Tearing hair out with collimation problem - please help!

[Igwiz]

Hi all,

I have blinded myself with the amount I have read about collimating my newt and have ended up thoroughly confusing myself.  Could you kindly take a look at the attached picture of an out of focus star that clearly shows my optics are out of whack.  Trouble is, I am going round in circles (pun unintended) and can't work out the adjustment required.  The primary and secondary have been out of the tube so it is no surprise it needs work!  The bit the really bothers me is the elongation at the bottom and also not being able to see the 3rd primary clip. 

ANY help from you wise old elves would be very greatly appreciated before I go utterly nuts.

Many thanks,

Ig

[dweller25]

The image you have posted is too far out of focus to show much but it looks elongated so possibly the primary mirror contacts are too tight ???

A better photo would be down the focus tube so we can see how things are lined up.....

[Charic]

Not sure what 'bible' your following appertaining to the art of collimation, but this one is a real help, http://www.astro-baby.com/collimation/astro babys collimation guide.htm
I would print it out and read it several times over in order to understand the process, then take your time, and follow this guide.
It's helped many folk here in the past, the present too.

Welcome to the SGL.

HTH.

[spaceboy]

As Charic says follow astro baby's guide and you'll be good to go. The trick is to use paper or card to block distractions. This is handy if your eye gets confused by the primary reflections or for the first time after flocking or cleaning mirrors to ensure your secondary is square to the focuser. Looking at your image it looks like you either need to rotate the secondary or move it up or down the OTA using a collimation cap as your guide. All instructions to do so are in AB's guide.

[Igwiz]

Thanks guys.  It is indeed Astro Baby's guide that I had been using and I thought I had it sorted until it was obvious I didn't! I put the donut picutre in as I thought was best example but here is the view down the collimation cap.  I have put the Mire de Collimation overlay over it and it is clear the mirror itself is producing a circle but that circle is not centred in the sight tube.  But the direction it is off is not the up/down which is all I can find referenced.  I have measured the spider vanes but perhaps not closely enough - I assume it is the vane adjustment screws that would allow me to move it the required direction?  Many many thanks!

[spaceboy]

The trouble with pictures is they can't be considered a 100% accurate representation as the camera may be slightly tilted or not perfectly lined up central to the collimation cap. If you consider your picture to represent what your eye is seeing then it is obvious the secondary isn't central. Measure the spider vanes to check they are equal, Then check the collimation bolts on the secondary are equally tightened and that one isn't introducing excessive tilt. Finally if that doesn't help depending on what focuser you have you may be able to tweak your focuser alignment.

If your still struggling your best bet is to find a local astronomy society and pop along to the next meeting and see if someone will show you how to collimate.

[Igwiz]

Thanks. Yep the photo is a fair representation.  Going to pop out know and have another play.

[Alkaid]

It's your secondary that is out.   This is why you can't see the primary mirror clips.

First of all, stick a Cheshire in the focuser and make sure that the cross hair is bang in the centre of the secondary.  If it isn't, then the secondary is not directly under the focuser.  To move the secondary up and down the tube, carefully adjust the central screw.  To move it perpendicular to the tube, adjust the spider arm lengths (in this case one spider arm will be longer than the other).

Once you've done that, tilt the secondary using the three adjustment screws so that all three primary clips are visible and the primary looks concentric.  This may mess up slightly what you did in step 1 above.  So re-adjust and then carry on. Once finished, the cross hairs of the Cheshire should be bang in the middle of the secondary AND the secondary should look perfectly circular AND the entire primary mirror should be visible AND the primary mirror should look concentric.....phew!  The secondary adjustment is quite hard - make sure you have no distractions and make some tea of coffee.  It could take an hour.

After this, it's much easier.  Adjust the primary mirror in the usual way with the Cheshire until collimated with the secondary.  Job done.

[Igwiz]

Thanks guys. To close this out, just reporting back, it was indeed my being to "soft" with the secondary.  I adjusted the spider vans by a couple of mm but the biggy was being a lot rougher with the rotation.  Am in a lot better place, still some tweaking to do but usable!  So for anybody reading this in the search for their own solutions, my learning on this is (and particularly if you have removed the secondary at any point) don't be afraid of giving it a good old tug!

Thanks again.

[Dave In Vermont]

Not knowing the 'F' of your Newt, I'll just say to you - or anyone reading looking for solutions - one very good shown in Astro_Baby's guide is the picture of the offset in fast Newts, like F4 or F5. Here it is:

 

This offset isn't described, or pictured, in just about any other collimation-guide out there. And has, no doubt, resulted in confusion & frustration of many Newt owners. Especially since fast Newts become so very popular. Hopefully this wide-spread cause of 'baldness' will be alleviated with this information in more people's armory of astro-tools and data. For good measure - here's a link to Astro_Baby's Collimation-Guide:

http://www.astro-baby.com/collimation/astro babys collimation guide.htm

Enjoy!

