What on is that hole for??

[nephilim]

This is a bit of a daft question but can somene tell me what the capped hole in my main scope cover is for, I keep meaning to look at the manual but it's at my girlfriends as I leave the scope there most days due to very dark skies.

[Helen]

You can put solar film over it to make a solar viewer, or you can use it with the small hole uncovered to reduce the brightness and increase the focal ratio for viewing plantes and the moon.

Helen

[Simes]

If I am understanding you correctly it's the so called moon filter. With the cap on the scope, remove the cap over the small hole and you will see everything, but less brightly. It's like stopping down a camera lens (or the iris closing in the eye).

[Matt Scunthorpe]

I used Baader solar film on mine to make a solar filter

[swamp thing]

I think it's for what matts done.

I can't see the point in closing down the aperture for anything else. By stopping down the aperture you would lose resolution on the moon and planets and not see so much.

Sent from my iPhone using Tapatalk

[nephilim]

Ahh, thanks all

[rowan46]

It's an apparture stop for the moon. you will lose some resolution but not very much on such a bright object.

[acey]

It's what Helen said. Other than reducing light, stopping down aperture (increasing focal ratio) is a way of reducing aberration. My refractor has a similar two piece cap for that reason. On the frac the smaller hole is concentric, the reason it's off-centre on a reflector cap is because of the central obstruction caused by the secondary mirror. In days of yore it was standard to stop down the aperture of a refractor as a way of reducing aberration (many refractors would have a baffle fitted that did this permanently).

[Helen]

It's an apparture stop for the moon. you will lose some resolution but not very much on such a bright object.

... and you take out the central obstruction too so that's a mitigating point too.

Helen