Jump to content


Photo

Collimating the AT102 F11 Achro

  • Please log in to reply
22 replies to this topic

#1 Martin

Martin

    Messenger

  • *****
  • Posts: 426
  • Joined: 09 Sep 2005
  • Loc: South Dakota

Posted 12 September 2013 - 03:49 PM

Hi,
Recently purchased one of these used and the collimation is quite aways off. I see there are 8 little screws that screw in from the side of the cell. I was told these are for collimating the lens. How does pushing in from the side of the cell and pushing on the lenses from the side collimate the telescope? I need to tilt the objective but I don't see how these screws could do that. I have played with the screws but see no change when looking through a Cheshire. Anyway, I was hoping that someone else may have tried to adjust theirs and has more info on this.

Thanks
Martin

#2 Niklo

Niklo

    Viking 1

  • -----
  • Posts: 581
  • Joined: 29 Mar 2013
  • Loc: Bavaria

Posted 12 September 2013 - 06:36 PM

Hi Martin,
I have that 4" f/11, too. Unfortunately I have no experience to collimate it. I'll try to ask somebody who already collimated the big brother
http://www.teleskop-...info/p2229_I...

By the way what do you see when you make a startest? Is the collimation really bad?

Clear skies,
Roland

#3 Martin

Martin

    Messenger

  • *****
  • Posts: 426
  • Joined: 09 Sep 2005
  • Loc: South Dakota

Posted 12 September 2013 - 08:36 PM

Hi Roland,
Well, just received the scope yesterday, so no first light yet. I happened to check the collimation with a Cheshire and found it to be quite a ways off. Called Hands on Optics because I know he sells these telescopes. He said the screws work as a push pull combination. There are 4 sets of screws, 2 screws in each set. I would think that these act more like centering screws. Like on the old Meade ED scopes from the 90's. I don't really see how these can collimate the scope though. They push from the side and push on each element.

Martin

#4 John Huntley

John Huntley

    Viking 1

  • *****
  • Posts: 956
  • Joined: 16 Jul 2006
  • Loc: South West England

Posted 12 September 2013 - 08:47 PM

Try shining a well collimated laser collimator through the scope and see where the beam exits the objective lens. Often it's the focuser that is not aligned with the optical axis of the objective lens and the laser beam will not exit in the centre of the objective lens.

You then need to tilt the focuser to get the beam to exit more or less in the centre of the objective. Once you have done that, you can think about tilting the objective lens to address any residual collimation errors.

#5 Don Taylor

Don Taylor

    Viking 1

  • -----
  • Posts: 650
  • Joined: 12 Jul 2009
  • Loc: South Kansas

Posted 12 September 2013 - 10:00 PM

Try shining a well collimated laser collimator through the scope and see where the beam exits the objective lens. Often it's the focuser that is not aligned with the optical axis of the objective lens and the laser beam will not exit in the centre of the objective lens.

You then need to tilt the focuser to get the beam to exit more or less in the centre of the objective. Once you have done that, you can think about tilting the objective lens to address any residual collimation errors.


Agree with this - and then star test before you do anything to the objective.

#6 T1R2

T1R2

    Surveyor 1

  • -----
  • Posts: 1665
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 12 September 2013 - 10:48 PM

My thought on this is, if you can see that the focuser is tilted then it needs to be fixed, if you can't then it isn't bad enough to bother, I'd be more concerned with a misaligned diagonal, misaligned Obj. Gary Seronik wrote a collimation article in S&T awhile back and he says when he's flippin the forums and see's someone start with "first square the focuser to the ota" your in for a rough ride." I know he is talking about newt's but it can apply to refractors as well. Bottom line is don't be afraid to learn to collimate. on my scope those screws on the side are for lens centering, and to hold the position of the index marks,(not collimation) though your's could be for collimation, I would retract the dew shield and see if that black ring on the front of the scope comes off, that's where some brands collimating screws are found. Let us know when you find them so we can know if the one you turned are for centering and we can help you get that back in line as well(don't worry, its not hard at all)

#7 AlBoning

AlBoning

    Viking 1

  • -----
  • Posts: 592
  • Joined: 06 Mar 2011

Posted 12 September 2013 - 10:53 PM

I have that scope. I'm envious you've been able to use a cheshire with it as I've been unable to see a darn thing when I've tried it, but then I wasn't particularly persistent about trying to do so. I seem to remember, but don't quote me on this, that what one sees with a cheshire can be quite a ways off and doesn't make one bit of difference at the eyepiece.

