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Forums Lobby MASTER YOUR TOOLS - Hardware & Software Nikon Speedlights & Lighting topic #61480
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Subject: "Guide Number vs ISO vs Duration" Previous topic | Next topic
grnzbra Registered since 28th Sep 2011Wed 15-May-13 02:26 PM
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"Guide Number vs ISO vs Duration"


Springfield, US
          

I have been shooting small birds flying across a three foot gap between a bush and a feeder. In order to freeze the wings, the shutter is set to 1/4000 sec, which then requires an ISO of 4000 in bright sunlight. However, at this time of year, the gap is in shadow at the time when the birds are most actively feeding. So I was hoping I could do something with an SB-700.

According to a review of the SB-700, it has a guide number of 92 at ISO 100 and a flash duration as short as 1/10000 second at a manual setting of 128 and a duration of 1/5000 second somewhere in the middle of the adjustment range.

So far, my cut-and_try efforts have not resulted in the freezing of the wings, which I assume is due to the shutter now limited to 1/200 second (I'm using a D-5100).

Is there any way to calculate where the guide number would go with a change in flash duration and ISO setting?

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Replies to this topic
Subject Author Message Date ID
Reply message RE: Guide Number vs ISO vs Duration
kodiak photo Silver Member
15th May 2013
1
Reply message RE: Guide Number vs ISO vs Duration
grnzbra
15th May 2013
2
     Reply message RE: Guide Number vs ISO vs Duration
kodiak photo Silver Member
15th May 2013
3
     Reply message RE: Guide Number vs ISO vs Duration
grnzbra
15th May 2013
6
          Reply message RE: Guide Number vs ISO vs Duration
kodiak photo Silver Member
15th May 2013
7
     Reply message RE: Guide Number vs ISO vs Duration
MEMcD Moderator
15th May 2013
4
Reply message RE: Guide Number vs ISO vs Duration
MEMcD Moderator
15th May 2013
5
Reply message RE: Guide Number vs ISO vs Duration
grnzbra
15th May 2013
8

kodiak photo Silver Member Nikonian since 28th Feb 2013Wed 15-May-13 03:11 PM
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#1. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 0
Wed 15-May-13 03:12 PM by kodiak photo

Montrιal, (Qc), CA
          

*
Hi there,

I understand your problem,

but I would need to know
•where your flash is ? and
•how far you (the camera) are from the subject ?

I'd be glad to help you,

Kodiak
Groovy Shootings
Image Mιdia
www.kodiakmedia.at

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grnzbra Registered since 28th Sep 2011Wed 15-May-13 04:16 PM
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#2. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 1


Springfield, US
          

The flash is on top of the camera and the distance is 15 feet. The lens is a Sigma 150 - 500mm f5.3-f6, usually set at 500mm.

With the flash set at 128, it didn't seem to bother the birds, but at 16, they seemed to dislike it.

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kodiak photo Silver Member Nikonian since 28th Feb 2013Wed 15-May-13 04:41 PM
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#3. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 2


Montrιal, (Qc), CA
          

*
Hi C. Lind Aitken,

I was hoping no to get this setup information!

As you noticed, at low flash power, the birds are not
disturbed. OK!

But in these conditions, your setup is not working. Not OK!

My 1st question was where is the flash: on camera
My 2nd question was where is the camera: +/- 15'. Not bad!

Your problem cannot be solved with this setup. The flash
light has to run 30 feet and you don't allow it more power
because of the birds! Humm!

What if you could reduce the distance flash/camera and
regain total freedom with your flash ?

Would that be a strategy to you liking?

Kodiak
Groovy Shootings
Image Mιdia
www.kodiakmedia.at

• • • • • • • • • • • • • • • • • • • • • • • • • • • •
In photography, light is free but catching it is not!
• • • • • • • • • • • • • • • • • • • • • • • • • • • •

  

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grnzbra Registered since 28th Sep 2011Wed 15-May-13 06:15 PM
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#6. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 3


Springfield, US
          

I might be able to move the flash, but not the camera. It depends if the flash will fire multiple shots while being radio controled. I can't move the camera because these little guys are naturally nervous to begin with. As it is, after I go out on the deck and set up I have to sit pretty much perfectly still for about 15 minutes before they come back. Wouldn't moving the flash closer have the same effect on the birds as increasing the power?

I was hoping to be able to calculate some apperture/ISO settings that would give me a starting point where flash, at 128, would light up the birds but wouldn't allow the ambient light (this is about 3:00 to 5:00 in the afternoon) to show the motion.

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kodiak photo Silver Member Nikonian since 28th Feb 2013Wed 15-May-13 06:34 PM
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#7. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 6


Montrιal, (Qc), CA
          

>I might be able to move the flash, but not the camera.

THIS IS THE STRATEGY! Move the flash…

*
Hi C. Lind Aitken,

If the birds predictably …
• come from the same direction
• fly at the same hight (+/-),
setting up a flash or two slightly higher and behind the bird for one
and the other somewhere to brighten up the face of the bird, could
be a good solution, radio triggered that is!

Is this something you would like to explore?


Kodiak
Groovy Shootings
Image Mιdia
www.kodiakmedia.at

• • • • • • • • • • • • • • • • • • • • • • • • • • • •
In photography, light is free but catching it is not!
• • • • • • • • • • • • • • • • • • • • • • • • • • • •

  

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MEMcD Moderator In depth knowledge in various areas Nikonian since 24th Dec 2007Wed 15-May-13 05:10 PM
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#4. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 2


US
          

To maximize the freezing effect of short duration flash you must under expose for the ambient light by about 3-stops and allow the flash power to make up the difference.

Best Regards,
Marty

  

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MEMcD Moderator In depth knowledge in various areas Nikonian since 24th Dec 2007Wed 15-May-13 06:02 PM
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#5. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 0


US
          

Hi C. Lind,

The SB-700 has a flash duration of:
1/40000 sec. at M 1/128 power
1/25000 sec. at M 1/64 power
1/18182 sec. at M 1/32 power
1/10000 sec. at M 1/16 power
1/5714 sec. at M 1/8 power

If you want to use the short duration of the flash to freeze the movement of your subject you must set the camera to under expose for the ambient by 3-stops or more.
You can do this by dialing in negitive exposure compensation using P, S, or A modes our Manually in Manual exposure mode.

The SB-700 has an exposure calculator built in.
When you set it to Manual mode and adjust the power level the "Effective flash output distance" will be shown in the display. 15 feet = 3m
That should get you close. You can then tweek the exposure settings or flash power as required.

Best Regards,
Marty

  

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grnzbra Registered since 28th Sep 2011Wed 15-May-13 06:42 PM
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#8. "RE: Guide Number vs ISO vs Duration"
In response to Reply # 5
Wed 15-May-13 06:47 PM by grnzbra

Springfield, US
          

Thank you very much. I'll try it when I get home this evening (about 5:00 PM)

Placement of the flash behind the bird might decrease the startle effect on the birds. Sounds very good. Thank you.

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