1 Strobe v. 2 strobe?

[geraldp]

Is there really a strobe out there rated at GN 16 underwater?

Thanks Bob:

The unit I was looking at was the Ikelite AF35. Guide # (ISO 100) feet... 28 surface, 16 underwater. Yes a GN of 16 meters would be a flamethrower

At $400 usd including strobe, tray, handle, arm, and autoflash sensor this apears to be a reasonably priced unit. There are cheaper units out there, and I was also looking at the Sealife SL960.

Also remember that the guide number does not tell the entire story. Beam angle, recycle time, shots per charge, user modes (how many manual settings if any, some form of TTL, possibly even "auto mode" as examples of user modes) and build quality may be just as important. In other words, there are many details to consider when purchasing a strobe, including future plans if any.

I've given this some thought, and with the price of a dSLR housing/strobe being almost an order of magnitude higher than a dP&S housing/strobe I really don't see myself moving to a dSLR setup for underwater use. The AF-35 seems to be designed specifically for dP&S cameras, which should fit my needs for quite a while. Especially if I can add a second one later.

The impetus of my question to H2OMAN211 was whether a GN of 16 feet underwater was sufficient for the vast majority of the shots I might want to take, and you've answered that affirmatively.

So as to not sidetrack this thread further, I'll bring this back to the original title. Will a second strobe increase the Guide Number? Or only change things like beam angle and width?

Thanks again,

Jerry

 

[bobf]

Jerry,

Thanks for reminding me about the Ikelite AF-35.

.........Will a second strobe increase the Guide Number? Or only change things like beam angle and width?

I don't think that most users add a second strobe to increase light intensity. The second strobe is used more to either increase the area of coverage (say for wide angle work) or to knock down harsh shadows (say in macro work). It's also common to set strobes at different intensity levels. For instance the second strobe is sometimes referred to as the "fill" strobe.

That said........even if you were to aim both strobes at the same area.....in theory doubling the amount of light where the beam patterns intersected........the GN would increase by no more than a factor of 1.4. So in theory, in the case of a pair of GN 16 strobes both set at full power and aimed at the same target, the guide number could be calculated roughly as 16 times 1.4........or around GN 22 at the intersecting beams.............iow, GN 22 is twice as "bright" as GN 16.

btw, someone earlier brought up the point of redundancy. This is another very good reason to have a pair of strobes imho.

regards,
b