Why is the 140mm Glass Dome Recommended vs the 230mm Glass Dome for the Canon 8-15mm and all other fisheye lenses?

[Interceptor121]

 

 

Something is going on with this post. second attempt.

 

People wonder why, if bigger dome is better, the smaller 140mm port with a radius of just 69mm is preferred to the larger 230mm dome that has a curvature radius of 120mm

 

Nauticam does test using a purpose built tank and MTF measures and says that of the two ports with the extension of 30mm the 140mm does better?

 

Why? it has to do with geometry of the port. The larger dome is not am hemisphere and quite a big chunk is missing. this means the centre of the dome is behind the port however if you try and use a longer extension it vignettes

The smalle port is closer to a proper hemisphere and the centre is a few mm behind the port, this port has a better position and therefore beats the other larger and heavier one

If the larger dome was a complete hemisphere the rule larger is better would hold true

 

Edited April 28 by Interceptor121

[Kamaros]

Does the 140mm dome actually provide better image quality than the 230mm for fisheye lenses? Is that just in the center, or does "larger is better" still apply to corners in this case?

[Interceptor121]

20 minutes ago, Kamaros said:

Does the 140mm dome actually provide better image quality than the 230mm for fisheye lenses? Is that just in the center, or does "larger is better" still apply to corners in this case?

I am answering the question on why the * is for the small dome

from my knowledge nauticam test tank has charts in many positions centre side edges 

my conclusion would be that due to incorrect position of the 230 dome with respect to the centre there will be additional chromatic aberrations and distortion that will eventually lead to loss of resolution off centre 

in the centre there would not be much difference 

i have a zen dp230 on arrival for some rectilinear lenses and have no plans to use it for the fisheye where I use both the 140 glass and the smaller 4.33” acrylic 

larger is better doesn’t apply if your port is not positioned correctly 

Edited April 28 by Interceptor121

[Chris Ross]

Fisheyes are also fundamentally different to rectilinear lenses in that the in focus area is curved rather than straight.  If you setup a rectilinear lens on a grid surface at close focus and wide open you will see the region that is in focus is defined by two parallel lines.  If you do the same with a fisheye the infocus region is annular centered around the lens. 

 

The fisheye region that is in focus is a closer match to the curved virtual image than a rectilinear lens in focus region.  

 

 

[Interceptor121]

4 hours ago, Chris Ross said:

Fisheyes are also fundamentally different to rectilinear lenses in that the in focus area is curved rather than straight.  If you setup a rectilinear lens on a grid surface at close focus and wide open you will see the region that is in focus is defined by two parallel lines.  If you do the same with a fisheye the infocus region is annular centered around the lens. 

 

The fisheye region that is in focus is a closer match to the curved virtual image than a rectilinear lens in focus region.  

 

 

I am not sure thats the case

A fisheye lens on land has barrell distortion so corners look further away not closer

perhaps this effect counters the dome geometry where edges are actually closer 

[Architeuthis]

I have asked this question some time ago to Nauticam/US. The answer was that the combination with best optical performance is rated with (*), but when they do not notice further obvious improvement with a bigger dome, the smallest dome that brings already best IQ is rated with (*).

 

=> This would mean that the 230mm dome does not bring substantial better optical performance over the 140mm dome with the fisheye lens (for split shots it is clearly the better choice)...

 

 

Wolfgang

Edited April 29 by Architeuthis

[Chris Ross]

13 minutes ago, Interceptor121 said:

I am not sure thats the case

A fisheye lens on land has barrell distortion so corners look further away not closer

perhaps this effect counters the dome geometry where edges are actually closer 

I can post some images to demonstrate what I'm talking about, but it'll have to wait a couple of days till I return home, I don't have them with me currently.

[Interceptor121]

45 minutes ago, Architeuthis said:

I have asked this question some time ago to Nauticam/US. The answer was that the combination with best optical performance is rated with (*), but when they do not notice further obvious improvement with a bigger dome, the smallest dome that brings already best IQ is rated with (*).

 

=> This would mean that the 230mm dome does not bring substantial better optical performance over the 140mm dome with the fisheye lens (for split shots it is clearly the better choice)...

