technical lense question? anyone?????

[ed68]

hi all,

i have a question, any help is really apprecited......
i take underwater photos in various underwater housings, for those of you that do not know when you use a dome port in front of a wide angle lense this effects the close up capabilities of a lense and pushes the all important close up further from the film plane. to supplement for this you can correct this by using a close up filter on the front of the lense, the strength of the close up is determined by distance of the dome port.
my problem.......
i want to use a fisheye lense that does not accept front filters. does anybody know if using a +4 lense on the rear filter holder would work the same as a screw in type filter on the front optic. i will have to get this made up so i can't trial and error this one, i don't want to go through the expence if it would not work....... my thoughts is it will not work but can anyone shed any light??????
my lense is a nikon 16mm f2.8 afd fisheye but i would consider a sigma 15mm f2.8 ex fisheye if easier to get a filter made. i use nikon f100's and fuji s2 pro.

thanks for your help.

 

[Hertz van Rental]

The answer to your question is: maybe.
Not a brilliant answer, I know.
To come up with a definitive answer would need a lot of information concerning the optics of the lens and supplementary lens.
A supp lens on the front affects the light coming in to the main lens. On the rear it affects the light coming out. Lenses in both positions will affect focus but will do it in different ways.
The probability is that what you are proposing will not do what you want it to. The best advice I can give is to approach your lens manufacturer to find out if they can tell you. If you draw a blank there then... but they might have an answer. It's worth a try.