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Mirror/collimation seems to be messed up after cleaning and reassembling the telescope

adarshajoisa

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adarshajoisa

adarshajoisa

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I recently took apart my 5-inch newt to clean the primary mirror ( I used just a good blower to blow away the dust before reassembling). After reassembling, I noticed while observing that the images are not very clear. When I try a star test, if I try unfocussing, when I move the EP closer, the image of a star/planet stretches horizontally, and if I move the EP further away, it stretches vertically. I checked the collimation with a collimating EP, and the collimation appears to be perfect. I'm not able to figure out what might have caused this issue. I'd love any help on how to fix this. I tried imaging the recent Venus - Jupiter conjunction, but I was never able to get a clear image. It appears to be a collimation/astigmatism issue, but the collimation appears perfect, and my Baader Hyperion EP also seems perfectly fine. The problem appeared right after I reassembled my scope.

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dweller25

dweller25

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Just to add to the OP, I've made sure that the mirror support is not too tight to avoid stress on the mirror. I'm completely baffled as to why this is happening.

I would suggest you double check there is no stress on the mirror from either the back, the sides or the front........

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adarshajoisa

adarshajoisa

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Can you the a pic down the empty focuser?

https://picasaweb.google.com/lh/photo/Ik7nBgr9FsY6lPl1E7N3E9MTjNZETYmyPJy0liipFm0?feat=directlink

https://picasaweb.google.com/lh/photo/GSCujibewKRpPMnPquDkzdMTjNZETYmyPJy0liipFm0?feat=directlink

The first photo is how the mirror looked with the problem. This morning, I removed the mirror, made sure all the mirror holders are loose enough for the mirror to rotate freely in the cell, and reassembled the telescope. The second image is how it looks now through my collimation cap.If weather permits, I'll test it tonight and see how iti performs now. Moonshane, do you notice any problems in the above images?

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adarshajoisa

adarshajoisa

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Turns out, the mirror holders were causing the problem. Today I disassembled the telescope and loosened the mirror assembly so that the mirror could rotate freely in the mirror cell. I did a star test a while back, and it looks pretty good now! Thanks a lot for all your help! :)

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Alkaid

Alkaid

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Classic mistake is to put the mirror back having rotated it from where it was.  For example, if there are four screws holding the cell to the OTA, you might have put it back in at 90, 180 or 270 degrees to how it was before. Before you try re-collimating, try this:

Turn the mirrow cell through 90 degree steps until it's back to how it was before.  (If only three screws, then less work as you will have put it back incorrectly at 120 or 240 degrees).

Once you've got it back, if you remove the mirror cell in future, remember to put a spot of masking tape on the mirror cell and also the tube (tape in line with each other) so that you can see how to put it back in the riight place straight away.

You'll get there, don't worry.

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adarshajoisa

adarshajoisa

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Classic mistake is to put the mirror back having rotated it from where it was.  For example, if there are four screws holding the cell to the OTA, you might have put it back in at 90, 180 or 270 degrees to how it was before. Before you try re-collimating, try this:

Turn the mirrow cell through 90 degree steps until it's back to how it was before.  (If only three screws, then less work as you will have put it back incorrectly at 120 or 240 degrees).

Once you've got it back, if you remove the mirror cell in future, remember to put a spot of masking tape on the mirror cell and also the tube (tape in line with each other) so that you can see how to put it back in the riight place straight away.

You'll get there, don't worry.

Shouldn't the mirror be symmetric about its axis? I don't think I understand how rotation of the mirror cell would affect the image. I'll try different rotations (I have 3 screws, so 3 tries should get me to the sweet spot), but I'd like to understand why this is important.

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adarshajoisa

adarshajoisa

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I can't really see what is what to be honest but the secondary reflection looks very odd. If you get sharp visual images you won't be far off

I've never really got very sharp images to start off with, even when I initially bought the telescope. I assumed it was because my mirror was spherical. I recently compared views with a friend's 6-inch telescope, which has a parabolic mirror, and the views of Jupiter and Venus through his telescope were exceptionally sharp compared to my telescope, and his telescope was badly out of collimation. The secondary reflection was off to a side, and so on. I'm not sure if having a spherical mirror would cause such a drastic degradation of image quality. I'd really appreciate some inputs about how much of a difference a spherical mirror makes on the image quality. It was also the reason I thought I'd check if my mirror is stressed and causing such bad quality images.

