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Any experience with Sony 20mm 1.8 / Zen DP-170 / N100-N85 20mm adapter?


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Hi all,

 

Posting a query as I have been unable to find answers since my last soirée into lens options for an upgrade to Sony full frame UW. I currently have a Zen DP-170 port for N85 system which I’ve been shooting with the Olympus 8mm fisheye for many years. I shoot Sony A7x topside and for a long time I have been wanting to consolidate to a single system for both. If I am able to upcycle my current Zen dome it will be a big win, but port charts are lacking updates on more recent lenses and combinations.

 

I saw some previous posts on wetpixel by @Phil Rudin using the Sony 20mm f1.8 with the Nauticam 180mm + 30mm extender (attached below), so I know it’s possible to use this fantastic lens underwater. I wonder if anyone else has also previously owned a Zen DP-170 port and tried using it with the N100 port system / Sony 20mm f1.8? I note there is a Nauticam N100 to N85 20mm port adapter (Part #36471) available to fit N85 ports to N100 housings, but there isn’t really any info on people using this anywhere online. My Sony 20mm lens physically fits inside the N85 opening of my Zen DP-170 port, so with the right extension & adapter combination perhaps I may be able to get similar performance to Phil’s previous tests with this lens and the Nauticam 180mm + 30mm extender.

 

Otherwise, perhaps I should save myself from going down the rabbit hole and just offload my Zen dome to go towards a new N100 180mm glass dome instead. I’ve been comparing this idea with the 28mm f2/28-60 + WWL1-B also, but I feel like the 20mm 1.8 that I already own will give better results to the WWL1-B combo however and closer to what I currently shoot UW (Oly 8mm fisheye).

 

Any advice is much appreciated and I am also in the market for any secondhand ports/adapters mentioned.

 

Cheers

Colby

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Which DP-170?   You say it's an N85 there are two of them, one with 60mm extension and the other with 30mm IIRC, sounds like you have the one with 30mm extension.

 

Phil Guessed at the right extension being 30mm.  The N85-N100 is 20mm long so you would be looking at 50mm total extension with the DP-170 port with 30mm extension built in and the adapter.  If it doesn't vignette with that you should be able to use it - albeit living with a possible non -optimal position in the port.

 

If you knew the flange back length of the Sony A7x housing (distance from lens flange to housing surface ) you could do some calculations.  An easier way might be to do some port chart comparisons:

 

First up the Nauticam 180 and Zen DP 170 both use the same extension for most lenses in their port charts.

 

Next Marelux include the 20mm f1.8 in their port charts where it uses 50mm extension with their 180mm dome

 

Marelux also list the Sony 16-35f4  Zeiss which requires 40mm extension for same port.  Similarly for the 16-35 f4G lens Marelux is 70mm while Nauticam is 80mm extension.  The Nauticam system requires 10mm more extension the Marelux system for these lenses. 

 

SO for Nauticam the 20mm f1.8 requires 50mm + 10mm = 60mm extension.  With the DP-170 N85 port you have 50mm extension. By this comparison it should work OK without vignetting with just the adapter.  The port charts suggest you need 10mm more extension, so you could try it with just the adapter and decide if you want to also get the a 10mm extension as well. 

 

 

 

 

 

 

 

 

 

 

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The correct extension for the sony 20/1.8 to use with Nauticam 180mm and 35.5mm N100 N120 port adapter is 25mm Phil guess is very close and the difference will be minimal 

therefore in total you need 60mm

am not sire how the zen is built but the 180mm nauticam port is not an hemisphere and requires additional 25mm 

If the zen is more flat it may require less

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Hi @Chris Ross and @Interceptor121 thanks very much for your advice and suggestions. I believe I have the original DP-170 with 30mm extension so those tips are very helpful, will do some more research. FWIW I think the Zen is a fairly flat dome.. I am purchasing a secondhand NA-A7Siii housing to fit the A1 in, will see if I can figure out the flange distance online or hopefully in the next couple weeks when the housing arrives. They have also offered to include a 20mm extender but I’m not sure if it’s an N100 or N120 so may not be useful with the N100-N85 adapter. But if it is, would 70mm total be too much extension then? I guess I can play around with both adapter + 20mm if they are compatible and go from there. Cheers!

