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Collimation nightmare.


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Ok, i have a cheap reflector scope i bought second hand and decided too try and collimate it-i thought im going too have too learn sometime and i may as well learn on a cheapy..so this afternoon i tryed to follow the instructions on this page here

How to collimate a telescope | Skymania News and Guide

I have massivly messed this up though, i think my secondary mirror is now very out, and objects are now too the right completely out of the FOV and much dimmer (the red dot sight is accurate) . Iv been trying and trying too fix this but im not getting anywhere. Both secondary and primary mirrors have 3 screws.

Can anyone help me? i have completly made a mess of this and its spoilt what seems too have been one of the clearest nights for a long time here:(

Do i need too buy tools to fix this?.

Edited by Madhatter
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hi i have had the same troubles as yourself first of a Cheshire collimator is a good tool for this.folk also use lasers to collimate but they may also need to be collimated:eek:

Collimation - Cheshire Collimating Eyepiece

and a good tutorial for using Cheshire

Astro Babys Guide to Collimation

but as long as nothing has been smashed or broken all will be well.tho you dont state what scope you have and maybe you could collimate you scope using just a collimation cap ?.so post what scope you have and the specs i.e focal length, aperture and then someone with more knowledge than me will be able to help with weather you need the Cheshire tho i would recommend one

star

Edited by star_chaser
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Hi Madhatter,

Ok don't panic you should be able to get it sorted, it would help if you could us give some extra info -

Make and model of scope and whether you used or have any collimating tools?

It does sound like the secondary is well out now, it can take a while to get you head round exactly what you are doing. I found Astro Babys Guide to Collimation to be the best overall. Aligning the secondary is probably the hardest part, the mirror reflections at this stage of the process can be a bit confusing. In the guide there's a very handy way around this using coloured card.

Sorry I know this advice is a bit too late for you but it's still worth posting for any other newbies reading this thread.

First always do a star test before you attempt to collimate that way you will know if the collimation is out to start with (check the bottom of A_B's guide for info on star testing).

Second, don't start it on a day when there is a chance of clear skies as you will end up rushing things.

Third take your time and don't worry, after you have done it a couple of times it will get easier!! :eek:

As you already know the collimation is way out skip the star test, read A_B's guide and start again.

Good luck, I'm sure with the help of the forum and the guide you will get it sorted soon. :)

EDIT - I need to learn to type quicker, great minds think alike star_chaser!! :)

Edited by stev74
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Hi guys, thanks for the quck responces. my telescope is a jessops TA800-80 reflector, i havent used any tools nope but did try and make the cap? out of a old camera film holder, it does not quite fit inside the EP holder though.

Iv just been reading astro babys tutorial and have just put some white paper partway down the tube so the secondry mirror is now white, and have now tryed too make the secondary as round as possible and as close too the center as possible, but all i can do right now is look through the empty EP.

Thanks for your help, i really hope i can get this working again! it would be good too learn how too do this though.

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Iv got the secondary as central and as circular as possible without tools, but it still seems too be out by the same distance. i did also adjust the primary mirror, could this be putting the scope out or is it more likely the secondary?.

I think the scope was out before i started so hopefully when sorted the views might improve abit:)

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Using a homemade collimation cap and astro babys tutorial i think i may have made some progress on the secondary, but i cant be sure just yet. There is a white spot in the center of the primary thats out a little so am going too try and center that too the newly adjusted secondary using the homemade collimation cap. If done correctly can everything be done with one of these?.

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Using the homemade cap the secondary mirror is centered too the EP tube now, the primary is centered too the secondary with the 3 clamps showing around the edges, and the white dot in the center of the primary mirror is centered to the secondary. I hope that makes scence. Am i getting anywhere?

Things are still out on the red dot sight:( im wondering if its the sight thats out now!, im quite familiar with how saturn looks through this scope so hopefully when its clear next visual quality can be tested.

Im going too call it a night, thank you everyone for your help:)

Edited by Madhatter
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i think i may need to collimate mine an you guys are confusing the hell out of me lol. my finder scope is out with my main scope.... does this mean it needs collimated?

no you just need to align it with scope try on a church tower(i used a tower block) about a mile away line up the scope so you can see whatever you are your using then turn the little screws to adjust finder so it to is pointing at the same object. job done

@ johntrob its just one of them jobs that seem a nightmare after a couple of goes its not that hard at all

glad to have helped star

Edited by star_chaser
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Things are still out on the red dot sight im wondering if its the sight thats out now!, im quite familiar with how saturn looks through this scope so hopefully when its clear next visual quality can be tested.

It seems 2 separate issues are being confused here, aligning the red dot finder (RDF) has nothing to do with collimation.

