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Author Topic: Best way to dampen down flash power  (Read 5401 times)

The View

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Best way to dampen down flash power
« on: May 31, 2014, 12:51:57 AM »

The minimum output of my Profoto 7b's is 37.5 ws - much too much for dark environments.

What's your experience to dampen down overly bright flashes?

This is needed in many situations like shooting at sunset - and you want to get the ambient light in and not have the background go black.

Or, even more so, in barely lit interiors.

I could put a sock over my beauty dish, but that won't do much, and if I used thicker fabrics - who knows what kind of light I will get out of it.

The other way would be to blast out the ambient light and light everything by flash. But that's now what I want (and I can't go out and buy a couple of new Profoto generators that go down to 9 ws).
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BartvanderWolf

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Re: Best way to dampen down flash power
« Reply #1 on: May 31, 2014, 03:42:41 AM »

The minimum output of my Profoto 7b's is 37.5 ws - much too much for dark environments.

What's your experience to dampen down overly bright flashes?

Hi,

Other than covering some of the light modifier's surface (assuming you cannot use a larger modifier further back/away, and your ambient exposure time is fixed due to subject motion), how about a double exposure? One exposure for the background without flash, and one with flash (to be reduced in relative weight by an exposure adjustment layer in Photoshop) should do it.

Or is the flash so powerful that the flash exposure over-exposes anyway, and you cannot increase the distance between flash and foreground? In that case an ND filter with a longer ambient light exposure should do it.

Cheers,
Bart
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sharperstill

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Re: Best way to dampen down flash power
« Reply #2 on: May 31, 2014, 04:27:08 AM »

ND gel?
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The View

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Re: Best way to dampen down flash power
« Reply #3 on: May 31, 2014, 04:54:13 AM »

ND gel?

Good idea, thanks.

Where would you put the gel to reduce the light out of a beauty dish for two stops?

As far as I know, one doesn't want to cover the front side. It would be somewhere closer to the flash head. Would I create a cylinder out of ND gel and put it over the dispersing disc of the dish, so no light can ever get out without passing through the nd gel?
« Last Edit: May 31, 2014, 05:05:55 AM by The View »
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sharperstill

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Re: Best way to dampen down flash power
« Reply #4 on: May 31, 2014, 05:18:03 AM »

Putting it there might also double it's effect as the light will pass through it twice (in theory).
Best to test of course.
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Ellis Vener

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Re: Best way to dampen down flash power
« Reply #5 on: June 02, 2014, 03:22:09 PM »

Good idea, thanks.

Where would you put the gel to reduce the light out of a beauty dish for two stops?

As far as I know, one doesn't want to cover the front side. It would be somewhere closer to the flash head. Would I create a cylinder out of ND gel and put it over the dispersing disc of the dish, so no light can ever get out without passing through the nd gel?

The only sensible place  to put the get is across the front of the Beauty Dish. Putting it next or near to to the flash tube will cause a maximum heat build up in a confined space. That could get messy, expensive, or both. For the same thermal reasons make sure you leave a gaps at the top and bottom of the get when you put it across the front of the BD so heat can escape.

Alternatively:  Does the Profoto Beauty Dish take a grid? Sure you'll get a narrower beam of light  (less spill) but that isn't necessarily a bad thing.
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BobShaw

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Re: Best way to dampen down flash power
« Reply #6 on: June 15, 2014, 04:16:34 AM »

The two easy ways to reduce the flash by two stops are:
1. Double the distance
2. Slow the shutter by two stops and decrease the aperture by two stops and tell the model to stand very, very still, ideally shooting with a tripod

You can also swap the beauty dish for a soft box. I assume you have a diffuser on the beauty dish?
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MrSmith

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Re: Best way to dampen down flash power
« Reply #7 on: June 15, 2014, 06:04:52 AM »

Plug another head in (if you can) or use an ND.
Adding a 1/4-1/2 CTO/CTB to balence the flash to ambient colour temperature is going to bring it down too.
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Fine_Art

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Re: Best way to dampen down flash power
« Reply #8 on: June 15, 2014, 01:59:56 PM »

The two easy ways to reduce the flash by two stops are:
1. Double the distance
2. Slow the shutter by two stops and decrease the aperture by two stops and tell the model to stand very, very still, ideally shooting with a tripod

You can also swap the beauty dish for a soft box. I assume you have a diffuser on the beauty dish?

Yes, bounce it off something further away.

