I think I need to Collimate my Astromaster 130EQ

[dag123]

Hello,

As the title suggests I have the feeling I need to have my first go at Collimination and throught I should ask for advice.

The last couple of times outside I have noticed that it has become harder to get stars to focus properly. Things are not to bad with a 32mm EP but when I switch to 10mm or less I always seem to get what looks like a small flare out of the side of a star. I also note that if I completely unfocus, such that when looking at a bright star (Vega last night) I can see a round circle with a dark shadow of the centre mirror and cross-hair-vanes, this shadow is not quite centred on the circle, slightly to the left by about a radius of the centre shadow as I looked at it.

I have read a number of tutorials on Collimimation on this forum and the web and based on this reading my current thinking is that as I can see a bright "circle" with the bright start completely out-of-focus my secondary mirror is probably okay. But as the shadow of the secondary is "not" central in this circle then the primary mirror is slightly out.

Does this sound about right?

I don't have any special collimination gadgets, but could probably find an old 35mm film case and put a hole in it,which I have read about. Without any gadgets is it best to perform the mirror adjustments at night pointing at a star? I am also slightly confused about which method to use. I have read most about fine-tuning with a star slightly out of focus looking at defraction patterns, but to me it would seem to be much easier to totally defocus and try and centre the shadow of the secondary in the middle of the bright circle.

I note that there seems to be three sets of three screws on the bottom of my Astromaster 130EQ. Three black ones that lie flush. I guess these hold the mirror mount in the tube and I should not touch. Then there are three medium silver cross-heads that I think lock the mirror in place, finally three-large thumb screws imagine actually move the mirror.

So I guess I loosen the three medium screws (how much?) and then start to play with the thumbscrews. Are there any rules-of-thumb? Say the secondary shadow is towards the left-of-centre, which screws to turn in which direction? Is it always in a certain way, ie. turn one one-way and the other two the same amount in the opposite direction to achive tilt?

Thoughts/Advice?

dag123

[NGC 1502]

Hi dag123. Sounds like from your description that collimation is close. If you use a 35mm film can (with appropriate small hole) then you will need to make the adjustments at night on a defocused star. Polaris is best with a non-tracking scope, saves chasing a star across the sky.

When viewing the defocused star, it needs to be in the centre of the field of view, and it's best not to defocus too far, as secondary mirror offset in a newtonian can confuse the issue. But it's easier to see what's going on if the star is well defocused, just do your best.

The screws - don't touch any on the side of the tube near the mirror cell, they will be holding the cell to the tube. There will be three sets of two, six in total for adjustment. Three are for adjustment, three are lock screws. You will have to look up any instructions, or experiment in daylight to see which is which.

Use the tutorials you have read to check the secondary, this can be done in daylight.

If the main mirror has a centre mark, then you can get adjustment fairly close in daylight, the final tweak with the defocused star at night.

To decide which primary adjustment screws to try, if you defocus the star, put a pencil or similar over the open end of the scope, protruding into the light path, move it around until it coincides with where the image is most off centre, then trace that along the tube to the cell, adjust the screws closest to that point. If that position is

between two sets of screws, try adjusting the ones opposite.

Unless you are very fortunate, it will take several tries to get it right. You will likely find that all three sets of screws will have been used before you are done.

After each adjustment, check the defocused star image. If things are better, tweak a bit more on the same screws. If worse, reverse what you just did. It could help if you make notes. It's basically trial & error. Keep calm, you will succeed !

HTH, Ed.

[Porl]

Hey dag123, Im currently messing about trying to collimate my 130EQ and i've tried following Astro_baby's guide and had no luck so far. You can't get the secondary mirror centered under the focusing tube so my collimation attempts constantly end up on the wonk. :S

I found a post on here from 2008 (i think) where Astro_baby fixed a guys 130EQ for him and described that you have to get the secondary mirror as centered as possible (because perfectly is impossible to get) and then adjust the primary mirror to off-set secondary. I've yet to really try it though. I keep getting worried I can't set it back to what it was and end up buggering it right up haha.

I think the key is to twiddle the collimation screws on the end of the OTA but i've found mine quite hard to do.

