Large domes and edge sharpness: sources

[Architeuthis 156]

We had somewhere a discussion, whether the Nauticam 230 domeport is a domeport for fisheye lenses or for rectilinear lenses (I do not remember where it was, but it was not completely in-topic, anyhow). It is also not completely in-topic here, but I think this is the right location to post a statement from Nauticam about this issue:

 

I asked: "I have a question regarding "230mm Optical-Glass Fisheye Dome Port II" - SKU # 18812:  The radius of curvature is 120mm (?), but the diameter is less than 2x120=240mm. Is this now a complete hemisphere as the name implies (Optical-Glass Fisheye Dome..."), is this the deviation from perfect hemisphere neglectible for fisheye use or should one put only rectilinear lenses behind this port?"

Just now Ryan Canon from Nauticam US responds: "You are correct - the dome is not a perfect hemisphere, but we have found in our testing that this slightly smaller segment doesn't create any noticeable image quality issues."

 

=> So the assumption, that, for practical purpose, the 230 dome is a fisheye domeport, intended for fisheye lenses, is correct.

=> Nevertheless, many prefer the 230 dome (r=12 cm) over the 250, truly rectilinear, dome (r=16cm), also for rectilinear lenses, probably because it is smaller, lighter and cheaper. Also Nauticam recommends the 230 port over the 250 for many rectlinear lenses in their portchards (in another request, some time ago, Ryan wrote me that they recommend the 230 over the 250 for lenses, where the 250 domeport does not bring noteworthy improvement over the 230 (because of size, weight and price)).

=> A smaller, less hemispherical, domeport with r=12cm would give identical results as the 230, but is, at present, not available...

 

Wolfgang

Edited February 23 by Architeuthis

[Interceptor121 773]

32 minutes ago, Architeuthis said:

We had somewhere a discussion, whether the Nauticam 230 domeport is a domeport for fisheye lenses or for rectilinear lenses (I do not remember where it was, but it was not completely in-topic, anyhow). It is also not completely in-topic here, but I think this is the right location to post a statement from Nauticam about this issue:

 

I asked: "I have a question regarding "230mm Optical-Glass Fisheye Dome Port II" - SKU # 18812:  The radius of curvature is 120mm (?), but the diameter is less than 2x120=240mm. Is this now a complete hemisphere as the name implies (Optical-Glass Fisheye Dome..."), is this the deviation from perfect hemisphere neglectible for fisheye use or should one put only rectilinear lenses behind this port?"

Just now Ryan Canon from Nauticam US responds: "You are correct - the dome is not a perfect hemisphere, but we have found in our testing that this slightly smaller segment doesn't create any noticeable image quality issues."

 

=> So the assumption, that, for practical purpose, the 230 dome is a fisheye domeport, intended for fisheye lenses, is correct.

=> Nevertheless, many prefer the 230 dome (r=12 cm) over the 250, truly rectilinear, dome (r=16cm), also for rectilinear lenses, probably because it is smaller, lighter and cheaper. Also Nauticam recommends the 230 port over the 250 for many rectlinear lenses in their portchards (in another request, some time ago, Ryan wrote me that they recommend the 230 over the 250 for lenses, where the 250 domeport does not bring noteworthy improvement over the 230 (because of size, weight and price)).

=> A smaller, less hemispherical, domeport with r=12cm would give identical results as the 230, but is, at present, not available...

 

Wolfgang

The 250 dome is even less of a  complete hemisphere

The radius of curvature per specifications is 16 cm so the dome is actually only able to support 102.75 degrees in fact it is called wide angle port

This port should be used for rectilinear lenses that do not focus very close that typically require this curvature

It would not make any sense to use this for a fisheye as the angle of view is very small so this is a good solution for not very wide rectilinear lenses up to 18mm

This port considering most lenses are at least 16mm is really a strange one

So to recap

There are only two full domes in Nauticam catalogue

4.33" acrylic

140mm glass

There are then 3 glass wide angle ports

180mm with 109 degree fov and 11cm radius 

230mm with 147 degrees and 12 cm radius

250mm with 103 degrees and 16cm radius

Of the above only one is kind of suitable for fisheye consider horizontal field of view is 172 degrees so the image is subject to more barrel distortion than a correctly positioned dome

We then have the following acrylic ports

8.5 dome port no specifications provided unclear what the radius and angle of view are

As of today if you want to have a fisheye lens with the same field of view that is offered on land the only options are the first two 4.33" and 140mm no others support the full field of view

The second options seems to be the 230mm to use  fisheye with additional barrel distortion and reduced field of view

The 8.5" acrylic port remains to be investigated it is not clear if it is a full hemisphere or not and what the angle of view is

Why the 230mm would have a benefit over the 140mm dome considering the positioning is suboptimal remains to be seen. I cannot understand why additional barrel distortion improves corners it should deteriorate them

Edited February 23 by Interceptor121

[ChrisRoss 150]

8 hours ago, Interceptor121 said:

Why the 230mm would have a benefit over the 140mm dome considering the positioning is suboptimal remains to be seen. I cannot understand why additional barrel distortion improves corners it should deteriorate them

Possibly because other factors are at play.  In any case Nauticam mark the 140mm dome as most optimised, though the criteria for that is not known.