 

 

Wolfgang

That sounds BS because otherwise both would have a star. In the same chart there is also the 8.5" acrylic that also looks big however it is even less of an hemosphere. Nauticam are not going to stop anyone thinking of buying a more expensive product

 

The reality is that looking at geometry the better domes in terms of position are size

140mm glass

4.33" acrylic

230 glass

8.5 acrylic

The acrylic is made with the same 24cm radius however it is a lower profile the centre of the dome is far behind and it would vignette

I have a zen DP230 which is the precursor of the Nauticam 230mm and could demonstrate the theory however I am not keen to spend time on this and the dome is so big I can't do tests in my sink however if I have time I can try the bathtub

 

The 230mm dome is useful for very wide rectilinear lenses that do not fit the 180 and 250 wide angle port basically anything wider than 16mm rectilinear

[Interceptor121]

1 hour ago, Chris Ross said:

I can post some images to demonstrate what I'm talking about, but it'll have to wait a couple of days till I return home, I don't have them with me currently.

I understand the idea however if the fisheye corner would look close with a dome they would look even closer due to the field of curvature

I think a fisheye has the opposite curvature as the things in the centre look bigger and in the corners smaller so further away. This goes against the dome

So it is not the fisheye lens that is sharper at the edges if you try one on land you can see that on a flat target the corners are horrible but inside a dome there is a compensation so they look better

From there to say that edges look better in a fisheye lens is a different story but the optical effect overall works for the underwater use cases

By the way the extreme barrel distortion is what makes the WACP type of lens look better after all they are a demagnifier with a dome on top

Edited April 29 by Interceptor121

[Chris Ross]

3 hours ago, Interceptor121 said:

I understand the idea however if the fisheye corner would look close with a dome they would look even closer due to the field of curvature

I think a fisheye has the opposite curvature as the things in the centre look bigger and in the corners smaller so further away. This goes against the dome

So it is not the fisheye lens that is sharper at the edges if you try one on land you can see that on a flat target the corners are horrible but inside a dome there is a compensation so they look better

From there to say that edges look better in a fisheye lens is a different story but the optical effect overall works for the underwater use cases

By the way the extreme barrel distortion is what makes the WACP type of lens look better after all they are a demagnifier with a dome on top

Perhaps, though I don't quite follow you, in a couple of days I can post some images which may help explain better.

[Interceptor121]

53 minutes ago, Chris Ross said:

Perhaps, though I don't quite follow you, in a couple of days I can post some images which may help explain better.

I think the fisheye effect means corners are further away

In the dome due to field of curvature the corners appear closer

The two effect combined may cancel each other to an extent

I am interested in looking at the images you mention

[Architeuthis]

4 hours ago, Interceptor121 said:

That sounds BS because otherwise both would have a star. In the same chart there is also the 8.5" acrylic that also looks big however it is even less of an hemosphere. Nauticam are not going to stop anyone thinking of buying a more expensive product

 

No BS, Massimo - that is what I was told officially by Nauticam: they do not give two stars when they IQ is very similar, but the smaller dome gets the star in this case...

 

I suggest you ask your question at Nauticam, they are usually very cooperative. Their answer would be of interest for many here...

 

Wolfgang

[Interceptor121]

Just now, Architeuthis said:

No BS, Massimo - that is what I was told officially by Nauticam: they do not give two stars when they IQ is very similar, but the smaller dome gets the star in this case...

 

I suggest you ask your question at Nauticam, they are usually very cooperative. Their answer would be of interest for many here...

 

Wolfgang

Not your BS their BS

 

It is not easy to get straight answers from Nauticam.

 

The standard answer to why there are * is as follows

1. We test all ports combination in our test tank

2. The combination with the highest MTF gets the *

 

In the case of the 230mm port vs the 140mm port the extension is the same 30mm however the geometry of those two ports is different. The 230mm port has the centre of the sphere futher back so it should have a longer extension however due to the way this port is built it would vignette.

If the 230mm port was the exact replica of the 140mm just made bigger I have no doubt edge performance would be better there is an increase in radius of 74% 

As I said based on the physicalshape of the port I already know the 230mm dome cannot be perfectly positioned when I have some spare time i will follow that up with some photos but this is not really a priority

For the the 230mm port is useful for 14mm and 10mm lenses that dont fit the other wide angle ports

 

 

 

[hellhole]

but u have live without a shade with a 140mm dome... most of the time...

 

i guess it a choice...

[Interceptor121]

11 minutes ago, hellhole said:

but u have live without a shade with a 140mm dome... most of the time...

 

i guess it a choice...

I don’t know where you get this from

the 140mm has more field of view it vignettes less than the 230mm

in fact the port that has the absolute widest field of view is the acrylic 4.33 i can put a 35mm extension with that

Edited April 29 by Interceptor121

[Phil Rudin]

I think he is suggesting that the sunshade needs to be removed from the 140mm port all the time when in fact it only needs to be removed if you want to shoot the 8mm circular fisheye end of the lens. 

 

[Interceptor121]

48 minutes ago, Phil Rudin said:

I think he is suggesting that the sunshade needs to be removed from the 140mm port all the time when in fact it only needs to be removed if you want to shoot the 8mm circular fisheye end of the lens. 

 

Thats true of any lens that has a hood not specific to port A

But the point is that the port chart doesn’t look at 8mm

[hellhole]

8 hours ago, Interceptor121 said:

I don’t know where you get this from

the 140mm has more field of view it vignettes less than the 230mm

in fact the port that has the absolute widest field of view is the acrylic 4.33 i can put a 35mm extension with that

i seen quite a few post from phil on using the laowa 10mm that the shade has to come off...  

i never said any thing about vignettes.  it probably maybe the wrong extension port used...

but it seems like that to me.  

[hellhole]

7 hours ago, Phil Rudin said:

I think he is suggesting that the sunshade needs to be removed from the 140mm port all the time when in fact it only needs to be removed if you want to shoot the 8mm circular fisheye end of the lens. 

 

how about the laowa 10mm?  is it different extension port will not need to remove the shade?

[Interceptor121]

On 4/30/2024 at 1:30 AM, hellhole said:

i seen quite a few post from phil on using the laowa 10mm that the shade has to come off...  

i never said any thing about vignettes.  it probably maybe the wrong extension port used...

but it seems like that to me.  

Nothing to do with this thread 

stop hijacking and ask questions on the laowa thread would be appropriate 

[Davide DB]

1 hour ago, Interceptor121 said:

Nothing to do with this thread 

stop hijacking and ask questions on the laowa thread would be appropriate 

 

Massimo, you do not have to respond. Please leave these evaluations to the moderators.

 

[Interceptor121]

I now have tested the Zen DP230 that is very similar to the Nauticam 230mm

 

The extension to place the Canon 8-15 at the centre of the dome is 60mm with this the lens is totally inside the extension and totally vignette

If you shorten to 30mm there is a mispositioning of 30mm too short increased barrel distortion, popping centre loss of field of view and weaker edges

The 230mm dome is really a solution for rectilinear lenses that don't focus close and are not wider than 14mm it is not good for fisheye lenses that focus close

[Adventurer]

On 5/3/2024 at 7:12 PM, Interceptor121 said:

The 230mm dome is really a solution for rectilinear lenses that don't focus close and are not wider than 14mm it is not good for fisheye lenses that focus close

I have looked into several domes more closely last week and would 2nd that statement. If the dome is not full sphere usually the optimal position limit ends with 14mm Full Frame lenses.

 

Therefore, for fisheye, the smaller dome is very often the better solution when it is a complete hemisphere.
 

Full sphere rules out dome size for fisheye lenses.

[Interceptor121]

5 hours ago, Adventurer said:

I have looked into several domes more closely last week and would 2nd that statement. If the dome is not full sphere usually the optimal position limit ends with 14mm Full Frame lenses.

 

Therefore, for fisheye, the smaller dome is very often the better solution when it is a complete hemisphere.
 

Full sphere rules out dome size for fisheye lenses.

It is more about position once you are off axis you loose field of view and gain chromatic aberration at the edges

The canon 8-15mm has its own CA issues and a dome off position does not help

Also fisheye lenses have horrible blurry corners and the CA just adds to the garbling. You stop down the lens to reduce it and destroy centre resolution in the process which is what matters most

[Interceptor121]

Some side by side shots 140mm vs 230mm

 

If your eye is really trained and have an idea of what a dome not positioned correctly does you should be able to identify what is what. Not an easy task.