Posted by Dennis (66.87.145.76) on January 02, 2004 at 14:53:32:
In Reply to: Aqualens focus posted by Marcelo on December 30, 2003 at 05:59:53:
: Hi,
: I am trying to set the focus in the Aqualens for my 16mm fisheye.
: The instructions say that you must find the minimum focus in the lens and align it with the zero mark. Then one must take note of the letter that coincides with the infinite mark. In the 16mm, that point is near the G. The 5 feet mark coincides with the F and so. But in the focus chart that appears at Aquatica website (www.aquatica.ca), the letters go from 0 to D. Is this chart made with apparent feet, and this explains the difference? Does it explain also that the 6 dome chart is different from the 8?
: I know I shouldn't care about exact focus points, because of the extreme depth of field of the lens, but just want to know where to put the focus, so my foreground subject and the subjects beyond and at infinite, are both in focus.
: By the way, how close are subjects underwater? One third or one quarter closer? All books that talk about apparent distance says that, but none tells it exactly.
: I mean, 3 apparent feet are really 4 measured feet? (just to make a chart).
: Thanks for your help and happy holidays,
: Marcelo
Marcelo:
I've never used the Aqualens, and so have no experience with focusing calibration. I'm the kind of shooter who would just pre-focus the 16mm at 2 feet, and let the depth-of-field do the rest.
So, for more accurate focus instructions, I must refer you to the manufacturer. They are usually the best source for information on how to use their product.
Contact Aquatica at 888-737-9481, 514-737-9481, or info@aquatica.ca. Good luck with that.
And, water has a 25% magnification factor. This means that if the fish is four measured feet away, it appears to the human eye to be three feet away. The camera sees the fish in the same way, which is why you set your focus for apparent distance, not measured distance. And you aim your flash for measured distance, not apparent distance.
For further assistance please contact us at 800-334-3549 x42 or 312-421-6000 x42.
Dennis
Helix UW Photo Dept