How Much Flash Power Do You Really Need

[doidinho]

Looking at the Alien Bee 800 and 1600 untits. I do a lot of outdoor stuff, so the 1600 would probally be more usefull; but how oftern (under what situations) would the 800 not be able to deliver enough power. Would the 1600 allow me to say have the sun as fill light w/ a 4:1 ratio at high noon on a bright sunny day. No experience with these large flash units, so I'm just trying to get an idea of what I couold do with them.

[doidinho]

Follow up question: if I wanted to use my speedlights with the AB flash would the 800 be able to provide enogh light to render the speedlights virtually useless or would I be still be able to use the speedlights with the the the 800 at it's highest output level?

[Curtis N]

The single most important factor in flash power requirements is distance. Move it in tight for a headshot and even the B400 will be plenty. Back it up 20 feet for a big group shot and a pair of B1600s may not be enough to compete with the sun.

I have used studio strobes and hotshoe flash units together. There are limitations, but sometimes flash units can be effective as hair or background lights.

[Lotto]

At high noon, B800 does not have enough juice to be used with modifiers like SB and umbrellas, to work with practical shooting distance. With 7" reflector, it has barely enough to over power the sun from 6-8 ft.

The B1600 gives one stop more light. Like Curtis says, if you move it closer to the subject, I guess you could get that 4:1 ratio.

If I don't have to shoot at hight noon, then the options for shutter speed, DOF, and modifiers will open up.

According to AB, the guild number for the B800 with the 7" reflector is 172, the 580EX at 105 zoom setting is 190, so speedlights can be quite powerful as bare flash.

[bobbyz]

You might want to take a look at white lighting X1600 which gives you AB1600 and AB400 in 1 strobe.

[doidinho]

The single most important factor in flash power requirements is distance. Move it in tight for a headshot and even the B400 will be plenty. Back it up 20 feet for a big group shot and a pair of B1600s may not be enough to compete with the sun.

I have used studio strobes and hotshoe flash units together. There are limitations, but sometimes flash units can be effective as hair or background lights.

Hmm, I didn't think about the factor of light falloff. If I will mostly be shooting one person (full body) do you think the 800 would be more usefull. Do you know of any online resources that my help me make mye decision?

At high noon, B800 does not have enough juice to be used with modifiers like SB and umbrellas, to work with practical shooting distance. With 7" reflector, it has barely enough to over power the sun from 6-8 ft.

The B1600 gives one stop more light. Like Curtis says, if you move it closer to the subject, I guess you could get that 4:1 ratio.

If I don't have to shoot at hight noon, then the options for shutter speed, DOF, and modifiers will open up.

According to AB, the guild number for the B800 with the 7" reflector is 172, the 580EX at 105 zoom setting is 190, so speedlights can be quite powerful as bare flash.

I will check out the tech specs on the strobes. Thanks

You might want to take a look at white lighting X1600 which gives you AB1600 and AB400 in 1 strobe.

Oooh, very nice, and very expensive. A little more than I want to spend considering I will be getting the power pack as well.

[symbolphoto]

Good information Lotto, thanks.

[epatt250]

According to AB, the guild number for the B800 with the 7" reflector is 172, the 580EX at 105 zoom setting is 190, so speedlights can be quite powerful as bare flash.

You are not comparing apples to apples. The guide rating for the flash is measured with it at its max zoom reach. The 7" reflector will have a much wider field of coverage than that. You are more measuring the internal reflector design than true 'power'.

For whats its worth. Last week I measured an AB800 against a 540EZ (set to 35mm zoom) with a shoot thru umbrella. Center of umbrella was 45" from the meter and the umbrella was a 43" westcott convertible.

AB800=f16 1/10
540EZ=f8 1/10

I also measured my Sigma 500 Super and it came it at F8 0/10. So given that there is guide number difference of 4 between it and the 540, you can guesstimate how much more powerful a 580 would be. Speedlites can do very well and many times I use them indoors b/c I like to get very close with the shoot thrus and just dont need the power of the AB800. However speedlites cannot compete with studio strobes for raw power, especially when using modifiers.

[Lotto]

That's true, epatt. I had the similar measurements on the 580 with a umbrella, about 1/4 of the power of the B800.

I just did another meter read with the 580 bare flash, full power @ 50 mm zoom, iso100 at 8 ft, I got f13, so without modifiers, the 580 can provide some nice working apertures.

[Curtis N]

Do you know of any online resources that my help me make my decision?Start with the Alienbees specifications.
http://alienbees.com/specs.html

They give you approximate apertures at a 10 ft. distance with various modifiers. Knowing that distance times aperture is always the same with a given flash and modifier, you can calculate the apertures at other distances.

To properly expose mid-day sun at 1/250 shutter speed you'll be around f/10. To underexpose that by 2 stops to get your 4:1 ratio, you'll need to be around f/20. That's a worst case scenario. Like Lotto mentioned, if you shoot during early morning or late afternoon and you'll have a lot more lattitude.

[Rudi]

Just an aside, but I hate the way AB give you the "effective Ws"! WTF is that?? ??? Why not just call is a B320 instead of the B800 and make it easier on everybody? Marketing at its worst! :(

[pcunite]

Looking at the Alien Bee 800 and 1600 untits. I do a lot of outdoor stuff, so the 1600 would probally be more usefull; but how oftern (under what situations) would the 800 not be able to deliver enough power?

Medium Format Digital.
You need another two stops of light from what 35mm needs.

[Curtis N]

Medium Format Digital.
You need another two stops of light from what 35mm needs.You're going to have to explain that one.

[pcunite]

You're going to have to explain that one.

Say you have a scene that with 35mm the exposure is:
ISO 200 f5.6 1/250 (flash sync). To get the same DOF with MFD it would be ISO 200 f11 1/250. Thus you need more powerful lights.

This problem (or preference) only gets worse the larger the format...

[Curtis N]

Say you have a scene that with 35mm the exposure is: ISO 200 f5.6 1/250 (flash sync). To get the same DOF with MFD it would be ISO 200 f11 1/250. Thus you need more powerful lights...A valid point, though increasing the ISO is an option if you want to preserve the DOF with a smaller aperture. There are always trade-offs. Sometimes a shallower DOF is a good thing, and it's part of the reason for using a larger format camera.

And I would point out that the scenario you describe does not apply to an outdoor situation where DOF is not a concern but competing with the sun is.

[pcunite]

A valid point, though increasing the ISO is an option if you want to preserve the DOF with a smaller aperture.

Unfortunately only the most expensive MFD backs look good past ISO 400 :(