On 6/4/2026 at 3:47 PM, Muellema said:

Hi guys,

Here is my "silly question" again. Can someone please explain the rationale behind applying the coating to the outer surface of a port? Does anyone have a technical or optical justification for this?

I do not know the optical sense, but the problem with coating on outer surface is, that we clean/wipe the port after every dive. Even if we use the softest cloth available, we inevitably remove a little bit of the coating each time—however minuscule that amount may be. Unless there is some specific optical purpose for it... why put the coating on the outside of ports? However, I’m certainly open to being corrected if someone can offer a clear explanation for a reason for outer surface coating on ports. May be there is difference on super macro lenses due to optical setup. Hope someone can help.

I use ceroxyd for years for my ports and my old macro wetlens and it works perfect. It removes watermarks and even tiny scraches without much effort.

Also Seacam confirmed that optical coating is on the inside of the ports.

Let me give you also two other example not UW related

-first not from the field of optics- but still related to the loss of coatings. I had my car's paintwork treated with a very expensive ceramic coating (a very hard coating). After three years—and very few hand washes the coating was virtually gone due to the washing process and environmental exposure and it had to be reapplied.

-second from my optician. I have glasses with expensive progressive lenses with hard coating for protection. My optician recommends to clean this one only with warm dishwashing liquid and use a supersoft close (no standard microfiber, no standard glasses cleaning cloths) to dry. He too, assured me that otherwise, the coating wouldn't last for a terribly long time.

May be our UW camerahousing supplier have a superformula coating😁

Best regards,

Markus

Hi Markus, what’s the exact product name / manufacturer for your ceroxyd?

Where do you find it?

Greetings and thx

Michi

5 hours ago, Michi said:

Hi Markus, what’s the exact product name / manufacturer for your ceroxyd?

Where do you find it?

Greetings and thx

Michi

Hi Michi,

I bought my cerium oxide on an online platform called hood.de (similar to eBay), though that was a few years ago. I don't recall the brand name. However, during my research at the time, I found out that there are quality differences reflected in the color of the cerium oxide. Yellow and light cream-colored varieties are the purest and are used in the semiconductor and optical industries. Reddish-brown versions contain slightly more impurities and aren't as pure. These are primarily used in the glass industry for polishing glass. I have the reddish-brown type (see photo), and in my opinion, it yields very good results on the ports.

Br Markus

2 hours ago, Muellema said:

Hi Michi,

I bought my cerium oxide on an online platform called hood.de (similar to eBay), though that was a few years ago. I don't recall the brand name. However, during my research at the time, I found out that there are quality differences reflected in the color of the cerium oxide. Yellow and light cream-colored varieties are the purest and are used in the semiconductor and optical industries. Reddish-brown versions contain slightly more impurities and aren't as pure. These are primarily used in the glass industry for polishing glass. I have the reddish-brown type (see photo), and in my opinion, it yields very good results on the ports.

Br Markus

Hi Markus, thx a lot! That´s very helpful! Greetings