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Collimation Cap

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#1 patindaytona

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Posted 08 December 2019 - 09:34 PM

Anyone know where to get one? I bought a combo chesire site tube which is good. But I also need a simple collimation cap because the chesire doesn't take in the whole view of the primary reflection and I can't see precisely where the mirror latches are at when viewing.



#2 fatrowbridge

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Posted 08 December 2019 - 09:38 PM

https://agenaastro.c...t-eyepiece.html


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#3 JohnBear

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Posted 09 December 2019 - 12:09 AM

The best collimation tool I have is a small $1 aspirin bottle (from the local dollar store)  

with a small hole carefully drilled in the center of the bottom. The white plastic bottle passes ambient room light in to make the reflection of the "pupil hole" clearly visible. The treads on the bottle (for the cap) are exactly 1.25" in diameter for a perfect fit in the eyepiece holder. There is also a plastic rim that holds the bottle perfectly vertical against the eyepiece holder. 

 

Thus simple device is, IMHO, far superior to any other collimation cap or tool that I have yet tried. 


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#4 patindaytona

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Posted 09 December 2019 - 08:13 AM

Since I already drilled a hold in a focus tube cap (that didn't have a hole), and ended up slightly off center, I just found some very thin, but stiff cardboard and traced around that cap for a circle, then found the center and poked a hole. I'll just tape it over the end of the focus tube. Serves same purpose. I won't need it after that. The chesire will do the primary collimating from then on.

I moved the hole around slightly and noticed it doesn't have to be super critical for the centering of it. But closer the better.



#5 gwlee

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Posted 10 December 2019 - 08:47 PM

1. If you can document buying a scope from Orion, Orion will sell you a replacement collimation cap. If you can't document buying the scope from Orion, they might or might not sell  you one.

 

2. The Orion Collimation cap is just a 1.25 dust cap with a small hole drilled in the center and its underside has a white sticker installed to reflect light. If you have a dust cap, you can make one easily. I often use a collimation cap with a piece tape over the hole for a dust cap, which is more convenient than keep track of two similar tools. 

 

3. FarPoint sells collimation tools, and one them is very similar to the Orion collimation cap, but made out of aluminum, so much more expensive. Forget what they call this tool. 



#6 Starman1

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Posted 11 December 2019 - 02:00 PM

1. If you can document buying a scope from Orion, Orion will sell you a replacement collimation cap. If you can't document buying the scope from Orion, they might or might not sell  you one.

 

2. The Orion Collimation cap is just a 1.25 dust cap with a small hole drilled in the center and its underside has a white sticker installed to reflect light. If you have a dust cap, you can make one easily. I often use a collimation cap with a piece tape over the hole for a dust cap, which is more convenient than keep track of two similar tools. 

 

3. FarPoint sells collimation tools, and one them is very similar to the Orion collimation cap, but made out of aluminum, so much more expensive. Forget what they call this tool. 

The Farpoint collimation tool you're thinking of is their Cheshire, and it functions exactly like the Cheshire part of a combination tool, just with the crosshairs of the sight tube part absent.

It is a primary mirror collimation tool, just like a collimation cap.



#7 brettecantwell

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Posted 27 December 2019 - 03:18 PM

Take a typical dust cap. drill a small hold in the middle and line the underside with aluminum foil.


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#8 aeajr

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Posted 27 December 2019 - 05:30 PM

Www.agenaastro.com

Edited by aeajr, 27 December 2019 - 05:32 PM.


#9 Miranda2525

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Posted 29 December 2019 - 01:14 AM

Best one I have ever used is the Orion one. When collimating, it is seen as a small black dot right inside the ring on the primary. I shine a bright light on the back of my primary and I can line the small black dot right inside of the ring on the primary. Works great. 


Edited by Miranda2525, 29 December 2019 - 01:17 AM.


#10 rodgpetersen

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Posted 29 December 2019 - 03:43 PM

if you have a plastic 35mm film container you can make a great collimation tool in about 2 minutes. Been using one for about 40 years.



#11 aeajr

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Posted 30 December 2019 - 12:18 PM

if you have a plastic 35mm film container you can make a great collimation tool in about 2 minutes. Been using one for about 40 years.

35 mm film canister?

 

Likely 90% of the people on this forum today would have to go buy a roll to get one of those canisters, then throw the film away.   Not too many people use film cameras anymore.   

 

But, if you have one, yes it will work.  Or you can buy a collimation cap for $7, ready made. 



