Tokina in Sea Frogs and AOI

[SFEgr]

My second question in one day!

 

So... I am muddling through trying to guess whether a OM5 + Tokina 10-17mm might work in an AOI housing. I do not own or have access to an AOI housing yet.

The  - short question - after trying a Tokina in a Sony/Sea Frogs housing, and finding it fit (sort of) I am trying to find how much space there is in an OM/AOI set-up. If I could get the separation between the flange and dome in an AOI that would be great, but that measurement is a bit tough so even an estimate between glass element of a 8mm fisheye and the dome would help.

 

The  - Long - background

I tried putting my Tokina 10-17mm on a Metabones (non 'speed boost') on my A6400 into a Sea Frogs housing behind an acrylic 6" Dome and it fits pretty good I think. But I know squat about optics so I tried it in the bathtub and the FOV is reduced a bit but seems quite serviceable. (Brings a 24 inch ruler down to about 22" at about 5" from front optic, 4" from acrylic dome under water)

 

What I can measure on the Sony set-up is

Metabones Flange to Flange = 25.8mm (1")

Metabones flange to Tokina front glass at 17mm = 99mm (3.9")

Metabones flange to Tokina front glass at 10mm = 96.7mm (3.8")

Sony flange (in housing) to inside face of acrylic dome is 130.8mm (5.1")
So I suppose my lens glass to dome is about +1"

 

Then I put the same lens on a Viltrox EM-M2 ii 0.71x on an OM-5 and quite interestingly the camera tells me the widest view is 7 degrees (???) and it is well wider than the Sony combo. And at that width I get the built in shade 'petals' coming into frame - a little bit. It still seems nice and sharp, so I find myself wondering if this combination might fit into an AOI housing. Their domes are 8" so it might be nice. (???)

 

Viltrox Flage to Flange 18.5mm (0.73")

Tokina flange to front glass is 71.6mm (2.81")

Tokina + Viltrox Flange to front glass is 89.5mm (3.52")

Tokina + Vitrox Flange to Front 'petal' is 91.4mm (3.6") - 94mm at 17mm lens position

Lens assembly widest Dia. 74mm (2.91")

 

The Oly fisheye 8mm is 80mm but I don't know if that is flange to glass or rear element to petals.

The Oly 12-40 pro is 84mm.

 So I am looking at being 6 to 10mm long but I am not sure it that is a big deal. I sure would appreciate any comments or insights!

[Chris Ross]

I assume you are trying to work out if you can use a Tokina 10-17 in an AOI housing with an OM-5 with the OM-D port system that goes with that housing.  If you look at the AOI port chart you will see that the 8mm fisheye uses the 22mm extension with the DLP-01/02.  If you look at the Nauticam charts you will the 8mm fisheye uses a 17mm extension with the 140mm port and to use the 10-17mm on a metabones speed booster you need the 34.7mm adapter and a 10mm extension to use with the same dome.

 

Based on this for AOI you need (34.7 + 10 = 44.7) - 17mm = 27.7mm more extension than the 8mm fisheye to use the tokina lens with AOI.  SO a total of 22 + 27.7 = 49.7mm.  OM-D ports only have two extensions 22 and 52mm and the Pen ports only offer 24 and 34mm extensions.  The 52mm might work but it could vignette.

 

If you could go to a store that has the housing and extensions in stock you could try them out - you can tell if vignettes on land in the shop if you put it all together.  A safer course might be to go with an Isotta or Nauticam housing it's more expensive but they have a full range of extensions to work with.  The 10-17mm will work perfectly well in the Nauticam 4.33" & 140mm domes, the Zen 100mm dome and the Isotta 4.5"dome.  

 

I use the Canon 8-15 on my OM-1 with a 140mm dome on Nauticam.  It's quite expensive to adapt these lenses on that system but the Isotta will be significantly cheaper.  From everything I hear the Metabones speed-booster/smart adapter is the better option for adapting canon mount lenses to Olympus.  The smart adapter is for the Canon 8-15 while the speed booster gives a 7-11mm fisheye with a Tokina 10-17.

 

[SFEgr]

14 hours ago, Chris Ross said:

I assume you are trying to work out if you can use a Tokina 10-17 in an AOI housing with an OM-5 with the OM-D port system that goes with that housing.

Exactly. Thanks for your careful response Chris. That is an interesting and resourceful approach going to the Nautical charts. Didn't occur to me. 😞 The numbers do correspond to my observations with the Sony/Seafrogs assembly. In that case the Sea Frogs dome has a sort of built in extension of about 45mm or so to the commence point of the dome curvature. And with this assembly if I pull the lens back (mimic an extension) I can only pull back 1/4" or 7mm before I get vignetting.

 

So yes, with the OM/AOI set-up it seems I will be at least 6-10mm further forward of the Oly 8mm (with the 22mm extension) or 22-26mm short (with the 52mm extension). As the Viltrox leaves me with a 7mm wide the former is risky and the latter would certainly vignette, and probably badly.

 

As I live in a place far from any shop that has any of these housings in stock, I will likely stick to the safety of prescribed housing/lens combinations unless someone has actually tried the combinations before. But I just thought I would put the question out there in case anyone had.

Edited Sunday at 07:29 PM by SFEgr

[Chris Ross]

16 hours ago, SFEgr said:

Exactly. Thanks for your careful response Chris. That is an interesting and resourceful approach going to the Nautical charts. Didn't occur to me. 😞 The numbers do correspond to my observations with the Sony/Seafrogs assembly. In that case the Sea Frogs dome has a sort of built in extension of about 45mm or so to the commence point of the dome curvature. And with this assembly if I pull the lens back (mimic an extension) I can only pull back 1/4" or 7mm before I get vignetting.

 

So yes, with the OM/AOI set-up it seems I will be at least 6-10mm further forward of the Oly 8mm (with the 22mm extension) or 22-26mm short (with the 52mm extension). As the Viltrox leaves me with a 7mm wide the former is risky and the latter would certainly vignette, and probably badly.

 

As I live in a place far from any shop that has any of these housings in stock, I will likely stick to the safety of prescribed housing/lens combinations unless someone has actually tried the combinations before. But I just thought I would put the question out there in case anyone had.

Well for safety - Nauticam lists how to do it in the port charts and Isotta has provided the method to use an 8-15 in their system that works, it was posted on here.  Using the Tokina is simply a matter of using less extension.  Isotta is really quite helpful by all accounts and will respond to requests like this.  Here is a link to the parts list for the 8-15 with Isotta.  From the port charts you need 20mm less extension with the Tokina compared to the Canon lens, but check with Isotta - you would also need to sort out a zoom gear.  :