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Joined: Tue Dec 08, 2009 11:49 am Posts: 1432
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Regarding Retro Laser: At the most focused position of 11° the beam circle will spread at about 2' per 10' of distance, so at 200' the beam will cover about a 40' circle. With 640WS, the GN is about 640 at ISO100 so the exposure would be about f3.2 at ISO100 (f2.8+ 1/3f). Each doubling of ISO will increase the exposure by one f stop. So at ISO400 you could expect about f5.6 + 1/3f (f6.4) at 200'
At the wide 30° focus setting the spread is about 5.4' in 10' so at 200' the beam will cover about 108' circle.I don't have exact Guide Number yet for 30° angle, but you can expect around 1 1/2f less output at 30° than at 11°.
200 feet is a lot of distance to cover with flash. At 100' the coverage circle would be 1/2 that at 200', but the exposure would be two f stops higher.
An AB1600 will provide identical Full power output to Einstein 640, but Einstein would offer way better action freezing in situations where you are closer to the subject and can afford to drop the power to say 1/2 power and use Action Mode. Einstein also recycles faster than AB1600.
Hope this helps.
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