Optimum dome size for MFT WA zoom lens

I plan to acquire a WA rig and decided to go for olympus MTF with original olympus housing (OM-D 1/PT-EP11; OM-D 5 MII/PT-EP13 or OM-D 1 MII/PT-EP14 - this will be decided later). The lenses will be Zuiko 7-14mm or Panasonic 7-14mm plus one of the fisheye lenses. Also a WA lens with fixed focal length will be included sooner or later.

The domeport size that Olympus recommends is 7".

Larger domes will give better results. The larger the dome, however, the heavier and bulky it is, compensating the advantage of small size/weigth of a MFT system.

According to this amazing webside (https://oceanity.com.au/tools/virtual-image-calculator/), using default parameters, the following relations apply (Domeportsize(in inches)/distance of the virtual image from the domeport in cm (infinity to 0,2m real object distance)/closest possible real distance of the object, when the lens is able to focus on a image that is 15cm apart from the domeport):

6"/20,8cm-8,1cm/0,9m

7"/24,6cm-8,7cm/0,6m

8"/28,4cm-9,1cm/0,5m

9"/32,2cm-9,5cm/0,4m

My question is what would be the optimum size of a domeport for such a rig, i.e. ports larger than the optimum would bring just insignificant improvements that are not relevant in practice?

Does someone have practical experience with domeports larger than 7" for MTF WA and does she/he think the results justify the extra size/weigth?

Thank you for your comments, Wolfgang

Some dome ports are segments of larger spheres, the radius of curvature is the critcal parameter that you need. My understanding is the big dome not only allows you to focus a little closer but the radius of cirvature of the virtual image is less

I went through this while back getting a dome port for the Pany 7-14. The general concensus was that the Zen 170mm dia glass dome (a 220 mm dia shere segment - http://www.zenunderwater.com/products/dp-170) was the best option, you can search for threads on the Pany 7-14mm. The Oly 7-14mm is bigger dia and needs a different solution. Even if you went with Zen's big dome which is 230mm diameter, its radius of curvature is 120mm (9.5" dome) vs the little 170mm dome at 110mm (8.6" dome equivalent) and the virtual image is only 0.7cm further away for an object 300mm away, which means you can focus 5cm closer with the bigger dome.

A search will find a few relevant posts:

http://wetpixel.com/forums/index.php?showtopic=53672

http://wetpixel.com/forums/index.php?showtopic=55223&page=1 (on the Oly 7-14mm)

There was a much larger post on the topic here or a similar forum which went through the issue in detail that I can't find right now.

Not sure how the Olympus housing effects this choice apart from probably limiting dome choice to a 7" dome and making the above arguments moot. Given the amount you are investing I would recommend the Nauticam housing option for an EM-5 II or EM-1. The availability of the vacuum leak check alone was enough to push me that way. I have an EM5-II in Nauticam, vacuum system, Zen 170mm dome and the Pany 7-14 plus 12-40 f2.8 Oly. Around Sydney the 12-40 (and macro lens) get much more use as I don't get to dive clear tropical waters that much. The usability and quality of the housing made it a no brainer for me. Also it allows you to use their big dome if you like, just get the N85-N120 converter and you can attach the big dome port to that with extension tubes if required, though placement with respect to entrance pupil may not be optimal.

http://www.zenunderwater.com/collections/optical-glass-ports

Do also note that the 7-14 Pany can be placed into the assembled housing/port from the back, the 7-14mm olympus being bigger needs to have camera in housing, then attach lens then place dome port over lens, due to limitations of the diameter of the port attachment on the Nauticam housings.

You realise you need a separate port for the fisheye? With its 180° field of view you need a full hemishere dome (not a segment) the small 3.5" or 4" Nauticam dome is generally used.

Thanks also for the link to virtual image calculator

Hi Chris,

Thank you for the interesting information on the Zen dome port.

I was considering to use the Athena OPD-F170II-OPD (6,9") port or alternatively the OPD-F200V-SS (7,9") with larger radius as one universal domeport for Olympus 12-40mm, 7-14mm and fisheye 8mm. From what you are writing it seems that the OPD-F200V-SS (7,9") port is the better choice (almost as good as the Zen port for 12-40 and 7-14, but also usable for the fisheye, since it is 180^o).

