Wow so much info, so much to read...I love it. I have a question about +4 diopter. Ive called blacks and henrys my local photo store and they never heard of a diopter that goes on the lens. They were trying to tell me it was to go over the view finder? Ive purchased canon 40D and a 17-85mm lens with the ikelite housing and the 6' dome port for the 17-85 lens. Many have told me to get a +4 diopter for this lens. Where can I buy this? Is it glass or plastic? Does if go over the lens or view finder?
It is made of glass and goes on the lens.
B+W makes one, and I think that's the one most people get for the 17-85 lens.
You should find this in Toronto easily, the thing to ask is for a close-up lens, for the +4 I would get the Canon 250D which if I recall is a +4 and a doublet (dual element) construction, less expensive is the B&W (try Vistek) and still less expensive but cheap optical quality is the Tiffen (in a pack of +1, +2 and +4) or Hoya.
Diopter are also used as corrective eyepiece on older film camera, mind you any salesperson worth its salt should know that close-up lenses are also called diopter.
I have that lens and use a +4 diopter. It screws on the front of the lens - very straightforward. I have a Hoya diopter which is glass.
Weedgal,
Generally, the German made B + W filters are of exceptional quality. As mentioned earlier, they are readily available...I use B&H out of NY... For the +4 Diopter, B + W's designation would be NL-4 ...
