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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 17 May 2007 (Thursday) 08:16
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studio - flash duration

 
vladnl
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May 17, 2007 08:16 |  #1

G-day people.
In couple of months, I'll be reinvesting in some strobes. I do mainly fashion, pregnancy and kids photography. To day I've photographed my son with some el-cheapo strobes, 150w and apparently 1/800-1/1000 flash duration, but I tend not to believe to the manufacturer, considering it's coming from China. Like any boy, my son couldn't keep still. I had enough of good images, but I've seen few with some motion blur in them. What I'd like to know is in which direction should I look at? How fast strobes should I buy in order to freeze children? :) giving me opportunity of having keepers. I am happy with my rate at the moment, but I'd like to be as closest to perfection as I can.
Now my problem follows...
We don't have AB's here, and I see FD on them is 1/6400. In that price range in EU, we have only Chinese stuff with FD varying from 1/800 to say 1/2000. Bowens units 1/800, Elinchrome 1/2050 but we're talking about massive increase in price.
Some people are shooting here with Jinbei (external link), and I'm looking at that unit or Elinchrome D-lite 2, but then I suffer 300w/s less, or 600 if I buy set of two. Unfortunatelly D-lite 4 has 1/800 flash duration, and I don't think that should be fast enough for my needs.

What do you guys think? Any oppinion would be appreciated.

Cheers
Vlad


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awad
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May 17, 2007 10:13 |  #2

man. 1/800 should be WAY more than enough to freeze motion from children. what was your shutter speed?


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PacAce
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May 17, 2007 10:16 |  #3

I don't think it's the flash duration that's your problem as most flashes won't have any problem freezing the motion of even very active children. Your problem is the shutter speed you have the camera set to and the ambient lighting that is being captured by the camera in addition to the stobe lighting. To reduce the effect of ambient lighting on your exposure, use as high a shutter speed as possible. Try setting your aperture to max sync speed (1/200 or 1/250) and see if you still have problems with motion blur.


...Leo

  
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vladnl
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May 17, 2007 10:29 |  #4

1/125s. But as far as I know Flash exposure is not affected by shutter speed. I've shoot in dim conditions, so no day or ambiental light, only strobes.


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PacAce
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May 17, 2007 10:36 |  #5

vladnl wrote in post #3221053 (external link)
1/125s. But as far as I know Flash exposure is not affected by shutter speed. I've shoot in dim conditions, so no day or ambiental light, only strobes.

You're right, flash exposure is not affected by shutter speed. It was the ambient light we were talking about. But since the room is dim, ambient light obviously isn't a problem. How about switching to an external flash instead of using a strobe. External flashes can have a much shorter duration than strobes, especially at less than full power.


...Leo

  
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Curtis ­ N
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May 17, 2007 10:44 |  #6

This is a puzzling thread. Makes me wonder if the blur problems you're seeing aren't from subject movement, but something else. Can you post a sample?


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FlashZebra
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May 17, 2007 10:57 |  #7

Even a 1/500 second flash burst length is sufficient to freeze subject movement in low light conditions.

There is some piece of important info missing in the OP's initial thread.

Is there any possibility the ambient light is a lot higher than your estimate? Are you positive about your shutter speed setting?

Are you using long telephoto lenses for the session?

An image showing the defect with EXIF data would like ferret out the issue most efficiently.

Enjoy! Lon


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PacAce
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May 17, 2007 12:18 |  #8

I wondering if the ISO is so high that even though the room may be considered dim, the light is still bright enough at the ISO setting that it's registering in the picture.


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May 17, 2007 13:23 |  #9

My take on this is that the OP is seeing blur, but that the reason for the blur is not the flash burst speed of the electronic flash they are using.

In other words there is an observable defect but the assignable cause for the defect is not a slow electronic flash.

Enjoy! Lon


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vladnl
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May 17, 2007 15:23 |  #10

This thread is cooking without me :)
Guys, I know what I'm doing :) And I am happy with the results, only looking to improve keeper rate. I always shoot ISO100 when using strobes, I shoot from 1/125 to 1/250, deppending on basically nothing (I use strobes only in studio). I'll post images, it's usually happening with limbs in movement, where I see motion blur. So we have ISO 100, 1/125 f from 5.6 to 11 focal lenghts 30, sometimes 50 and sometimes 70-200.
Wait a minute, I have one picture of the baby on the server where the same thing is happening....

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
Byte size: ZERO | Content warning: NOT AN IMAGE


Check the right foot.
I've seen the same motion on somr of the Franks jumping models.

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vladnl
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May 17, 2007 15:43 |  #11

Okay just to add, previous shot was shot at f8.0 1/125 at 131mm (70-200F4) Iso 100.
And then following two shots... what I came to realise is that effect is noticable in the parts of the image that are not in focus, but it is not typical oof, not for me at least :)
here are two more samples both of them shot with 30mm lens, f6.3 1/125 iso 100.

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
Byte size: ZERO | Content warning: NOT AN IMAGE


IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
Byte size: ZERO | Content warning: NOT AN IMAGE

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PacAce
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May 17, 2007 17:11 |  #12

OK, it looks like the close proximity of the subject to the camera is "amplifying" the movement of the subject so that the relatively "slow" strobe is not able to freeze the motion. Other than getting strobes with a much shorter flash duration, I'm not sure if there's a way to get around this problem unless the subject sits still. :confused:


...Leo

  
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vladnl
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May 17, 2007 17:25 |  #13

Hi Leo,
that corresponds with last two images, but the first one with a baby is also weird. See that dof is good, everything sits good in focus, except that tiny right foot. That actually makes me wonder more than last two images, where hands from my son are quite oof, with addition of motion blur *imo*.


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May 17, 2007 17:38 |  #14

Vlad, I don't think that you are seeing any motion blur. What you are seeing appears to be out-of-focus areas within the image. You are probably using fairly wide apertures and the depth of field is too short to get the entire subject in focus. I think it's just that simple.

Getting further from the subject would help the depth of field and possibly improve perspective for portraits. Getting further away would require longer focal lengths, of course.


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Curtis ­ N
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May 17, 2007 18:04 |  #15

Okay, time for a little math.

I can wave my arm, moving my hand in a two-foot arc, four times in the duration of one second.
That's an average velocity of 8 ft or 96 inches/sec.
During a flash duration of 1/800 second, my hand will move 0.12 inches.
That's enough movement to create the kind of blur shown in the second shot (the boy with his hand in front of his face).

I have never measured the velocity of a baby's foot, but I reckon they can kick pretty quick when they're in the mood to do so.


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studio - flash duration
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