What kind of power will I need to overpower the sun?

[njmanigan]

I am looking to purchase some studio strobes, but I want to be able to use these outside as well on a brightly lit sunny day. What kind of wattage will I need from a strobe set that will overpower direct sunlight from behind the subject and nicely light the subject as well as give me a nice blue sky in the background?

Thanks in advance for any helpful suggestions and tips. :)

[mattograph]

Questions to consider:

1) How close will you be to the subject? The closer you are, the closer your light source can be and remain out of view, and the less juice you will need.

2) How will you modify the light? Are you looking for soft light from the strobes, which means a modifier (and more gas) or a hard light (which needs less).

3) Where are you shooting from? Are you shooting directly into the sun, which causes exposure difficulties, or will you be shooting cross light, which is easier on the camera and requires less power?

If we assume that you will want the equipment that will give you the juice to handle the worst case scenario, check out the alienbees. An AB800 with their vagabond portable power pack will set you back about $500, but will give you the juice you need.

For an interesting take on this subject, check this out. The speedlight tree is kinda funny.

http://strobist.blogspot.com/2008/05/joe-mcnally-desert-shoot.html

[njmanigan]

Questions to consider:

1) How close will you be to the subject? The closer you are, the closer your light source can be and remain out of view, and the less juice you will need.

2) How will you modify the light? Are you looking for soft light from the strobes, which means a modifier (and more gas) or a hard light (which needs less).

3) Where are you shooting from? Are you shooting directly into the sun, which causes exposure difficulties, or will you be shooting cross light, which is easier on the camera and requires less power?

If we assume that you will want the equipment that will give you the juice to handle the worst case scenario, check out the alienbees. An AB800 with their vagabond portable power pack will set you back about $500, but will give you the juice you need.

For an interesting take on this subject, check this out. The speedlight tree is kinda funny.

http://strobist.blogspot.com/2008/05/joe-mcnally-desert-shoot.html

Hi Matt,

Thanks for the reply. To answer your questions,

1. I wont be any further away than about 15-20 feet from the subject.
2. Large softboxes and maybe shoot-through umbrellas. Soft light, probably not hard light.
3. Shooting mostly when the sun is overhead. But if the sun is lower, I may have the subject blocking the sun with their head or upper body, and then I want to have enough power to light the subjects body and face with soft light.

Hope this info helps. Thanks for the tip about the alienbees and power pack. I hear nothing but good things about AB's. :)

[suyenfung]

as much as you can afford. i would say 1200ws minimum to be covered in the scenario you describe.

[TMR Design]

Agreed. If you're going to be as much as 15 or 20 feet away that means your lights are going to be some distance from your subject so as to not be in frame. An Alien Bee B800 with 320ws is just not going to cut it.

I've gone though this myself and quite honestly, if you can get away with shooting at other times instead of in midday sun that's your best bet and will save you a ton of cash. Competing, much less overpowering the sun is a tall order.

At close range things change dramatically, and in early morning or late afternoon light you'll have a much easier time as well.

If you're insistent on working in midday sun at that distance I would say that 500 to 600ws is the minimum I would get and you'll still be limited in terms of working apertures.

A 1000 or 1200ws strobe is probably what you're looking at to do what you want and cost goes way up for something like that. Depending on brand and analog vs. digitally controlled strobes you may also find the V2 incompatible.

[René Damkot]

15 - 20 foot subject to light distance is *far*.
You need a huge modifier to get soft light then... (which has an added drawback of acting like a "sail" and being blown over unless you're carefull and use sandbags)

I'd get the light in as close as possible....

GN would need to be 20*11 = 220 (feet) when shooting at ISO 100 (sunny sixteen gives abour 1/200 (sync, more or less) at f/11 then).

So a 580ex without modifiers would just be too weak. (GN of max. 191)

Something with a bit more power might be needed. 400Ws should just do IMO.
If you want to overpower the sun, you'll need more still.

[mattograph]

That is indeed far back. Didn't anticipate that distance.

A shoot thru umbrella is designed to get up tight -- at that distance, it would be virtually useless, unless it was about 8 ft wide :).

A closer light and a wider lens might be the answer -- you might already have that in your arsenal.

Now -- a couple white lightnings fired into a lastolite hi-lite -- that might do it!

[DocFrankenstein]

You'll need a 1200 ws powerpack at a minimum. Or 2400 - that's just one stop more.

It's cheaper to rent it when you need it - anything decent will run you about 2-3 grand new.

[René Damkot]

and a wider lens

Focal length of the lens has nothing to do with the issue at hand, as long as the light is as close to the subject as possible, and *just* outside of the frame, you're fine...

