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I ran into a great deal of trouble researching and building this set up so I wanted to share in case it helps save someone else a few weeks of reading countless articles, books, websites, and company calls.

 

I already owned a Sony so I went with what I felt the best lens is that still fit based on what I measured in the extensions.

Again: This is not a supported lens from Ikelite at this time but it works and you can add in a zoom ring if desired with a simple mod. My guess is they allow for some fudge room the on stated width allowed for port extensions (~1 mm) to avoid lenses not working in cases where measurements are not exact or help insure the standard included zoom ring will fit.

Facts for this lens setup in case you care to try a different one (sample photos below).
- The entrance pupil or nodal point for this lens measures at 62-68 mm (10-20 mm zoom) from the base (ends up near the gold ring).
- 8" Dome.
- Port Theory says that as a general rule the entrance pupil should rest at the same distance from the dome as it's radius or 4" in my case. Port theory and reality of what looks good aren't always the same but is a great starting point.
- I ended up using the 5510.16 extension at 51.76 mm length along with the 5510.50 extension ring at 32.66 mm. This is short of the optimum length but to go any longer means you'll see the port extension in the frame at the corners (see photo).

What needs to be done to make the zoom ring work:
Cut off the springs which hold the grabby part to the zoom ring because it's too fat with them. You can then hold the two remaining pieces to the lens with double sided tape if you like but not needed. I'm told there may be a low profile zoom ring component available as well. Alternatively, you can just use the right thickness of adhesive foam on the inside of the clear zoom ring (same as what comes with it). Often there is an optimum zoom for clarity in the corners on a rectilinear lens... so if you find it just set it and forget the zoom ring all together.

Other extension dimensions per Brett w/Ikelite (thank you). This is the total physical length of each.
Extensions:
5510.16 = 51.76 mm

5510.22 = 67.64 mm
5510.24 = 71.13 mm
5510.28 = 93.31 mm

Extension Rings:
5510.50 = 32.66 mm
5510.54 = 44.95 mm
5510.58 = 58.14 mm

Sample Photo Showing cropped photos (to left side) of my Test results. Keep in mind the optimum zoom for the last photo would have been somewhere between 10-20 mm and not right at the 10 mm I shot but I wanted consistency. From left to right goes what other photographers suggested, middle was the manufactures best guess and right was what I calculated.

post-52792-0-73338000-1445906551_thumb.jpg

My calculations to find the needed extension ring:
For purposes of my calculations I always went off the inner radius of the dome vs. the outer, I have no idea which one is best.

The entrance pupil or nodal point for my lens measured at 62-68 mm from the base.
The dome is not a full half sphere so my best measurement puts the physical inner distance at ~67 mm from glass to the outer flat base of the dome port. This means it's still ~34.6 mm short of the true 4" (101.6 mm)
inner radius of a complete half sphere.


To find length of extension needed from camera body to dome I added the nodal point to the short fall of dome radius. EX: 34.6 mm (+) 62 mm (=) 96.6 mm of needed extension length but doesn't account for the extension overlap with the dome due to o-rings and threading.

Next, account for the fact that the port extension doesn't connect flush with the camera body like the lens.
My best guess is the entire physical port extension connects at a distance
~20 mm from the camera body.

EX: I take 96.6 mm (-) 20 mm = 76.6 mm. Then account for the overlap mentioned which was ~13 mm so 13 mm (+) 76.6 mm (=) 89.6 mm of total physical extension length needed at 10 mm zoom or 95.6 mm at 20 mm zoom.

Again, I opted not to go with the extension 5510.28 even though it's likely the right length because it was visible in frame at 10 mm zoom. It did provided more clarity then the other extensions tested but it wasn't worth it to me at the time. In hind site is was a rookie mistake to worry about the zoom function instead of just setting my lens to 12mm before diving. You can see what I mean in the sample photo.

So what do you think, did I get it mostly right or would you go back to the longer extension and slightly zoom the lens?

Edited by Turf

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post-52792-0-37179600-1445908893_thumb.jpg

 

Here is a photo taken with the middle extension.

SONY SLT-A65V
f/6.3
1/400 sec
ISO-100
Exposure bias: 0
10mm
Max Aperture 3.6

Edited by Turf

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post-52792-0-88743600-1445909649_thumb.jpg

Cutting down the image quality to 1mb doesn't exactly let the gray blend well but you get the idea.

SONY SLT-A65V
f/6.3
1/160 sec
ISO-100
Exposure bias: 0
11mm

Edited by Turf

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post-52792-0-35991900-1445910251_thumb.jpg

SONY SLT-A65V
f/5.6
1/320 sec

ISO-100
Exposure bias: 0
12mm
Max Aperture 3.6

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Could you please post a picture of how you modified the lens?

 

Interesting work, I considered buying a rectilinear ultra-wideangle lens once but ended up buying the Sigma 10/2.8 diagonal fisheye.

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Absolutely... in hindsight that would have been the most obvious picture to show.

 

Sent from my SCH-I535 using Tapatalk

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Could you please post a picture of how you modified the lens?

 

Interesting work, I considered buying a rectilinear ultra-wideangle lens once but ended up buying the Sigma 10/2.8 diagonal fisheye.

Sorry for the slow response.

 

post-52792-14489457530753.jpg

You can see where I shaved off the ring that normally is used to mount the shade.

 

post-52792-1448945758715.jpg

This is an unmodified zoom ring grip, all I did was cut off the springs because they were too fat.

 

Update: ikelite started making an extension that is likely the perfect distance (between the best two above) so it shouldn't show the port at 10min. Going to check it out this weekend or next.

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Thank you for the image and description. I think this is a good solution. If you still want to use a shade for topside shots you can as well use some generic screw-in shade.

 

Update: ikelite started making an extension that is likely the perfect distance (between the best two above) so it shouldn't show the port at 10min. Going to check it out this weekend or next.

 

Having the ability to zoom from 11(/10)-20mm would be great for fish portraits. Have you already made the test with the new extension?

 

Happy holidays!

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Thank you for the image and description. I think this is a good solution. If you still want to use a shade for topside shots you can as well use some generic screw-in shade.

 

 

Having the ability to zoom from 11(/10)-20mm would be great for fish portraits. Have you already made the test with the new extension?

 

Happy holidays!

The sales guys I was talking to at my local shop ended up not knowing what he was talking about and the extension he was suggesting for this lens was very far off so I'm staying with my current setup of 5510.16 + 5510.50 to get me as close to the optimal distance without seeing the port in frame.

 

Sent from my SCH-I535 using Tapatalk

Edited by Turf

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Updated photos from recent trip to Guadalupe Mexico. Used Shark Diver, can't say enough good things about the way they ran things... real care and thought put into every part of the experience.

 

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cc633041b6184a127a007a8e2e40e5a8.jpg

1698b6b06104fb153f80cf1bd799c3e0.jpg

db518c4add711962be52d122a9f7ca65.jpg

Edited by Turf

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Few more from Anilao PH.

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3ea1ce714b6d6cf6ececfa873c8cd664.jpg

5a56a75c2b304e24cf38c24611276b2b.jpg

618961bbc25d1d2e398fb1fdc65aa949.jpg

Edited by Turf

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Here is an example of the tightest shot I could take of a pygmy seahorse the size of a pinky nail. The second is a zoom and crop in Photoshop of the same photo to show the detail captured.

Before

c1961e2d05b35001602335cf120aa713.jpg

After

c6cd4bf80401c2011c21c1ed838a273b.jpg

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