I'm really interested in any info people can post on collimating these scopes too. :S

cheers

Porl''

[tyler_jrb]

I should think that you are right a small hole in cap will work but if you can get hold of 25 pounds buy the cheshire collimation eyepiece of flo(first light optics). much more easier to use and much more reliable than most lasers, and the hole in cap. as you are using a crosshair in the cheshire. hope this helped .

[dag123]

NCG1502,

So the suggestion is to use the 35mm film canister with a hole in order to check the secondary alignment which could be done in daylight. Then using a de-focused star with a normal EP at night to align the primary.

Tyler,

One of these you mean? First Light Optics - Cheshire Collimating Eyepiece

And with this I could collimate in daylight rather than having to point the scope at a bright star? And just to be sure I have understood it correctly, this tool helps to align both the primary and secondary mirrors.

I guess it comes with instructions?

dag123

[Porl]

hey dag123, I have the cheshire collimating eyepiece from FLO and I've still been struggling to get the collimation right. I think you use the cheshire to collimate the primary mirror but I still havent got my head round how the mirror adjustments work. :S

Mine didn't come with instructions, it just comes in a white cardboard box with the eyepeice in a zip lock bag inside it. Astro-baby's tutorial ( Astro Babys Guide to Collimation ) explains how to use the cheshire but I think her mirrors have a central dot on them which the 130EQ doesn't have.

Porl''

[dag123]

Thanks for that Porl.

I understand from my reading that the central point on the main mirror never gets used as it is in the shadow of the secondary so it is quite safe to remove the mirror and measure and mark the exact centre on the mirror with a marker pen or a sticky circle.

Can someone confirm that I am right in this and if it would this help should I get a Chesire, or even if just using the 35mm film canister trick?

dag123

[Porl]

I've not looked up about putting the center dot mark on the primary mirror, it would make sense. I'm a little nervous to take the primary out myself so im interested to know wether this is possible and would help as well.

I'm determined to not give up on trying to collimate my scope but I seem to be going round in circles at the mo.

Porl''

[tyler_jrb]

yes you are right, my 150p dobsonian, they have a hotspot which is really i think how you are able to collimate it with a cheshire. Dont know about doing the 130eq, you would have to look around for where abouts you put the spot im sure its just central on the mirror. Dont be too worried about taking the primary out because its only held into place, not a complicated mechanism. A dot on the central of the mirror would be fine but I would try not scratch it.

[callisto]

This is how I marked the centre of my primary, hope it helps

Orion Optics GP 250

(scroll down to "dotting the primary" bit)

[dag123]

Hi all,

Thanks Callisto for the idea about how to make a dot in the centre, although as I write this, it is a little late.

Okay, so having read various webpages and watched a youtube video I think I understand what all the mirrors are supposed to do. I have just put it to the test with a bit of open-heart surgery on my 130EQ.

Those of a nervous disposition turn away now, those interested please read on.

So I put the scope on the mount in the house. When I looked through the focuser it was too dark to see anything much so I angled the scope to one of the spot lights in the ceiling. This gave pretty-good light and I could see all the various reflections I had read about.

I put the the film canister with the hole (~2 or 3 mm diameter) into the focuser and as far as I could see the outline of the secondary mirror seemed to be pretty much central. That saved me hunting for the Alan keys as I assume the secondary mirror position is good.

It was also obvious that the reflection of the primary was not central in the secondary. But how to line it up? I had read about central dots and had read that putting a mark in the middle of the mirror would not affect anything. So how to mark the centre? I should also say that it was also pretty clear that there was a lot of dust on the primary and the only way to clean that was to take out the whole mirror assembly. Which I did by unscrewing the three small black screws lying flush on the end of the scope.

Now with the mirror out I took some clean cotton wool balls and gently brushed off the dust. I went from the centre outwards which I had read somewhere. I am sure there might be better and safer ways to clean the mirror,but the end result was that it shone and I could not see any marks as I angled it round under the spotlight.

Now to mark the centre I took a few ideas from various websites. I turned the mirror over and drew a circle round it on a sheet of A4. I then cut this out and folded it into 1/8ths. Then cut a tiny bit off the pointed end. When I unfolded it I had a stencil with a tiny hole in the middle. I positioned this on the mirror and using a tiny blob of blutac, made a greasy smudge through the hole. So I now had a mark in middle but it was hardly visible. So now, like Callisto, with tweezers and a steady hand lowered a paper circle(from a hole punch) with a small blob of blutac over the centre spot.

