Collimation.... Spot on.... It does really matter !

[deepspacehunter]

If you are observing with a reflector, your collimation should be as close to perfect as you can get it ( in my opinion )... I have been observing for many years before I realized the IMPORTANCE of GOOD COLLIMATION...  On a night of observing several years ago, I decided to collimate my Dob, after tweaking collimation for a few minutes ( on Polaris )..... I turned the scope to some star fields in and around PUPPIS and.... WHOAH..... The stars appeared 3 dimensional. and I realized @ that moment that there is a very different image when you get collimation right, I know that some beginners are hesitant to adjust there optics, however, the reward for precise collimation is awesome, so take a few minutes, and do a star test, It is well worth it.... Just my opinion...

Mark

[nicoscy]

First of all, that's a great photo you got there. Second, while my wife encourages me to engage in the hobby, she is a person "that loves astronomy" so she won't join me, so kudos on finding a partner who has common interests.

As for collimation - you either do it and you get razor sharp images to complement the light gathering of a large Dob / Newt or you don't and are stuck with mediocre views, bloated stars, views with coma that looks like seagull droppings (and it gets progressively worse after that).

Indeed many people are hesitant to touch the optics, but a few hours invested in reading material freely available on the internet, asking questions in various forums and then actually *gasp* playing with the optics of your telescope is an investment worthwhile...

[laser_jock99]

Uncolimated

Same scope/camera but now collimated

For imaging good collimation is essential!

[John]

I agree that having the scope in as good collimation as you can is an important part of getting good results from it.

As scopes get faster the "sweet spot", where collimation is good and diffraction limited performance is delivered, gets smaller and smaller:

F/8 = 11mm

F/6 = 4.8mm

F/5 = 2.8mm

F/4.5 = 2mm

F/4 = 1.4mm

[Daniel-K]

I agree that having the scope in as good collimation as you can is an important part of getting good results from it.

As scopes get faster the "sweet spot", where collimation is good and diffraction limited performance is delivered, gets smaller and smaller:

F/8 = 11mm

F/6 = 4.8mm

F/5 = 2.8mm

F/4.5 = 2mm

F/4 = 1.4mm

thanks for that informatio john, it has done nothing for my OCD

[estwing]

must get round to doin mine.....

[Moonshane]

I have never understood why anyone would collimate a scope and leave it slightly wrong?? it is easy to do (esp. the more critcal primary) so just do it and enjoy the views :0)

[laser_jock99]

I agree that having the scope in as good collimation as you can is an important part of getting good results from it.

As scopes get faster the "sweet spot", where collimation is good and diffraction limited performance is delivered, gets smaller and smaller:

F/8 = 11mm

F/6 = 4.8mm

F/5 = 2.8mm

F/4.5 = 2mm

F/4 = 1.4mm

My example images were at F2.9- collimation is still possible even on superfast scopes!

[Austin]

To collimate prior to observing is as necessary as fitting an eyepiece for me it's part of my setup ritual. Very quick and easy to do with a laser collimator which are worth buying imho.

[Altitude]

This is a good post.

While it's sounds easy, I have a problem doing collimation on my scope (and maybe someone can help me out here).

I see a slight misalignment in the view if I make a star little bit out of focus. The "donut hole" is off center. I looked at the telescope manual and all what it says to do a collimation is "locate three adjustment screws at the end of the telescope"... Well, I did that (look at the picture). Tried to adjust three screws that you see, but they're all were tightened hard to the end. Twisting them made no change in the view. It felt like they're some sort of a cover screws. I did not try to unscrew them completely out of fear to cause something bad. The telescope I have is a Celestrone CN-6, 750mm reflector. If anyone can tell me if screws in the picture are collimation, or a cover screws, I will be appreciate. The manual is useless for that.

[Dave In Vermont]

I believe the reason a great many people don't collimate their scopes is due to a lack of communication. Knowing how-to is one thing, but explaining how-to is quite another. I have often found the instructions for a this or that I purchase are worthless. I'm sure this has happened to you, too. And the "Why?" of this is simply that the writer fully understands how-to, and inadvertently writes the instructions out as though they were for themselves. 

