Apologies for silly question

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Apologies for silly question

Postby andymu » Wed Jun 29, 2011 12:46 am

I bought a skywatcher startravel 80mm telescope. Now I know it should ideally be polar aligned
to view objects.

I tried for my daughter just using the polar alignment eyepiece to locate a star, but when I look
through the scope I don't see it. Even though in the polar eyepiece it is bang on the middle of the
crosshairs.

Am I doing something wrong. I tried zooming the telescope eyepiece in and out to focus but still nothing.

I do apologise for what is probably a very stupid question on the forum.

Thanks


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RE: Apologies for silly question

Postby sftonkin » Wed Jun 29, 2011 12:10 pm

Most likely, you have just made a completely independent discovery of the "polar hole". It is notoriously difficult to find objects near the pole with equatorial mounts; there is an equivalent "zenith hole" for altazimuth mounts. Unless your mounts axes and the optical axis of your scope are all exactly orthogonal (the likelihood of this is vanishingly minute); you probably don't have a snowball's chance in hell -- and, even if they are, you'll still struggle).

Forget about it -- most of the nice stuff is in the south at this time of year anyway!

Edit: By the way, it's not a stupid question; the stupid thing would have been to [b]not[/b] ask it!
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RE: Apologies for silly question

Postby uea74 » Thu Jun 30, 2011 7:33 pm

Could you supply details of exatly what you have?
Never heard of a polar alignmnet eyepiece, a polarscope yes, finder scope yes.

And having 2 equitorial mounts, HEQ5 and EQ5, I have no idea what a polar hole is either, equitorial mounts are built to be orientated to the pole so it seems strange that a mount designed for the purpose of being polar aligned has this problem of not being able to view Polaris.

As to Alt/Az mounts looking over head, all 3 of mine do so. The motors drive the scope to the vertical, I look through the eyepiece and behold the zenith is there. Easy.

So Albeirio is in the Southern hemsiphere and not visible is it? Strange I was looking at it 2 nights back.
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RE: Apologies for silly question

Postby sftonkin » Thu Jun 30, 2011 8:40 pm


[quote]ORIGINAL: uea74
I have no idea what a polar hole is either, equitorial mounts are built to be orientated to the pole so it seems strange that a mount designed for the purpose of being polar aligned has this problem of not being able to view Polaris.[/quote]

#1 You seem not to have read (or understood) what I wrote about orthogonality.
#2. If you try tracking something [b]near[/b] the pole for any length of time, you may discover what I was talking about.

[quote]As to Alt/Az mounts looking over head, all 3 of mine do so. The motors drive the scope to the vertical, I look through the eyepiece and behold the zenith is there. Easy.[/quote]

Certainly easier to get the exact zenith if your axes are precisely orthogonal and your altitude axis is precisely horizontal, but note that we were discussing objects [b]near[/b] (i.e. not [b]at[/b]) the centre of the hole. Dob (a particular incarnation of altaz) users would certainly disagree with you about it being easy...

[quote]So Albeirio is in the Southern hemsiphere and not visible is it? Strange I was looking at it 2 nights back.[/quote]

Sorry, haven't a clue what you are on about; nobody has mentioned either Albireo or objects in the southern hemisphere being invisible -- in fact, the words "Albireo" (or "Albeirio" [:)] ), "Southern" and "hemsiphere" {sic} were introduced to this thread by you). Perhaps you could try (a) reading (and understanding) what was actually written and/or (b) seeking to be less unnecessarily confrontational? We're trying to help someone who is struggling, not having a pissing contest!

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RE: Apologies for silly question

Postby splog » Thu Jun 30, 2011 9:30 pm


[quote]ORIGINAL: andymu

I bought a skywatcher startravel 80mm telescope. Now I know it should ideally be polar aligned
to view objects.

I tried for my daughter just using the polar alignment eyepiece to locate a star, but when I look
through the scope I don't see it. Even though in the polar eyepiece it is bang on the middle of the
crosshairs.

Am I doing something wrong. I tried zooming the telescope eyepiece in and out to focus but still nothing.

I do apologise for what is probably a very stupid question on the forum.

Thanks



[/quote]

Hi Andy

I'm not sure I fully understand what you are saying but to me it sounds as if your finder scope and main scope arre not aligned correctly? Have you tried using it during the day on a distant object?
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RE: Apologies for silly question

Postby sftonkin » Fri Jul 01, 2011 8:53 am

[quote]ORIGINAL: Splog

it sounds as if your finder scope and main scope arre not aligned correctly? Have you tried using it during the day on a distant object?
[/quote]

Ah! "Polar alignment eyepiece" = "finder scope"? If that's the case, Andy, strike what I said. (Polar scope fits in the bore of the RA axis of the mount, finder scope is a small scope attached to the main scope.)


[b]Edit:[/b] I've just had a look at an EQ1/2 manual (the ST80 usually comes on an EQ1), and the reason for conflation of finderscope with polarscope is obvious: It suggests a rough polar alignment by orienting the RA axis approximately to the NCP, then refining it with the finder, by aligning it (the finder) to Polaris. Given the wide field of the finder, locating Polaris is not an issue. However, this method results in inaccurate polar alignment, so getting Polaris in a scope with a narrower field of view is pretty difficult (for the reasons I stated in my first post in this thread). FWIW, this does come a few pages after the bit on aligning the finder with the OTA (method given is perfectly sound).
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