing is lit by ambient, hence no "drag shadows", the only reason for 1 sec is to get green background. I shot rear curtain but think this is a moot point for that reason maybe?

 

Subtronics? Ebay! About £300 a pop with a long wait and a quick pounce. Good value at that price and lovely if you never fly. Fortunately I am more a boat person!

 

Thank you again.



#5 decosnapper

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Posted 07 October 2013 - 12:40 PM

Remember the camera has limitations; the shutter will only sync up to 1/250th of a second (or thereabouts). The camera won't (shouldn't at least) allow you to select a shutter speed in excess of what the mechanical curtain can cope with.
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#6 bobanderson

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Posted 07 October 2013 - 01:01 PM

if I took a picture of a hummingbird, I could freeze the wings with a fast shutter speed. I believe I could do the same thing with a flash too? How would I work out the timings bar small light output, more freeze, large output less freeze?



#7 Julian D

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Posted 07 October 2013 - 08:05 PM

Interesting post.  I had a look at this a while ago and ended up rather confused.  I'm just learning but noticed the foreground in some shots were slightly less exposed at 1/320 than at 1/250th. (D7000, wide angle looking into the sun with DS125 strobes on full).

 

I figured it must be a sync speed issue (strobes are fibre optically triggered if that makes a difference?).  Then I stumbled across an article: http://wetpixel.com/...al-explanation/ that shows flash duration curves for different strobes.  If I understand this correctly you can see the InonD2000 has a very sharp curve with a quick decay curve.  Whereas the YS90DX has a very long duration in comparison - if I do my maths correctly this is getting close to 1/320th.

 

I couldn't find any info for Ikelite strobes so I emailed them explaining the above and they said that the cause was in fact due to the flash duration.  I asked them about DS160's given they are more powerful and they said the full power flash duration on a DS160 was longer than a DS125.

 

At this stage I just let it go as I was out of my depth.  It would be really interesting to hear from someone with technical expertise in this area and see hard data for different strobes at different power levels.  Maybe I'm completely off track with this and maybe it has no practical application in the underwater world but I would be curious to know - particularly if the make of strobe influences ability to achieve sync speed.

 

Cheers


Edited by Julian D, 07 October 2013 - 10:51 PM.


#8 tdpriest

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Posted 08 October 2013 - 07:26 AM

... you seem to contradict each other as a strobe "lit" duration of 1/1000 puts it within the shutter speed range? Am I right in thinking my fastest shutter is 1/8000? How do the "lit" durations vary with light emitted strength?

 

Strobe power is determined by the duration of the flash, except at very low power when the colour of the flash can also change. I can't find the specifications for a Subtronic strobe, but a typical flash's duration is indeed about 500 microseconds to 1millisecond. It takes a typical camera's shutter about 1/200 second to open and close, so faster shutter speeds (where both shutter curtains are moving at the same time) are incompatible with flash photography, as only a band is illuminated. In practice the only things that you can't freeze with a strobe in underwater photography are the strike of a mantis shrimp and the snap of a hungry frogfish's jaws...

 

... you need studio lights and a fast shutter speed or highly specialised and expensive strobe lighting to freeze a hummingbird's wings!



#9 tdpriest

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Posted 08 October 2013 - 07:39 AM

I couldn't find any info for Ikelite strobes so I emailed them explaining the above and they said that the cause was in fact due to the flash duration.  I asked them about DS160's given they are more powerful and they said the full power flash duration on a DS160 was longer than a DS125.

 

At this stage I just let it go as I was out of my depth.  It would be really interesting to hear from someone with technical expertise in this area and see hard data for different strobes at different power levels.  Maybe I'm completely off track with this and maybe it has no practical application in the underwater world but I would be curious to know - particularly if the make of strobe influences ability to achieve sync speed.

