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.

3 hours ago, Chris Ross said:

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,

I'm not intimately familiar with this dome, but how can you say that?

If this dome is a portion of a larger dome, its optical centre will be well behind the port's mounting flange, and therefore (depending on the lens and its position in the housing) should be capable of aligning with the EP of at least some lenses, subject to adjustment with an extension ring if applicable.

Regarding mis-alignment of WA rectilinear lenses' EPs with dome optical centres: the greater the mis-alignment, the smaller the central area of sharpness in the frame (some portion of the centre will always be sharp, regardless of alignment).

2 hours ago, dentrock said:

I'm not intimately familiar with this dome, but how can you say that?

If this dome is a portion of a larger dome, its optical centre will be well behind the port's mounting flange, and therefore (depending on the lens and its position in the housing) should be capable of aligning with the EP of at least some lenses, subject to adjustment with an extension ring if applicable.

Regarding mis-alignment of WA rectilinear lenses' EPs with dome optical centres: the greater the mis-alignment, the smaller the central area of sharpness in the frame (some portion of the centre will always be sharp, regardless of alignment).

Ikelite recommend it to be used with a fisheye and the specifically for CFWA, the lens needs to be up in the dome to not vignette and the entrance pupil is right up front. So for that and many wide angle lenses it will vignette if you attempt to place the EP at the centre of curvature. The sample pics provided look OK but they 1024 x 1024 images so at lets partly cropped and a little small to judge critical sharpness but they certainly look OK on the website at that size.

On 2/3/2026 at 9:21 AM, Isaac Szabo said:

On the other hand, the Tamron 90mm entrance pupil is much closer (near the center of the lens), and it works very well behind dome sections typically used for macro lenses (such as the dome from the Zen WA-100 port, which is a section of a ~170mm diameter dome).

Isaac,

Just to confirm your thoughts on the Tamron 90 macro with your dome: have you noticed any negative results with AF, in particular AFC? And is it the latest version with VXD focus motor?

I'm determined to keep testing the Sony 100 with a dome and AFC, but if I can't get it to perform as well (or better) than the Sony 50 macro with dome, passing the Sony 100 to my wife for spiders and getting a Tamron for underwater might be an option.

Thanks

@dentrock Mine is the latest version with VXD. However, I only tested it briefly with a few domes using AF-S on my A7RII in my home test pool. I was only testing for sharpness. I was not testing autofocus performance. I have not shot it behind a dome for real world photos yet. I'll likely start doing that in the coming months, but I'm not necessarily a hard core AF-C user. I could try an AF-C test in my test pool, but since we have different cameras (with different AF settings), I'm afraid my results wouldn't necessarily apply to your setup. In summary, I would not recommend that you make the switch based on my positive report since I was only looking at sharpness, not AF-C performance.

By the way, ignoring the AF-C issues for a moment, I'm curious if the Sony 100mm behind a dome gave you edge to edge sharpness if you did manage to get a shot in focus?

Edited yesterday at 09:04 AM1 day by Isaac Szabo

OK, thanks. Look forward to your AF update on the Tamron in due course.

Regarding sharpness right across the frame with the Sony 100, I can't give you a clear answer, even though I went back to the original uncropped raws just now. My priority was the AF, and I assumed the sharpness question would fall into place. But because the AF target jumped away from what I intended, my sharpness reference point (always an eye, if there is one) is no longer accurate.

So I have to look for what appears to be the sharpest point in the image and compare that with the far corners. And even then, perhaps the AF had not been properly acquired, so there may be no useful comparison.

Best I can say at the moment is 'OK' into the corners (i.e. better than a flat port), but overall sharpness doesn't jump out like it does with the Sony 50 and 140 dome. I hope that changes if I get the AF sorted!

At least I got some keepers, which is more than I can say I got with the 90 macro and MFO-1.

I have just acquired a Nauticam 37122 4" WA port (as per Alex Mustard 'curved port' video quoted on another thread). I struggled a bit developing specs for it (Nauticam didn't bother to answer my query about the radius), but have firmed up on an estimate of 110mm outside dome radius, which makes sense as it would be the same as the 180 dome and possibly the 8.5" dome.

But applying this radius to the port length suggests that Alex using a 16mm extension with that port and 50 macro means it is still quite a long way mis-aligned (my estimates suggest 45mm extension for the 50 macro with this port).

Although he also said a longer extension was better for optimal sharpness, without saying how long!

Anyway I have ordered 30 and 40 extensions which I think should cover the 50, 100 and also part of the 20-70 range (from about 40-70), using the 37122. OK, the 20-70 isn't macro, but it does a remarkable job with AF and close-up, so is good for moving fish.

I will test everything AF with the 100 before giving up, as the combo would suit me perfectly if I can get it to perform.