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Viewing through the Collimation cap

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#1 druhela

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Posted 11 October 2018 - 02:04 AM

Hi everyone! I'm back with more newb questions. My observation sessions have been constrained by clouds and rains of a cyclonic storm brewing near my region. So I've decided to spoil my new scope's collimation. lol.gif  And I've done a pretty good job at spoiling it. Learning how to collimate is still work in progress (CN has been very kind on PMs) and if weather forecasts are to be believed, I have over a week more to sit indoors looking at these mirrors. While looking through the collimation cap and attempting adjustments, I've come across certain things that I'd like as many experienced views on as possible. 

 

So I have this collimation cap provided as a freebie by the seller: 

 

IMG_20181007_140034.jpg IMG_20181007_140107.jpg

 

Here is a picture I took recently through the collimation cap using my cell phone:

 

IMG_2772.JPG

 

Now, I've marked the above picture with some areas of my concern using a light blue marker. The first thing I want you to notice is that I'm unable to view the third clip appreciably as marked in the picture below. But, even after dragging the view of the third clip to the centre, I'm unable to view it as per the textbook collimation standards. My concern is that I'm not really sure whether this a collimation issue because when I took the following picture of the primary mirror through the front of the OTA, I noticed that the two clips that are visible through the collimation cap hold the primary a shade more than the third clip. I've marked the third clip in blue for you to observe whether its normal or I need to adjust the third clip (or live with it as it is). 

 

IMG_2772_No clip.JPG  IMG_2775.JPG

 

Also, notice in the following picture how the edges allow light to come from behind the primary. Standing behind the primary end of the tube, I can actually see some light coming out from these gaps at corners. Is this normal in a scope or some adjustments are required?

 

IMG_2772- edges.JPG

 

Lastly, is there any collimation tutorial/ video that teaches collimation exclusively through the collimation cap? I've been referring to Astrobaby's atm (which are good), but they use a Cheshire along with the cap. Others tend to start with the cap but midway through the tutorial, they'd summon lightsabers. I'd just like to get good at collimating through the cap over time, without buying other unnecessary equipment. But if you guys suggest something else, do let me know.  

 

 

 

 



#2 emflocater

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Posted 11 October 2018 - 06:28 AM

The first thing to do in any collimation of a reflector is to start with squaring the focuser and then the diagonal in that order FIRST. There are plenty of instructions by searching the internet and Youtube on squaring the focuser and then collimating the diagonal. Once this is done than you can make your way to adjusting the primary mirror and or mirror cell in the tube. Hope this gets you to a starting point where to begin. If done properly you should see all 3 clips centered. What size reflector and focal length do you have?  Shorter focal length reflectors are a tad tougher to collimate but still easily doable.

Cheers

Don


Edited by emflocater, 11 October 2018 - 06:29 AM.

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#3 clearwaterdave

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Posted 11 October 2018 - 07:54 AM

Check out Astrobabys website.,These were the easiest instructions I found.,good luck


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#4 Gregory2012

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Posted 11 October 2018 - 09:51 AM

Hi,

 

I am in desperate need for help to understand why I can not see all six primary clips. I can only see the top 3 and no matter what, I can not center the view to see the clips. Why is this happening?

 

Secondary adjustment doesn't work, I have rotated that thing almost a complete 360. My primary is currently aligned according to my laser collimator and still only the three clips at top. I can align the optics to the center dot on the primary but nothing allows me to see all of the clips. The ones I can not see are always on the bottom of the primary view.

 

These views do not change. The only thing I havn't done is mess with the spiders or focuser. The way I see it, I started out trying to align a simple discrepancy, now I have completely destroyed my collimation, and I can not get back to a normal alignment.

 

Any advice would be appreciated.

Gregory Gig Harbor, WA.


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#5 druhela

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Posted 11 October 2018 - 10:27 AM

The first thing to do in any collimation of a reflector is to start with squaring the focuser and then the diagonal in that order FIRST. There are plenty of instructions by searching the internet and Youtube on squaring the focuser and then collimating the diagonal. Once this is done than you can make your way to adjusting the primary mirror and or mirror cell in the tube. Hope this gets you to a starting point where to begin. If done properly you should see all 3 clips centered. What size reflector and focal length do you have?  Shorter focal length reflectors are a tad tougher to collimate but still easily doable.