BTW, with some effort I managed to get a hold of a copy of Cheshire's original article. A rather short article about using it for "squaring on" a refractor.

Cheshire, F. J., Note on an eyepiece for testing the squaring-on of telescope object glasses. Trans. Optical Society, 22, 235 (1921)

OTOH with whatever scope I have in the field it is routine for me to at least once star test during a night of observing. I sure wish my newts would test like the AT102f/11. The rings of the diffraction patterns are beautifully symmetrical, evenly spaced, uniformly illuminated, can't see how it could be better, on both sides of focus.

I'd say wait until you see a star test before messing with the objective, but do check the focuser as recommended.

#8 beanerds

beanerds

    Messenger

  • -----
  • Posts: 404
  • Joined: 15 Jul 2008
  • Loc: Darwin Australia

Posted 12 September 2013 - 10:58 PM

I agree , be very careful with those side push/pull screws , remember an article a while ago down here in Australia on our 'Ice in Space' web site an owner of a 127mm (?) triplet playing around with them and he cracked one of the lenses :bawling: .
Sad but true , be very careful and if it was me I would return it and get the manufacturer fix it , that's if it needs to be , for sure do a star test first after checking the focuser .
Brian.

#9 Niklo

Niklo

    Viking 1

  • -----
  • Posts: 581
  • Joined: 29 Mar 2013
  • Loc: Bavaria

Posted 13 September 2013 - 05:55 PM

Hi,
I want to show some pictures of the objective of my 102mm/1100 mm achromat refractor from the side that shows
the screw pairs. There are 4 screw pairs.

Posted Image

Another picture that shows the objective from the side showing 2 screw pairs:
Posted Image

from the front :
Posted Image
Clear skies,
Roland


#10 T1R2

T1R2

    Surveyor 1

  • -----
  • Posts: 1665
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 14 September 2013 - 01:31 AM

yes, those look like some collimation screws that I've seen, I would confirm that with the guys from Astronomics since their in partnership with AT, they should be able to tell you, you might be able to view a manual online for faster results hopefully.

#11 Martin

Martin

    Messenger

  • *****
  • Posts: 426
  • Joined: 09 Sep 2005
  • Loc: South Dakota

Posted 15 September 2013 - 09:54 PM

Hi everyone,
Yes those are the screws that I was referring to. I should have mentioned that my scope was purchased used and the previous owner changed focusers, so this is not the original focuser. A cheshire shows it be off quite aways. I shimmed the focuser and now the cheshire shows it almost perfect. So, while I had it out tonight i decided to see what those screws do. I tightened and loosened all of them in various sequences. I could not detect any change in the star that I was viewing at around 220x. I tried it with an out of focus star also. So, I am still curious what purpose those screws serve. They do not collimate or tilt the lens, they do push on the side of the lenses but I see no change when I do so.
I did have the scope on the moon last night and was quite impressed, was able to go past 300x and craters still showed nice detail and very little false color. No false color in the craters and just a hint of yellow on the limb. Havent had a chance to view any planets yet but have been doing a few double stars. I wonder why there is no manual to go with these scopes?

Later,
Martin

#12 T1R2

T1R2

    Surveyor 1

  • -----
  • Posts: 1665
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 15 September 2013 - 11:04 PM

Some ads that I've seen say nothing of that scope being able to collimate, usually they will say that they are, does not look like this one is, it did however come with a Feathertouch rotatable focuser, that may be why he kept it. those are probably to hold the lens index marks in place, and could possibly affect lens centering if screwed in or loosened too much, the only way to check that is to view the little dot(purple usually) in the center of a defocused star inside or outside of focus with 4-5 rings showing, you should be able to see it because its fairly noticeable and should be right in the center, not offset.

