This is probably a stupid question, but.....

Can someone explain to me about the cap at the end of my optical tube? I have an Orion Skyview Pro 120 refractor and at the end of the tube is the dew shield, then an end cap that has 2 pieces to it. There is an inside "circle" of the cap cover that measures around 1.5 inches in diameter that can be removed, while the main end cap cover can remain in place.

Since I'm new to astronomy and scopes, I haven't a clue how I would use this. In what case(s) would I leave the end cap cover on and just remove the small center portion of the cap? Is it common to view with the cap cover on and just the center portion removed?

On another issue, for backyard city viewing I've been enjoying this scope, but I'd like some advice from the experts out there. I was thinking about buying a 2nd scope (not only for my viewing, but to share with my wife so we both have scopes to view with at the same time). I don't want to spend more than $2000 total (tube assembly, mount and tripod). What would you folks recommend that would give me more than what I already have? Viewing would be from my city backyard view. I enjoy planetary viewing and deep space objects but find results with my Skyview Pro 120 (even with Nagler EPs) limiting in brightness, clarity and details compared to many photos I see on this site.

Thanks in advance to everyone for their guidance, help and suggestions.

That little cap is to cut down the brightness on some objects. You can also cover it with solar filer material. or use just that small hole bare for solar projection viewing.

For $2000., you can get a really big dob. Lots of options there.

Charlie

Actually you will convert it to F26 but the diameter will be 1.5 inches. The aperture will be reduced by a factor of 3, light gathering by a factor of 10, the resolution by a factor of 3.

The Dawes limit for this scope is right at 1 arc second, masking it will reduce it to about 3 arc-seconds. I had one of these scopes and I was able to resolve Porrima with it which at the time was 1.3 arc-seconds. Clearly not doable with the reduced aperture mask in place.

The improvement would be in the false color but the reduction is resolution would offset any advantage gained here.

jon isaacs

As you may or may not have gleaned from the other responses, putting the cap on and then unplugging the hole will eliminate most of the false color at the expense of EVERYTHING else. I can't figure out when you'd ever want to do this, except to further your optical education by the experiment, but it must have seen like a good idea to the marketing division of the Sirius Cybernetics Corporation, you know, that bunch of mindless jerks who'll be the first up against the wall when the revolution comes. (c.f. Hitchhiker's Guide to the Galaxy)
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Mike

On my reflector's instruction manual, it explicitly stated that the little aperture was for eyepiece projection of the sun (otherwise the eyepieces would get too hot) and for viewing a bright moon.
Renato