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I tried to collimate my SCT, after 2 hrs. I didnt do much.

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#1 EEBA

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Posted 27 February 2020 - 01:36 AM

I am new to the hobby, and I got my celestron 8 Se, in my previous thread,I was complaining about my telescope. I was thinking it is a telescope that doesn't produce sharp images. Most of the people that replied only spoke great things about this scope. They mentioned it could be the seeing quality or bad collimation.
After reading ed's guide to sct collimation, I tried to follow the steps to improve collimation. I put masking tape identified the 12 o clock screw, right and left screw. I took the scope outside and I pointed to capella. I used my 8-24 zoom with and without 2x barlow. I noticed the black shadow of the secondary mirror seem to be centered in the concentric circles[fresnel image], I also noticed that I am suppose to identify clearly the first 3 rings. I did but they weren't clear. They were fuzzy. Also I was looking for the Airy disk. It was never visible. Just an irregular shaped star. It makes me think the telescope is not focusing efficiently or not well collimate. But while performing the star test, the fresnel pattern look symmetrical,but blurry. I feel stuck here. What will be the next step?

#2 Tapio

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Posted 27 February 2020 - 01:43 AM

If you see black shadow centered and rings concentric then I'd say you have a pretty good collimated scope.

 

But basic stuff:

You are letting your scope acclimate about an hour before trying to use it ?

You are looking objects as high as possible ? (My personal limit is 20 degrees above horizon).



#3 CeeKay

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Posted 27 February 2020 - 01:44 AM

Is there a astronomy club in your area?  Try to reach out to them to see if someone an walk you through the process (I had problems putting the process together and got help from my local club).


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#4 EEBA

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Posted 27 February 2020 - 01:56 AM

Tapio, I used Capella. It was almost my zenith. I have the feeling it needs more collimation. The star distorts even with my 20 mm eyepiece.
Ceekay, there are cou po le here a few miles where I live in Los Angeles California. I am going to a sky party, but it will be march 21, so I dont wanna wait till then. I was thinking going back to the telescope store, but what can they do with day light.

#5 EEBA

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Posted 27 February 2020 - 02:12 AM

Is there any book about collimation that I can buy?

#6 Gary Z

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Posted 27 February 2020 - 02:17 AM

You are better off without a zoom eyepiece and use say a 13mm eyepiece.  These will be a bit more precise.  As you get apparent collimation with your 13mm, go up in magnification and check collimation again.  Of course if you can't do all of this in one night, you'll have to continue another night and also need to let your scope get thermally adjusted.  Also, be sure to always center the star after any adjustment before rechecking collimation.  

 

I have to say, if you can locate an astronomy club near you, even if you need to travel some, having a more experienced person show you how to collimate would be best and then after going through that, you'll be more at ease when you feel you have to collimate down the road.

 

Gary


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#7 Astro-Master

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Posted 27 February 2020 - 02:45 AM

You said you live in the Los Angeles area, I live in San Diego, the seeing lately has been poor in our area.  Before you go messing too much with collimation, it would be wise to have someone with experience look at your scope.

 

It may be just the poor seeing, or the scope has not cooled enough for a good view.  Try looking at a land object like a telephone poll about 100 yards away during the day, and see if you get a good image.  Don't use your lowest power or you may see the dark shadow of the secondary mirror.

 

If you get a good image during the day, let your scope sit outside in the shade for a couple of hours to cool, then try it on the moon.  If the image looks good at low power, but not at high power, it maybe just bad seeing.



#8 akvik

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Posted 27 February 2020 - 02:58 AM

I am new to the hobby, and I got my celestron 8 Se, in my previous thread,I was complaining about my telescope. I was thinking it is a telescope that doesn't produce sharp images. Most of the people that replied only spoke great things about this scope. They mentioned it could be the seeing quality or bad collimation.
After reading ed's guide to sct collimation, I tried to follow the steps to improve collimation. I put masking tape identified the 12 o clock screw, right and left screw. I took the scope outside and I pointed to capella. I used my 8-24 zoom with and without 2x barlow. I noticed the black shadow of the secondary mirror seem to be centered in the concentric circles[fresnel image], I also noticed that I am suppose to identify clearly the first 3 rings. I did but they weren't clear. They were fuzzy. Also I was looking for the Airy disk. It was never visible. Just an irregular shaped star. It makes me think the telescope is not focusing efficiently or not well collimate. But while performing the star test, the fresnel pattern look symmetrical,but blurry. I feel stuck here. What will be the next step?