This done I then put the shiny mirror and centre mark back into the scope. Now looking back in the focuser I could see the new mark and it was not central. Now all the information I had read seemed to suggest I should use a gadget or point the scope at a star. But now as I had the centre marked and I could see it did not align with the vane-shadows on the reflection, why could I not just adjust it now?

So that is what I did. I loosened the smaller silver screws and then tried to adjust the larger thumbscrews. This proved quiet hard, as they did not seem to want to move and I was worried if I applied too much force the mirror might crack or something. However eventually I did manage to get all three to move and I could see my new central dot moving about as I messed with the screws. It only took a few minutes of fiddling to work out which screws and direction were needed to get the central mark to align with the vanes shadows in the secondary reflection. At this point I tightened up the locking screws and had a final look through the focuser.

I could now see what seems to match what I have seen and read about, everything nice and central and aligned.

The cloud cover is total and there is drizzle falling so no chance to test what I have done tonight.

In the meantime, can anyone confirm if I might have actually managed to collimate my scope correctly?

Once I get clear skies again I guess I'll find out.

Anyway I hope this may be useful to someone, if nothing else as a basis for a warning of what not to do ;-)

dag123

[NGC 1502]

In the meantime, can anyone confirm if I might have actually managed to collimate my scope correctly?

dag123

Hi Dag123, sounds like you have done very well.

If it were me, I'd do a final check on a defocused star. If that shows your collimation is ok, or at least very close, then I would quit while your ahead

Regards, Ed.

[Porl]

It was a clear night where I am last night from about 11pm on to 2am. Did you manage to get a star test in?

I did a star test with my last attempt at collimation and I still had the small flare out to the side of the star. Thankfully the moon looked nice and sharp though last night which I was really grateful for cus I needed to get some sketching done for my course.

It did get me thinking, does collimation effect your views on the moon less than when your looking at stars and planets. It just made me wonder because my collimation is slightly out for looking at stars (i checked with Vega) but the moon looked nice and crisp. Would the collimation being out become more apparent with using higher power eyepieces or using the barlow?

clear skies

Porl''

[dag123]

Sorry Porl, the cloud cover was pretty much total last night with just the odd star poking through. Certainly not enough time to set the scope up and perform any useful tests.

I checked upto 23:30 and gave up.

It was almost perfect blue skies this morning when I woke though *sighs

However one thing I did try was to point the scope out of the window before it got dark. I know looking through double glazing is ill-advised but I did get some very crisp views of leaves on the fig tree at the end of the garden.

I am sure there must be major differences in the way collination effects daytime/moon and nighttime viewing, but at least I can rest a little easier with this confirmation that my efforts have not totally broken the scope.

Hopefully better skies over the weekend when I can also stay up later.

dag123

[dag123]

Just a quick note for now to say that I have just been outside with the scope and as far as I can tell it seems to be working just fine, I no longer have flares shooting off stars and when totally defocused I can see a nice and central shadow of the secondary mirror and vanes. With a 2xbarlow and Celestron X-Cel 5mm I am pretty-sure I was able to split the double double near Vega, Certainly Mizar in Ursa Major. I'm just off to check Stellarium as I think I managed to spot M32 just above two star above M31 (my view through the scope)

dag123

[Porl]

Nice one dag I was hoping you got your collimation spot on. I'll be popping my primary mirror out now I think and get that central dot put on

woop

Porl''

[dag123]

Good luck Porl, I hope you have as much success as I did. Just take things slowly, carefully and try not to sneeze when placing the centre dot with tweezers!

One extra tip, well probably? I labelled all the screws and put stickers on the scope casing and mirror unit so that they would all go back exactly where they came from. I am nor sure if that is being overly fussy but taking the scope apart was quite daunting for me so I was being cautious.

I'll write up all the new things I saw last night in the other forums.

Just need another coffee now. Why or why did I decide to stay outside so late until Jupiter appeared from behind the fence??

Okay I know, clear skies, like when are going to get those again!

dag123

[Porl]

Good thinking dag, I've been really daunted to take my scope apart so thats a good idea with marking the screws and locations.

I'll let you know how I go if I get chance to get the primary out and dot it up

I'm going to check the other forums now to see what to expect once my mirror is collimated up.

