Using + Diopter filters?

[Cussy]

Originally Posted by KenByrne

There aren't that many straight lines underwater so the fisheye effect is less noticable but there's also a lot less distorting the longer the focal length you use.

As Mike's thread shows though (Why you need a wide-angle lens) you can play with the distortion and strange persepctive to your own effect.

But as these show:


and one of Gareth's:


It probably is best not to use one as a portrait lens!!!
Rob

[Tazzie]

Hmmm right I've played around with the wide angle (out of the housing) and you guys are right, I can focus up to about 10cm with the wide angle then closer still with the diopters which is great news Couldn't get in the water to see why the same isn't happening when it's in it's housing underwater... Will try and get in the pool on friday and experiment further

[KenByrne]

There's an explanation of dome port optics at the bottom of this page that might help. Cameras Underwater: Interchangeable Lens Ports.

[Tazzie]

Thanks for that Ken, most useful


Well I did some more practising last night, here's the results:

No diopter, 22mm


+2 Diopter, 22mm


+ 4 Diopter, 22mm


Thanks very much for your help and links chaps, I've got my head around it now Hoping to get wet this weekend to try it out in the water now I understand what I'm looking to do!


PS PLease note the photos were taken of an image in Martin Edge's book

[whacky]

Originally Posted by Tazzie

PS PLease note the photos were taken of an image in Martin Edge's book

I'm so glad you pointed that out i was a bit confused for a second.

I was reading Martins book when I was on lunch today so many people kept on interuppting me to say how grat the pics were I gave up.

[Cerianthus]

I am sure you are all realising that a dome port above water has no optical qualities, other then being a rounded bit of glass / perspex with extra smudges? The virtual image is only produced in water. The only test you can do above water is put a diopter on and measure the shortening of the focus distance. You will note it also effects the infinity setting, which is no longer infinite but closer. That is not so bad as it sounds, because the infinite image in water is also much closer (for the end of the pool, my sigma 15mm fisheye focuses at 1 m )

Gerard

[simonmort]

Thought i would ask the question, can diopters be used on normal compact camera housings?

Would be interested in trying to find some + 4 diopters, that i could use on my tetra light and motion housing.This would need to be 85mm and slide onto/over the flat port.
Anybody any ideas?
simon.

[ATJ]

Simon,

I believe you can use a diopter lens on a flat port (that's what Woody's wet diopter does), but it is for a different reason than on a dome port. A dome port creates an apparent image much closer than the subject and you often need a diopter lens to allow the camera lens to focus on the apparent image. If you are using a diopter with a flat port, it will allow you to focus on subjects closer than you normally could.

Is your port threaded? If not, you might have to go with something slightly larger and work out a way to secure it in place.

Woody's Diopter can be bought in a 90mm size. That might work for you.

[ATJ]

By the way, I have done a little testing with dome ports and diopters. It appears (from my limited testing) that a +4 will preserve the reproduction ratio of the lens at its closest distance when used in a dome port.

Here's what I mean... This is for the Nikkor 18-55mm f/3.5-5.6G ED II.

The bare lens above water at its closest focusing distance at 55mm:


Underwater, behind a dome port with the +4 diopter lens:


So, even if the lens focuses close enough that you can go without a diopter, using a +4 means you can focus as close as you could on land and get the same reproduction ratio.

I actually use a +5 on the 18-55mm now:

[aquakiwi]

With the Sigma 10-20 it focuses to about 24cm (same as the Canon) and in my experience won't focus on anything on the dome, my Tokina however will focus
on something touching the dome.