Some how-to collimation-instructions are very well written: Made for the absolute novice and very clear and replete with step-by-step pictures. But too many are written that you need a degree in physics to crawl through. I'm certain (I hope) this is unintentional. Not everyone can communicate well by means of the written word. I'm working on a re-write of some instructions myself here. A friend of mine will be buying some materials for an upgrade to their scope - which I installed on my own. And the instructions it came with were hopeless. I managed as I'm skilled in engineering. Otherwise..... So this is what compels me to do the re-write. 

I'm thinking of sending a copy of my re-write to the manufacturer.

Clear & 3D Skies,

Dave

[Moonshane]

This is a good post.

While it's sounds easy, I have a problem doing collimation on my scope (and maybe someone can help me out here).

I see a slight misalignment in the view if I make a star little bit out of focus. The "donut hole" is off center. I looked at the telescope manual and all what it says to do a collimation is "locate three adjustment screws at the end of the telescope"... Well, I did that (look at the picture). Tried to adjust three screws that you see, but they're all were tightened hard to the end. Twisting them made no change in the view. It felt like they're some sort of a cover screws. I did not try to unscrew them completely out of fear to cause something bad. The telescope I have is a Celestrone CN-6, 750mm reflector. If anyone can tell me if screws in the picture are collimation, or a cover screws, I will be appreciate. The manual is useless for that.

I think your picture shows and end plate that needs to be removed first. Undo the three screws and carefully remove the plate. This should then show what the instructions suggest. Hide the plate somewhere and don't use it again.

[Moonshane]

My approach to collimation is a little different to some. Hope the pdf here http://stargazerslounge.com/topic/197640-collimation-and-star-hopping/ helps.

[laser_jock99]

It took me some time and several changes in collimating tools to gain 'the knowledge' and have confidence in critical collimating of ultra fast scopes. The four main things I learned/discovered along the way are:

1) Invest in a quality collimation tool(s). E-bay 1.25" fit laser collimators are not good enough for fast scopes. Get a 2" fitting precision collimator like the Howie Glatter or similar. Expensive- yes, but I don't think there's any shortcut here.

2) Check the centre spot on your primary mirror. On my 10" Newtonian it was off by several mm.

3) Adjust the secondary mirror first. Assuming it's roughly correct, all that needs to be done is use the secondary adjuster screws to make the laser hit the middle of the doughnut centre spot. 

4) Adjust the primary screws so the laser beam goes exactly back down it's own path. That's pretty much it as far as pre-session adjustments.

Longer term there are various improvements you can do to the scope to make collimation easier (replacing the adjuster screws and the acting surfaces) and more stable in use (replacing the mirror springs).

[Macavity]

I am (as ever) interested in an attempt to quantify any above statements. 

To Laser_Jock: As a fellow fan of budget F4 Newts, what is the chip size of

the "before and after" images (the North American Nebula) above, please? 

Aside: With my 8" F4, the results are [iMO] acceptable for *video astronomy*

(6.4 x 4.8 mm, 1/2" chip) with only "reasonable" care and LASER collimation.

There is though some evidence of star elongation to one side of the frame...

I have a *theory* (measurements!) that this is due to GSO Newts making no

provision for a secondary offset. I intend to introduce an appropriate shift. 

I sense you can do this by flipping / reversing two of the spider supports! 

I also intend to buy one of those "centering" 2" -> 1.25" eyepiece adapters.

I am never convinced that collimating on just ONE position of a wobbly laser

within brass ring retainers means too much anyway. For now, I "jer-jer-jiggle

it a bit" (As "Arkwright" was wont to say) and collimate on a sort of average! 

As ever, the problem is getting sufficient clear skies to do coherent tests.

I certainly agree that the main problem is (was) a reluctance to experiment. 

But be bold... be BOLD! With *thought* and confidence, things get easier.

[laser_jock99]

I am (as ever) interested in an attempt to quantify any above statements. 

To Laser_Jock: As a fellow fan of budget F4 Newts, what is the chip size of

the "before and after" images (the North American Nebula) above, please? 

