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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Collimation Questions... new [Re: TahoeNoob]
      #5554928 - 12/05/12 12:39 AM

First off it looks like a nice scope! Flocked, nice GSO two speed focuser. Good stuff.

Hmm...I would agree with you that it appears to be short screws. Let's maybe try the ATM/DIY forums with these pictures and the situation. Maybe they have some good solutions for this issue.


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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Collimation Questions... new [Re: TahoeNoob]
      #5554933 - 12/05/12 12:44 AM

Quote:

That's a 3/8" gap between the Spider Hub & the Secondary Hub:




mine looks to be closer to an inch...maybe a little less than an inch.

Hopefully there an easy fix to fill that gap without needing new screws.


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frito
Pooh-Bah


Reged: 10/05/12

Loc: Fremont, CA
Re: Collimation Questions... new [Re: GOLGO13]
      #5554936 - 12/05/12 12:48 AM

i'm pretty sure if you make a few milk jug washers you'll get the extra distance you need and it will make fine adjustments much easier as well. i ditched my spring and made milk jug washers last weekend for my XT8. rotating and adjusting the angles are now super easy to do and i don't even have bob's knobs i'm using an allen.

on another note your secondary is A LOT farther off the holder base than my XT8's this may be a result of the GSO focuser though i have no idea.

also another thing to note do not concern your self with the shadow of the secondary mirror, it should look somewhat oval shaped and not at all centered and offset tword the primary mirror. this is completely normal. i'm surprised Jason hasn't crashed this thread yet to talk about that one


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howard929
Member
*****

Reged: 01/02/11

Loc: Low End of High Ground
Re: Collimation Questions... new [Re: frito]
      #5554942 - 12/05/12 12:53 AM

Quote:


also another thing to note do not concern your self with the shadow of the secondary mirror, it should look somewhat oval shaped and not at all centered and offset tword the primary mirror. this is completely normal.




I beg to differ. Offset towards the primary, yes but still centered and round.


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TahoeNoob
sage
*****

Reged: 10/31/12

Loc: Sierra Nevada
Re: Collimation Questions... new [Re: howard929]
      #5554960 - 12/05/12 01:09 AM

I can't say why this is going on. It's entirely possible that this is the result of the upgraded focuser. It also crossed my mind that maybe the scope was dropped, or something like that, but I don't believe that to be the case. The scope is in very good shape. No signs of abuse...

Tomorrow, if it doesn't snow (hard), I'll drive into town to see if I can find some longer screws. I think I'll try to find a longer center screw too, just to be safe. I doubt the hardware store will have what I want but there's only one way to find out.

What exactly are "milk jug" washers? I don't think a washer made from a plastic milk jug is going to do me much good... unless I start stacking washers. Would plexiglass hold up to the collimation screws? I've got some plexiglass.

In the end, I'll probably have to contact Bob's Knobs. The thing is, I think these might actually be Bob's Knobs. I was told the screws were upgraded. I'll have to go back and read the CraigsList ad again... I think it was mentioned there.



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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Collimation Questions... new [Re: TahoeNoob]
      #5554964 - 12/05/12 01:14 AM

Quote:

The tube is flocked. Could the upgraded focuser be mounted crooked




Looking at picture 3 it does look a little crooked...but hard to tell with the flocking around it. That's an area worth looking at. Check screws and fitment.


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howard929
Member
*****

Reged: 01/02/11

Loc: Low End of High Ground
Re: Collimation Questions... new [Re: TahoeNoob]
      #5554970 - 12/05/12 01:22 AM

I'm not a fan of using milk jug washers. They are made out of plastic milk containers and are inserted between the spider and the mirror stalk. They're supposed to allow for adjusting the secondary easier then without them but I found they just get chewed up by the screw ends. And it's a PITA to replace them when that happens.

Anyway. Plexi would work fine if you can shape it to be sized like the open end of the stalk and locate a hole for the center screw.

(slow typist and we noticed the same thing) That one photo of the focuser shown inside the OTA: is it the photo or is it titled to one side? Actually, I copied and pasted to a drawing program and rotated it. The focuser looks tilted but it may be the photo.

Edited by howard929 (12/05/12 01:27 AM)


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TahoeNoob
sage
*****

Reged: 10/31/12

Loc: Sierra Nevada
Re: Collimation Questions... [Re: howard929]
      #5554976 - 12/05/12 01:29 AM

I'll check the focuser in the morning. I hadn't noticed that. (My guess is that it's just the flocking, that's making it look like that.)

