Flat vs dome port for one lens?

Noticed on Ike's port chart there are a few lenses - 24, 28, 35 and 50 where both a flat and dome port is offered.

I understand that the camera takes a pic of the virtual image on the inside of a dome port, but what's the difference between the two ports where flat and dome are offered for one lens?

Thanks

Chris

For a very wide angle image, the corners may actually be farther away than the center of the image. Draw some lines from the lens to the center and then from the lens to the corners and you'll see what I mean.

A dome corrects for this.

With "medium angle" lenses like 35, 50, 85 this doesn't really affect the image too much and a flat port will give "acceptable" results. You may find some chromatic aberration in the corners, but they won't be too soft or have too much pincushion distortion.

Once you get down to about 28mm, it starts to really become a problem. Look at the 28mm photos from an Oly 5050 or 5060 shot through the flat port on the housing to see what I mean.

Cheers

James

I didn't quite get what James was trying to say in his first paragraph, but the rest is spot on, as usual.

I would just add that a flat port, like your dive mask reduces the angle of view of the lens. Using a domeport restores the full view angle, as the light passes though it at right angles, hence avoiding refraction at the port.

Hope that helps,

Martyn

Chris: Did you understand what I was saying?

Cheers

James

Yeah, I did

Thanks