[Wilt]

I am looking to purchase some studio strobes, but I want to be able to use these outside as well on a brightly lit sunny day. What kind of wattage will I need from a strobe set that will overpower direct sunlight from behind the subject and nicely light the subject as well as give me a nice blue sky in the background?

Thanks in advance for any helpful suggestions and tips. :)

For anyone reading this thread, here is the approach you can take...

1. Use the Sunny 16 rule for estimating exposure in sunlight...
e.g. ISO 200, 1/ISO f/16 is the Sunny 16 rule...
2. Adjust the Sunny 16 shutter speed (and aperture) to your max X-sync speed for studio flash chose (some do NOT let you use max X sync speed of the camera body, which assumes speedlight not studio flash use!)
3. For the subject-to-light distance involved, multiply times the aperture in Step 2, to calculate the GN at the ISO chosen.

I suggest ISO 200 for calculations for APS-C bodies because that is often just under the max X sync speed, which is what is often needed for studio flash with APS-C dSLRs. Then by multiplying the ISO 200 Guide Number by 0.7x you get the ISO 100 guide number.

Applying this principle to the OP...
(Assume ISO 200, distance of 15' from light-to-subject)
Sunny 16 = 1/200 f/16
16 * 15' = ISO200 GN rating of 240, 240 * 0.7 =ISO100 GN rating of 170

Now you have a basis for determining the ability of the flash to equal the power of the sun.

[mattograph]

Focal length of the lens has nothing to do with the issue at hand, as long as the light is as close to the subject as possible, and *just* outside of the frame, you're fine...

It does, if you have to be 15 feet away to get everything in the frame, which is where I was going. (and where you were taking me.)

[cvt01]

I like this article on the subject:
http://www.stepheneastwood.com/tutorials/skychart/skychart.htm

[TMR Design]

For anyone reading this thread, here is the approach you can take...

1. Use the Sunny 16 rule for estimating exposure in sunlight...
e.g. ISO 200, 1/ISO f/16 is the Sunny 16 rule...
2. Adjust the Sunny 16 shutter speed (and aperture) to your max X-sync speed for studio flash chose (some do NOT let you use max X sync speed of the camera body, which assumes speedlight not studio flash use!)
3. For the subject-to-light distance involved, multiply times the aperture in Step 2, to calculate the GN at the ISO chosen.

I suggest ISO 200 for calculations for APS-C bodies because that is often just under the max X sync speed, which is what is often needed for studio flash with APS-C dSLRs. Then by multiplying the ISO 200 Guide Number by 0.7x you get the ISO 100 guide number.

Applying this principle to the OP...
(Assume ISO 200, distance of 15' from light-to-subject)
Sunny 16 = 1/200 f/16
16 * 15' = ISO200 GN rating of 240, 240 * 0.7 =ISO100 GN rating of 170

Now you have a basis for determining the ability of the flash to equal the power of the sun.

Thank you Wilt. That's excellent!

[René Damkot]

It does, if you have to be 15 feet away to get everything in the frame, which is where I was going. (and where you were taking me.)

Only if the subject is centered :p

[René Damkot]

ISO100 GN rating of 170

Now you have a basis for determining the ability of the flash to equal the power of the sun.

About the same as what I was getting ;)

Be aware however that this is the GN *with modifier*. So if you use a big softbox, the flash might need to have a GN of maybe 1,5 stops more !

[njmanigan]

Thanks for the great tips and healthy discussion. You're correct, I should anticipate to have the light closer to my subject. I dont want to be using 8 foot modifiers. ;)

Following the sunny 16 rule, and using a couple of B800s at a close enough range, I should be able to get the results I am looking for i think. Im just not prepared to spend 2-3 grand on lights. :)

[Wilt]

About the same as what I was getting ;)

Be aware however that this is the GN *with modifier*. So if you use a big softbox, the flash might need to have a GN of maybe 1,5 stops more !

While what René says is true, it is also necessary for us to remind that very often you do not want light as bright as the sun, because seeing someone 'in shade' but illuminated as intensely as in the sunlight looks horribly unnatural to the eye!

[njmanigan]

While what René says is true, it is also necessary for us to remind that very often you do not want light as bright as the sun, because seeing someone 'in shade' but illuminated as intensely as in the sunlight looks horribly unnatural to the eye!

You have a good point there. Now that I think about it, I only want to have pleasing light on the subject, not have a power source with equal intensity of the sun. I guess you could say that I want a nice balance that looks natural, and yet light the face and body appropriately.