The images were both through my 6" F4 GSO/TS Newtonian with an ASA Keller 0.7 corrector/reducer fitted- so effectively F2.9 the collimation isn't that far out in the image, but from an imagers point of the frame is a write off.

Both images are the full, uncropped APS-C sized (23 x 15.5mm) DSLR frames. The correction circle of the ASA Keller 0.7x corrector reducer is only 20mm diameter- therefore the corners of an APS-C are outside the corrected area and will start to show coma effects.

Other 'challanges' beyond collimation at F2.9 include focusing, CCD orthogonality and CCD spacing issues..........

[laser_jock99]

The images were both through my 6" F4 GSO/TS Newtonian with an ASA Keller 0.7 corrector/reducer fitted- so effectively F2.9

Correction - the first (uncollimated) image was at F4, the second image was at F2.9

[lensman57]

It is easy to visualise a perfectly collimated F8 or even F6 Newtonian but when it comes to F4 and faster a picture speaks a thousand words. I also believe that these budget F4 Newts do not have the necessary tools engineered in for critical collimation and thereafter holding the collimation so some degree of DIY is necessary.

Squaring the focuser for example would be a very easy job using a laser if the center of the hole was marked inside the tube on the opposite side of the focuser during the manufacture, I think this is where everything starts as all collimation tools that I know of rely on the focuser being perfectly square to the optical axis, this is the case even with the Catseye collimation tools.

Regards,

A.G

[orion61]

Collimation is critical for fine image detail. Especially on Planetary observing.

But back to inviting Ladies to observe.... Every time I have, they want to bring Candles, Build camp Fires, or bring Wine and get me drunk..

Observing has always failed..

[laser_jock99]

It is easy to visualise a perfectly collimated F8 or even F6 Newtonian but when it comes to F4 and faster a picture speaks a thousand words. I also believe that these budget F4 Newts do not have the necessary tools engineered in for critical collimation and thereafter holding the collimation so some degree of DIY is necessary.

Squaring the focuser for example would be a very easy job using a laser if the center of the hole was marked inside the tube on the opposite side of the focuser during the manufacture, I think this is where everything starts as all collimation tools that I know of rely on the focuser being perfectly square to the optical axis, this is the case even with the Catseye collimation tools.

Regards,

A.G

I have never found the need to 'square the focuser'. Colimation is the process of aligning the optical axis of the mirrors with the centre axis of focuser tube. I do this by moving the mirrors - not the focuser tube.......

[lensman57]

I have never found the need to 'square the focuser'. Colimation is the process of aligning the optical axis of the mirrors with the centre axis of focuser tube. I do this by moving the mirrors - not the focuser tube.......

This is true but wouldn't this effect the offset of the secondary ?

A.G

[Moonshane]

Yes and no http://www.skyandtelescope.com/astronomy-equipment/offsetting-your-secondary-mirror/

it won't really matter though

[Moonshane]

The secondary collimation is far far less critical than the primary collimation especially for visual

[nicoscy]

I have never found the need to 'square the focuser'. Colimation is the process of aligning the optical axis of the mirrors with the centre axis of focuser tube. I do this by moving the mirrors - not the focuser tube.......

Squaring the focuser includes ensuring the focuser is also aligned to the optical path as any camera / eyepiece that is inserted in a  focuser that does *not* directly point to the secondary will be affected by the light beam entering at an angle.

It is an easy thing to check anyway with a good laser. Remove the secondary,fire up the laser and measure the distance from the *lip* of the OTA to the beam with a ruler. Repeat the process from the focuser end by sticking the ruler inside the focuser side of the OTA and measuring the same thing, only letting the laser beam hit the ruler so that you can visually see it and measure the distance from said *lip* of the OTA.

Adjustments are done via the mounting screws of the focuser base and if there aren't any, use washers.

[Moonshane]

But surely pointing the secondary at the focuser is the same as pointing the focuser at the secondary?

The suggested laser method would presumably only measure focuser tilt in one plane? If the focuser tilts from top of ota to bottom the measurement could seem correct. Maybe I misunderstand your method.