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collimating a newtonian help


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Hi guys,

Hoping someone can help me out here. I purchased a laser collimator and a cheshire collimator but having a little trouble.

If i use the cheshire collimator and adjust the secondary mirror as per astrobaby's instructions Astro Babys Guide to Collimation

i cant center the primary mirror on the cross to the center circle on the primary mirror along with seing all three mirror clips at the same time. I can either see all three clips and the cross hairs are way off the center spot or i can get the cross hairs on the center spot but cant see all three clips

I can use the laser collimator to center both secondary and primary mirror circle and the bounce back laser on the collimator and see all three clips with a collimation cap once laser removed

the reason for asking is which one to trust?

I also watched astrosheds collimation tips on youtube and he states not to trust a laser collimator as it can lie when collimating the secondary mirror. so not accurate!

I have ensured the secondary mirror is as per astrobaby's instructions

please help

please help

Edited by soggybongo
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yes mate done that as per astromsheds youtube vids - here :-

there are nine vids to follow when collimating.

and he states a laser lies when collimating the secondary mirror. so if i use my cheshire to collimate my secondary mirror then insert my laser to collimate the primary mirror as per astroshes vids that works as far as the rebound laser dissapears in the collimator but when i look down the telescope tube the laser dot is way off the center spot on the primary which sort of contradics the point of laser collimation.

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Question: When you insert the cheshire collimator, do you see the edge of the secondary mirror? If no, you need to rack out the focuser and/or pull-out the collimator until the secondary mirror edge is visible. The reason I asked the above question is to understand whether the primary mirror clips are obscured by secondary mirror or the cheshire collimator. Make sure they are not obscured by the cheshire collimator.

If the primary clips are obscured by the secondary mirror, then you need to move the secondary mirror. Check the following thread (only the first few pages) for more info and insight.

Telescope Reviews: Useful info about secondary mirror alignment

As far as the collimation cap versus the Cheshire collimator, bear in mind that the collimation cap has much wider view and gives more freedom to move the eye around. That does not mean it is better but rather it gives more of a relaxed assessment of collimation – not necessarily more accurate.

As far as the video you referred to, I hope this person would remove it. Lasers do not “lie”. He just does not understand their usage in collimation. Unfortunately, many beginners will see that video and return the laser collimators or avoid them because someone who presents himself as an authority on the subject of collimation said so a public video.

Jason

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Question: When you insert the cheshire collimator, do you see the edge of the secondary mirror? If no, you need to rack out the focuser and/or pull-out the collimator until the secondary mirror edge is visible. The reason I asked the above question is to understand whether the primary mirror clips are obscured by secondary mirror or the cheshire collimator. Make sure they are not obscured by the cheshire collimator.

If the primary clips are obscured by the secondary mirror, then you need to move the secondary mirror. Check the following thread (only the first few pages) for more info and insight.

Telescope Reviews: Useful info about secondary mirror alignment

As far as the collimation cap versus the Cheshire collimator, bear in mind that the collimation cap has much wider view and gives more freedom to move the eye around. That does not mean it is better but rather it gives more of a relaxed assessment of collimation – not necessarily more accurate.

As far as the video you referred to, I hope this person would remove it. Lasers do not “lie”. He just does not understand their usage in collimation. Unfortunately, many beginners will see that video and return the laser collimators or avoid them because someone who presents himself as an authority on the subject of collimation said so a public video.

Jason

i'll try and explain it a little better. if i collimate the secondary mirror using the cheshire collimator so i can see all three primary mirror clamps through the small peephole having a perfect round circle and center the cross hairs on the small spot on the primary mirror.

If i remove the cheshire collimator and replace it with a laser collimater the laser light/ spot is way off and i'm talking 2cm off the center spot on the primary mirror. I have ensured the laser is also collimated

now if i collimate the secondary mirror using the laser onto the primary mirror spot so it is dead center then remove the laser and replace it with the cheshire i cannot see all three clamps "just 2 clamps"

Edited by soggybongo
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If i remove the cheshire collimator and replace it with a laser collimater the laser light/ spot is way off and i'm talking 2cm off the center spot on the primary mirror. I have ensured the laser is also collimated

Is your secondary mirror perfectly aligned (Rotation)??