#12 patindaytona

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Posted 30 December 2019 - 12:43 PM

35 mm film canister?

 

Likely 90% of the people on this forum today would have to go buy a roll to get one of those canisters, then throw the film away.   Not too many people use film cameras anymore.   

 

But, if you have one, yes it will work.  Or you can buy a collimation cap for $7, ready made. 

Where can you buy a $7 collimation cap? I tried looking and not easy find any at all. What I did already though, was use the solid cap that came with the telescope and drilled hole. Unfortunately it was off a bit. Not perfectly centered, but close (how close is close!?)

Then, i just used some heavy paper and punched a hole into that, and glued it to the underside of the cap (think i had to make the diameter of the cap hole bigger again first). That gave me some wiggle room with the paper to move it around till very centered when looking thru.

Anyway, i found that it doesn't have to be dead perfect because you're not looking down any type of a tube (chesire etc), so their's not kind of visual angling involved. I tried moving the homemade collimation slightly and could tell, that accuracy doesn't need to be perfect.

Sidenote: Since I got my new 12" dob. I noticed the little donut sticker on the primary is way way smaller than my previous 10" Orion xt10i was. I thought something was wrong, till i saw that was what it was. Not sure, still what's going on, but when you adjust the primary mirror, is it supposed to be about centering the donut onto a black dot? It's so small now, I'm not sure what I'm looking for.



#13 Vic Menard

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Posted 30 December 2019 - 01:29 PM

Where can you buy a $7 collimation cap?

See link in post #2 above.


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#14 Vic Menard

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Posted 30 December 2019 - 01:38 PM

...Anyway, i found that it doesn't have to be dead perfect because you're not looking down any type of a tube (chesire etc), so their's not kind of visual angling involved. I tried moving the homemade collimation slightly and could tell, that accuracy doesn't need to be perfect.

Actually, it should mimic the axis of your (moderate to high magnification) eyepiece--which is one of the reasons I prefer a Cheshire eyepiece over a press-fit collimation cap.

 

Sidenote: Since I got my new 12" dob. I noticed the little donut sticker on the primary is way way smaller than my previous 10" Orion xt10i was. I thought something was wrong, till i saw that was what it was. Not sure, still what's going on, but when you adjust the primary mirror, is it supposed to be about centering the donut onto a black dot? It's so small now, I'm not sure what I'm looking for.

 

It should look like this:

https://www.cloudyni...n-f5/?p=5821746


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#15 aeajr

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Posted 30 December 2019 - 01:51 PM

Where can you buy a $7 collimation cap? I tried looking and not easy find any at all.

 

snip...

 

https://agenaastro.c...t-eyepiece.html


Edited by aeajr, 30 December 2019 - 02:02 PM.


#16 NorthernlatAK

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Posted 30 December 2019 - 02:09 PM

When my collimation cap is in an I am collimated, it appears like a bullseye. The hole is the center of the bullseye, followed by a very thin white ring and then the donut sticker. When it looks like this, I am able to get to 400× on a good night.
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#17 patindaytona

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Posted 30 December 2019 - 03:37 PM

Can't believe the collimation went off again. I only use it outside and am extremely gentle about carrying it...no bumps at all. Not sure how it happened. Wasnt' off alot, but enough.

Just collimated it again. I do have a chesire. Thing is. that if you rotate the chesire in the site tube, the cross hairs will slightly migrate away from dead center. The black spot stays very close all way around though. I'm sure it's fine.



#18 Starman1

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Posted 30 December 2019 - 03:59 PM

Check your crosshairs with a caliper.  Many of the inexpensive Sight tube/Cheshire combination tools have off-center crosshairs.

Usually, they can be tweaked a bit to center the crosshairs a bit better.



#19 patindaytona

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Posted 30 December 2019 - 05:06 PM

Check your crosshairs with a caliper.  Many of the inexpensive Sight tube/Cheshire combination tools have off-center crosshairs.

Usually, they can be tweaked a bit to center the crosshairs a bit better.

Ok, thanks. I did just re-collimate once again. It's much more accurate now. Didn't have to calibrate. On the "down side" of the primary mirror reflection of the telescope tube as your seeing it thru the collimation cap, I had usually tried to adjust so it's a equal amount of space there against the right side of the site tube. I found that by adding a touch more width there to the primary reflection it seems to align better when rotating the cross hairs.

The left side of the reflection isn't the best way to go by because of the open area of the telescope tube there.

I sure hope this all makes some sense!



#20 Starman1

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Posted 30 December 2019 - 05:37 PM

Pat,

No, that doesn't make sense, since right and left can mean anything depending on where the focuser is pointing.

It sounds like you're describing having the primary reflection be slightly off center in the secondary, and that could very well be if

it is not centered under the focuser perfectly.

That doesn't mean you are not collimated, though.

If the crosshairs stay centered on the hole in the primary marker reflection as you rotate the tool, then it is likely your tool has its crosshairs centered

and that you have adjusted the tilt of the secondary correctly.

If, when using the collimation cap you see your pupil dead center in the reflection of the primary center marker, you likely have your primary properly adjusted.

If your combination sight tube + Cheshire also shows your center marker centered in the bright ring of the Cheshire reflection, you have an additional confirmation

your primary is adjusted correctly.

 

If after all that, the reflection of the primary is off-center in the secondary, don't worry about it.  It just means you have a tiny bit more illumination on one side of the field than the other.

 

It would be helpful if you could post cell phone photos of what you see through the pupils of your tools, though.



#21 patindaytona

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Posted 30 December 2019 - 06:24 PM

Pat,

No, that doesn't make sense, since right and left can mean anything depending on where the focuser is pointing.


That doesn't mean you are not collimated, though.

If the crosshairs stay centered on the hole in the primary marker reflection as you rotate the tool, then it is likely your tool has its crosshairs centered

and that you have adjusted the tilt of the secondary correctly.

If, when using the collimation cap you see your pupil dead center in the reflection of the primary center marker, you likely have your primary properly adjusted.

If your combination sight tube + Cheshire also shows your center marker centered in the bright ring of the Cheshire reflection, you have an additional confirmation

your primary is adjusted correctly.

 

If after all that, the reflection of the primary is off-center in the secondary, don't worry about it.  It just means you have a tiny bit more illumination on one side of the field than the other.

 

It would be helpful if you could post cell phone photos of what you see through the pupils of your tools, though.

I tend to describe things with some difficulty.

Starman, maybe you remember me posting quite a while back about collimation. Jeeze, the posts went on forever and i spend 100 hours in that couple weeks re-doing it!

But I am sure it's collimated very well now. I have a cheap cellphone without a card, so no photos.

It sounds like you're describing having the primary reflection be slightly off center in the secondary, and that could very well be if

it is not centered under the focuser perfectly"          Yes, that is what i meant. But it's actually NOT, off center. It seems that it's a little bit of an optical illusion when centering because I align the reflection usually by racking my focuser all the way out so it shows a thin circumference of the primary reflection and I look at the "right" side of that circumference mainly because it's just easier to visualize. I use a collimation cap for that.

But when I put in the chesire, it seemed it was slightly off, so i went back and moved the primary reflection "leftward" (as viewing thru the chesire) very slightly till it looked good in the chesire.

And when i put the collimation cap in, it DID match up.

And it was not off center afterall.

Yea, it's good. I'm sure of it. Florida here.....cloudy entire week...moon will be perfect phase tomorrow when it's clear, so I'll test it (also the high magnification of a star out of focus) but I have gone thru all of this so many time. I'm confident it's good.



#22 ButterFly

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Posted 30 December 2019 - 11:38 PM

Align one of the crosshars with the focuser for consistency.  That way, you have toward and away from the focuser on one crosshair, and perpendicular to that on the other cross hair.  It is much easier to know which direction needs to be adjusted that way.  If you can't see your focuser tube, stick a finger out over the focuser.

 

Don't look at the primary when adjusting the position of the secondary - look only at the edge of the secondary with respect to the edge of the sight tube.  Look at the center spot of the primary when adjusting the tilt of the secondary.  The position of the secondary rarely needs to be re-adjusted, but the tilt often does.  Check so you know.

 

Don't worry too much about the mirror clips.  Most commercial dobs have adequately sized secondaries so centering the secondary under the focuser by adjusting its position, then adjusting its tilt, will get you there.  If you were trying to see them with too long a tube on your combo tool, you could have backed out the focuser way too far and would never have been able to see them anyway.  On the flip side, a collimation cap may be too short to allow you to position the secondary easily, leaving too much distance between the end to the collimation cap and the edge of the secondary.  Just add a skirt to the collimation cap with the length of the skirt divided by the diameter of the collimation cap approximately at your scope's f-ratio.

 

Collimation is easy once you get the hang out it.  Position, tilt secondary, tilt primary, repeat until all agree.  Just keep checking throughout the night for best results.




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