Right now, I'm tired. I've been fighting with this almost all day.

Thanks for the help, everybody! I'll let you know what I find out, in the morning!


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howard929
Member
*****

Reged: 01/02/11

Loc: Low End of High Ground
Re: Collimation Questions... new [Re: TahoeNoob]
      #5554980 - 12/05/12 01:38 AM

I'm heading off too. One last thought though. The bezel around the focuser hides the condition of the OTA right around the opening as does the flocking on the inside. I'm not saying you need to remove the focuser to see what the OTA looks like right around the hole. But if it is crooked, you may want to and hopefully it's not tilted.

Edited by howard929 (12/05/12 01:39 AM)


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frito
Pooh-Bah


Reged: 10/05/12

Loc: Fremont, CA
Re: Collimation Questions... new [Re: howard929]
      #5554996 - 12/05/12 02:09 AM

Quote:

Quote:


also another thing to note do not concern your self with the shadow of the secondary mirror, it should look somewhat oval shaped and not at all centered and offset tword the primary mirror. this is completely normal.




I beg to differ. Offset towards the primary, yes but still centered and round.




you are correct, it just kind of appears oval due to the offset but it is not in fact oval

here is one of Jason D's posts about it with a link to another thread discussing it.

http://www.cloudynights.com/ubbthreads/showthreaded.php/Cat/0/Number/5503304/...

OP make sure that the secondary shadow is not whats making you think its not centered, many people get tripped up by this that much i know.

Edited by frito (12/05/12 02:13 AM)


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tag1260
scholastic sledgehammer
*****

Reged: 10/07/12

Loc: Ohio, USA
Re: Collimation Questions... new [Re: frito]
      #5555224 - 12/05/12 07:44 AM

If you can't find longer screws, you can get a couple of "fender washers" and use. They're just those big round washers with a small hole.I use one under a milk jug washer on mine. I use the fender washer to protect the secondary and the the milk jug washer makes the screws easier to turn (at least in my mind).

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JLovell
scholastic sledgehammer


Reged: 01/12/10

Loc: Georgia
Re: Collimation Questions... new [Re: tag1260]
      #5555255 - 12/05/12 08:12 AM

Another thing to possibly try to make it easier to see the mirror and the edge of the peep sight against the flocking background is to put a piece of paper in there across from the focuser. You'll only see the paper around 2/3 or so of the secondary. The edge of it and the stalk will hide the rest. You are trying to center only the reflective surface, right? I'm guessing you are, but just want to make sure.

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TahoeNoob
sage
*****

Reged: 10/31/12

Loc: Sierra Nevada
Re: Collimation Questions... new [Re: JLovell]
      #5555374 - 12/05/12 09:52 AM

I looked at the focuser last night before I went to bed. It's fine. It just looks crooked because the bottom of the focuser is flat and it's sitting in a tube with a 10 inch diameter. (I think that think another possible answer to this problem is to put a shim under one edge of the focuser. I'm not sure how thick that shim would have to be and I don't like that idea though. I'd rather extend the secondary, further back.)

Yes, I'm only trying to center the reflective surface of the secondary in the eyepiece. It does get confusing though. Sometimes it's not easy to see where the mirror stops and the stalk begins. The paper trick helps a lot, but not in the area where the secondary's stalk is.

"Fender washers," I'll look for them when I go into town today. First I'm going to have to take the secondary out and get some good measurements though.

I was thinking that I could make a washer out of an old plastic cutting board. (The plexiglass idea bothers me a little bit. Plexiglass tends to crack. I don't want chipped plastic falling down onto my primary.)


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TahoeNoob
sage
*****

Reged: 10/31/12

Loc: Sierra Nevada
Re: Collimation Questions... new [Re: TahoeNoob]
      #5555404 - 12/05/12 10:11 AM

BTW, I don't have a laser collimator yet. I haven't figured out which one I want to get, or how much I'm willing to spend. What I'm using is both a 2" peephole eyepiece, and a 1.25" Orion Cheshire/sight tube combo with cross hairs. (Both eyepieces seem to be quite high quality.)

I don't think a laser eyepiece would help at this stage of the collimating process, even if I had one.

When using my "manual" collimation tools, I rock my head side to side... and center everything, below, in the center of the two extremes of paralax view. In this way, I feel like I'm centering my view down the eyepiece as best that I can.


