16-35mm canon blur corners

Hello

Does anyone have the right setting for a canon 5d and 16-35mm MKI to have sharp corners???

My housing is an aquatica with 8" dome and I use the ext ring adviced by aquatica but it is not satisfactory

a +3 diopter???

thanks for your answer!

Still fighting mine.

Different housing and I even calculated the entrance pupil.

I'm thinking we are chasing dragons at this point.

Perhaps a diopter is necessary...

If the dome is positioned properly (the center of curvature is located at the entrance pupil) & edges are still soft, then a diopter is needed, even if the lens focuses ok. I'm using +3/+4 on my 12-24 & 17-55 Nikons.

thanks for your answers I'll try with a +3 diopter

I 'll be very interested to know if somebody with a 16-35 mm using a +3 dipoter has good results (as the manufacturer do not advice to use one)

Is a larger dome (9") maybe the solution?

a great idea probably would be to have a "zoom extension ring"! but still does exist on the market

i find the corners on the 16-35 horrible at wider apertures even on a 1.3x 1dmk2, and i don't even use the lens underwater! a +3 diopter i'm sure is a must with this puppy. stop it down as much as possible to help the corners too, go for f8-f11.

be careful not to buy a diopter with a thick mount, as you could get vignetting at 16mm on a 5d.

which filter brand would you recommend that does not have thick mount, B&W?

i find the corners on the 16-35 horrible at wider apertures ....... go for f8-f11.

When I had the original version of the 16-35, using f16 was the only way I could get acceptably sharp corners on land.

I tried a few combinations when I used it on my EOS 50 (remember film?) underwater in a Subal housing but was unable to get sharp corners at any aperture that was usable underwater.