Fisheyes certainly do not suffer from corner issues to the same extent as rectilinear lenses as the shape of their focal field is different to a rectilinear lens as I noted in a previous post.  A rectilinear lens you can see a parallel plane to the sensor is in focus taking a shot of using focus peaking in the viewfinder.  With a fisheye the focal field is roughly circular so a near perfect match to a curved virtual image.

Yet I also observe that Ikelite recommends their compact dome port 75344 which is a very shallow dome segment as the CFWA solution for the Canon & Nikon 8-15 lenses.  The lens needs be positioned way up close to the port glass well forward of the centre of curvature to avoid vignetting .  I'm not saying for a second that the image including the corners is as "good" as a fully optimised setup, but people use the Ikelite setup and are happy with what they are able to shoot.

[Interceptor121 773]

There are inconsistencies in Nauticam port chart depending on who tested the set up

On the nikon f chart the best dome for the sigma fisheye is 230 in all others format and lenses is 140mm

There is no reason for that other than mustard said so?

For me getting a fisheye to reduce the field of view and then moving backwards compared to the glass because the dome takes some space is not logical

Fisheye lenses perform terribly in the corners they don’t do well at all topside the focal plane is curved opposite to a dome due to barrel distortion

Maybe this effect is countered by the dome and therefore things improve unclear

If the dome helps improving the fisheye lens then smaller dome would be better but there are considerations of depth of field

I think the confusion here depends on the fact that corners are affected by field of curvature which is similar but different from depth of field

 

 

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[phxazcraig 117]

Just a personal data point in this thread - I shot my Nikon 16-35 behind a 230mm dome (and 90mm extension) for years, and I was always disappointed with the corners.   Even more so considering both the dome expense and the hassle of traveling with it.  Sure wasn't a payoff.

Then I added the Sea and Sea Internal Correction Lens, which I think was designed for this dome/lens combo.  Or generally 16-35 lenses.

It made a big difference!   Before the ICL I cropped the edges and corners from virtually every shot, no matter how stopped down I was.  With it, I'm shooting at F5.6 - F8 a lot, though for shots where edge-to-edge is both important and where the subject ranges from fairly close to distant I may stop down as far as F14.

I'm now shooting Nikon 14-30 behind the same 230mm dome (50mm extension), and I added the 82mm ICL to it.   Seems to work very well.  (I'd hope so, since the price of the ICL jumped from $400 to $750 in the past couple of years.)

I have one OK example to show.  I suspect it nears the best performance I'm going to get with this combo.  It was shot at F14 and shows a lot of lettuce coral from edge to edge.

https://www.cjcphoto.net/roatan2022/images/page3.htmlk

There are definite limits that I'm still trying to nail down.   Basically, when part of the edge subject is pretty close (I'm trying to learn just how close) and then extends off in the distance, the closer edge is just not going to be sharp.  This is when you actually focus somewhere in the center at a greater distance.  As a hypothetical example, I may have an edge that is 4-5 feet from me and a subject like the one in the link, you get decent edges.  But if that close part of the background is another foot closer, you just can't make it look good while still focused on that more-distant subject.  DOF doesn't cover things, and the results are bad.  But simply moving the camera back a bit can make a huge difference.

[TimG 62]

2 hours ago, phxazcraig said:

I have one OK example to show.  I suspect it nears the best performance I'm going to get with this combo.  It was shot at F14 and shows a lot of lettuce coral from edge to edge.

Thanks, Craig. That's really useful. Look pretty good, I reckon. That ICL is a chunk of change though especially in addition to the 230 dome.

[LarryHallas 44]

4 hours ago, phxazcraig said:

I'm now shooting Nikon 14-30 behind the same 230mm dome (50mm extension), and I added the 82mm ICL to it.   Seems to work very well.  (I'd hope so, since the price of the ICL jumped from $400 to $750 in the past couple of years.)

I also have the Z 14-30 + SS ICL + 230mm dome and get good results. I have to adjust the distortion slider a bit but I think that’s due to the lens profile in LR. I paid $600 at Reef Photo. Here is a shot at 14mm:

https://larryhallas.com/portfolio/reef-and-sunball/

Edited February 26 by LarryHallas

[Interceptor121 773]

This post was about fisheye
For rectilinear lenses the predominant issue is field of curvature
This is influenced by angle of view and where you focus
If you shoot something flat os different than shooting something where the focus point is closer than the other part of the frame
The sea and sea field flattener claims an improvement of 2 stops to obtain equivalent edges but is meant for particular combinations lens port


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