 

Cheers

 

There was concern about colour film being incorrectly exposed at very fast and very slow shutter speeds (reciprocity failure). As far as I know this isn't a problem with electronic sensors, and the duration of a strobe's flash has little impact on underwater photography. Sync speed depends on the camera, not the strobe, and is highest in cameras with an "electronic" shutter (ie data from the sensor is registered rapidly and not integrated over the time that a mechanical shutter allows light to fall onto the sensor):

 

http://electronics.h...utter-speed.htm



#10 bobanderson

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Posted 08 October 2013 - 09:41 AM

righto, this is not about sync speed: I understand that concept (and have a thousand pictures of black bands to prove the point)!

 

Have a look at the picture: the tentacles were waving in a current yet the pigment in the tissues is sharp in the tentacles that are in focus yet the shutter speed is 1sec. In ambient light, this would have been a blurry mess but the strobes have frozen the action.

 

I know if I take a picture of a gull on the sea, i need to be in the thousanths shutter speed to freeze water droplets on the birds. I know when to take a picture and when not to if I want to see sharp water droplets.

 

What I would like to see and understand is how a strobe does this, if at all. An explanation using Z240 data would be fine as they are the most common strobes..

 

so for example, say I was taking a seagull and was wanting to freeze the drops underwater (bear with me) I could use a low strobe light setting (ie fast light burst = fast shutter speed). To get the exposure, I could move the strobes closer to the subject to compensate for the  low strobe setting.

 

Or is it all just a big box of magicdoodoo where pixies paint delicate waves of fairy dust over nudibranches?



#11 John Bantin

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Posted 08 October 2013 - 10:02 AM

The flash makes a burst of light. Its duration is dependent upon the size of the flashtube and the power output of the flash. For example, I have a studio flash at full-power (2000j) that has a long duration of about 1/150 sec. The duration of a little flashtube at low power is very fast indeed. So as long as the pulse of light can fit into the time the camera shutter is open, it will be effective. I suggest it was so dark that the ambient light on the tentacles was so little as to be negliable. (By the way, Bob, I was just thinking I should get rid of my Subtronic strobes too - if they still work!)


Edited by John Bantin, 08 October 2013 - 10:02 AM.

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#12 decosnapper

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Posted 08 October 2013 - 07:43 PM

You could recreate this technique on dry land. Find a dark room, set the camera up on a tripod with an exposure of (say) 10 seconds. Trigger by hand a strobe as you walk past (without tripping over the camera - it's dark remember!) the open shutter. Until that burst of light appears - its duration measured in milliseconds - the sensor/film sees and records nothing. The camera records the short burst of light from the strobe and freezes your motion.

Keep walking and trigger the strobe again and the walker will be recorded twice on the same exposure.
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#13 errbrr

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Posted 08 October 2013 - 09:23 PM

If it helps, shutter speed is irrelevant in cave diving. I choose one that the strobes will sync at and don't worry about it again. It's nice and dark underground so there's no ambient light to worry about unless your buddy shines her light down your lens.

#14 tdpriest

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Posted 09 October 2013 - 01:34 AM



... is it all just a big box of magicdoodoo where pixies paint delicate waves of fairy dust over nudibranches?

 

 

You aren't making friends by missing the point, you know: the range of flash durations is from, roughly, 250 to 1200 microseconds, corresponding to shutter speeds of about 1/800 to 1/4000 sec.

 

http://wetpixel.com/...ial-explanation

 

Manipulating the strobe power causes more problems than it solves, largely because macrophotography uses small f-stops and you would have to get prohibitively close at low power.

 

In practice, and some of the contributors here have a lot of practice, manipulating the duration of the flash just isn't important in underwater photography, as very little moves so fast that it isn't frozen at 1/600 sec. All strobes are faster than that.

 

As has been said above it's the ambient sunlight that blurs most images, and it's the use of that ambient light that defines some of the very best underwater photography.

 

The only magicdoodoo in underwater photography is the sense that comes from spending lots and lots of time underwater with a camera, although following the advice of Martin Edge comes a reasonable second...

 

... and the problem with your original image is simply depth of field, as anemones are circular animals and it's almost impossible, when close, to have all of their tentacles at the focal point. It has nothing to do with strobe illumination.

 

 

For my part, I like to paint my pixels with the delicate wave/particle duality of nudibranch-interacting quantum electrodynamics...

 

... not too different from fairy dust, as far as most of us are concerned.

