WA distortion with 5D/Ikelite 8"

[Paul Kay 41]

Hi Martyn

 

I'm sure you're right - in the past there have been some amazingly small 'fisheye' ports in us including one which 'pushed' onto a Subal bayonet because its diameter was the same as the bayonet. Trouble is that fisheye's appear pretty forgiving if you don't look too closely, and dome port theory, and its associated problems, has only started to become more important as people demand the quality available from high MPixel sensors to be producable underwater.

 

In poorer visibility where CFWA has to be the norm, the softness is apparent more too. I'm starting to look into what remedies might exist for ultra-wide (weitwinkel) rectilinear correction - I suspect nothing cheap, but.........

[TomStack 0]

A good thread, thank you all for you input. I'm not going to pretend, for even a nonosecond, that I'm

an expert here. I just need results and I'm not getting it from Canon when compared to what I've

seen others do in our Digital UW Workshops with a Nikor 10.5. We have the new Tokina 10-17mm

on order, but while it may prove to be better than the Canon 10-22mm I honestly don't think it

will compare to the Nikor 10.5. Wide angle is our "bread and butter" and I may have to switch

back to Nikon to get what I need.

 

My question: Why did I get sharp corners when shooting a Nikor 16mm on film with an Aquatica 8" dome

port? Yes, the corners were sharp as I've spent 30+ years with a Schneider 4X loupe looking at film on

a lightbox.

 

Someone at DEMA suggested the current problem had something to do with the corner edges of the

sensor??

 

Thanks,

 

Tom Stack

 

http://www.tomstackphoto.com

[synthetic 4]

I did a few dives on an oil rig yesterday, using the 17-40mm and many of your tips, and I was happy with some of what I got.

 

f/22, 1/200, 17mm, no cropping

 

f/14, 1/160, 24mm, some cropping

 

I shot the entire day at ISO 800, so I could crank down the aperture, and you can barely see the grain. (I only see it when I upped the exposure 2 stops in the RAW converter.)

 

More Photos

 

So I guess this is a happy ending. I have more to learn, but at least I'm starting to get acceptable results. Thanks everyone and especially pgk for your help.

[RogerC 4]

Seems to me the gist of this discussion is that the following hypothesis is being put forward as being true:

 

Hypothesis: Using a dome you will always have soft edges when shooting wide.

 

I'd change that.

 

I'd say I came into the thread thinking:

 

Using a dome you will always have soft edges when shooting wide, unless your lens can focus close enough to work behind the dome.

 

and Paul taught me that

 

Using a dome you will always have soft edges when shooting wide unless your lens can focus close enough to work behind the dome, and has enough depth of field to capture the whole image, which has some curvature to it.

 

Which is a different way of thinking about what happens when your lens can or can't focus close. Pretty interesting.

 

It's basically the same thing you're saying, but by adding the detail, you figure out how to fix it: focus close and have depth of field, or change the dome or some other optic to flatten the image.

Edited November 13, 2006 by RogerC