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digital_davem

First collimation attempt

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I've read a lot about collimation and much of it makes it sound like trying to develop a theory of quantum gravity!

Two resources make it sound so simple it's child's play:

1. A youtube video made by two guys in a telescope shop who start off by loosening everything so badly that you can't see anything then use a laser collimator to do the secondary and primary collimations in about 2 minutes flat.

2. This website http://www.garyseronik.com/?q=node/169 which says most resources grossly complicate things by going for perfect collimation when a basic collimation is good enough for most purposes and very simple. He says use a collimation cap to collimate the primary only as that will do for most people.

I followed these instructions by:

1. Drilled a hole in the focuser cap

2. Made a hole in a circle of white paper which I put inside the eyepiece cap

3. Removed the backplate of my 130P/650  to expose rear of mirror

4. Loosened the 3 tiny allen locking bolts

5. Adjusted 2 of the big silver phillips head bolts while looking through the hole in the collimator cap

After this I can now see:

i) the whole of the primary mirror, including the 3 mirror clips

ii) The black circle of the secondary centred in the middle of the primary

ii) The secondary vanes (look like cross hairs)

ii) A doughnut shaped white circle positioned right in the middle of the black circle of the secondary mirror

I stopped at this point and re-tighted the allen head locking bolts.

As far as I can make out from Gary's website, this should be good enough to start.

The thing that worries me slightly is that he says I should be able to see a black dot in the middle of the doughnut (the reflection of the hole in the collimation cap).  I don't see this because the view is too dark in there.

- Should I worry?

- Have I pulled off a basic collimation or not?

How can I tell if it's correct?  Can you tell in daytime with terrestrial viewing or is a star test the only true test?

Thanks

Dave

 

 

 

 

Edited by digital_davem

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3 hours ago, digital_davem said:

I've read a lot about collimation and much of it makes it sound like trying to develop a theory of quantum gravity!

Two resources make it sound so simple it's child's play:

1. A youtube video made by two guys in a telescope shop who start off by loosening everything so badly that you can't see anything then use a laser collimator to do the secondary and primary collimations in about 2 minutes flat.

2. This website http://www.garyseronik.com/?q=node/169 which says most resources grossly complicate things by going for perfect collimation when a basic collimation is good enough for most purposes and very simple. He says use a collimation cap to collimate the primary only as that will do for most people.

I followed these instructions by:

1. Drilled a hole in the focuser cap

2. Made a hole in a circle of white paper which I put inside the eyepiece cap

3. Removed the backplate of my 130P/650  to expose rear of mirror

4. Loosened the 3 tiny allen locking bolts

5. Adjusted 2 of the big silver phillips head bolts while looking through the hole in the collimator cap

After this I can now see:

i) the whole of the primary mirror, including the 3 mirror clips

ii) The black circle of the secondary centred in the middle of the primary

ii) The secondary vanes (look like cross hairs)

ii) A doughnut shaped white circle positioned right in the middle of the black circle of the secondary mirror

I stopped at this point and re-tighted the allen head locking bolts.

As far as I can make out from Gary's website, this should be good enough to start.

The thing that worries me slightly is that he says I should be able to see a black dot in the middle of the doughnut (the reflection of the hole in the collimation cap).  I don't see this because the view is too dark in there.

- Should I worry?

- Have I pulled off a basic collimation or not?

How can I tell if it's correct?  Can you tell in daytime with terrestrial viewing or is a star test the only true test?

Thanks

Dave

 

 

 

 

I have been through my first collimation today. This is useful http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm.

It has put my mind at rest as the view of my focuser is slightly off set which is apparently normal for faster scopes. The video you mention is probably the Astronomy and Nature TV one that I have seen (classic astronomy banter). Lasers look nice and easy, but you still have to get the secondary nice and round in the first place and one of these will not help with aspect I don't think.

For me I am just going to try a basic star test when I can. I think this is explained at the bottom of the above guide and should hopefully tell you (and me) if we're on the right track

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Sounds ok, but a star test is the final piece of the puzzle

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Doing a comparison between the 130p and my 3" classic refractor tonight using the Moon and Jupiter.  Both seem at the crispest around 100x and there isn't much (anything?) between them on the Moon. It's suddenly gone cloudy; if it clears again I shall try Jupiter.  Then a star test though that will be pure experiment as I'm not sure what to expect.  I did notice that if I totally defocus Jupiter it becomes a big circle with a black circle in the middle with cross hairs - looks remarkably like the view through the collimation cap!

p.s.

I shoved the eq mount out in the garden randomly this evening and am amazed to discover I have achieved an excellent polar alignment by sheer chance. Can track target perfectly with RA manual slow motion control! Bet I'll never manage this again on purpose.

 

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Completed around 3 hours of observing mostly of moon and jupiter with 130p/650 f/5 and 76mm/1250 f16 classic refractor.

Moon comparison:  At 100x both showed essentially the same detail but the frac was a little crisper and contrastier. Not so much that you would really be able to tell unless you were swapping back and forth.

Jupiter comparison: Again at around 100x both showed the equatorial bands clearly but the frac also hinted at some polar texture missing from the newt. Again, there was a slightly crisper/contrastier view from the frac.  Also, the Galilean moons were rendered at points by the frac but the newt made them slightly starburst like.

Star test:  According to this site: http://www.garyseronik.com/?q=node/238 you can check collimation by defocusing a brightish star and examining the "donut" blob this creates. If you see a central dark area surround concentric rings with the dark spot dead in the middle then you OK.  If the dark spot is offset, things are not square and need adjusting. Happy to report that my dark blob was a perfect bullseye in the centre of the blob.

Still can't quite get over the perfect polar alignment entirely by luck!

Edited by digital_davem

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Somehow we all start out mystified and intimidated by collimation. But you'll get an epiphany-like understanding and do it the 'first-time.' After this has happened, you'll wonder what all the worries were about. It becomes like riding a bicycle - you just do it as needed without a thought.

I'd suggest a Cheshire when you start off. A collimation-cap will also do. Once it's sorted in centering the secondary-mirror, then a laser will be fine if you so wish. You may actually find that you (:eek:) enjoy collimating your scope! I do now.

You will arrive,

Dave

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Guest
6 hours ago, Dave In Vermont said:

Somehow we all start out mystified and intimidated by collimation. But you'll get an epiphany-like understanding and do it the 'first-time.' After this has happened, you'll wonder what all the worries were about. It becomes like riding a bicycle - you just do it as needed without a thought

Exactly Dave....too much worry to start lol. All i do now is periodically use my cap with a hole to be happy with the concentric circles down the drawtube then its a quick siting of the laser dot on the primary

then to finish and be proper happy its just a barlowed laser test to check the dark hole of the primary's doughnut mirror marker is central on my laser siting hole and that's a sweet spot enough for me as a visual observer.

Like Dave said, it can be enjoyable once your on board with it, i love doing mine. Gives me a sense of pride to know she is ready for use lol.

Good luck with riding that bike :p

Edited by Guest

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