Porl''

[Porl]

wow its been a while since i last posted to having enough time to try and centre mark my primary mirror. Well i took the primary cell out earlier and was really surprised at how thick the glass element is really cool how its all done. I followed your idea of cutting a piece of paper Dag and finding the center of the mirror. I didnt have a sticky spot to put on so i used a fine tipped perminant marker.

When i put the mirror back in i noticed that the center dot wasnt anywhere near the center of the collmination tool/secondary mirror. I think that might have been how it was after my last messing about. I adjusted my screws and got the collimation target lined up with the new center spot. Hopefully this is all how its ment to be

Im constantly checking out the window to check if there will be gaps in the clouds tonight. Im itching to see if i've finally got it collimated and see the difference in my views of jupiter.

Porl''

[dag123]

Hi Porl,

Glad to hear it all seems to have worked out. I think your permenent marker-pen idea is more long term than the small bit of blu-tac I employed.

I hope it is not long until you get to see Jupiter.

A few nights ago I was able to see it and the four large moons very clearly, the planet being a full clean disc. With my 10mm X-Cel I was able to make out two weather bands. At 5mm and/or with my 2x barlow, these bands were lost as the image in the viewfinder became too fuzzy. Plus without a motor drive it did not spend too long in the viewfinder.

Perhaps when Jupiter is higher in the sky and less air in the way the results at 5mm might improve.

Dag123

[Gina]

Very interesting thread - thank you for all the info I have the same scope and it definitely wants collimating - I got crescents instead of doughnuts last night! And Jupiter nearly always seemed to have a comet tail. I shall have a go at centre dotting the primary and fiddling with the knobs And I'll order a Cheshire collimating tool from FLO.

[chrismann1]

Hi dag,

Just so say thanks, I have read all of you're post and its been really helpful! Just got the same scope for Christmas from my girlfriend as a surprise. I think she heard me saying how much I liked Brian cox's tv shows!

Anyway, after a week of waiting for clear skies I pointed the scope at Jupiter but couldn't get it to focus. It seemed to have a comet tail. So I have started the collimation process. The secondary was badly mis aligned so sorted that today, just tested in daylight and already seems much sharper. I didn't have a collimation eyepiece so drilled a hole in the focuser cap, seemed to do the job.

I think I will do the same as you and remove the primary mirror to mark he centre when I have tested my progress. Hopefully I won't mess it up!

[dishmop]

Not sure if you have a few quid spare or not, if you do I can recommend a laser collimator like this one - I have one of these for my Astromaster 130eq and it really is rather good for the job. You can just insert it into the eyepiece, turn it around so the "display" is facing the bottom of the tube, and start adjusting the mirror until the laser dot is in the center of the crosshairs, then fix the mirror again. Very fast and it works very well.

Hope that helps,

[dag123]

Hi, just to update my own thread.

I am glad this trhead is proving useful.

Chrismann1, I would not worry about messing things up by removing the primary mirror. As long as you take care and don't drop it, or anything on it, you should be fine. As long as you remember which orintation it was in, I did not find that the collimation moved by much when taking the mirror in and out.

Regarding Collimation, I was given a Cheshire Collimating Eyepiece (from FLO) for Christmas. I have since read a number of websites on how to use it, such as

Astro Babys Guide to Collimation

Firstly I have to admit that it does do the job and if there is not a 35mm film canister to hand I'd certainly suggest going out and getting one. The results are certainly no worse than what I was doing previously with the film canister, however it was not that much easier or simpler either! I still found the need for minor tweaking during a star test outside. I know from the reflections that my secondary mirror is pretty much okay so maybe I will find more use for it later.

Anyway, from my own experience I'd find it hard suggesting anyone spends too much on collimation kit. That said, gadgets are gadgets and I am sure I would not complain if I was given a nice shiny laser collimation tool for my birthday!

dag123

[Porl]

HI didn't have a collimation eyepiece so drilled a hole in the focuser cap, seemed to do the job.

Hey Chrismann1, thats what I did with my focuser cap too I used a combination of chesire and drilled focuser cap to get my collimation a lot better.

Its pretty daunting taking the main mirror out but like Dag says, if you take your time and are careful not to drop it or touch the mirror with your fingers you should be good to go

Hope you guys get your scopes collimated as I think its a great little scope

Porl''