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adarshajoisa

adarshajoisa

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Also, to be more specific about the kind of views I get through my telescope, I think I should explain a bit. Most objects appear a bit smudged to one side. For example, If I'm observing saturn or Jupiter, I'll always see an image of saturn, and a smudge of light to one side, almost as if it's a comet with a very short tail (usually about half the size of the object). Also, the brighter stars like Sirius and Vega don't appear as points, but as bight points with minute spikes radiating outwards, prominently in one direction. I'm pretty sure this isn't coma, because irrespective of which part of the field of view the object is in, the spike/smudge is always in the same direction (upwards in my case). Also, I've noticed that very bright objects like Venus usually cast a double image - one very bright primary image, and a much fainter second image almost overlapping the primary image. Do any of these faults ring any bells? Is there any way I can fix them, maybe by better collimation or reducing stress on the mirror? I've had the same results with the stock Kellner EPs that I got with the telescope, and a Baader Hyperion 8-24mm that I recently acquired. I'm pretty sure the Hyperion is good, as I tested it with my friend's telescope with exceptionally good results. So I assume the fault is either with my mirrors or the collimation of my scope.

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Alkaid

Alkaid

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Shouldn't the mirror be symmetric about its axis? I don't think I understand how rotation of the mirror cell would affect the image. I'll try different rotations (I have 3 screws, so 3 tries should get me to the sweet spot), but I'd like to understand why this is important.

In theory, yes, should be symmetrical. In practice, no, cos if the secondary is 'out' by just a few mm, then the primary must be tilted to compensate. So a well collimated scope could have a slight primary tilt. If you put it back in the wrong plane, then its all out. I discovered this with my TAL-1 when I put the primary back in the 'wrong' place. I could have just re-collimated by tilting the primary, but I rotated it once and hey presto.

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adarshajoisa

adarshajoisa

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If it's the Celestron 130EQ, it has a parabolic mirror, not a spherical one. The 114EQ is spherical however.

A while back, I was searching to find if the 130 EQ has a spherical or parabolic mirror. I read several astronomy forums with conflicting results. I've read accounts of several people who have written to Celestron with the same query, and they've sometimes responded saying it's parabolic and sometimes saying it's spherical. I consulted a telescope/astrophotography expert who works at my local planetarium and he told me it's a spherical mirror. I tried a foucault test at home, but it was unsuccessful. :( After a while, I gave up and started assuming it's a spherical mirror!  :huh: When Celestron doesn't seem to know what kind of mirror it is, I've lost hope!  :grin: Are you certain that the 130EQ has a parabolic mirror?

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adarshajoisa

adarshajoisa

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Also, I've read that telescopes with parabolic mirrors are more expensive than the spherical mirror counterparts. The Astromaster 130EQ cost me around 250 USD equivalent in India, where telescopes are almost twice as expensive compared to the United States. So I concluded that the mirror must be spherical :D

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adarshajoisa

adarshajoisa

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See here where contact was made directly with Celestron. There was some confusion which is why everyone thinks it has a spherical mirror.

http://stargazerslounge.com/topic/133179-celestron-130eq-info/

Interesting! The Knowledge Base article in the Celestron website says it's spherical! I guess it's a parabolic mirror after all! :)

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brantuk

brantuk

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When doing up mirror clips I always ensure the mirror is not pinched by sliding a very thin piece of paper through between the mirror and the clip. It should be firm enough to support the mirror in place, but loose enough so the mirror can move if turned. :)

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adarshajoisa

adarshajoisa

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When doing up mirror clips I always ensure the mirror is not pinched by sliding a very thin piece of paper through between the mirror and the clip. It should be firm enough to support the mirror in place, but loose enough so the mirror can move if turned. :)

That's a great idea! I'll try that the next time I assemble my mirror! Thank you!

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