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Advice for a noob with a newtonian...

Aenima

By Aenima
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Aenima

Aenima

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Hello. Thank you muchly for my membership status. :)

I have an Explorer 130p by Sky-watcher, and recently observed Jupiter for the first time.:D

As excited as i was, I couldn't help noticing the next night i went out that the planet seemed to repeatedly 'slip' out of the eyepiece, or behind a phantom obstruction which caused me to briefly lose sight of it, or it jumped away like there was a fault in the tube or lens so i had to keep readjusting my eye and refocusing my vision - but as I said the previous viewing was spot-on.

Fearing I had knocked it or something, I looked up how to collimate and gave it a tweak but could not improve on its current alignment as far as i can tell.

Apart from correct alingment and removal of all the right caps and dust shields does anyone have any idea as to what i might be experiencing in the viewing of small objects?

p.s. as for collimating, it advised to use an out of focus star and check the symmetry of the rings but i can only ever get a washed out disk of light with the black dot being the secondary mirror. Is this because a parabolic mirror is different somehow or are the rings something i should be getting regardless?

Thanks for your time and help, Jay (Aenima)

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malc-c

malc-c

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I assume that you have the non motorised version of the 130P ?. The Earth is rotating at the rate of 15 degrees per hour, or 1/4 degree a minute. When viewed through a telescope that isn't driven it will move through the view in the eyepiece quite quickly, unless the mount is driven at the same rate, but in the opposite direction.

Other factors include:

Polar alignment is off

Windy conditions

Change in atmospheric conditions

Loose optics - if it jumps

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Aenima

Aenima

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Thank you for the speedy reply,malc-c. but although i do have the goto mount i am not currently using its capabilities other than for slewing the scope whilst observing. No, the problem is more with FOV and what seems like a trick of the light. As if at a certain pupil distance the image is slightly obstructed or light is deflected so that only part of the FOV is reaching the eye. Its quite difficult to explain, i just know that the night before it didnt happen, or i didnt notice it, but now even a average star has moments of misalignment.

Taking those aforementioned issues into account i still feel there might be something else i need to consider.:)

Any and all advice is greatly appreciated, thank you.

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Carbon Brush

Carbon Brush

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Jay,

Good question from Malc-c as some eyepeices can give something like you describe.

Another possibility though. This sounds a bit like something I suffered with a scope.

Not just about collimation, but some loose optics!

Take a look at your scope in daylight.

Are all of the screws holding the main mirror, secondary mirror, spider, focus tube, etc all tight? Try to waggle the focus tube and spider by hand.

Stand a few feet away, looking straight down the tube. The main mirror should be reflecting straight back at you. That is a good first check of primary mirror collimation.

After that, there are other checks, but an image jumping around could be something loose. It also fits with a previous good viewing.

Hope something here helps. David.

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JamesM

JamesM

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Hi Jay and welcome to the forum. Nothing like a bit of a puzzle to help you bed yourself into astronomy! You are in the southwest but is it possible to be a bit more specific. If near to me, you might want to meet up with myself and some other fellow observers to try and iron it all out. Some eyepieces do have shorter eye relief than others which can make eye positioning a little tricky till it becomes second nature. Hope we can help.

Clear skies

James

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Aenima

Aenima

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Hello and thank you for the many kind welcomes.

I greatly appreciated the varied and helpful advice. I am currently trying to learn more about the technical aspects of my telescope, especially accurate collimation. Since adjusting the primary mirror in an attempt to fix the strange disappearing object issue, I cant work out if the collimation is now off or not (and when defocusing a star the 'concentric rings' arent apparent, just a white disc with the black middle from the secondary mirror - is this related to the 'parabolic' effect?). I saw spikes but havent had the conditions or resolution to get perfect focus so still not sure about the optics being aligned.

Someone mentioned standing back a few feet. How do I set that up, and what should I be looking for?

thanks again to all who left me replies and advice,

Jay.

:)

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Aenima

Aenima

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sounds like kidney beaning to me. Some eyepieces are more prone to this than others. Eye position is critical with some eps.

Bart

Hi there, thanks for your input. I never heard of kidneybeaning, could you elaborate on the details? bit stuck at the moment, much appreciated.

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RikM

RikM

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Hi Aenima, welcome to SGL.

Checking collimation using a star is not as easy as it sounds. You need to use quite a bright star, your highest power eyepiece (probably a 10mm) and you need to have the star image in the exact centre of the eyepiece. You only need to defocus a little bit and you should see a pattern of rings, but they will probably sparkle and shimmer a bit from the movement of the air.

Your location tag says South West UK. If you are anywhere near Gloucester / Cheltenham, Cotswold AS are hosting a public observing evening next Saturday. I would be happy to take a look at your scope for you if you like.

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Aenima

Aenima

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Hi Aenima, welcome to SGL.

Checking collimation using a star is not as easy as it sounds. You need to use quite a bright star, your highest power eyepiece (probably a 10mm) and you need to have the star image in the exact centre of the eyepiece. You only need to defocus a little bit and you should see a pattern of rings, but they will probably sparkle and shimmer a bit from the movement of the air.

Your location tag says South West UK. If you are anywhere near Gloucester / Cheltenham, Cotswold AS are hosting a public observing evening next Saturday. I would be happy to take a look at your scope for you if you like.

That's really nice, thank you. My location is on the sw coast - south devon. But your advice is well recieved, I have much to learn and there isn't many people into astronomy around here so websites are my best link to knowledgable stargazers like yourself. Many thanks.

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Bart

Bart

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Hi there, thanks for your input. I never heard of kidneybeaning, could you elaborate on the details? bit stuck at the moment, much appreciated.

Hi Aenima,

Kidney beaning is when your eye is placed in a certain position relative to the eyepiece such that a large portion of the visible field appears to 'blackout '. Repositioning your eye brings everything back

Hope this helps

Bart

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