Do you ever do something....

[Zephyr]

That goes against every fibre of your being?

I had a bit of a boo-boo on the weekend that resulted in a major scratch in the acrylic wide angle lens port on my underwater camera. As we shoot 4k video, we need a flawless port. Step one involved using increasing grits of sandpaper, starting with the roughest at 1500 grit and getting finer and finer.

While it appears to have worked well and I won't know until I get to test dive it, intentionally scratching the face of it made me feel sick to my stomach the whole time I was doing it.

[Further]

Was it one of those drown or scratch the camera dilemmas ?

 

[AirwickWithCheese]

1 hour ago, Zephyr said:

That goes against every fibre of your being?

I had a bit of a boo-boo on the weekend that resulted in a major scratch in the acrylic wide angle lens port on my underwater camera. As we shoot 4k video, we need a flawless port. Step one involved using increasing grits of sandpaper, starting with the roughest at 1500 grit and getting finer and finer.

While it appears to have worked well and I won't know until I get to test dive it, intentionally scratching the face of it made me feel sick to my stomach the whole time I was doing it.

This is boring. Where's Megan?

[Zephyr]

1 hour ago, Further said:

Was it one of those drown or scratch the camera dilemmas ?

 

Nope, then I wouldn't care.  This was a momentary brain fart, looking one way, pointing the camera another, stupid bone headed move.  I was just being stupid.

[Zephyr]

47 minutes ago, AirwickWithCheese said:

This is boring. Where's Megan?

She is awesome, loving life and her job.

[Airehead]

1500 is pretty fine to start with isn't it ?

[Zephyr]

Not for acrylic.  A coarser grit makes too large of a scratch to buff out.  My scratches were big but not big enough to require any coarser

[KrAzY]

I have some ranging up to 3k grit if you need it. 
I use it for polishing my acrylic fish tank when it gets scratched. 

[AirwickWithCheese]

She's gorgeous, Zephyr.    

[Thaddeus Kosciuszko]

2 hours ago, Zephyr said:

That goes against every fibre of your being?

 

Sometimes the lessons in life you best remember are the ones where you start from      scratch.

 

[Parr8hed]

Please tell me it was initially scratched in a shark attack?

[Ralphie ★]

2 hours ago, Parr8hed said:

Please tell me it was initially scratched in a shark attack?

Ok. It was initially scratched in a shark attack. 

[Dirtyhip]

11 hours ago, AirwickWithCheese said:

She's gorgeous, Zephyr.    

Yes, so is the girl.

[pedalphile]

Along the lines of before we can be cured our sickness must grow worse.

[Zephyr]

4 hours ago, Parr8hed said:

Please tell me it was initially scratched in a shark attack?

It is now.  I am totally using that when people ask.  It is my new version.

Whenever I am injured topside and someone asked how it happened, I usually start with "So a busload of Nuns and Orphans were going over a cliff......."

[MickinMD ★]

I don't know how much clarity for an optical surface you can get from grit. My only experience is with telescopes and the magnification may affect the very high polish required there.

When making telescope mirrors and lenses, we amateur telescope makers (and the pros) use fine grit aluminum oxide or silicon carbide to grind the surface to shape and then either jewelers rouge or (faster working)( cerium oxide as a polishing agent.  The polishing agent is applied with a "pitch lap" which is needed to bring the glass to super-smooth condition.  There's a test where you look at the reflection of a lamp on the glasses surface at a certain angle and if it's still clear you've done the job.

The pitch lap is made to fit the shape of the glass being polished by pressing the glass. Pictures explain it better:

A backing plate is usually a glass disk but I've also made one by taking two 3/4" disks I cut from a piece of plywood, screwing them very solidly together to make a 1.5" thick disk, then shellacking it to make it waterproof first.

Tape is applied on the top of the backing plate to hold the pitch, then the pitch is heated to liquid:

The pitch is poured in the dam, channels are cut in it before the pitch hardens and cerium oxide is very thinly spread over the top before the glass to be polished is pressed against the pitch:

Sometimes a commercial channel tool is used. After the pitch hardens, the cerium oxide allows it to separate from the glass to be polished, and you have a "pitch lap" shaped to the glass you want to polish:

 

 

 

The annual Amateur Telescope Makers convention at Stellafane, Vermont has a webpage with lots of info: https://stellafane.org/tm/

[Zephyr]

Thanks Mick, that is very interesting stuff.  Luckily I do not require that kind of precision.  Water, it turn out, is a cool medium.  When taking a housing in the water, all the minor scratches and blemishes on the outside get filled with water and make the face of the viewport perfectly smooth.

Only the most agregious of mistakes end up being actually visible