 

 

Bali 2012 89 0815 Menjangan Nudibranch.jpg

 

 

 

PS There's no "e" in even a plurality of nudibranchs: they have gills, and aren't part of the plant Kingdom.


Edited by tdpriest, 09 October 2013 - 01:52 AM.


#15 Alex_Mustard

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Posted 09 October 2013 - 01:51 AM

To confuse matters further, this was taken with flash at 1/1000th:

 

http://www.naturepho...?showimage=1106

 

I used such a fast shutter speed to be able to shoot into the sun with a wide aperture and get the pretty bokeh circles behind the fish.

 

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#16 MikeVeitch

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Posted 09 October 2013 - 03:22 AM

It also depends on the speed of your subject.  Can still freeze the motion of the subject with flash, but it also creates that "motion shadow" in both macro and wide.  I shot this shark at 1/30 trying to get some ambient light as it was 16:30 and deep, thinking that the flash would "freeze" the motion, and it did, but then I also got shadow around the fins and the remora as well as a bit around the eye as well as the divers hand.  So, although the flash "froze" the action, there was still a lot of blurry motion and shadow created by the combination of slow shutter and flash

 

250252_10150336646055211_6965197_n.jpg


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#17 bobanderson

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Posted 09 October 2013 - 09:15 AM

To confuse matters further, this was taken with flash at 1/1000th:

 

http://www.naturepho...?showimage=1106

 

I used such a fast shutter speed to be able to shoot into the sun with a wide aperture and get the pretty bokeh circles behind the fish.

 

Alex 

 

 

Righto, without blowing too much smoke up your arse: I like this picture for two reasons both inextricably linked. To me there is a deep understanding both the tools used to take this picture and the animal itself so the technique/proces/photo stuff brings out the attributes of the fish which gives me a real flavour of the animal in a sympathetic, endearing way and tell a story too. There is more than just a portrait at work here, there is a story told too.

 

Likewise with the shark, the image portrays a moment, an action, an emotion and a story about the animal. There are a thousand words told.

 

I work in scapa which is home to some of the worlds greatest wrecks yet they have a skin of organisms which are under-represented that also have a story to tell but too many of the 'usual' (sorry wrong word but I don't have a better one to hand) macro techniques fail to tell the wider picture. When I dive, the animals are in green water, they don't have black backgrounds. They are moving, dynamic part of a whole organism, be that a wreck. They have "location", if you like.

 

I have never before seen a picture of the tentacles of a sea urchin frozen against a green background. I didn't know each one had a crown at the end and a small lump on one side slightly further down. To me that is interesting and part of the story it would be nice to tell and in order to do that I have to explore the set of circumstances that led me (albeit by happenstance) to take that picture. I have never managed to take that picture any other way but don't know how to vary what I am doing to expand the range of possibilities. There is something to understand here which I can't grasp and from my reading of the replies, it seems is not widely known either.

 

I appreciate the technical suggestions offered, I would like to hear more. Thank you for taking the time to reply and if you have any "I wonder what would happen if" thoughts, I would be chuffed to bits to hear. I know the question is asked poorly but I don't know what I am asking really so I'm stuck!

 

Thanks loads



#18 tdpriest

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Posted 09 October 2013 - 10:37 AM



 

I have never before seen a picture of the tentacles of a sea urchin frozen against a green background.

 

Urchin?

 

Shetland 2011 12 1234 Bohus .jpg

 

 

Or anemone?

 

Bali 2012 24 0384 Tulamben Anemone.jpg

 

 

The second image is a cheat, because it's tropical.

 

Scapa photography is difficult: I have great respect for your plan. Last time out (on board Valkyrie), not only did I tread in fear of Hazel, I only managed black & white photography:

 

 

2009 Scapa Flow 008 117 Seydlitz wreckage .jpg



#19 bobanderson

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Posted 09 October 2013 - 12:06 PM

Urchin: nice picture, I like it, but what the story doesn't tell was that it now grazes the wreckage of this ship..

 

 

 

283955155_803cc10875_m.jpg

 

Like your photo, there is a greater depth to my question than you are giving credit.