Cheers

Don

Well, this is a start! While playing with the collimation, the thought did strike me out of common sense that what if my Crayford Focuser is the cause for the issue with the third clip, but I suppressed it, cause well I'm not a pro at this. This seems like a lead for me to pursue. Thanks! 

P.S. Mine is a 150mm F5 reflector. 

 

 

Check out Astrobabys website.,These were the easiest instructions I found.,good luck

They don't seem to have worked for me till now. I'll make sure to come back to this post and point out the reason why once I succeed. 

 

 

Hi,

 

I am in desperate need for help to understand why I can not see all six primary clips. I can only see the top 3 and no matter what, I can not center the view to see the clips. Why is this happening?

I know how that feels after hours of trying. smile.gif I'm sorry I can't answer your questions right now. But follow this post, and maybe someone would come up with an answer to our combined misery. Otherwise, I'm on it. Will reach you once I figure this out completely. 



#6 Vic Menard

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Posted 11 October 2018 - 10:29 AM

...Now, I've marked the above picture with some areas of my concern using a light blue marker. The first thing I want you to notice is that I'm unable to view the third clip appreciably as marked in the picture below...

 

...Also, notice in the following picture how the edges allow light to come from behind the primary...Is this normal in a scope or some adjustments are required?

 

Lastly, is there any collimation tutorial/ video that teaches collimation exclusively through the collimation cap? I've been referring to Astrobaby's atm (which are good), but they use a Cheshire along with the cap. Others tend to start with the cap but midway through the tutorial, they'd summon lightsabers. I'd just like to get good at collimating through the cap over time, without buying other unnecessary equipment. But if you guys suggest something else, do let me know.  

First... the visibility of the primary mirror clips is not, by itself, an indicator of good collimation. It is not, by itself, a good indicator of optimal secondary mirror placement. To use the visibility of the primary mirror clips as an indicator of optimal secondary mirror placement, you must first have the secondary mirror correctly centered under the focuser. To center the secondary mirror under the focuser you'll need a good sight tube, a thin beam laser, or--if you want to use annotated images--an image through your collimation cap that shows these three circles: 1.) the bottom edge of the focuser, 2.) the actual edge of the secondary mirror, and 3.) the reflected edge of the primary mirror. With a sight tube (or Cheshire/sight tube combo tool), you center the secondary mirror by aligning the sight tube cross hairs with the primary mirror center spot and the actual edge of the secondary mirror with the either the reflected edge of the primary mirror or the bottom edge of the sight tube. With a simple thin beam laser, you center the secondary mirror by aligning the outgoing laser beam with the primary mirror center spot and the actual edge of the secondary mirror with the reflected edge of the primary mirror. If you're using annotated images through a collimation cap, it's critical that you use all three alignment references (the 3 circles listed above).

 

The images you've provided don't show the three alignment references (the background is too dark). Try putting a piece of white paper behind the secondary mirror against the inside of the OTA wall opposite the focuser--then you should be able to see the actual edge of the secondary mirror and the bottom edge of the focuser.

 

Second... don't worry too much about light infiltration from behind the primary mirror (many scopes are left completely open behind the primary for ventilation purposes--although some use baffles).

 

Third... the modern collimation cap is a derivative of the Cheshire eyepiece--which is a primary mirror alignment tool. Many Newtonian enthusiasts use a collimation cap with a simple thin beam laser to achieve collimation--you might find this tutorial helpful:  https://www.cloudyni...ment/?p=5260727

 

Finally, I'm assuming you're trying to collimate your 6-inch f/5 Newtonian? If so, there are specific tolerances that need to be met for richest field visual, planetary visual, wide field imaging and/or planetary imaging. It helps to know, both your goal, and your expectations.

 

So, let's get you collimated! I already checked your direct primary view (next to the last image) and your center spot/donut appears to be pretty well centered. If you can put up another collimation cap view with a lighter background so we can see all 3 circles, we'll get a better idea about where you are now and what you need to do to get your secondary mirror sorted out.

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#7 Vic Menard

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Posted 11 October 2018 - 10:35 AM

...I am in desperate need for help to understand why I can not see all six primary clips. I can only see the top 3 and no matter what, I can not center the view to see the clips. Why is this happening?

 

Secondary adjustment doesn't work...

What collimating tool are you using?

What scope are you collimating (include aperture and focal ratio).

Is your focuser racked almost all the way in?

Can you provide any pictures?



#8 csrlice12

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Posted 11 October 2018 - 10:40 AM

Google Vic Menard (above)  He wrote THE book on mirror alignment/collimation.  When you get to the point where you need to square the focuser, his book will help.  I consider it the bible of telescope collimation.


Edited by csrlice12, 11 October 2018 - 10:42 AM.

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#9 druhela

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Posted 11 October 2018 - 02:14 PM

So, let's get you collimated! I already checked your direct primary view (next to the last image) and your center spot/donut appears to be pretty well centered. If you can put up another collimation cap view with a lighter background so we can see all 3 circles, we'll get a better idea about where you are now and what you need to do to get your secondary mirror sorted out.

Thanks a lot, Vic for your reply! I am indeed trying to collimate my GSO 150mm F5 Newtonian which comes with a stock 2" Crayford focuser. I use it with a 1.25" adapter (all my eyepieces are 1.25" atm) and a 35 mm extension tube for visual use only. I am not doing any astrophotography atm. 
 

Trying to collimate the scope since yesterday, I've made some adjustments to almost all the mirror alignments. I am attaching the image with a lighter background I clicked just now. Note that I've clicked the following picture through the collimation cap when the focuser is just outside the reflections (and still the third clip is not visible). I've attached another picture below where I've racked in the focuser a little and brought it into the picture (sorry about the change in lighting conditions and position, I've clicked these indoors during night time).

 

IMG_2795.JPG

 

IMG_2800.JPG

 

 



#10 druhela

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Posted 11 October 2018 - 02:18 PM

Google Vic Menard (above)  He wrote THE book on mirror alignment/collimation.  When you get to the point where you need to square the focuser, his book will help.  I consider it the bible of telescope collimation.

Can I order this here in India as well? :) 



#11 emflocater

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Posted 11 October 2018 - 02:32 PM

 

Can I order this here in India as well?

Click HERE

 

Cheers

Don


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#12 Vic Menard

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Posted 11 October 2018 - 04:54 PM

Thanks a lot, Vic for your reply! I am indeed trying to collimate my GSO 150mm F5 Newtonian which comes with a stock 2" Crayford focuser. I use it with a 1.25" adapter (all my eyepieces are 1.25" atm) and a 35 mm extension tube for visual use only. I am not doing any astrophotography atm. 
 

Trying to collimate the scope since yesterday, I've made some adjustments to almost all the mirror alignments. I am attaching the image with a lighter background I clicked just now. Note that I've clicked the following picture through the collimation cap when the focuser is just outside the reflections (and still the third clip is not visible)...

OK--this is better. I've annotated your first image--the light blue circle (with the cross hairs) is the bottom edge of the focuser. The green circle represents where the actual edge of your secondary mirror should be--you're already very close! The red circle is where the reflection of the primary mirror should be. 

 

At this point, I would suggest adjusting the secondary mirror tilt (the three screws surrounding the secondary mirror mounting screw) until you can get the bright primary mirror reflection centered in the secondary mirror (the green circle). Once you get the primary mirror reflection centered, you'll have to tweak the primary mirror tilt to get the primary mirror center spot centered in the collimation cap reflection. Then post another picture and we'll discuss what you need to do next... (The dark offset circle surrounding the collimation cap reflection will NOT be centered relative to all of the other circles--it's supposed to appear offset toward the primary mirror--and that's what it looks like now. When you get the primary mirror reflection centered, the spider vane end attachment (yellow circle) should also be less visible.) 

 

Don't worry about the third primary mirror clip (orange circle)--it's just set back away from the reflective surface of the primary mirror a bit more than the other clips, so it will always appear the way it is now unless you change it. As long as it keeps the primary mirror from falling out of the cell, it's doing its job.

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#13 emflocater

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Posted 11 October 2018 - 05:08 PM

Vic, excellent analysis with annotations! I agree with you that the diagonal needs to be tilted. Tilting up a tad should make a world of difference. Maybe close enough to do a star test for final collimation.

Cheers

Don


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#14 Jond105

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Posted 11 October 2018 - 06:23 PM

I just went on through this recently with my dob, I couldn't see my clips or only partial. I'm spot on now, one of my major problems was my primary was lifted too high to see all the clips. Is your primary pulled all the way back?
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#15 Jond105

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Posted 11 October 2018 - 06:26 PM

Note? At least start with the primary pulled all the way back? That's what I did, centered secondary not caring about the primary. Then with that centered up the best I could I backed off the primary only one turn and centered the primary. That's when I checked it all with a a well collimated hotech laser and both my sight tube and laser matched all centered. Before I had my primary way to far up to not be seen in the secondary all that well

#16 Vic Menard

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Posted 11 October 2018 - 08:14 PM

I just went on through this recently with my dob, I couldn't see my clips or only partial. I'm spot on now, one of my major problems was my primary was lifted too high to see all the clips. Is your primary pulled all the way back?

You can see the entire reflection of the primary mirror in the secondary mirror--look at the position of the orange circle in post #12 above. Pulling the primary mirror back will not make the mirror clip in the orange circle more prominent.


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#17 Mike W.

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Posted 11 October 2018 - 08:49 PM

Vic's book title, New Perspectives on Newtonian Collimation - Vic Menard, do a local search for it in your area, might be just down the block, if not here's a link to a source on your side of the pond.

https://www.firstlig...vic-menard.html

 

With out his help and several others here, my learning week would easily been a month,,,,,,,,, 

Matter of fact I think it did take at least a month,,,waytogo.gif

 

To be fair, there were others that are just as important and helpful, Don, Jon, Jason, I won't ever forget your assistance.


Edited by Mike W., 12 October 2018 - 06:52 AM.

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#18 Vic Menard

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Posted 12 October 2018 - 09:40 AM

...there were others that are just as important and helpful, Don, Jon, Jason...

I wholeheartedly agree!  bow.gif


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#19 druhela

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Posted 12 October 2018 - 10:36 AM

I noticed that the two clips that are visible through the collimation cap hold the primary a shade more than the third clip. 

 

Don't worry about the third primary mirror clip (orange circle)--it's just set back away from the reflective surface of the primary mirror a bit more than the other clips, so it will always appear the way it is now unless you change it. As long as it keeps the primary mirror from falling out of the cell, it's doing its job.

Precisely what I wanted to say! bigshock.gif  THE THIRD CLIP IS onto the less reflective surface of the mirror compared to the other two clips and thus appears to be holding the mirror a tad lesser than the other two clips. To think that I spoilt a perfect collimation to make that third clip visible! 4.gif I'm inclined to take the primary out and adjust the third clip, but that isn't going to help me right now (and it is as you said doing its function of holding the primary mirror well), so have to live with it for now. I took closer pictures of the third clip vs the other clip to show the difference:

 

The Third clip                                                                                                                            The Other clip

IMG_2802.JPG                         IMG_2803.JPG

 

 

I'm making the suggested adjustments to the mirrors right now. Will post when I succeed (god bless me lol). 


Edited by druhela, 12 October 2018 - 10:37 AM.


#20 emflocater

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Posted 12 October 2018 - 11:52 AM

For now concentrate on the tilt of the diagonal. Remember the clips should barely touch the primary mirror. Some slip a business card between the clip and mirror for a consistent space. I have used a thin piece of white foam under my clips and the foam just touches the mirror. The foam helps keep the clip from scratching the mirror. Some people have their clips too tight against the mirror which will cause the mirror to be pinched. This will cause astigmatism in which the stars look triangular or squarish.

Cheers

Don


Edited by emflocater, 12 October 2018 - 12:26 PM.

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#21 druhela

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Posted 12 October 2018 - 02:55 PM

Some people have their clips too tight against the mirror which will cause the mirror to be pinched. This will cause astigmatism in which the stars look triangular or squarish.

Cheers

Don

That's the last thing I want. Thanks for the heads up.

 

 

Then post another picture and we'll discuss what you need to do next... 

I can't seem to make it any better than the following picture (I can't spot much offset from my original position tbh). The spider vane end attachment has been stubborn. Another thing I noticed is that whatever adjustments I make, I'm unable to get the last spider vane attachment into the view (the one opposite to the stubborn one).

