AF strikes under water with some objectives...

Hi

When i put my camera (Canon EOS 350D) to the IKELITE Housing no problems appear. I use a DOOM PORT (#5503.50) on this IKELITE Housing.

With this objectivs, everything works fine, also AF:

- Canon EF-S 10-22 USM

- Canon EF-S 17-55

with this objectivs, the camera strikes to focus (AF Mode)

- Canon EF-S 17-85 IS USM

- Canon EF 50 1.4

...but it strikes only, if the doom port is in the water (doesn't matter if the rest of the housing is in water or not). so the problem must be there... at the doom port. maybe any reflexions irritating the camera? but how can i fix this? do i need other ports? any ideas?

please help me... my holidays going to end and i have only few day's to make pictures...

thank you

The lenses probably can't focus close enough to focus on the apparant image of the dome. (this will only exist under water, so thats why there is no trouble above water.)

it needs a diopter (screw-in). Ikelite lists the 17-85mm as needing a +4 diopter. it doesnt list the 50 1.4 lens.

Yes, but is only for macro isn't it? Like above water; to reduce the distance between frontlinse and motive. For widerange it doesn't solve my problem... i think <_<

Text on IKELITE Homepage:

'Zoom lenses usually require a +4 diopter close-up lens available from camera stores unless the lens will focus closer than 12" distance.'

It looks like you do need a diopter with the 17-85mm, as its closest focusing distance is more than 12". The reason you need the diopter is that with a dome port, the camera focuses on a virtual image created by the dome very close to the surface of the dome. There are a number of threads on this topic, just try doing a search...

I see you didnt understand. Above water, you would use diopters only for macro, but with dome ports its different. The dome port "projects" an image to the camera lens at close distance (the 12 inches mentioned), and the lens has to focus on that. If it cant focus this close It will need a diopter.

50mm and 100 mm lenses used under water are mostly macro lenses behind flat ports.

It only happens under water because of the water-air interface. Above water it is just a bit of glass. This dome port virtual image projection is explained in most textbooks. A search here could come up with some interesting discussions as well.

It is not only the text on the website i refered to. The * en ?* markings in the table give the need for individual lenses

Good luck !

Gerard

OK... now i understand. Thank you all for the fast and serious help.

Im still sitting here in Negros Phillipina. To buy a diopter (here) is mission impossible. So i try to buy an EF-S 18-55 Standart Objective... wiht this it works... but first i have to take a taxi... the next shop with this objectiv is 7 hours away

Thank you all