#13 T1R2

T1R2

    Surveyor 1

  • -----
  • Posts: 1665
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 15 September 2013 - 11:20 PM

I just notice that is a F/11 scope and not the F6.95 that I thought it was, so It did not come with a Feathertouch focuser, so its a focal length thats usually not able to collimate, I'm 99% certain that those screws are for holding the lenses in place

Edit: do NOT over tighten, those screws are touching directly on the lens edges, it could crack. If you did get one to tight and it affects the centering don't worry, I can walk you through getting it corrected, its not hard there are 2 ways to fix it.

#14 Agatha

Agatha

    Apollo

  • *****
  • Posts: 1262
  • Joined: 04 Jun 2012
  • Loc: Coulee Region, Wisconsin

Posted 15 September 2013 - 11:37 PM

I would confirm that with the guys from Astronomics since their in partnership with AT, they should be able to tell you, you might be able to view a manual online for faster results hopefully.


I don't think so. This confusion with the AT designation has been around for awhile. Astronomics is AT (Astro-Tech, short for Astronomy Technologies. I don't believe they have anything to do with the telescope being discussed. This 102 F11 achromatic is part of Astro Telescopes who decided to use the AT designation after Astronomics was already using it. This unfortunately does cause confusion and I'm sure the good people at Astronomics aren't crazy about it either. :crazy:

Just wanted to clarify...different telescopes.

#15 T1R2

T1R2

    Surveyor 1

  • -----
  • Posts: 1665
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 15 September 2013 - 11:45 PM

Thanks for that info Linda, no wonder I was having trouble trying to find what I was looking for :foreheadslap:

#16 Niklo

Niklo

    Viking 1

  • -----
  • Posts: 581
  • Joined: 29 Mar 2013
  • Loc: Bavaria

Posted 16 September 2013 - 08:00 AM

yes, those look like some collimation screws that I've seen, I would confirm that with the guys from Astronomics since their in partnership with AT, they should be able to tell you, you might be able to view a manual online for faster results hopefully.


Hi,
I think that the screws are for tilting/shifting the lenses but they are not pull and push screws so probably it's better not to change anything there.
Clear skies,
Roland

#17 Niklo

Niklo

    Viking 1

  • -----
  • Posts: 581
  • Joined: 29 Mar 2013
  • Loc: Bavaria

Posted 16 September 2013 - 08:08 AM

Hi everyone,
Yes those are the screws that I was referring to. I should have mentioned that my scope was purchased used and the previous owner changed focusers, so this is not the original focuser. A cheshire shows it be off quite aways. I shimmed the focuser and now the cheshire shows it almost perfect. So, while I had it out tonight i decided to see what those screws do. I tightened and loosened all of them in various sequences. I could not detect any change in the star that I was viewing at around 220x. I tried it with an out of focus star also. So, I am still curious what purpose those screws serve. They do not collimate or tilt the lens, they do push on the side of the lenses but I see no change when I do so.
I did have the scope on the moon last night and was quite impressed, was able to go past 300x and craters still showed nice detail and very little false color. No false color in the craters and just a hint of yellow on the limb. Havent had a chance to view any planets yet but have been doing a few double stars. I wonder why there is no manual to go with these scopes?

Later,
Martin

Hi Martin,
I think it's possible to shift the lenses parallel to each other so the optical axes of the lenses could be matched. So I would change too much because it's easy to make it bad.
Just be happy that everything is fine now.
Jupiter is a good test object for CA. It can be seen in the morning.
Cheers,
Roland

#18 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12966
  • Joined: 01 Feb 2006

Posted 16 September 2013 - 09:17 AM

IF they are adjustment screws, these are more likely radial centering screws. They are not usually found on long focus achromats though, and these could simpy be some kind of retention screw.

The role of these screws (f they are indeed radial adjustment screws) is to allow the lenses to be aligned so that the curves are all centered on the optical axis.

In a technical sense, any kind of optical aligment could be called "Collimation" but traditional "Push/Pull" collimation screws tilt the leneses with respoect to the optical axis.

These screws push the lenses back and forth across the optical axis.

I am going to say this: AT f/II, Collimation (tilt) is not usually critical on a refractor!

Before I go any further, I am going to say this in big screaming letters: BE CAREFUL. LENS CENTERING IS TEDIOUS WORK!

My best advice is to try to determine if you should muck around with the lens cenetering at all.

A bit of miscollimation in an f/11 refractor does almost no damage to the image for visual use.

