Is there any good way to tell your tubes you send out are the same tubes you get back? I got thinking about this as i just sent my tubes out to get installed in a set of rnvgs and got thinking about it. Im newer to night vision and only have a pvs 14 but i bought 2 brand new tubes on the ee and im just wondering.

I did not but there is a small L and R etched one each from the previous owner i think. Can you check them with out losing your nitrogen purge though?

You can use a flashlight to look into the ocular lens edges and you maybe able to see the serial numbers and the markings your looking for.

When a diamond gets left at a shop for service, they can weight it and show you the imperfections through a loupe, and those imperfections are drawn on the work order.
When you pick up the diamond, you inspect it with the loupe again and verify the match.
If your tubes have any blemishes (black spots, etc.) you could take a photo with a camera through the tube to document.
Obviously serial numbers or other markings as mentioned previously would be a superior method.

If you shine a flashlight in the back of the ocular, sometimes you can see the tube housing around the screen a little bit if you look at an angle. If you wind out the lens a little, you might see more.

Outside of that, if you take the ocular lenses off, you will not only lose the purge, but also the collimation - This would be a bigger issue with bino's I think.

You can repurge youself. A can of air duster is a suitable purge in the absence of nitrogen... It's all big molecules and they have reasonable properties that make them an OK home-brew alternative.

But you might want to mark your lens position before you unscrew them or you will lose collimation.

David

But what about a tube with no blems?