Diopter and Tokina 12-24

Using a D200 with a Sea & Sea optical dome port the edge sharpness seems quite soft

In trying to sharpen the corner edges I went from a +2 diopter to a +4 with the result that

minimum and infinity focus was sharp but everything in-between wa out of focus

are you using the glass dome port?

which extension ring are you using?

the S&S website recommends the large dome port for the best results..

however, if you are using the glass dome port (which is smaller), you'll need to use the SX extension ring (20mm ring), or your corners will be soft.

hope this helps,

Scott

Here is some stuff to read on the subject.

http://wetpixel.com/i.php/full/proper-dome...-and-placement/

http://wetpixel.com/i.php/full/dome-theory/

Enjoy