Should not the IQ with the fisheye also be better when using the large dome compared to a 4" dome? Or is the setup just too bulky for close focus, making strobe positioning difficult?

May be a good idea to start with the OPD-F200V-SS (7,9") port and, just in case, one can acquire a dedicated, second, port afterwards.

I am discouraged of using Nauticam housings because of the problem with camera/lens insertion you are mentioning for the Olympus 7-14mm. Do you have the same problem with the 12-40mm lens? Do you have an idea how it would be with the Sony 8 mm fisheye?

If it is only the 7-14mm lens that makes the problem, I would acquire a Panasonic 7-14mm instead and use Nauticam housings.

In many hundreds of dives with videorecorder or compact camera, water entry never occurred. I think leak alarm is nice to have but I could live without it in the future also...

Wolfgang

You would need to go into the specifics of the the dome and the extension size, if the fisheye is too far back in the dome it will vignette and if the entrance pupil is not in the right spot you'll have issues. I had a look at the Athena website and it is damn confusing I did find this page for the EM-5II as far as I can tell:

http://www.athena-opt.com/EP-0506/EP-0506.html

It's the Japanese site as the English site doesn't seem to have this info. You will see that the port for the 7-14mm pro has a longer extension than the port for the Panasonic fisheye. so the fisheye would be way back in the dome.

Yes I use the 12-40mm in the Zen dome and yes I have to insert it from the front, not a big deal really for the diving I do as it's mostly 2 dives in a day once a week and the port comes off anyway.

Don't forget that the vacuum preloads the o-rings, you can't physically open the housing or remove the port without releasing the vacuum, helps guard against surface leaks due to bumps etc.

There is some discussion on using the Oly 7-14mm PRO in this thread:

http://wetpixel.com/forums/index.php?showtopic=55223&page=2&hl=athena&do=findComment&comment=361856

Phil Rudin seems to know quite a bit about what fits what so may pay to PM him with specific questions, he seems to be saying these ports will only fit the EM-5 and EM-1 oly housings as the EM-5II reverted to the Pen housing port size. What this means in practice I'm not sure but seems to imply you can't fit the Oly dome to the EM-5II. Check to make sure.

I know the Pany 7-14 in the Zen dome is good as is the 12-40mm but I think the 7-14 f2.8 doesn't fit, you need the n85-N120 adapter and either the extension less ZEN dome of the 180mm Nauticam glass dome, which will also take the 12-40. I'm also quite sure the Pany fisheye will need its own dome, the optics for a fisheye are different to a rectilinear wide angle and are said to perform much better I think largely due to the curved virtual image not being a problem for them, I did find an explanation for it once but it escapes me now,

Here's a post which may be useful:

http://wetpixel.com/forums/index.php?showtopic=54567

Looks like the small dome for the fisheye also suits the 12mm f2 . Pros and cons for the smaller port are discussed. The port you link may be suitable for the fisheye if the port is available with an extension you can remove and you can fit dome alone to the housing. There is no combo of the big port and the fisheye lens on the port chart.

This link says you can use the 12-40 and 7-14 in an Oly housing with Oly ports (Athena ports being the same) only with the EM1: http://wetpixel.com/forums/index.php?showtopic=58458

This one says you can't do that with the Oly housing for the EM-5 II as the port is smaller dia: http://wetpixel.com/forums/index.php?showtopic=57129 It also states you may be able to remove the extension from the port to use it with the 8mm fisheye.... but again check to see if this is correct and you of course lose the CFW capabilities of the small dome

Sorry for reviving this thread, would the Nauticam 7" work for both the Panasonic 7-14 and olympus 12-40?

I would love to get the Zen but it's too expensive!

Hi Diver4fun and all others,

I decided now to acquire the Oly EM-5MII in Nauticam housing with 12-40mm Pro and the Zen DP-170-N120 (thanks to the great suggestion by ChrisRoss). I made few dives so far, but can already say that the image quality is very good and I am happy with the setup.

It seems that I will be able to use both the Zuiko 7-14mm Pro and the Zuiko 8mm FE Pro with the same dome (see my recent posting in this tread: http://wetpixel.com/forums/index.php?showtopic=59963

I want to thank all for the valuable input, in case we meet some day I'll spend a

Wolfgang