Confused about flash output...

[matty D]

I recently attended a workshop where we only used bare speedlights, and was amazed that these little things could put out so much juice! I was using an SB 900, zoomed in to 105mm and it was giving good exposures at f16 from about 10'.

I also own a Profoto B1, so as an experiment at home, I set up the B1 next to the SB900 (zoomed to 105mm), and fired them both on full power at my light meter. I was surprised to see that the B1 was only 0.4 stops more powerful. WTF! I thought these were supposed to be '10 times more powerful than a speedlight'. I feel a bit cheated by the B1 now!

Fair enough the speedlight doesn't have the spread that the B1 has, and add a modifier and I'm sure the differences will be greater, but still a bit surprised at how little difference in output there was.

 

[Nionyn]

If you had no modifier on the B1 that made its beam spread also roughly equivalent to your hotshoe flash's zoom set to 105mm, it's really an apples to oranges comparison.

Try it again with your hotshoe flash set to its widest. With your B1 still bare (no reflector) it will still cover a much greater area than the hotshoe flash, but will also be very much brighter.

Try it with both flashes in identical modifiers and you will have a much fairer, accurate and meaningful comparison.

 

[Garry Edwards]

As above.
Also, bear in mind that, leaving the effect that the zoom has on the exposure aside (for the moment), the modifier can make an enormous difference.
And the built in reflector on a hotshoe flashgun has an almost mirror-like surface which is extremely efficient in terms of the amount of light that it delivers, but which, because of this and its very small size, is extremely harsh.

For an apples -v- apples comparison, don't just stick the zoom on its widest, stick it in a modifier such as a softbox and do the same with the other flash - the effect that this has on delivered energy will be dramatic.

Lighting is at least as much about quality as quantity.

 

[matty D]

Ok so I retested following the above advise, and sure enough, at the widest zoom, the SB900 was exactly 2 stops under the B1.

And through a 100cm octa the B1 lost 2/3 of a stop, and the SB900 lost 3 stops!

Thanks for the explanations

 

[HoppyUK]

As above.

Also, the SB900 is the most powerful speedlite I've ever tested - above the SB910, Canon 600EX, big Nissins etc. I'd put it around the 120-150Ws equivalent mark, depending on what you think a Ws is worth in terms of light - that varies almost as much as guide numbers.

Manufacturers of powerful flash units like to say speedlites are around the 50-60Ws equivalent mark, but many of them are way above that, even the Yonguos are easily in the 100Ws equiv range.

 

[matty D]

As above.

Also, the SB900 is the most powerful speedlite I've ever tested - above the SB910, Canon 600EX, big Nissins etc. I'd put it around the 120-150Ws equivalent mark, depending on what you think a Ws is worth in terms of light - that varies almost as much as guide numbers.

Manufacturers of powerful flash units like to say speedlites are around the 50-60Ws equivalent mark, but many of them are way above that, even the Yonguos are easily in the 100Ws equiv range.

Thanks Hoppy, good to know