As per Dion's vid tutorial have you rotated and adjusted your secondary to make a perfect central circle.

I find using red card to block the primary mirror reflection helps a lot.

Wayne

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If i remove the cheshire collimator and replace it with a laser collimater the laser light/ spot is way off and i'm talking 2cm off the center spot on the primary mirror. I have ensured the laser is also collimated

now if i collimate the secondary mirror using the laser onto the primary mirror spot so it is dead center then remove the laser and replace it with the cheshire i cannot see all three clamps "just 2 clamps"

You have already stated that you have verified your laser collimator is collimated. I assume when you rotate your laser collimator in the focuser the laser dot on the primary will not move.

One possible explanation is that either your laser collimator or your cheshire collimator do not seat well in the focuser. Is your laser collimator or cheshire collimator little loose in the focuser?

Jason

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Is your secondary mirror perfectly aligned (Rotation)??

As per Dion's vid tutorial have you rotated and adjusted your secondary to make a perfect central circle.

I find using red card to block the primary mirror reflection helps a lot.

Wayne

Wayne, the secondary mirror rotate/tilt errors are irrelavent with respect to the OP's issue. The heart of the issue is that the OP's cheshire cross-hairs and his laser beam do not point at the same distant spot. The primary mirror clips is only a manifestion. If we can get both the cheshire cross-hairs and the laser beam to agree then the primary clips issue will be resolved.

To the OP: Bear in mind to get both collimation tools to agree with high precision, then both tools as well as the focuser need to be of high precision.

Jason

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Many thanks Jason for your input. I have just read the last post you placed in this thread - http://stargazerslounge.com/discussions-scopes-whole-setups/177056-laser-collimation-not-all-its-cracked-up.html

I think my problem is with the secondary mirror not being correctly positioned under the focuser, it is round but i think it is very slighlty twisted as i cant see all three clips on the primary. i also have another problem - when i insert either the lasor or cheshire they both have a very slight wobble so dont fit perfect. When i tighten the thumb screws that hold them in place this tilts them slightly. I am going to wrap some plumbers ptfe tape around them to get a more snug fit and see if that makes a difference or is there some gadget that will fit in a 1.25" focuser to center them?

Edited by soggybongo
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As far as the video you referred to, I hope this person would remove it. Lasers do not “lie”. He just does not understand their usage in collimation. Unfortunately, many beginners will see that video and return the laser collimators or avoid them because someone who presents himself as an authority on the subject of collimation said so a public video.

An interesting observation jason (and I defer to your experience).

I found most of those videos quite informative, particularly one on checking collimation of lasers. I found my old laser one to be way out (and nigh on impossible to collimate). Gave up in disgust and bought one of the cute Cheshires from FLO.

I'm still getting to grips with collimation but having more consistency (hence joy) with the cheshire.

However, I have been considering buying a Hotech laser collimator to compliment the cheshire (e.g. a "double check" and easier to collimate in the dark).

You think this might be a good idea?

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An interesting observation jason (and I defer to your experience).

I found most of those videos quite informative, particularly one on checking collimation of lasers. I found my old laser one to be way out (and nigh on impossible to collimate). Gave up in disgust and bought one of the cute Cheshires from FLO.

I'm still getting to grips with collimation but having more consistency (hence joy) with the cheshire.

However, I have been considering buying a Hotech laser collimator to compliment the cheshire (e.g. a "double check" and easier to collimate in the dark).

You think this might be a good idea?

this is the cheshire i'm using

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However, I have been considering buying a Hotech laser collimator to compliment the cheshire (e.g. a "double check" and easier to collimate in the dark).

You think this might be a good idea?

Having a quality laser collimator is a good idea -- especially in the dark as you have mentioned.

I do not have first hand experience with Hotech; therefore, I can't comment. However, I have seen many comments about Hotech on this site made my those who used them.

Jason

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going to start from scratch with both the secondary and primary mirrors by removing them and giving them a clean as i have had this scope for over a year and even then it was bought second hand so there is a fair ammount of crud on both mirrors, got nothing to loose really as my new scope (Altair Astro 115mm f805 EDT APO) will be with me soon.

cheers for your help Jason D

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