Deep-sea Camera - Watt Seconds
Posted 26 April 2006 - 01:32 PM
If anyone has worked with deep-sea camera's please contact me or post below.
Posted 27 April 2006 - 08:13 PM
I did a quick check on www.digitaldiver.net strobe finder comparison database and found the Ikelite Sunstrobe 50 and DS50 models with a 50 watt/second rating have a GN of 17 (air) - 9 (u/w).
This may be a rather simplistic reply for the level of accuracy you may be demanding, as there are a number of variables affecting the power output of a flash. Water turbidity, reflector design, colour temperature, and flash tube have to be taken into account.
The above GNs should “get you in the ballpark” for exposure calculations. If you require more detailed information two interesting articles can be found at:
Otherwise, using a flashmeter in air and halving the resultant reading will probably be just as precise as anything mentioned above.
Hope this helps.
Nikon D2x, D7000, Aquatica D2x, AD7000, SunStrobe 200 x2, Inon Z240 x2, TLC Arms
Posted 28 April 2006 - 03:32 PM
I'm told the water is very clear at 1000 m and the strobe is daylight balanced (or what passed for daylight in the early 70's). The reflector needs to be replaced or polished.
Posted 28 April 2006 - 04:25 PM
Another important variable is the coverage angle. The DS50 has a 70 degree angle and therefore concentrates its 50 watt-sec in a smaller cone giving similar light density as the more powerfull DS125. I don't know the definition of the "guide number" but I expect that it is independent of coverage angle. However, if you only know the watt-sec for your strobe it is something you should look at. I expect it will scale with the square of the sine of half the coverage angle.
Sigma 15mm FE, 35mm f2.0, 50mm f1.8, 100mm macro, 18-55mm kit lens
magic filters, cc30m magenta filter
Posted 29 April 2006 - 03:51 PM
Z* = (1.6 times the square root of (ASA times Watt Seconds))/Aperature
They don't define Z*, it is on a log scale, I though it was distance from flash to subject. . . Maybe Z* is the amount of turbidity?
With 100 Watt seconds, 200 ASA and f11 they say you can correctly expose a subject 23 feet away – which seems like one heck of a lot of light to me! I get 14 feet when I try it. . . hmmm that is what is on the X axis. So Z* must be turbidity?
The actual strobe is 50 WS, not 100 and the film will be 100, not 200.
So, at f11 I should get a correct exposure at: 10.6 feet (wow!???) Seems to high for a 2 stop loss.
Guide number, which is independent of area of coverage as you mentioned is GN = Distance * Aperture (at a set ASA/ISO). It is an easy way to do exposures if you aren't on TTL. I'm just trying to get into the ball park here. . . apples and oragangs. . .
So that equation gives me a correct theoretical exposure at 2.5 feet, not 10.6 feet! Who knows how much the beam is focused by the big reflector. It looks like I'll have to shoot a series when we get it working and find out, at least I have a reasonable range to play with. Also, it looks like the 28 mm lens may be wider than the flash coverage.
Posted 01 June 2006 - 04:10 PM
Canon 7d, 50D, Nauticam,Subal, Inon Ringflash, Athena Ringflash, Inon z240 etc.