My best collimation setup is an artificial star, no doubt. I put a small led lamp right next to the telescope, pointing towards a tiny metal ball bearing 8 meters in front. Then I quitely, in my own time, collimate the socks off my C8.
 


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#9 james7ca

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Posted 27 February 2020 - 03:36 AM

Yes, the seeing conditions in San Diego were pretty bad on the night/morning of Feb. 25/26, but it was a little better the night before. In either case, you need a night with fairly good seeing to do a decent job on collimation. Also, using an artificial star only works if you live in an area that has stable air near to the ground (like over grass or an open field). So, if the light path goes over any man-made structures (houses, streets, sidewalks, etc.) then you may still have problems (even if you wait hours after dark to allow things to cool).

 

That said, SOME collimation even under less than ideal conditions is usually better than NONE (unless you just happen to be lucky and get a scope that is already well collimated).



#10 aa6ww

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Posted 27 February 2020 - 04:28 AM

Unfortunately, the last thing you should ever do with a brand new scope is try to collimate your optics. Sounds like you were getting the correct advice from the place where  you bought your scope.

 

Beware of too many people out here making you think you have to adjust the optics of your scope. In most cases, you should never have to adjust your optics ever, on a brand new scope. Especially if you picked it up at a local store.  People out here are quick to give you advise on screwing up the optics on your new telescope without first helping you understand your situation clearly.

 

To me, it sounds like your scope is collimated properly. Leave the optics alone and start focusing on the real issues you are dealing with. Sounds like you are experience either bad seeing conditons or you are looking through an over head jet stream. This is assuming you are letting your scope acclimate outside, and in our current California conditions should require about an hour outside before your views become very crisp. If you are looking at Venus, I have a feeling you are not giving your scope enough time outside to let it fully acclimate. 

 

If youre in Los Angeles, use the clear sky clock from your area to check for seeing conditons. 

 

http://www.cleardark...LAXCAkey.html?1

 

Learn how to read that chart, or whatever clear sky Chart is closest to your location. This should always be something you reference every single day you plan to go out with your scope. This will tell you at a glance what to expect out of your optics before you even go out.

 

Also, check for overhead jet streams. If your location has a big jet stream passing over your area, this will surely effect how sharp your optics will be on any given night. The exception will be that small aperture scopes, like your 70mm scope, will probably give you sharper performance.

 

https://www.wundergr...wind/jet-stream

 

An 8" SCT is not a grab and go scope. You have to let it acclimate properly. Look at galaxies or planetary nebula's for the first hour or so. Things should clear up nicely.

 

Finally, you wont ever need to wrap your scope to help it acclimate faster, Never. California never gets that cold. Especially now, most of our nights are going to be in the high 40's or higher. 

 

You've explained your optics perfectly in your opening message. Anyone with even the slightest bit of experience should know that your optics sound just fine. "Fuzzy" is not a collimation issue, your stars looking like comets  as you focus is a collimation issue. "Fuzzy" sounds like seeing condition issues.

 

Just put a dew shield over the front of your scope, and give it time to acclimate. Just remember, if it was sharp one day, its going to be sharp again. Nothing is more valuable then experience in situations like this.

 

...Ralph


Edited by aa6ww, 27 February 2020 - 05:17 AM.

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#11 Cali

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Posted 27 February 2020 - 04:32 AM

This may help, or at least give you something to search on. Its long winded but applies to your scope.

 

Best of luck.

 

- Cal


Edited by Cali, 27 February 2020 - 04:37 AM.


#12 epee

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Posted 27 February 2020 - 08:30 AM

Chances are, your scope was adequately collimated when you bought it. That is beside the point now.

 

I hate collimating an SCT, but at least I don't have to do it often.

 

When I do, I cheat. I use an artificial star. You can build one, but you can buy this one:  It's overpriced for what it is, but still not expensive enough to not be worth the saved time.

 

If you have a large indoor area you might be able to work inside, which is ideal. If not, wait until nightfall, let your scope acclimate for at least an hour and then set the artificial star far enough away that you can bring it to focus. Get comfortable but remember, you'll be up and down a lot so don't trap yourself in a chair with arms. This lets you work in relative comfort on a target that isn't moving and isn't experiencing a lot of atmospheric aberration. You can even collimate when it's cloudy.

 

Take your time, be very careful not to scratch your optics. Loosen, then tighten, starting with a moderate magnification and working your up to crazy high magnification; as much as you can muster. Once you have alignment, continue to tighten while holding that alignment until the screws are as tight as you can manage with hand tools; this will insure that you don't have to do it again for a very long time.

 

Your views of the planets will really thank you for it.



