Must Watch Video: Dome Port Theory Explained

11 hours ago, KPV said:

How does the position of the dome's center relative to the lens center affect the image? What will the effect be and how pronounced is it? I saw a YouTube video by Alex Mustard where he said that if positioned incorrectly, a 230mm dome will be as soft in the corners as a 160mm canopy. Is that the only effect?

There's also a small 8" dome from Ikelite, which is part of an 8" hemispherical dome. Its center is clearly not aligned with the center of the lens, but no one has ever complained about the photo quality.

Ikelite seem to promote using this dome with a fisheye for CFWA, the discussions mention that the edges of the image may not be great and imply it's not important. Fisheyes seem less prone to problems with dome positioning but you usually won't see the problems in a 1024 pixel wide image on the web. Rectilinear lenses show more pronounced problems if not positioned correctly. You can look at the post by Dreifish here to see some examples of different dome positions:

Testing Nauticam N120 Port Extension for 140mm and 180mm domes with wide angle lenses - Photography Gear and Technique - WaterPixels

Keep in mind that these domes are maybe up to 10-15mm out of ideal position, the dome you mention will be much further from the correct position for many lenses. One of the problems is that most test images you can find online might be up to 1200 pixels wide and it is hard to find problems in such images.