Underwater dome UV pass for an ROV

[ori333]

Hello everyone,

 

They sell off the shelf ROVs that I would like to put my UV camera inside.

 

Any suggestions how to fabricate a dome like this one that will pass UV light?

The dome is about 9 inches in diameter.

 

P.S. I have access to an industrial vacuform machine and a laser cutter.

[ori333]

Image attached

[dabateman]

See if you can get some uv clear acrylic (PMMA). I got 10 sheets of 100x100mm that cut off around 250nm about 2 years ago. Its used for plastic disposable UV lab cuvettes.

 

But make sure it's not uv blocking coated. The last 2 200x 200 mm sheets I got cut off at 380nm. Upset by that as useless for UV transmission and UV cutting.

I was going to use them for sample support on a home made stage.

 

You can buy a large a sheet, verify the transmission with a spectrometer or your UV camera. See it doesn't block the signal, then melt it to the dome. Then retest to see it still transmits.

Or see if a Chinese seller can make one out of PMMA for you. I got a 30cm fresnel lens made in PMMA for a hype lens idea I still have to build to see objects behind other objects.

 

Actually seems to be quite a few on Ebay. Just ask the seller if you can get it non uv blocking.

[Cadmium]

http://www.polymerplastics.com/transparents_uvta.shtml

 

You can get that in large sheets.

[nfoto]

The less easily solved issue is getting sufficient UV for the underwater scene ... UV tends to be absorbed rather quickly in most waters, unless you have pristine water with extrmemely low levels of particles and organic matter.

 

I did a lot of spectral underwater profiling in my former scientific days. We found very low levels of detectable UV in most waters except for lakes influenced by acidic precipitation, or in some mountain lakes.

[Stefano]

Seems visible light (especially blue) is a special window for underwater photography. IR is quickly absorbed, and UV doesn't reach deep as Birna said.

[ori333]

Yes, that seams to be the dogma of underwater UV photography. I'm hoping to get a glimpse of what the mantis shrimp sees. It's got those UV receptors...so I'm assuming there is something to see.

[Stefano]

UV should penetrate at least a few meters, given the water is reasonably clean. I have photographed swimming pools in UV and IR, and although the water there is crystal clear, it is transparent in UV and very dark/black in IR. In dual band UV/IR (I used 2 mm thick ZWB2 only) it appears blue.

[ori333]

Looks like we can find them in very shallow water.

 

[colinbm]

https://www.gsoptics.com/transmission-curves/

[Cadmium]

Come to think of it now,m I guess I have not seen any underwater reflected UV done.

ins13 has shown some underwater UVIVF on here (as well as underwater IR), but I didn't think she did any underwater reflected UV.

Like Birna said, might be hard to do that... but if one can do underwater UVIVF, then...? maybe...?

[nfoto]

In the upper 1m, some UV can be seen in clearer waters. Sorry that my spectral data sampled in those research projects now are inaccessible to me.

[ulf]

The tropical locations where the mantis shrimps are found might have a better transmission too.

 

http://omtab.obs-vlfr.fr/fichiers_PDF/Morel_et_al_LO_07.pdf

http://plymsea.ac.uk/id/eprint/2146/1/The_ultra-violet_absorption_of_sea_water.pdf

[ulf]

I bought UV Grade Perspex Sheets for my quartz flash DIY projects, two years ago.

 

https://www.plastics...ylic-Sheet.aspx

 

They are a part of Bay Plastics Ltd

that has manufacturing capabilities too.

I wanted round discs and had them cut to the dimensions I needed.

 

Bay Plastics Ltd

Unit H1, High Flatworth, Tyne Tunnel Trading Estate,

North Shields, Tyne & Wear, NE29 7UZ, United Kingdom

Tel: +44(0)191 258 0777 Fax: +44(0)191 258 1010

Web site: www.bayplastics.co.uk or www.plasticstockist.com

Email: sales@bayplastics.co.uk or accounts@bayplastics.co.uk

VAT Reg.No. GB 499 9881 39 Company Reg.No. 2325035

 

As you will not go very deep for this a rather thin wall will be OK as a dome is very strong.

That is good as thicker materials naturally will attenuate more

[ulf]

In the upper 1m, some UV can be seen in clearer waters. Sorry that my spectral data sampled in those research projects now are inaccessible to me.

Did you do some research in tropical waters?

[nfoto]

Nordic inland waters mainly. I did a later project in New Zealand lakes and in the more transparent of these, UV could penetrate beyond 1m depth.

[ori333]

New Zealand, that's fantastic. I'll be shifting my PhD to Australia soon and we have plans to collaborate in New Zealand (for a different project).

 

My marine connections are in Washington State (Friday Harbor Laboratory). They gave me the green light to put a UV camera on their UAV. If we can get some pilot data with them that would be nice.

[Cadmium]

Before constructing a UV dome, I might try some underwater UV shots using one of those underwater bags first, just to see what kind of UV you will get.

https://www.ultravioletphotography.com/content/index.php/topic/3186-a-small-river-underwater-infrared/page__view__findpost__p__26344

Of course, then you will need to use a UV transmitting front glass for the bag, or whatever it uses.

[ori333]

With a laser cutter and published dimensions, I can get a low cost waterproof enclosure and replace one of the faceplates with UV Acrylic.

 

That's the best path I see before getting a dome for the ROV.

like this end cap:

 

https://bluerobotics.com/wp-content/uploads/2015/03/end-cap-no-holes-e1483036673248.png

 

for this enclosure

 

https://bluerobotics.com/store/watertight-enclosures/4-series/wte4-asm-r1/

[otoien]

Out of curiosity I brought out the uncoated glass dome for my Subal Procase underwater housing (for 20mm f/2.8 AF lens/Nikon F4, so a fairly small dome). My crude test was shining my Convoy 365 nm on to a brightly fluorescencing target like white paper. I could only detect a very slight attenuation that could have partly be due to reflection in the dome. (A similar test though my UV safety glasses would cause complete attenuation.) Of course that does not prove anything about what is happening deeper into UV.