By your description it seems you have got the scope back into better collimation. Please don't check collimation on Saturn the problem is there are too many variables - Saturn can look different each time you view it due to good or bad 'seeing'. Atmospheric turbulence can also be an issue if it's viewed too close to the horizon.

The best way to check collimation is to do a star test as described at the bottom of A_B's guide. :)

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hi, i used astrobabies instructions for collimation using nothing but an empty 35mm plastic film case and a couple of bits of card, a small allen key for the secondary mirror and 1 phillips screwdriver. All these things i had kicking about in the house so it didn't cost anything (bonus ).

Good luck,

Adamski

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Excellent thanks guys:) im really hoping its done correctly now, just hopeing for some clear skys tonight but the forcast is clouds:(

Thanks for pointing out saturn is not suitable, i will try the star test on the brightest star:)

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Thanks for pointing out saturn is not suitable, i will try the star test on the brightest star

No worries, let us know how you get on with the star test. :D

Edited by stev74
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FINALY!!

Tonight i finaly got a chance too do a star test, its littiraly the first time the clouds have even parted for days, its still cloudy now but i did manage too do a quick test, everything is spot on!!!

Big thank you to everyone that helped me here (and the writers of those guides!) it feels great too have my first sucsessfull collimation under my belt! id have never have done it without you guys help:)

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Great job, Madhatter!

Just for practice, you can sight a bright star, and rack the focuser well out of focus so the eyepiece comes out toward your eye. The image of a star will now look like a donut. The black "hole" in the middle is the image of the secondary, and you can tell if the collimation is off by seeing how symmetrical that donut appears. This only works if the bright star is near the center of the field of view. If it's not even all the way round, place your fingers in front of the tube while looking in the eyepiece, and you can see your fingers... which is pretty cool! Move your finger around until you find the place where the donut hole is too close to the edge of the donut. If you then run your finger down to the rear of the 'scope, staying on the same side of the tube, you have identified the side of the mirror cell that needs to be tightened. You can either tighten the adjustment screw nearest your finger, or loosen one on the opposite side. Repeat as needed until it's spot on.

By daylight you can aim the scope at the blue sky with a medium power eyepiece in the focuser, and perform the same alignment by looking at the image of the sky visible from about 1' to 2' away from the eyepiece, though not with quite as much accuracy as using a star image at night. In a pinch, you can also try collimation using a bright reflection of the sun off a curved shiny object, such as a automobile bumper or a shiny ball bearing.

If you ever get into a real mess, and suspect the secondary is also out of whack, carefully take the primary mirror and cell right out of the tube, and create a target at the center of the open end of the tube (where the mirror cell used to be) by crossing two lengths of masking tape or string across the mirror end, getting them to cross as close to the center as you can. Now look in the eyepiece tube (no eyepiece -- using the film can or something like it will help keep your eye centered), and adjust the secondary to aim right at that cross, and lock it in place. Now remove the tape or string and replace the primary mirror, and don't touch the secondary, as and you know that only the primary needs any significant adjustment. You should be able to adjust the primary to give sharp images from there.

Hope you have very clear views on your next attempt.

Clear skies,

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Re- star test, if you defocus the star just a little, not enough to create a huge donut, you will see (if correctly collimated) a tiny central bright dot surrounded by a ring of concentric circles. If this image is symmetrical you are collimated. This is what I believe you should be seeking when doing a star test. The defocussing should not be much - certainly not enough to show the primary mirror.

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XYZ,

I completely agree that you can judge the collimation with a slightly de-focused star image in the center of the field of view -- you are correct. If the alignment is good, you are off and running and all is good. However, if the alignment is poor, it's pretty hard to tell what to do about it without going a bit further, to the donut image that shows the secondary. If the collimation is off a bit, I find it easiest to touch up in the field using the no-tech donut method. I've built my telescopes so no tools are needed to align the primary, but the secondary can still be a difficult job.

A telescope on a permanent pier rarely needs adjustment, while a scope that is transported to dark sky locations can be easily bumped out of collimation.

BTW: there's a lot of information in that slightly de-focused image, and you can tell a whole lot about the quality of the optics with this technique, especially comparing the images inside of focus and outside of focus, but that's getting pretty advanced for a beginner's forum. For those interested, search under "star testing optics" for more than you care to know!

Hope your skies are clear and steady,

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From FF: "If it's not even all the way round, place your fingers in front of the tube while looking in the eyepiece, and you can see your fingers... which is pretty cool!"

Yes, how true, I was messing around with this a week or two ago and was surprised at the visibility of the hot air rising off my hand (like translucent flames) and how easy it was to see this - placing a warm hand low down on the scope tube produced a similar stream of very visible convection currents - interesting stuff. The importance of scope cool down was immediately obvious !.

Richard

Edited by xyz
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