#13 WadeH237

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Posted 27 February 2020 - 08:57 AM

Part of the issue is that Capella is way too bright to do fine collimation.

 

It's fine to get started, but once the out of focus donut looks concentric, you should slowly move closer to focus while checking for concentricity.  As you get closer to focus, dimmer stars (still donuts) will start to appear.  You should pick a much dimmer one and center it.  Keep moving a bit closer to focus and checking for concentricity.  Each time you get a bit closer to focus, it will reveal a smaller amount of error.

 

Also, it is critical that any time you check to see if the rings are concentric, the star you are using must be absolutely centered in the field.  This is hugely important, as when the scope is correctly collimated, stars that are not in the center will show a bit of non-concentricity.  For example, if you use a field with lots of stars, a slight defocus will show that any stars not in the center of the field will be a bit non-concentric, with the error of each star oriented towards the center of the field.  Only a star at the center will be perfectly concentric.

 

Also, as has been mentioned, the scope needs to be fully acclimated.  I would suggest making sure that it's been out under the night sky for at least two hours before checking for collimation.  And finally, if you are in an area with lots of pavement and houses, the local seeing might be pretty poor until many hours after dark.  All the pavement and rooftops heat up during the day, and then radiate that heat back after dark.

 

And finally, I've not done much observing that far south, but I had a friend from Phoenix who used to come up to the Pacific Northwest to do observing because our seeing here tends to be better.  He said that the jetstream could really soften the views.  If that's the case in Los Angeles, then you might be expecting more than the conditions will deliver in terms of sharpness.  The focal length of your C8 is pretty long at 2000mm.  I find that I like to use somewhat longer focal length eyepieces with it.  I think that something like the Panoptic 24 is a fantastic match for that scope.  If you are using 8mm (even without a barlow), you'll need pretty good seeing to get a sharp image at that magnification.  It's fine for doing collimation, but you'll find the images more pleasing at the 24mm end of the zoom eyepiece.

 

I hope that this helps.


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#14 aa6ww

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Posted 27 February 2020 - 11:55 AM

pages 50-52 describe how to collimate your SCT:


https://s3.amazonaws...em11097inst.pdf



...Ralph


Is there any book about collimation that I can buy?



#15 Jeffmar

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Posted 27 February 2020 - 01:04 PM

There have been a lot of good points discussed so far. This is my list, most of which have been discussed already.

  1. ​Let the scope reach ambient temperature. It might take an hour or more.
  2. Don’t expect to get good collimation if seeing isn’t good. turbulence makes it very difficult.
  3. Pick a star that is bright enough to see well while using a higher power eyepiece, but not so bright is creates glare.
  4. That star needs to be at least 20-30 degrees above the horizon. I like more than 30 degrees
  5. Start with a lower power eyepiece and work your way to a high power eyepiece.
  6. Turn the collimation screws very slightly with each adjustment. Even a quarter turn can throw collimation way off.
  7. With each adjustment center the star in your scope again.
  8. Be patient. Sometimes I have to make fine adjustments even after I think I got it the first time. 
  9. The screws need to be tight enough to keep the secondary mirror from moving over time. Just be careful not to strip the screw heads or threads with too much torque.
  10. Ralph has a good point about not messing with collimation when the scope is new. I have bought several sct scopes and struggled to get collimation back to where it was in the first place when I messed with it.
  11. After a good collimation your scope should stay that way for months, at least.

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#16 Don W

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Posted 27 February 2020 - 01:09 PM

Unfortunately, the last thing you should ever do with a brand new scope is try to collimate your optics. Sounds like you were getting the correct advice from the place where  you bought your scope.

 

Beware of too many people out here making you think you have to adjust the optics of your scope. In most cases, you should never have to adjust your optics ever, on a brand new scope. Especially if you picked it up at a local store.  People out here are quick to give you advise on screwing up the optics on your new telescope without first helping you understand your situation clearly.

 

To me, it sounds like your scope is collimated properly. Leave the optics alone and start focusing on the real issues you are dealing with. Sounds like you are experience either bad seeing conditons or you are looking through an over head jet stream. This is assuming you are letting your scope acclimate outside, and in our current California conditions should require about an hour outside before your views become very crisp. If you are looking at Venus, I have a feeling you are not giving your scope enough time outside to let it fully acclimate. 

 

If youre in Los Angeles, use the clear sky clock from your area to check for seeing conditons. 

 

http://www.cleardark...LAXCAkey.html?1

 

Learn how to read that chart, or whatever clear sky Chart is closest to your location. This should always be something you reference every single day you plan to go out with your scope. This will tell you at a glance what to expect out of your optics before you even go out.