Dave

 

[SteveBz]

Hi Guys,  I am also having trouble with collimation, particularly step 2 of Astro Baby's guide (centring the secondary mirror).  And this is my solution (made from an old supermarket pizza carton with graph paper glued on):

As you can see, I cut the sides off to make it fit through the vanes and cut a slit to allow the bottom vane through.

This is what you see through the collimating cap (home-made, natch), before:

I count 13 squares above, 18 below and 17 to the right.

And after:

16.5 to 17 all round.

I haven't managed to test it yet, because it's just started raining.

I also tried a borrowed laser as in Andy's Shot Glass video, but sadly the laser also needed collimating.

Regards

Steve. 

[algady]

I'm having exactly the same problem with my 12" f4 Newtonian!  

[Dave In Vermont]

If it's looking (the 2nd. mirror) centered with a look through a collimation-cap in the focuser un a good amount of light to see, go with that. It doesn't require millimeter-precision. Centered enough to direct the image off the primary straight-up to the focuser.

You'll get there. If frustrated, take a walk, play ball with the kids, visit some Funeral Homes - whatever relaxes you!

Dave

[SteveBz]

5 hours ago, Dave In Vermont said:

If it's looking (the 2nd. mirror) centered with a look through a collimation-cap in the focuser un a good amount of light to see, go with that. It doesn't require millimeter-precision. Centered enough to direct the image off the primary straight-up to the focuser.

You'll get there. If frustrated, take a walk, play ball with the kids, visit some Funeral Homes - whatever relaxes you!

Dave

Really?  I thought that's what I did, but the stars all still have flares.  I assumed that my 'centring' of the secondary mirror just wasn't up to standard.

Before I used the graph paper I tried to follow AstroBaby's guide to the letter and then I followed it up with my friend's laser collimator and it just wasn't OK.

We've had a few OK nights, but now it's just pouring down.

I'm collimating an f/5 c8n.

Regards

Steve

[SteveBz]

6 hours ago, Dave In Vermont said:

You'll get there. If frustrated, take a walk, play ball with the kids, visit some Funeral Homes - whatever relaxes you! 

Ah well...  people everywhere talk very fondly of the luxurious funeral homes in Vermont, the quality, the music, value for money and especially the after-sales service. 

Sadly the funeral homes in the UK still get their inspiration from Charles DIckens.

[Ricochet]

4 hours ago, SteveBz said:

Really?  I thought that's what I did, but the stars all still have flares. 

If by "flares" you mean coma then this is an artefact of the parabolic primary mirror and will require the addition of a coma corrector to remove. If you mean diffraction spikes then this is caused by the secondary spider and you would need to replace the existing spider vanes with curved vanes to reduce it.

[SteveBz]

Hi Ricochet,

I mean diffraction spikes. But it's standard c8n, second-hand and a bit bruised. I can't believe it's so bad I can't use it (which is the case now). How could Celestron sell them?  They're not flares like the star of Bethlehem, they look more like comets with four tails, all trailing to one side. Or the bow-wave of a boat.

I have a smaller 114eq which doesn't have the same problem.

Do you really think it's the vanes and where can I get curved ones?

Regards

Steve.

 

[Ricochet]

That sounds like coma to me. Point your scope at a star and then move the star around the field of view and watch what happens. It should be symmetrical all around the centre and disappear (or change to standard diffraction spikes) when the star is centred. If it is not symmetrical and the point at which a star is point like is not in the centre then your collimation is off. 

[SteveBz]

20 minutes ago, Ricochet said:

That sounds like coma to me. Point your scope at a star and then move the star around the field of view and watch what happens. It should be symmetrical all around the centre and disappear (or change to standard diffraction spikes) when the star is centred. If it is not symmetrical and the point at which a star is point like is not in the centre then your collimation is off. 

I'll take a photo and post it when it stops raining!!!!

Wish me luck.

[Ricochet]

If you put a different coloured card/paper in the tube to block the reflections from the primary it makes it a lot easier to see the shape and position of the secondary when you're lining it up. 

 

Good luck 

[CraigT82]

I have seen the flares you describe in my own newt, bright stars had a comets tail but the tail danced and shimmered. This was due to a very warm mirror! 

[Peter Drew]

SteveBz. I don't think coma from a F5 8" parabola would be that noticeable, it looks to me as though your secondary needs rotating a little.  

[SteveBz]

The interesting thing is that the tails nearly disappear when viewed at the edge of the eyepiece.  I'm hoping to view tonight and I'll give you an update if I'm successful.

The last time I looked it was a warm night, but the tails were static.

My own theory was a skewed secondary, hence all the pieces of graph paper, so I hope I can tell which it is tonight.

Regards

Steve

[SteveBz]

Ok, here is an update.  The night is relatively clear for Gatwick.  The aberration, whatever it was, seems much better now having adjusted the secondary mirror. 

Here is a photo of Vega, what do people think of the collimation?  It still doesn't look very point like.  Should I try to get it better, or is it good enough?

I think the next problem is the camera, probably the subject of another post.

Thanks,

Steve.