What is the 2 cap/hole on the 5 tube cap of the Celestron 130 SLT used for?

[jaam1969]

Just received a Celestron 130 SLT for Christmas. I haven't had a chance to use it yet due to clouds and winds. I live 15 miles east of Cleveland,OH.
Anyways, my question is: what is the purpose of the 2" cap/hole on the 5" tube cap?

Thanks,
Joe

 

[russ_watters]

That's for cutting down the brightness when you view the moon.

 

[jaam1969]

That's for cutting down the brightness when you view the moon.

Thanks, Russ,
That had crossed my mind, but this being my first telescope and there is no mention of it in the manual, I thought I'd ask.

Joe