 

2.jpg



#22 emflocater

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Posted 12 October 2018 - 03:33 PM

Did you adjust and tilt the diagonal with the 3 small screws? Still looks like the diagonal tilt need to be adjusted straight up a little toward your focuser. Keep the cap in the focuser and slightly loosen 2 of the 3 screws and adjust the other one and see what it looks like in your cap. If worse go back and re-adjust the last screw  you touched and make your way to one of the other 2 screws. Repeat until your happy. Then after, fine adjust the primary mirror.

Cheers

Don


Edited by emflocater, 12 October 2018 - 03:36 PM.


#23 Jason D

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Posted 12 October 2018 - 04:21 PM

 The spider vane end attachment has been stubborn. Another thing I noticed is that whatever adjustments I make, I'm unable to get the last spider vane attachment into the view (the one opposite to the stubborn one).

 

 

You are using the collimation cap which is not the best tool for focuser axial alignment. A laser collimator or a sight-tube with cross hairs will be a better tool. Check attachment. Your reflected focuser axis (center of the red cross hairs in my attachment) is striking the primary mirror away from the focuser behind the center spot. As a result, you had to "over" tilt the primary mirror to align the primary mirror center spot reflection with the collimation cap reflection. In doing so, the primary mirror sees the spider vane end that is directly above the focuser. Interestingly, your secondary mirror positioning under the focuser is good.

 

If above sounds gibberish, forget it about it. Let me tell you what you need to do to fix your issue:

 

1- You need to align your focuser axis. If you do not have a laser collimator or a sigh-tube with cross-hairs, you need to get one of the two -- or build your own sight-tube with cross-hairs. There are several DIY threads about how to build one from a PVC pipe.

2- Using the sight-tube with cross hairs, make slight adjustments to the secondary mirror to align the cross-hairs with the primary mirror center spot reflection.

3- Finally, adjust the primary mirror to align the primary mirror center spot reflection with the collimation cap.

 

Your current issue is with missing step#2 

 

Jason

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#24 Vic Menard

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Posted 12 October 2018 - 04:47 PM

As Jason noted above, and as I noted in post #12, you still need to adjust the secondary mirror tilt (usually 3 screws surrounding the center mounting screw behind the secondary mirror). The screw that you'll need to turn is the one behind the spider vane with the visible end attachment (next to the focuser, ref: the yellow circle in post #12). If there isn't an adjustment screw behind that vane, then look for the adjustment screw 180-degrees opposite the vane that attaches next to the focuser.

 

You need to tilt the far end of the secondary mirror (the end closest to the primary mirror) away from the focuser side of the OTA. This will bring the primary mirror center spot into the center of the field of view (my blue cross hairs in post #12, Jason's red cross hairs in post #23). When you make this adjustment, it will change the primary mirror alignment (primary mirror center spot/collimation cap pupil), so you'll need to realign the primary mirror tilt after you've made the secondary mirror tilt adjustment. And, as Jason noted, when you make the corrective primary mirror tilt adjustment, the spider vane end attachment will either become less prominent or it may disappear entirely. 

 

And, as I noted in post #12 (and Jason in post #23), your secondary mirror placement already looks pretty good.

 

Be fearless! But be patient too--if you make small adjustments, the primary mirror reflection in the secondary mirror should move into the center of the secondary mirror with minimal change to the secondary mirror placement.


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#25 druhela

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Posted 12 October 2018 - 06:13 PM

I see I've brought out quite a party out on this post. smile.gif  Thanks, everyone for bearing with me on this marathon collimation session. bow.gif

 

You are using the collimation cap which is not the best tool for focuser axial alignment. A laser collimator or a sight-tube with cross hairs will be a better tool.

I understand after today, that I require a pointing tool with an axis for effective adjustments of the secondary, but I don't happen to own one atm. Trying to procure a Cheshire-Sight tube combo kit, but that would take a while. So even though impossible as it seems for me, I'm still trying to collimate the scope with the collimation cap for now. lol.gif

 

 

The screw that you'll need to turn is the one behind the spider vane with the visible end attachment (next to the focuser, ref: the yellow circle in post #12). If there isn't an adjustment screw behind that vane, then look for the adjustment screw 180-degrees opposite the vane that attaches next to the focuser.

 

You need to tilt the far end of the secondary mirror (the end closest to the primary mirror) away from the focuser side of the OTA. 

That was great advice, Vic. Those steps seem to have helped me make some progress. How does it look now? 

 

IMG_20181013_041651.jpg

 

 

 




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