There are lots of ideas here:
http://www.youtube.com/channel/UCUbAIlQq6qdOCW7nURh9Qog
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MrSmith

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Re: Best way to dampen down flash power
« Reply #9 on: June 15, 2014, 03:14:45 PM »

All of the above change the look of the light though, beauty dishes have a unique look which changes as you move it further away. "Tell the model to stand still" ??  ???
Not trying to be funny but i wonder if a lot of people base their answers on actual shoot experience or something they read on the internet somewhere?
Me I would have some pre/cut discs of .3 .6 .9 ND of the same diameter as the dish in the bag and just use clips/tape to get the f stop you need.
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Ellis Vener

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Re: Best way to dampen down flash power
« Reply #10 on: June 16, 2014, 08:18:01 PM »

Me I would have some pre/cut discs of .3 .6 .9 ND of the same diameter as the dish in the bag and just use clips/tape to get the f stop you need.

yep.

I could put a sock over my beauty dish, but that won't do much, and if I used thicker fabrics - who knows what kind of light I will get out of it.

There's a simple way to find out.
« Last Edit: June 17, 2014, 05:06:26 PM by Ellis Vener »
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BobShaw

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Re: Best way to dampen down flash power
« Reply #11 on: June 19, 2014, 03:34:57 AM »

"Tell the model to stand still" ??  ???
Not trying to be funny but i wonder if a lot of people base their answers on actual shoot experience or something they read on the internet somewhere?
Me I would have some pre/cut discs of .3 .6 .9 ND of the same diameter as the dish in the bag and just use clips/tape to get the f stop you need.
You are neither funny nor polite, however I was interested in helping the OP, who already said he didn't want to cover the flash.

It's called "Dragging the Shutter", and predates the Internet. Generally flash will freeze the foreground but if you slow the shutter enough then ambient will affect the subject.
If you are already running a slow shutter for the ambient then going even slower may introduce more movement.

Changing the aperture and shutter speed takes a couple of clicks. Sure you can fiddle with the lights but the sun will be gone by the time you finish.
« Last Edit: June 19, 2014, 03:36:48 AM by BobShaw »
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Dave Pluimer

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Re: Best way to dampen down flash power
« Reply #12 on: July 03, 2014, 02:23:04 PM »

In flash, aperture is the main on-camera control. Shutter, as already pointed out, mostly controls ambient light.

Try stopping your aperture down.
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Ellis Vener

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Re: Best way to dampen down flash power
« Reply #13 on: July 03, 2014, 03:26:45 PM »

Try stopping your aperture down.
That of course will mean going to a longer shutter speed or raising the ISO  - assuming of course that the aperture+shutter speed+ ISO setting without the flash are already producing the overall exposure that he wants. It may also increase the apparent depth of field beyond what he is looking for.
adding a second head and having  it fire into a box or pointing up into space away from the subject  will also drop the energy going to the flash by a half.

Honestly it sounds like he is a prime candidate for the Profoto B1 instead of the Pro 7b.

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Ellis Vener
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Ajoy Roy

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Re: Best way to dampen down flash power
« Reply #14 on: August 10, 2014, 09:25:38 AM »

The only method that is easily implementable is to use extra heads (if it is supported) and point them some where else. Two heads should half the power and three make it one third. Apart from this the only other method is to change the power pack, but that is expensive.
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Chris_Brown

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Re: Best way to dampen down flash power
« Reply #15 on: August 10, 2014, 12:00:51 PM »

I use an ND on the lens. This allows me to place lighting wherever I need/want.
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Re: Best way to dampen down flash power
« Reply #16 on: August 10, 2014, 12:56:38 PM »

Good idea, thanks.

Where would you put the gel to reduce the light out of a beauty dish for two stops?
All depends on your particular flash attachments.
ND gels come in different strenght 1 stop, 2 stop, 3 stop etc. Often referred by .3, .6, .9 which is a log scale IIRC.
Either way you can get a roll of 0.5 or 1 stop gel and fold it over/wrap around until it dims enough for the task at hand.
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Ellis Vener

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Re: Best way to dampen down flash power
« Reply #17 on: August 10, 2014, 01:44:35 PM »

The only method that is easily implementable is to use extra heads (if it is supported) and point them some where else. Two heads should half the power and three make it one third. Apart from this the only other method is to change the power pack, but that is expensive.

Dope slap! I completely forgot about that very sensible option!
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digitaldog

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Re: Best way to dampen down flash power
« Reply #18 on: August 10, 2014, 02:09:07 PM »

Plug another head in (if you can) or use an ND.
That's what I did with my old Balcar units. But they are pretty darn old so I don't know if modern strobes work the same way. I also recall head extenders might have reduced the consumption too.
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Ellis Vener

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Re: Best way to dampen down flash power
« Reply #19 on: August 10, 2014, 02:15:50 PM »

The old "second (or third or fourth)  head trick firing into space or a box" trick still works if the flash you are working with has multiple head connections and can be switched into symmetric energy distribution.

Some systems have automatic asymmetric energy distribution as a default when two heads are plugged in, and plugging the head you are using into the weaker side (some packs have a built in 2:1 ratio)  and the unused head in to the more powerful port works as well.
« Last Edit: August 10, 2014, 02:24:18 PM by Ellis Vener »
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