The primary effect of tilt on an f/11 refractor will be that the focal plane is slightly titled so that if I am a CCD camera and you focus me so that one side of the field is in perfect focus, the other side might not be.

But If I am a visual observer, this will be very difficult to see unless the tilt is very bad.

That is why many long focal lenght refractors did not even come with collimation screws. The designers knew that for visual use (which is the primary use for systems like this), a little tilt does not matter.

The first thing to do is determine if there is impact on the image, and the way to do this is star test.

I would use an artificail star. If you don't have one, they are easy to make. Three or four sheets of aluminum foil on glass with a sewing needle to "Drill" a hole, then taped to the inside of a box with a hole cut in it, and a light source, palced at 30 or 40 feet (if you can reach focus).

This is not a suitable star for testing spherical aberration, but for alignment, it is fine.

Now, look at the first diffraction ring.

If the ring fairy even all the way around the Airy Disk and there is no uneven color fringing, turn off the light and leave everything alone.

Next chance that you get with good seeing at night, do the test again using a brightish star high in the sky.

Once again, for centering, you are looking more for unequal ring illumination or uneven color fringing. If you see any kind of prism effect where one side of the star has a red fringe and the other has a blue fringe, you MIGHT have a centering problem.

If this is the case, I would not touch it until I checked the warranty. If the warranty will void from fussing with it, send it back.

If not, you may want to try to use the centering screws to move the lenses as needed using the Chesire (and yes if it is bad enough you can see decentering in the Cheshire, but usually it has to be pretty aweful), but I have had bad luck using the Cheshire for this. Typically it is easier to do it with the centering screws watching the fringing.

But dude, I would not mess with this.

If you can determine that you have a centering error (chromatic fringing) ask the seller to have it adjusted.

A resource you can look for is the centering instructions for the Meade 152ED or the Meade 178ED. Lens centering was a common issue on these scopes (and yes sI owned one, and yes, I did radial centering, and yes it was very tedious).

Don't go mucking around with these screws though unless you can absolutely determine that it is needed and you are sure you won't kill your warranty.

If you can't see fringing though, and you get a good even first diffraction ring on a medium bright star, do yourself a favor and move on. At f/11, a bit of tilt in the lens stack simply doesn't hurt anything.

I would of course also check the focuser tube tilt and things like that, but don't touch those screws without understanding what they do and if it is necessary to touch them.

The most serious symptom of radial aligment issues is unven color fringing. If you don't see this, I would be very reluctant to mess with those screws.

#19 Niklo

Niklo

    Viking 1

  • -----
  • Posts: 581
  • Joined: 29 Mar 2013
  • Loc: Bavaria

Posted 16 September 2013 - 10:04 AM

The first thing to do is determine if there is impact on the image, and the way to do this is star test.

I would use an artificail star. If you don't have one, they are easy to make. Three or four sheets of aluminum foil on glass with a sewing needle to "Drill" a hole, then taped to the inside of a box with a hole cut in it, and a light source, palced at 30 or 40 feet (if you can reach focus).

This is not a suitable star for testing spherical aberration, but for alignment, it is fine.

Now, look at the first diffraction ring.

If the ring fairy even all the way around the Airy Disk and there is no uneven color fringing, turn off the light and leave everything alone.

Next chance that you get with good seeing at night, do the test again using a brightish star high in the sky.

Once again, for centering, you are looking more for unequal ring illumination or uneven color fringing. If you see any kind of prism effect where one side of the star has a red fringe and the other has a blue fringe, you MIGHT have a centering problem.

If this is the case, I would not touch it until I checked the warranty. If the warranty will void from fussing with it, send it back.

Hi Eddgie,
thank you for your advice. I'll try to make an artificial star and test my 4" f/11. If the artificial star test is too difficult I'll try to do it at a bright star at night.
Maybe I can take photos.
By the way does the effect that a star show a blue fringe on one side and a red fringe on the other side have a name?