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1 minute ago, ColbyJames said:

Hi @Chris Ross and @Interceptor121 thanks very much for your advice and suggestions. I believe I have the original DP-170 with 30mm extension so those tips are very helpful, will do some more research. FWIW I think the Zen is a fairly flat dome.. I am purchasing a secondhand NA-A7Siii housing to fit the A1 in, will see if I can figure out the flange distance online or hopefully in the next couple weeks when the housing arrives. They have also offered to include a 20mm extender but I’m not sure if it’s an N100 or N120 so may not be useful with the N100-N85 adapter. But if it is, would 70mm total be too much extension then? I guess I can play around with both adapter + 20mm if they are compatible and go from there. Cheers!

The zen 170 is very similar to the 180mm if I recall with same curvature radius but smaller field of view

It is a wide angle port not a dome

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23 minutes ago, ColbyJames said:

Hi @Chris Ross and @Interceptor121 thanks very much for your advice and suggestions. I believe I have the original DP-170 with 30mm extension so those tips are very helpful, will do some more research. FWIW I think the Zen is a fairly flat dome.. I am purchasing a secondhand NA-A7Siii housing to fit the A1 in, will see if I can figure out the flange distance online or hopefully in the next couple weeks when the housing arrives. They have also offered to include a 20mm extender but I’m not sure if it’s an N100 or N120 so may not be useful with the N100-N85 adapter. But if it is, would 70mm total be too much extension then? I guess I can play around with both adapter + 20mm if they are compatible and go from there. Cheers!

I believe the Zen 170 and Nauticam 180 are very similar, the extension recommendations between those two are identical for most lenses.

 

70mm may or may not be too much.  You can test for vignetting which is the most likely issue with too much extension on land. This test would work if it were a N100 or a N120 extension, but only a N120 extension is compatible with a zoom gear.  If you are talking a prime lens though either one could be used I think as the critical thing with a N100 vs N120 is purely the placement of the zoom gear. 

So if it doesn't vignette you could try it with and without the extra extension to see if you can notice a difference.

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17 minutes ago, Chris Ross said:

I believe the Zen 170 and Nauticam 180 are very similar, the extension recommendations between those two are identical for most lenses.

 

70mm may or may not be too much.  You can test for vignetting which is the most likely issue with too much extension on land. This test would work if it were a N100 or a N120 extension, but only a N120 extension is compatible with a zoom gear.  If you are talking a prime lens though either one could be used I think as the critical thing with a N100 vs N120 is purely the placement of the zoom gear. 

So if it doesn't vignette you could try it with and without the extra extension to see if you can notice a difference.

 

Classic error here

You test for vignetting when the lens is very close to the port field of view. 

If you go as far as vignetting with a 20mm lens you will have a horrible amount of pincushion distortion

The extension I mentioned for the 180mm port is almost exact as it is based on the entrance pupil position from the lens design (dome article soon to follow features the workings)

For lenses that are not super wide dome positioning is actually more tricky than it is for lenses that are near the dome field of view

Looking at the Zen DP170 I think those ports were made by the same people of reefphoto and have then been made the nauticam ones so they are the same

On my 180 port the internal diameter of the glass is 170 and the external 180 because it sits on a 5mm ridge

this matters little to the field of view because if you take 5mm form the radius you get arcsin(8.5/10.5)=54 dome fov 108 degrees or 15.7mm

If the ZP170 has 30mm extension built in a further 30mm is what is required. the 25mm extension will be 5mm short but this will not be too bad as the lens is not super wide. For ideal performance you need those extra mm

However for other lens the opening diameter will be too small. Example Sony 16-35 GM are larger lenses wont fit

Tamron 17-28 to be checked it could be borderline

 

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37 minutes ago, Interceptor121 said:

 

Classic error here

You test for vignetting when the lens is very close to the port field of view. 

