Hey Gang,
I've been testing my wide angle setup (Canon 40D, Canon 10-22mm, Ikelite 8"dome port, dual Ike 125 strobes), but have been disappointed with the underwater results. The center of the shot has fair sharpness, but once you get away from the center of the shot (outer 50%) the sharpness deteriorates. Of course you have the normal distortion when I'm at 10mm or so, but you also now have the focus issue. Even at 22mm the outer 50% of the shot is completely out of focus, and this is true at shooting distances of ~1ft to ~4ft. I don't quite understand the physics of this problem, but my understanding is that a +2/+4 diopter can help improve the sharpness at the edges. Appearently you can use this equation to find the diopter power; f (focal length) = 2d (d = dome diameter), and in my case 8†dome comes out to f =40.62cm. Then to find the power of the diopter you can divide your “f†result into 100cm, and this comes out to 2.46 diopter. Now I’ve been recommended a +4 diopter, but it appears I’m closer to +2 diopter?
Can any of you folks please explain the dynamics of what is going on and how the diopter can help;
1. What results I should I expect in either case (+2 vs. +4).
2. What are the physics of this issue, I’m just trying to understand what is going on with the edge focus problems, and how the middle of the shot can be in focus, but everything else out of focus?
I would appreciate your recommendations and what I should expect to see with these changes. Also, if any of you understand the physics of what is going on I’m interested.
You know I just went to Ikelite's web site and looked up the port specifications. Interesting thing is that they specifiy a Ike 5510.22 port for the Canon 10-22mm. However, when I measure the lens I only get 3.5", which puts me into a 5510.16" port??? How could this be wrong?
Thank you
Derek…