Clear skies,
Roland

#20 Martin

Martin

    Messenger

  • *****
  • Posts: 426
  • Joined: 09 Sep 2005
  • Loc: South Dakota

Posted 16 September 2013 - 10:36 AM

I also owned a Meade 127ED at one time. It had the centering screws also but the screws pushed on a metal spacer ring, not on the lenses themselves, and yes, centering of the lenses on the old Meade ED's was a pain. I am really doubtful that these are centering screws. I do think that one could possibly pinch or damage a lens on this AT102 F11 if your not careful. I did call one of the dealers of this scope and he said those screws are for collimating, but I believe he is wrong. I would have never messed with these screws or even questioned them if I didn't have to take the lens completely out for cleaning. The previous owner tried to clean the lens before shipping the scope to me. They took a rag and wiped it across the front and back of the lens. Yes, the lens got scratched and smeared really bad. Long story short, the lens needed a really good cleaning. Anyway, that's when I noticed the screws on the side of the cell.
However, I took the scope out this morning and looked at Jupiter and was really impressed with the image. At 164x it looked fantastic, lots of detail, very little false color. Took it up 231x and still looked good. So, I am happy with the lens in this unit. But just curious why they would put those screws in on the side of the cell.

Thanks
Martin

#21 T1R2

T1R2

    Surveyor 1

  • -----
  • Posts: 1665
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 16 September 2013 - 02:22 PM

the reason you could not see any changed when you turned one is because their not collimating screws, they are for holding the lenses, and in order for it to move, the one on the other side has to be moved, applying to much pressure will surely crack the lens (or pinch the optics), also when taking the lens out for cleaning, the retaining ring has to be removed, then before the lens can be lowered over a elevator(not poked out with a finger) they have to be loosened, by several threads usually not all the way. so basically centering has to be adjusted every time the lens is removed for cleaning, but its not hard, just make sure the index marks are lined up on the edge of the lens and with a gloved fingers, make sure the lens edges are even all the way around them. when the cell is lifted back up to capture the lenses take care in not tilting them or shaking them, gently screw in the screws till they just *touch* the lens, that was the hard way (if your not used to doing it) and theres no way around having to do it if the lenses are removed from the cell for a deep cleaning, But what about if centering is off and I don't want to remove the lenses cause they already been cleaned?? easy! Place scope on the mount, find a star at the zenith, intra or outra focus until a purple dot appears( if centering is off, so will be this dot) lock clutches, retract dew shield loosen all screws but be careful not to back them out too far they are small and hard to find in the grass, then gently tap with your knuckles around the cell, view dot in center of pattern, repeat until satisfied. theres nothing to it and your not going mess anything up, I do mine once a year when I remove the cell to get to the backside of the lenses

#22 Niklo

Niklo

    Viking 1

  • -----
  • Posts: 581
  • Joined: 29 Mar 2013
  • Loc: Bavaria

Posted 17 September 2013 - 12:26 PM

Hi T1R2,
which elevator are you using for lowering the lens?
Maybe that would be an interesting youtube video to show how to remove, clean, insert and adjust again.
On the one hand that sounds not too difficult on the other hand it sounds too dangerous for me. ;)
Clear skies,
Roland

#23 T1R2

T1R2

    Surveyor 1

  • -----
  • Posts: 1665
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 17 September 2013 - 03:58 PM

an elevator is something that is taller than the lens cell, and smaller in diameter(by an inch or two) and you lower the lenses and cell over it to raise the lenses out, theres lots of info already online about it, I use a toilet paper roll with the correct amount of tp taken off, cover the cardboard tube end with a few squares of tp, just use non-powdered cleaning gloves, remove the retaining ring, loosen the small screws around the cell, and lower the whole cell and lenses over it to raise out the lenses, simple as that, make the adjustments(line up the index marks if there are any), make sure the edges of the lenses are flush(this is the lens centering part), raise cell back up the tp roll to capture the lens, keeping both lens edges to be flush with each other, and gently screwing the screws back in the sides so they just touch the lenses and doesn't push a lens out of alignment with the other(this will keep the lenses centered), install the retaining ring and your done.

Edit: if you'll notice that when the lenses are in the cell that theres really very little space between them and the cell, so their really already sorta self centered, it only sounds like you can mess it up, and just tapping on the lens cell with the scope up like I said before will get the very close, but theres no way of knowing what the lens index marks are doing when this is done, I've done it both ways but now I just remove the lenses every now and then to clean and make the adjustments when I do this, and it doesn't have to be done but one time if you don't plan on cleaning the back of the lenses ever.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics