how and why I collimated - Reflectors - Cloudy Nights (2023)

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

My new 3 MM eyepiece came. It hardly worked. I switched to my 6 MM. Now it's performing bad. I looked down the focuser. Huh? It was off. The oval mirror was loose, too. There's a center Phillips screw in the center of the spider. Loosen it first to adjust? Nope. The whole barrel and oval mirror spun. I straightened and gently tightened it. Folks, don't touch the center screw. The Allen's outside, were loose. 5/64ths fit. I gently fiddled both loosening and tightening. Looking down the focuser, the innermost tube reflection said it all. Swing your view around. I gently tightened the Allens. Now the eyepieces work again. It's not hard to collimate.

Edited by Philip Jodry, 27 January 2023 - 12:00 PM.

• SoCalPaul and photomagica like this

RoofMonkey911

Ranger 4

• 
• 
• Posts: 327
• Joined: 22 Jun 2022
• Loc: Palmetto, Florida

So you center spotted your primary?

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

Nope. When you look down the focuser, you see your eye in the center. Swing your head around and you start to see the tube you're looking down. Keep doing it and you will figure out how the oval mirror is sitting.

• photomagica likes this

RoofMonkey911

Ranger 4

• 
• 
• Posts: 327
• Joined: 22 Jun 2022
• Loc: Palmetto, Florida

Nope. When you look down the focuser, you see your eye in the center. Swing your head around and you start to see the tube you're looking down. Keep doing it and you will figure out how the oval mirror is sitting.

Not very accurate, but hey… if it works for you, that’s all that matters.

Just curious though.. Is there some reason you haven’t center spotted the primary and used a Cheshire, sight cap etc.. to get the best collimation you can?

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

I'll make a Cheshire and try it someday. The rear mirror? It's like my cat sleeping on a windowsill. I don't bother it.

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

Another way to put it is my mirror is like Big Julie's dice with no spots, in Guys and Dolls.

rblackadar

Messenger

• 
• 
• Posts: 459
• Joined: 01 Mar 2019
• Loc: Northern California (Mt. Tam)

A center spot would be for collimating the primary mirror (with a Cheshire or collimating EP) which you really want to do, to avoid bad coma. You've made your scope usable, but very likely you could make it sharper by tweaking the primary.

Alternatively you could use a laser collimator for the primary, but even then, a center mark can be helpful.

That said, of course you want the secondary to be right, so you should adjust that first. (Especially if it's loose and not pointing toward the primary at all!) For most purposes it's good enough just to eyeball it, as you did. As for the center screw, it's for adjusting the secondary's longitudinal position -- should that be necessary -- and for locking in your adjustments when you are done. You want it to be firm but not overtight.

• RoofMonkey911 likes this

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

If my rear mirror had adjustments, I could just remove the front spider ring with 3 screws, lay a piece of cheesecloth on the opening, and crank the screws. I'm seeing and reading that there are many ways to collimate both ends of a telescope.

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

Jake...small optics on YouTube, points his telescope at a star and throws it out of adjustment. The star will turn into concentric rings. If the big mirror is off, the rings will pinch.

RoofMonkey911

Ranger 4

• 
• 
• Posts: 327
• Joined: 22 Jun 2022
• Loc: Palmetto, Florida

Found this out about your model scope… interesting….

”NOTE: The 1145PS telescope has a non-collimateable primary mirror which is collimated during manufacturing. Some adjustment can be made to collimation with the secondary mirror but we have found, as long as the scope arrives to you in collimation then it holds collimation very well over time.”

briansalomon1

Surveyor 1

• 
• 
• 
• Posts: 1,563
• Joined: 21 Jul 2018
• Loc: Oxnard CA

There is a way to get your collimation alignment and secondary offset right. It makes a stunning difference.

TayM57

Surveyor 1

• 
• 
• Posts: 1,684
• Joined: 15 Nov 2012
• Loc: Ten-Forward, U.S.S. Enterprise NCC 1701-D

Just so that using the correct terminology is clear to the OP:

Oval mirror = secondary mirror

Rear mirror = primary mirror

The faster the scope, the harder it is to collimate by eyesight alone. I highly recommend getting Vic's book. I also recommend getting the Glatter collimation system. I have the Glatter laser and tublug. Makes collimating at night easy.

I also have the Catseye sighttube, the cheshire and the autocollimator.

But for a novice like the OP, I'd recommend the glatter laser + tublug.

• Waynosworld likes this

TayM57

Surveyor 1

• 
• 
• Posts: 1,684
• Joined: 15 Nov 2012
• Loc: Ten-Forward, U.S.S. Enterprise NCC 1701-D

Found this out about your model scope… interesting….

”NOTE: The 1145PS telescope has a non-collimateable primary mirror which is collimated during manufacturing. Some adjustment can be made to collimation with the secondary mirror but we have found, as long as the scope arrives to you in collimation then it holds collimation very well over time.”

If the primary is non-collimateable, my $$$ says it is probably not properly supported or pinched.

• RoofMonkey911 likes this

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

Terminology: I call the secondary mirror the oval and the primary the big mirror so the most new people catch on. When I alternate, they put the picture together. My oval secondary went way off with loose adjusters so I started with coarse adjustments and finished with teeny tiny turns of the Allen key. My telescope is purring, now.

SteveG

Voyager 1

• 
• 
• Posts: 11,842
• Joined: 27 Sep 2006
• Loc: Oceanside, CA

Terminology: I call the secondary mirror the oval and the primary the big mirror so the most new people catch on. When I alternate, they put the picture together. My oval secondary went way off with loose adjusters so I started with coarse adjustments and finished with teeny tiny turns of the Allen key. My telescope is purring, now.

All Secondaries are oval and all Primaries are larger than the secondary.

The center screw on the secondary hub is a critical part of your secondary placement, but has nothing to do with tilt.

There are 3 steps to properly collimate a Newtonian:

1. Secondary position and rotation - (done with a site tube tool). This step ensures that the secondary is centered under the focuser, and not rotated away from the focuser axis.

2. Focuser Axis - often called secondary tilt - done with a site tube with crosshairs, or a thin beam laser. (these require a primary center spot).

3. Primary Axis - often called primary tilt - done with a collimating cap, or a true Cheshire, or a barlowed laser technique.

Of the 3, #3 is most important.

Many beginners do not realize that the secondary center screw and tilt screws work against each other - push me, pull me. When done with alignment, you want them very tight.

Additionally, your spider vanes should be in a straight line across the tube, and perpendicular to the sky. They should also be very tight.

RoofMonkey911

Ranger 4

• 
• 
• Posts: 327
• Joined: 22 Jun 2022
• Loc: Palmetto, Florida

All Secondaries are oval and all Primaries are larger than the secondary.

The center screw on the secondary hub is a critical part of your secondary placement, but has nothing to do with tilt.

There are 3 steps to properly collimate a Newtonian:

1. Secondary position and rotation - (done with a site tube tool). This step ensures that the secondary is centered under the focuser, and not rotated away from the focuser axis.

2. Focuser Axis - often called secondary tilt - done with a site tube with crosshairs, or a thin beam laser. (these require a primary center spot).

3. Primary Axis - often called primary tilt - done with a collimating cap, or a true Cheshire, or a barlowed laser technique.

Of the 3, #3 is most important.

Many beginners do not realize that the secondary center screw and tilt screws work against each other - push me, pull me. When done with alignment, you want them very tight.

Additionally, your spider vanes should be in a straight line across the tube, and perpendicular to the sky. They should also be very tight.

But if there are no collimation screws for the primary…. I’m wondering WHY they did that on that particular model? Weird to me.

TayM57

Surveyor 1

• 
• 
• Posts: 1,684
• Joined: 15 Nov 2012
• Loc: Ten-Forward, U.S.S. Enterprise NCC 1701-D

But if there are no collimation screws for the primary…. I’m wondering WHY they did that on that particular model? Weird to me.

