Sort of newbie question. I have got a D300 in a Sea & Sea housing with a Nikon 12-24mm lens. As mentioned here in copious other posts, this combination is well known for smudging of the edges of the image unless it is sorted out.
Solutions to this are
a) correct port and extension - fair enough
b) use of dioptres
I sort of realise that a dioptre is a magnifying glass that screws to the front of your lens, but where do you get them from and what type should I get. I have heard that there are single element and dual element type - anyone want to shed any light on this issue ? Also, what other effects do they have, such as reducing the angle of the image and bringing the minimum focal point nearer.
Hope I understand your responses - I am but a simple man :-)
Blucky
