Using + Diopter filters?

[Tazzie]

Originally Posted by 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

Yes pretty sure, that's only one out of a series of about 10 where i was focussing on the coral in front and then moving the camera with focus locked on to get more of the dappled light in

It is too small to show really, unfortunately that seems to be the largest i can upload to show you.

[Tazzie]

Originally Posted by Cussy

Tazzie,

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

Oops just seen your edit, great thanks very much for the info and help I'm off to play with the diopters and my rubber duckie!

[Cussy]

Tazzie,
Another question then. What was the shutter speed and was there any current. Could the blurring be movement?
Rob

[Cussy]

For the record. This is a shot with the Tokina 10-17 of a Radox bottle that is touching the dome, no problems with it focusing (it is backlit by an Ikelite strobe as I had to illuminate it someway):

Apologies for the image quality as I took it as a RAW, I'm on my laptop so I've had to view it in the Windows thing and do screen capture!! Compressing for the internet then looses the quality.

I then took the dome off and slowly moved the bottle in. It stopped focusing about 2.5cm off of the end of the lens.

HTH,
Rob

PS Acknowledged that this is an air-air interface and not air-water

[aquakiwi]

Interesting topic, I'm using a Sigma 10-20mm and had fish swim up to the dome (8") and they have been out of focus. I've just a few minutes ago ordered a Tokina 10-17mm. The min focus of the Sigma is 24cm and the Tokina 14cm. This would suggest the Sigma would need a diopter. Probably another topic, but how do the above lenses compare. The Tokina being a fisheye and the Sigma rectilinear?

[Cussy]

Originally Posted by aquakiwi

Interesting topic, I'm using a Sigma 10-20mm and had fish swim up to the dome (8") and they have been out of focus. I've just a few minutes ago ordered a Tokina 10-17mm. The min focus of the Sigma is 24cm and the Tokina 14cm. This would suggest the Sigma would need a diopter. Probably another topic, but how do the above lenses compare. The Tokina being a fisheye and the Sigma rectingular?

I don't have evidence to prove it, but from what I've seen I would say the 17mm end of the Tokina is similar to the 10 end of the Sigma. So I like to think of my Tokina as a 10mm fisheye-rectilinear!
Rob

[KenByrne]

I struggled to find a halfway decent shot using the 17mm end of my Tokina, my problem not the lens. Anyway attached shot in the viscount at Stoney you can see that there's slight curvature of the verticals at the side but nowhere near as extreme as the fisheye effect at 10mm.

[KenByrne]

This 10mm shot inside the container at Capenwray shows the greater distortion at 10mm.

[Cussy]

I was thinking more of angle of coverage. The Sigma at the 10 end is quoted as 102.4 degrees. The Tokina at the 17 end is 100 degrees. So in terms of how wide they are 10 (Sigma) or 17 (Tokina), they are virtually identical.
Rob

[KenByrne]

I also have the Nikon 12-24 and it's the same story the Nikon picks up where the Tokina leaves off. I've not used the Nikon underwater since I bought the Tokina the close focus is so much better and that 180 degree field of view at 10mm is brilliant. 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.