Likely because it would be cost prohibitive to manufacture proper cells. Much cheaper to just glue or clip a mirror on a piece of wood or plastic and call it a day.

• RoofMonkey911 likes this

Philip Jodry

Ranger 4

• 
• 
topic starter
• Posts: 303
• Joined: 26 Dec 2022

The glued in primary big mirror is a clear fork in the road for factory telescopes. The rear cap can come off any number of times. It's like my Farberware coffee pot. Just a better way to do it.

swmavocet

Lift Off

• 
• 
• Posts: 24
• Joined: 27 Aug 2017

Thank you all for this timely discussion. I'm trying to verify my new (used) 15" f/4.2 is collimated the best it can be. Up until now I've been using a cheap laser but I'm seeing a lot of coma in stars and plants won't focus to round discs. So today I dug into the non-laser fundamentals described here and other help chats. Immediately I found the secondary not centered in the focuser tube. See a photo of what I found here : https://drive.google...?usp=share_link

My rough measurements indicate I need to shift the holder upward toward the spider about 0.25" to center the mirror. Since I have no threads left on the main holder bolt to achieve this, the only way I see to do this will be to shift the entire spider assembly out toward the truss-scope "tube" opening by 0.25".

Question: I entered my system data into a web-based secondary offset calculator and the result said to offset toward the primary by around 0.22" That's seems to be the position I found today! So I'm confused.. Do I center the mirror in the focuser tube for collimination...or do I leave it where it is because it needs to be offset out-of-center toward the primary? I had never heard of 'secondary offset' until today.

Thanks,

Steve

Vic Menard

Cosmos

• 
• 
• Posts: 9,364
• Joined: 21 Jul 2004
• Loc: Bradenton, FL

Question: I entered my system data into a web-based secondary offset calculator and the result said to offset toward the primary by around 0.22" That's seems to be the position I found today! So I'm confused.. Do I center the mirror in the focuser tube for collimination...or do I leave it where it is because it needs to be offset out-of-center toward the primary? I had never heard of 'secondary offset' until today.

When you "center" the secondary mirror under the focuser, the offset will be correct, and you'll be able to see it in the reflection of the secondary mirror relative to the reflection of the underside of the focuser.

I annotated your image (even though I suspect that you took the image with a handheld camera above the empty focuser drawtube). The light blue outer circle is the bottom edge of the focuser drawtube and the light blue cross hairs show the center of the focuser. The green ellipse is your secondary mirror (the green cross hairs show the major and minor axes of the ellipse). The red circle is the optimal position for the secondary mirror.

• SteveG likes this

SteveG

Voyager 1

• 
• 
• Posts: 11,842
• Joined: 27 Sep 2006
• Loc: Oceanside, CA

Thank you all for this timely discussion. I'm trying to verify my new (used) 15" f/4.2 is collimated the best it can be. Up until now I've been using a cheap laser but I'm seeing a lot of coma in stars and plants won't focus to round discs. So today I dug into the non-laser fundamentals described here and other help chats. Immediately I found the secondary not centered in the focuser tube. See a photo of what I found here : https://drive.google...?usp=share_link

My rough measurements indicate I need to shift the holder upward toward the spider about 0.25" to center the mirror. Since I have no threads left on the main holder bolt to achieve this, the only way I see to do this will be to shift the entire spider assembly out toward the truss-scope "tube" opening by 0.25".

Question: I entered my system data into a web-based secondary offset calculator and the result said to offset toward the primary by around 0.22" That's seems to be the position I found today! So I'm confused.. Do I center the mirror in the focuser tube for collimination...or do I leave it where it is because it needs to be offset out-of-center toward the primary? I had never heard of 'secondary offset' until today.

Thanks,

Steve

You don't have any tools or means to measure your offset - and like Vic stated it's a thing that just "happens" when you do everything right.

Offset is simply moving the secondary up or down the main tube, not to or from the focuser (in your case).

Any low-cost collimating tool that has a peephole will do this job.