Using + Diopter filters?

[Tazzie]

Does anyone here use a +2 or +4 diopter on their wide angle lens to allow you to photograph larger fish full frame?

I've recently ordered both off the internet (after visiting 5 camera shops in the south, none of which had any in stock, some of which even told me they didn't exist!) and have had a play around with them on the camera out of water but I am really struggling!

The +2 doesn't seem to have any affect on my 10 - 22mm wide angle lens and I really can't tell the difference of when it's on and when it's not. The +4 has a slight difference but has such a small focussing distance I wonder if it's going to be useable underwater.

Has anyone got any experience of this, what might I be doing wrong? Are there any better lens solutions for taking photographs of fish and critters the size of a medium wrasse?

[Cussy]

Tazzie,
Don't forget the lens is focusing on a "virtual image" on the dome surface, and not an actual image. You normally add the diopter if that virtual image is too close or to a non-macro lens to make it a macro one. My Tokina has an amazingly close focus, in fact I have an image at home of a critter that attached itself to the outside of the dome and the lens focused no problems.
Rob

[Tazzie]

That's intersting Rob, I have lots of photos taken on the Tokina 10 - 17mm which just would not focus as they were too close (although for some strange reason the camera allowed me to take the picture)

I'm surely not experienceing the limits of the Canon 400D am I? All my lenses are of good quality but I defo couldn't take a pic of something on the dome port...

[Cussy]

Tazzie,
Just looked it up, minimum focus distance of the Tokina 107 is 14cm. There should be 14cm between the sensor and the dome's virtual image.

How close are you calling close?

It shouldn't be the camera.

I'll have a play with the lens tonight and see how close I can get to things.
Rob

[KenByrne]

As Cussy says a diopter won't affect the field of view of a wide angle lens it just lets it focus closer. I have a Nikon 12-24 and I've tried it with and without a diopter and found no real difference as the lens already focusses close enough.

It does get complicated behind a dome port as the radius of the dome affects where the image appears to be. Ikelite use a 6" dome which places the image about 1/3 of the true distance from the dome. However you first have to focus through the air inside the dome which will also add to the distance.

Realy not sure why your having close focus issues with the Tokina 107 as I have one of these and haven't found any problem with close focusing behind a dome.

[Tazzie]

Brilliant, thanks chaps I now know what I should be getting with the diopter, I obviously misunderstood initially.

Cussy, I'll upload a couple of pics tonight with the focussing issues, I think they were defo taken under 14cm away from the subject so that may well be the issue (although I'm still confused how I managed to take the shot. With my camera if it can't focus you can't usually take one)

Another issue I am finding is the gear mechanism that allows me to go between the 10 and 17mm ends of the lens - despite setting up the camera very carefully, ensuring the gear will move to both ends prior to the dive it seems during the dive moving the gear mechanism actually causes the camera to move within the housing and "unmesh" itself from the gearing.

Martin Edge has given me the name of someone to talk about with regards to that, I need to get around to it.

[Cussy]

The 107 is published as being 71.1mm long. The sensor will be at least 15mm off the end of the lens (lets call that 85mm). That means the lens, in theory, should be able to focus on an object 5.5 cm away from the end of the lens (that's my understanding of it anyway). Your Hugyfot has quite a big dome, my Ikelite is smaller, but I would say the dome has at least 5.5cm between it's surface and the end of the lens.
Rob

[Tazzie]

Thanks Rob, I'll put it in it's housing and have another play around tonight.

Thanks for your help (again! )

[Tazzie]

An example of the blurred images I was getting... I think i'm probably 10 cm (from the end of my port), maybe a teeny bit more, infront of the coral. Too close?

(Taken on the Canon 10-22mm wide angle lens)

[Cussy]

Tazzie,
A bit small to tell.

But, are you sure its focusing on the bit closest to you? You sure it hasn't focused behind and then the front is out of focus because of the depth of field?

Just looked up the Canon lens. Closest focus is 24cm, so maybe it can't focus on the virtual image? So you would then be right to add a diopter.
Rob