Wet Lense Diopters

Hi, i have a Canon G9 in an ikelite housing.

I always seem to be in a no win situation when shooting macro.

The camera has a minimum focus distance of 1 cm with the lense at its widest (30mm) which in theory would be great for getting in close on macro and filling the frame.

But shooting this close means i cant get any light into the shot.

If i use the zoom i can shoot from further out which solves the light problem but the minimum focus distance goes up to 50cm (on full zoom) which pushes the subject further away and it no longer fills the frame.

Does anyone know what hapens to focus distances if i was to use an external wet diopter ?

They get shorter. The maximum focusing distance will be comparable to your current minimum one. Because your camera does not have good close focus at it's longest focal length your focusing range will not be too great. You can always use a diopter in combination with the zoom though.

They get shorter. The maximum focusing distance will be comparable to your current minimum one. Because your camera does not have good close focus at it's longest focal length your focusing range will not be too great. You can always use a diopter in combination with the zoom though.

Im not sure if i get this right but -

my lense at wide angle focuses from 1 - 50 cm and at full zoom focuses from 50 cm to infinity

If i use a x2 diopter on wide i get 0.5 - 25 cm and on full zoom 25 cm to some shorter distance ?

I, too, have a Canon G9 with Ikelite Housing and wet diopter. I, too, have had difficulty with the wet diopter, though mine is with the autofocus. So let me add a little "pork" as we say in American politics, and see if anyone knows the answer...

I have noticed the autofocus works better when the camera is not zoomed in very far (just enough to get rid of the dark corners from the shadows in the housing). In fact, I can't really get the autofocus to work at all when I am zoomed in far/all the way.

So:

• Is there any benefit to using the diopter (presumably not zoomed far) over the camera (zoomed in)? (I thought the answer would be that you can focus closer with the diopter (and reduce backscatter) but I haven't observed that)
   
  
• Should one use the macro setting on the G9 when shooting underwater (with or without a wet diopter)?
  

Im not sure if i get this right but -

my lense at wide angle focuses from 1 - 50 cm and at full zoom focuses from 50 cm to infinity

 

If i use a x2 diopter on wide i get 0.5 - 25 cm and on full zoom 25 cm to some shorter distance ?

First off, there isn't any such thing as a "x2" diopter. It's a popular mistake these days. The diopter you are referring to is a "+2". It doesn't multiply anything by 2.

See here: http://scubageek.com/articles/wwwpow.html

A +2 diopter has a focal length of 100cm/(+2) or 50cm. That means it will convert infinity focus to 50cm regardless of zoom setting.

Your minimum focus distance is more complicated. When zoomed wide it will be essentially on the port. When zoomed long it will be about 25cm.

See here: http://scubageek.com/articles/wwwdiop.html

Is there any benefit to using the diopter (presumably not zoomed far) over the camera (zoomed in)? (I thought the answer would be that you can focus closer with the diopter (and reduce backscatter) but I haven't observed that)

Perhaps you should try it out and see? Are you seriously saying a diopter doesn't allow closer focusing in your tests?

A diopter works in two ways. First, it shortens focusing distances. Second, it provides magnification due to it being a distance from the primary lens. You can see both these effects by simply playing with a magnifying glass. It's also true that a diopter shortens the focal length of a lens and thus works against you, but this effect is mild compared to the other two.

Virtually all lenses vary their focal length over their focusing range. That is, most every lens shortens its focal length as its focus distance shortens. A diopter "tricks" the lens into focusing further away than it otherwise would and thus enables it to use a longer focal length. The more pronounced the variable focal length is, the more powerful an effect the diopter has. Diopters work the same way on all lenses, but their effect is more pronounced on some than on others.

Should one use the macro setting on the G9 when shooting underwater (with or without a wet diopter)?

Are you shooting macro?