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tag1260
scholastic sledgehammer
*****

Reged: 10/07/12

Loc: Ohio, USA
Re: Collimation Questions... new [Re: TahoeNoob]
      #5555412 - 12/05/12 10:19 AM

Just my opinion. I have a laser but just bought the Catseye from Catseye Collimation. It's nice Chelshire eyepiece. While it may take a little time to get accustomed to it, I don't think I'll go back to my laser. After lining up with my laser, the Catseye showed being still out of collimation. It only took a couple of minutes to line everything up. The nice thing about the Catseye is that it NEVER needs aligned like the laser does. I hope to get the money for the rest of their collimating tools in the future.

Like I stated in the beginning, this is only MY OPINION!!!!


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TahoeNoob
sage
*****

Reged: 10/31/12

Loc: Sierra Nevada
Re: Collimation Questions... new [Re: tag1260]
      #5555460 - 12/05/12 10:50 AM

Your opinion is, of course, welcome... and at this point, I tend to agree with you!

I don't think a laser would help me with what I'm fighting with, anyway. For me, right now, I think this is a process that I just have to go though. The good news that I think I understand collimation much better now than I did yesterday... and probably better than I would've if I had been dealing with a fancy laser "toy."

I really do think there's something, physically, wrong with my scope. No laser is going to fix this problem.

BTW, that video/link posted above is awesome! It ought to be required viewing for every new newtonian owner!

As a beginner, I tend think that every problem is "user introduced." Nothing could possibly, ever, be wrong with my scope! Oh no! Not that! I'VE gotta be WRONG! In this case, I think I was wrong. The scope IS fouled up. Can't win! LOL


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tag1260
scholastic sledgehammer
*****

Reged: 10/07/12

Loc: Ohio, USA
Re: Collimation Questions... new [Re: TahoeNoob]
      #5555481 - 12/05/12 11:02 AM

I just bought a large dob myself after only using a 4.5". There is something to be said in the long run on having problems. You won't be afraid to tear into your scope for other things now as you will have already done so.

I would check out the fender washers as I couldn't find any screws long enough THAT HAD THREADS far enough down to use. Most longer screws only have about an inch of threads and these being metric usually limits your choices in the hardware store even more. You'll need one or two almost the same size as your secondary's base. That's providing your main screw is long enough. Just put these against the secondary, under the spring, when you assemble and let the adjusting screws push against them. I also used a Milk Jug Washer as I think your screws will turn easier that when against the metal.


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JLovell
scholastic sledgehammer


Reged: 01/12/10

Loc: Georgia
Re: Collimation Questions... new [Re: tag1260]
      #5555528 - 12/05/12 11:34 AM

One other thing you could try that may help if/when you remove the secondary would be to carefully blacken the edges with a sharpie. That would make it a little easier to discern where the reflective edge ends and the side begins. It may also help to put a piece of paper of another color down the tube a little way so that it is what you see in the secondary instead of all the reflections from the primary.

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lamplight
Carpal Tunnel
*****

Reged: 09/18/12

Loc: western MA, U.S.
Re: Collimation Questions... new [Re: uniondrone]
      #5555777 - 12/05/12 02:26 PM

Quote:


http://www.andysshotglass.com/Collimating.html




Makes senseofsomemissinconcepts! Thanks


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TahoeNoob
sage
*****

Reged: 10/31/12

Loc: Sierra Nevada
Re: Collimation Questions... new [Re: lamplight]
      #5556286 - 12/05/12 07:42 PM

I'm still not collimated, but I think I solved one problem:

Today I made a plastic bushing to use as a spacer. It allowed me to center my secondary in the eyepiece. I also bought a longer center screw, so that I'd have more threads holding the secondary in place. (Better to be safe than sorry!)


The shim worked as planned, so now the three collimating screws are long enough to give me some adjustment play:


Now, on to today's problems... I think I have the scope perfectly collimated, except for the minor fact that it's blowing out the side of my OTA! I'm not quite sure where I should start, trying to fix this. I have two drawings that show what I'm seeing in my eyepieces.

One of the things that I don't understand is why it is that with the 2" peephole, I can see that the whole primary image is hitting the secondary mirror. If that's the case, why can't I see the whole image with my Cheshire Sight Tube, even if it is aimed out the side of the scope? (Both of these drawing were made without making any changes to my collimation settings.)

If it's not clear that I'm totally confused, it probably should be.

This is what I see though my 1.25" Cheshire Sight Tube, with the built in cross
hairs:


This is what I see though my 2" eyepiece:


Why am I seeing the whole primary image in one eyepiece, but not the other?

Edited by TahoeNoob (12/05/12 07:45 PM)


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