If you go as far as vignetting with a 20mm lens you will have a horrible amount of pincushion distortion

The extension I mentioned for the 180mm port is almost exact as it is based on the entrance pupil position from the lens design (dome article soon to follow features the workings)

For lenses that are not super wide dome positioning is actually more tricky than it is for lenses that are near the dome field of view

Looking at the Zen DP170 I think those ports were made by the same people of reefphoto and have then been made the nauticam ones so they are the same

On my 180 port the internal diameter of the glass is 170 and the external 180 because it sits on a 5mm ridge

this matters little to the field of view because if you take 5mm form the radius you get arcsin(8.5/10.5)=54 dome fov 108 degrees or 15.7mm

If the ZP170 has 30mm extension built in a further 30mm is what is required. the 25mm extension will be 5mm short but this will not be too bad as the lens is not super wide. For ideal performance you need those extra mm

However for other lens the opening diameter will be too small. Example Sony 16-35 GM are larger lenses wont fit

Tamron 17-28 to be checked it could be borderline

 

Thanks very much Massimo, look forward to the pending dome article and have been reading up a lot on your website already. So in my case with the N100-N85 adapter and Zen port I’ll have 50mm vs. adding the extra 20mm extender I’ll have on hand for 70mm, both likely not ideal then if 60mm total length is exactly correct. I guess I’ll aim to sell/trade the 20mm extender for a 10mm then and get it exact if the above combos don’t look any good. If the Sony 20mm 1.8 is not quite wide enough and causes issues with positioning in my Zen port, perhaps I can look at the Sigma 17mm or Tamron 17-28 lens then. Both of these lens with my current port options look to be cheaper than fitting the housing out with the WWL-1B and an entirely different lens setup. However I could also get the 32 flat port for the Sony 28mm lens fairly cheap as part of the sale of the housing.

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1 minute ago, ColbyJames said:

Thanks very much Massimo, look forward to the pending dome article and have been reading up a lot on your website already. So in my case with the N100-N85 adapter and Zen port I’ll have 50mm vs. adding the extra 20mm extender I’ll have on hand for 70mm, both likely not ideal then if 60mm total length is exactly correct. I guess I’ll aim to sell/trade the 20mm extender for a 10mm then and get it exact if the above combos don’t look any good. If the Sony 20mm 1.8 is not quite wide enough and causes issues with positioning in my Zen port, perhaps I can look at the Sigma 17mm or Tamron 17-28 lens then. Both of these lens with my current port options look to be cheaper than fitting the housing out with the WWL-1B and an entirely different lens setup. However I could also get the 32 flat port for the Sony 28mm lens fairly cheap as part of the sale of the housing.

tamron 17-18 works very well with this port there are examples on my blog and is the rectilinear lens i recommend in terms of value for money

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2 hours ago, Interceptor121 said:

 

Classic error here

You test for vignetting when the lens is very close to the port field of view. 

If you go as far as vignetting with a 20mm lens you will have a horrible amount of pincushion distortion

The extension I mentioned for the 180mm port is almost exact as it is based on the entrance pupil position from the lens design (dome article soon to follow features the workings)

For lenses that are not super wide dome positioning is actually more tricky than it is for lenses that are near the dome field of view

Looking at the Zen DP170 I think those ports were made by the same people of reefphoto and have then been made the nauticam ones so they are the same

On my 180 port the internal diameter of the glass is 170 and the external 180 because it sits on a 5mm ridge

this matters little to the field of view because if you take 5mm form the radius you get arcsin(8.5/10.5)=54 dome fov 108 degrees or 15.7mm

If the ZP170 has 30mm extension built in a further 30mm is what is required. the 25mm extension will be 5mm short but this will not be too bad as the lens is not super wide. For ideal performance you need those extra mm

However for other lens the opening diameter will be too small. Example Sony 16-35 GM are larger lenses wont fit

Tamron 17-28 to be checked it could be borderline

 

If you have data on flange position and entrance pupil location that certainly allows you to do the calculations exactly.  60mm certainly seems to agree with what Marelux recommends  versus the Nauticam charts based upon comparisons with other combinations.

 

I don't believe it would be close to vignetting with the 20mm lens and 70mm of extension.  I have found that manufacturers very often recommend port combinations with significantly less extension than what the precise location of the entrance pupil would indicate.  They likely steer well clear of vignetting in most applications as people can easily detect that.  That Is why I suggested you try both configurations before you make any decisions or spend money on more extensions. Testing for vignetting on land is merely a precaution which would save you taking the rig UW only to find it was unacceptable.

 

From what I can tell manufacturers make their port and extension recommendations based upon shooting tests with the lens/camera on slide shooting through the dome mounted in a test rig.

 

One example I have is the calculations I did on my 7-14mm panasonic lens in the Zen 170mm dome.  I measured the entrance pupil location and did the geometry for field of view at the 7mm end and found the entrance pupil was about 15- 20mm forward of the entrance pupil IIRC.  As I understand it too little extension means some barrel distortion which may or may not be acceptable for what you shoot.   You may well find 50mm acceptable. 

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For Colby,

 

While I found the classic 94 degrees of the 20mm F/1.8 worked very well in the 180mm port my current preference for a wide rectilinear prime would be the Sigma 17mm F/4 for Sony full frame. This lens is wider at 103.7 degrees but even more exceptional is its 12cm (4.7") minimum focus distance v. the 18cm (7.08") of the 20mm. I have tested this lens with 15mm and 20mm extensions in the Marelux housing with the 180mm and 140mm ports. Because of its very close minimum focus distance it will do in a pinch with the 140mm port I use for fisheye zoom lenses.

 

Second I would go to the 180mm port in N100 to avoid the expense of the N110 to N120 adapter as you can use the N100 port extensions for other lenses.

 

Regarding the issue of making port extension comparisons between Marelux and Nauticam I offer the two photos below which show the Sony 28-60mm lens in both housings extended to 28mm. The Oliver Green Marelux housing has the 20mm Nauticam N120 to Marelux 5" extension which I use for WACP-1 and Matty Smith 12 inch dome for splits. The Black Nauticam housing has the N100 to N120 35.5mm port adapter also for the WACP-1 and 12 inch dome. As you can see the lens in both images is in the same plane with the end of the adapter. So by quick mental calculation the difference between the two is 15.5mm 35.5mm-20mm=15.5mm. Using 15.5 as the difference does not always reflect the corresponding recommended extensions for Marelux or Nauticam. They both do testing and come to a conclusion for each dome size.

 

Regarding the 7-14mm on 4/3 and M4/3 I gave up on the 170/180 ports and went to Zen 200mm with a noticeable difference in corners using the extension of my choice since none was on any port chart.

 

I have also included an image of WACP-C on Marelux adapter and the Sigma 17mm in a 140mm port with the port glass touching the pool light.

 

 

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Some guesswork going on here... Might be a good idea to measure the curvature of your dome, as a starting point for calculating extensions required. This will give you the actual radius, which is info manufacturers should provide, but generally don't.

 

You will need: paper, compass (the sort you used in primary school, not the one on your phone), ruler, pref in mm.

Measure the outside diameter of the visible curved portion of your dome. Measure the height at the midpoint. This can be tricky, but within a couple of mm is OK.

 

Draw a horizontal line on the paper and mark the diameter on it, as well as the height above. Find the mid point and draw a vertical line through that. Get your compass and by trial and error, adjust it until its pencil can swing an arc through the three points. Measure from the point of the compass to the height mark and that gives you the true radius of your dome, at least on the outside.

 

You can safely ignore the thickness of the dome for the purposes of this calculation, but you will need to account for the thickness of the metal dome mount, to arrive at a figure to use for calculating a required extension from the port face.

 

FYI, some fisheye domes may not be full hemispheres. Case in point: Nauticam 140 is approx 6mm shy of a full hemisphere... why?

 

I wouldn't mind knowing the figure for where the optical centre is for the Nauticam 180mm dome, if someone cares to measure theirs. I calculated it as approx 42mm behind the port flange (meaning you will need to add approx 40mm of extension to get to the equivalent of using a full half hemisphere dome), but that was guessing from photos, as I don't own one and have no intention of buying one.

 

 

 

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21 minutes ago, dentrock said:

Some guesswork going on here... Might be a good idea to measure the curvature of your dome, as a starting point for calculating extensions required. This will give you the actual radius, which is info manufacturers should provide, but generally don't.

 

You will need: paper, compass (the sort you used in primary school, not the one on your phone), ruler, pref in mm.

Measure the outside diameter of the visible curved portion of your dome. Measure the height at the midpoint. This can be tricky, but within a couple of mm is OK.

 

Draw a horizontal line on the paper and mark the diameter on it, as well as the height above. Find the mid point and draw a vertical line through that. Get your compass and by trial and error, adjust it until its pencil can swing an arc through the three points. Measure from the point of the compass to the height mark and that gives you the true radius of your dome, at least on the outside.

 

You can safely ignore the thickness of the dome for the purposes of this calculation, but you will need to account for the thickness of the metal dome mount, to arrive at a figure to use for calculating a required extension from the port face.

 

FYI, some fisheye domes may not be full hemispheres. Case in point: Nauticam 140 is approx 6mm shy of a full hemisphere... why?

 

I wouldn't mind knowing the figure for where the optical centre is for the Nauticam 180mm dome, if someone cares to measure theirs. I calculated it as approx 42mm behind the port flange (meaning you will need to add approx 40mm of extension to get to the equivalent of using a full half hemisphere dome), but that was guessing from photos, as I don't own one and have no intention of buying one.

 

 

 

You can calculate all of this from geometry, the radius is published in multiple places as being 110mm, this is outside radius.  If you know the radius and actual diameter of the widest part (chord length)  you can calculate the the dome height. 

 

Previously Massimo advised his was 105mm internal/110external radius and the ID is 170mm.  You can use this calculator to do the calculations:

 

https://planetcalc.com/1421/

 

Scroll down to the complete calculator at bottom and select Radius and chord length (R= 105, C= 170mm)

the solution gives the Height of dome as 43mm and the included angle is 108° which is a little more than a 16mm lens on full frame.  This means the centre of curvature is 62mm (105 -43 mm) below the bottom of dome element. 

 

The included angle is the maximum field of view possible with the entrance pupil at the centre of curvature and 108° is just a little bit more than a 16mm lens which is 106°.  This assume that the dome structure doesn't get in the way of seeing the edges of the dome, in practice you may find it's necessary to place the lens a little bit forward to avoid vignetting.  In calculating extensions you need to account for any built in extension in the dome itself.

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6 hours ago, dentrock said:

Some guesswork going on here... Might be a good idea to measure the curvature of your dome, as a starting point for calculating extensions required. This will give you the actual radius, which is info manufacturers should provide, but generally don't.

 

You will need: paper, compass (the sort you used in primary school, not the one on your phone), ruler, pref in mm.

Measure the outside diameter of the visible curved portion of your dome. Measure the height at the midpoint. This can be tricky, but within a couple of mm is OK.

 

Draw a horizontal line on the paper and mark the diameter on it, as well as the height above. Find the mid point and draw a vertical line through that. Get your compass and by trial and error, adjust it until its pencil can swing an arc through the three points. Measure from the point of the compass to the height mark and that gives you the true radius of your dome, at least on the outside.

 

You can safely ignore the thickness of the dome for the purposes of this calculation, but you will need to account for the thickness of the metal dome mount, to arrive at a figure to use for calculating a required extension from the port face.

 

FYI, some fisheye domes may not be full hemispheres. Case in point: Nauticam 140 is approx 6mm shy of a full hemisphere... why?

 

I wouldn't mind knowing the figure for where the optical centre is for the Nauticam 180mm dome, if someone cares to measure theirs. I calculated it as approx 42mm behind the port flange (meaning you will need to add approx 40mm of extension to get to the equivalent of using a full half hemisphere dome), but that was guessing from photos, as I don't own one and have no intention of buying one.

 

 

 

Nauticam as well as zen publish their dimensions

what you don’t know is how much the port goes backwards and the gap between the glass and the dome hood

example nauticam 230 wode angle port is 112mm this is the distance between the top of the hood petal to the port

there is a further 5mm between the glass and the hood so to get your 120mm position in the center you need

120-112+5=13mm offset from entrance pupil normally the round this down to 10mm

the most complicated thing is to know where the entrance pupil is the rest can be worked out with a calliper

for the 20mm my dimensions are accurate I have this lens myself for the 180mm dome port.

all is required is to measure the zen dp170 bottom to glass take out the part that goes into the extension 

make a difference between 110 and this number if any this is what you need to add or subtract to your entrance pupil 

I guess this value is nearing zero with a built 30mm extension

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21 hours ago, Chris Ross said:

 

 

https://planetcalc.com/1421/

 

Scroll down to the complete calculator at bottom and select Radius and chord length (R= 105, C= 170mm)

the solution gives the Height of dome as 43mm and the included angle is 108° which is a little more than a 16mm lens on full frame.  This means the centre of curvature is 62mm (105 -43 mm) below the bottom of dome element. 

 

 

Thanks for bringing the calculator to my attention!

Easy... if you know the radius. But when I was measuring my Nauticam domes I couldn't find info on their radii - hence the measuring.

Can you provide a link?

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Thanks again. Wasn't aware of that one. Pleased to see my crude measurements for my N 140 are spot on.

 

Curious about 62mm figure for N180 as it is the same as I calculated for my (now discontinued I think) N 6 inch acrylic WA dome. Will recheck that one.

 

Anyway, great to have the N180 figure and radius as you can then cross-check Nauticam port chart suggestions against any other combos of stuff you might have handy and want to try with a particular lens.

 

And you could use my drawing method if you can't find a published radius for your dome.

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Chris / Interceptor: clarification requested re amount of extension required for Nauticam 180 WA dome port:

 

1. The calculator as mentioned by Chris delivers a dome height of 43 if you input R=105 and C=170 (inside dimensions; height is 40 if R=110).

 

2. Interceptor states in his interesting article on dome port calculations:

 

"I have access to the 180mm dome and I know that the port is actually 8.5cm tall from mount to glass edge because I measured it. This means I need to add 25mm to the extension required." [subtracting 85 from R=110]

 

Now I fully realise that you have to add the thickness of the port mount to the calculator's answer (c. 14mm with my N140), but that is a big discrepancy. 85 vs 43 (+ say 14) =57. Subtracting 57 from R=105 = 48 as the required extension, before you start accounting for EP position etc.

 

So can either of you confirm that only 25mm ext is needed (to account for the 180 WA dome being less than a full half hemisphere), or is it actually quite a bit more  ?

 

Thanks!

 

 

 

 

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1 hour ago, dentrock said:

Chris / Interceptor: clarification requested re amount of extension required for Nauticam 180 WA dome port:

 

1. The calculator as mentioned by Chris delivers a dome height of 43 if you input R=105 and C=170 (inside dimensions; height is 40 if R=110).

 

2. Interceptor states in his interesting article on dome port calculations:

 

"I have access to the 180mm dome and I know that the port is actually 8.5cm tall from mount to glass edge because I measured it. This means I need to add 25mm to the extension required." [subtracting 85 from R=110]

 

Now I fully realise that you have to add the thickness of the port mount to the calculator's answer (c. 14mm with my N140), but that is a big discrepancy. 85 vs 43 (+ say 14) =57. Subtracting 57 from R=105 = 48 as the required extension, before you start accounting for EP position etc.

 

So can either of you confirm that only 25mm ext is needed (to account for the 180 WA dome being less than a full half hemisphere), or is it actually quite a bit more  ?

 

Thanks!

 

 

 

 

The dome has built in extension which you can see here:

 

https://wetpixel.com/forums/index.php?/topic/59042-nauticam-180-optical-gladss-dome-for-sale/&tab=comments#comment-380898

 

The 43mm is the height of the glass, luckily Massimo has measured the height if the port as 85mm from glass to mount in his post here: 

 

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My measurements are accurate to 1-2mm

the 180 wide angle port is quite tall as you can see from the photos

You can also ignore the glass thickness because you subtract it anyway and it is in fact unknown in addition the position would be related to a middle point not inner not outer

we are talking about 2mm here

moreover the centre of the inner and outer diameter are in the same point what changes is the effective curvature radius

if this things sound a bit obscure I would recommend you don’t attempt your own calculations unless you already have plenty of extension rings and are happy to take the risk

my article anyway shows various method to calculate everything and I recommend you follow one of those as you see fit

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Chris,

Aha! Thanks. That explains it. I didn't see the built-in extension in looking at the photo on Nauticam website, and of course they don't bother to mention it, just as they don't bother to mention radii on their website, and are happy to misquote port weights....

 

Makes you wonder what is their aim. Perhaps push buyers towards those expensive water contact optics?

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9 minutes ago, dentrock said:

Chris,

Aha! Thanks. That explains it. I didn't see the built-in extension in looking at the photo on Nauticam website, and of course they don't bother to mention it, just as they don't bother to mention radii on their website, and are happy to misquote port weights....

 

Makes you wonder what is their aim. Perhaps push buyers towards those expensive water contact optics?

If you read my article there is a link to Nauticam documentation for the glass ports where most of the measurements are provided

If you read some of my comments on how they go about determining extension the situation may become a bit clearer, this is of course a guess 

Nauticam and Zen are the best in providing documentation and details therefore I would not single them out as worst in fact they are the best for that

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Interceptor,

My point was that Nauticam should provide the info up front to assist dome choice, rather than via instructions that come with the port.

 

I read your dome calculations article carefully and you pull together lots of info which makes an interesting read - for those interested in the detail. Sadly, I think there are not many such people who like to go 'off piste' from the port charts, like you and me!

 

You also make a couple of points which don't tell quite the whole story, but it's not my job to critique.

 

Regarding the N180 which I never intend to buy (and have never even seen one) I was only interested in the detail to be able to cross-check Nauticam port chart recommendations against other possible solutions, using bits and pieces I already have.

 

I accept your measurement of 25mm required extension, and thank you for that. I guess the built-in extension will be in the order of 20-25mm then.

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7 hours ago, dentrock said:

Interceptor,

My point was that Nauticam should provide the info up front to assist dome choice, rather than via instructions that come with the port.

 

I read your dome calculations article carefully and you pull together lots of info which makes an interesting read - for those interested in the detail. Sadly, I think there are not many such people who like to go 'off piste' from the port charts, like you and me!

 

You also make a couple of points which don't tell quite the whole story, but it's not my job to critique.

 

Regarding the N180 which I never intend to buy (and have never even seen one) I was only interested in the detail to be able to cross-check Nauticam port chart recommendations against other possible solutions, using bits and pieces I already have.

 

I accept your measurement of 25mm required extension, and thank you for that. I guess the built-in extension will be in the order of 20-25mm then.

There is no built in extension the port is not flat like the others. If you had a flat cut and extension each lens would vignette

 

Nauticam design for this port is indeed very good. Considering that most underwater photographer are more creative than else and do not bother doing any tests of their equipment Nauticam do a quite good job at supporting a variety of lenses over several formats.

My impression, but am not nauticam spokeperson employee or elses is that they do not look at determining the entrance pupil, they start with a first guess put the camera in their test rig and  move it 1 cm back and forth to see where is the best MFT

This generally works well for lenses that are close to the dome field of view. It works less well for lenses that are not so wide

There are also inconsistencies of this method, the ports are fixed they don't move so the gap in the extension between port A and B should always be identical instead it is not. Which to an extent proves my point

 

Majority of users will not be able to tell those fine differences and don't have skill and resources to do their check and following the port chart will have good results in most cases, but in my opinion there is room for further optimisation

 

If you have any comment on my article feel free to post them on my site I always answer them

 

 

Edited by Interceptor121
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