Lens cap

[compassrose]

Hi all.

Anyone know why the lens cap on my 4" skywatcher short tube refractor has a removable centre portion - is it something to do with using the centre, more optically correct part of the lens? If so, when would be an appropriate time to use it?

Cheers

David

[seigfriedwilson]

Hello,

You can use it to stop down the apature when looking at bright objects, such as the full moon.

Some ccds can be used with it to help improve focus as well.

Seigfried

[compassrose]

Thanks.

[cotterless45]

It's also good for splitting doubles,

Nick.

[compassrose]

Thats interesting Cotterless45, can you elaborate for the sake of a complete newbie?