Tube Cap Fool

[procky1845]

Hi,

I have a small, cheap Seben 3" telescope that I have been using and enjoying for the past few months.

My telescope tube cap that goes on the end of the scope can be removed in full or a smaller central cap can be removed. I've been using my scope all this time by just removing the small cap! In fact I only discovered the main cap came off accidentally when collimating the scope for the first time at the weekend. Its a hell of a lot brighter now unsuprisingly! 

Anyway, what is the purpose of the small cap in the center? When would I ever want to use the scope like this?

Thanks,

Lee

[D4N]

That is a cheap way to view the moon when it's too bright.

It is also useful for solar viewing as you only need film for the small hole.

Finally it is useful for checking your setup in the day.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

[procky1845]

I thought it must be something to do with reducing the brightness.

Can't believe I've been observing all this time with the end cap on! I haven't had time to have a proper go with it yet since I've made this little discovery but did have a quick look at Albireo. Previously I'd barely been able to make out the colours and had just assumed it was because the aperture of my scope wasn't quite big enough. I can now see the yellow and blue clear as a bell!

Its a bit like having a new scope! What a fool... 

[Uplooker]

It increases the focal ratio of the scope or as above dims the moon as less light gets in, as you have already discovered

It should be noted that when you view only through the small hole you will significant reduce the resolution with which you view objects.

You may also see that there is what looks like another cap next to the one you have already removed / viewed through. The other does not come off - this is used to store the first cap, once it has been removed.

Ian

[procky1845]

It increases the focal ratio of the scope or as above dims the moon as less light gets in, as you have already discovered

It should be noted that when you view only through the small hole you will significant reduce the resolution with which you view objects.

You may also see that there is what looks like another cap next to the one you have already removed / viewed through. The other does not come off - this is used to store the first cap, once it has been removed.

Ian

Only the one smaller cap on mine, ironically if there had been two I would have probably have worked it out a bit quicker!

[Andrew W]

That's the sort of thing I'd do!  nice one procky. The upside is the increase in aperture means you've got the equivalent of a brand new upgraded scope for free

[wxsatuser]

Setting up my ST80 guide scope last night and could'nt figure why no stars.

Doh!

Left cap on and could'nt see it in the dark.......so easily done.

[D4N]

Very common to do this in the dark, I was wondering how I had diffraction spikes on my frac but soon realised I still had my Bahnitov mask on the scope.

Sent from my iPad using Tapatalk

[Astrosurf]

You may also see that there is what looks like another cap next to the one you have already removed / viewed through. The other does not come off - this is used to store the first cap, once it has been removed.

Ian

Doh, you're all in good company - I didn't know this! Yep, but did wonder. But my daft brain says 'This is not important at this time. May be discounted'