 

Also, check for overhead jet streams. If your location has a big jet stream passing over your area, this will surely effect how sharp your optics will be on any given night. The exception will be that small aperture scopes, like your 70mm scope, will probably give you sharper performance.

 

https://www.wundergr...wind/jet-stream

 

An 8" SCT is not a grab and go scope. You have to let it acclimate properly. Look at galaxies or planetary nebula's for the first hour or so. Things should clear up nicely.

 

Finally, you wont ever need to wrap your scope to help it acclimate faster, Never. California never gets that cold. Especially now, most of our nights are going to be in the high 40's or higher. 

 

You've explained your optics perfectly in your opening message. Anyone with even the slightest bit of experience should know that your optics sound just fine. "Fuzzy" is not a collimation issue, your stars looking like comets  as you focus is a collimation issue. "Fuzzy" sounds like seeing condition issues.

 

Just put a dew shield over the front of your scope, and give it time to acclimate. Just remember, if it was sharp one day, its going to be sharp again. Nothing is more valuable then experience in situations like this.

 

...Ralph

I could not agree more. I would never tell a newbie that their SCT may be out of collimation and that they should try to fix it. NEVER!!


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#17 MrJones

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Posted 27 February 2020 - 01:11 PM

For finest collimation you need to be able to see the first diffraction ring when focused and have the star perfectly centered. As per above you need really good seeing and an acclimated SCT. The best seeing before midnight is often around dusk FYI. I use a 5mm EP for collimating my C8 whether I am using the focused method or defocusing with good seeing. If the seeing is not so good (often) I use a 10mm EP. It's pretty simple, you don't need a book. Just remember to defocus a small amount if using that method, just enough to see the beginning of the rings.



#18 carolinaskies

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Posted 27 February 2020 - 03:29 PM

This winter season has seen some of the worst jet stream inconsistency across the US. On top of this in your area unless you are observing on the coastline you're going to likely have severe heat plumes from Los Angeles metro.  It's just a fact of life out there.  This means you observe at lower powers on the nights when seeing is less than ideal and hold off putting higher magnifications until the skies permit it. 

I live in South Carolina and we've had perhaps a handful of days in three months where not only was the weather cooperative but the actual seeing was reasonable. Most of the time even with non-cloudy skies the jet stream has been killing any high power viewing.  

So, this new scope, if you're getting a good centered secondary leave it be until you get better skies and a seasoned SCT owner who can judge if you need any adjustments. 



#19 EEBA

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Posted 27 February 2020 - 04:32 PM

New updates.
I called the telescope store and explained what bothers me. The owner told me just bring it and we take look. In less than 5 min kenny,(store man). Look through an open door to a light pole. He said something is funny.Then he tried to remove the part the holds the diagonal in n the back focuser. He said it wasn't fitting properly. He reached and put another brand new same part back to the focuser. This time he said it looks good. According to him, it was the problem. And he promised me the telescope is aligned. I will be able to see the airy disk. I was so happy for the news that I bought a focal reducer. I will be working the next 4 nights beginning tonight, so I won't be able to test it for a few days.
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#20 Asbytec

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Posted 27 February 2020 - 07:10 PM

I could not agree more. I would never tell a newbie that their SCT may be out of collimation and that they should try to fix it. NEVER!!

Well, if it's not out of collimation based on their description of the problem, that's fine. But every SCT owner, in fact everyone who owns a scope that can be collimated, aught to know how to collimate it and not be afraid to collimate it. Otherwise they could be stuck with perpetual blurry views when, in fact, collimation is so important to a good clean view. I guess, when appropriate, I would always tell a newbie how to collimate his scope. 

 

In this case, when someone complains of a blurry view and difficulty coming to a clean focus, then collimation is one of the factors to consider. Along with the other usual suspects like seeing, thermals, and poor optics. Which is why so many posters brought up these usual suspects as potential causes. 

 

It's true, "fuzzy" diffraction rings are most likely not caused my miscollimation, but they are concerning in terms of potential optical issues. Or seeing or thermal instability. And all of these can cause soft images passing through or in focus. So does miscollimation. So, these are the usual suspects when someone complains about their images not coming to sharp focus or not seeing an Airy disc at high magnification. 

 

I just hope the diagonal repair, not fitting correctly, fixed the OP's issues with his scope. I'd be curious to know if it is fixed and, really, how that fixed it. If it fixed the fuzzy diffraction rings issue. 


Edited by Asbytec, 27 February 2020 - 07:13 PM.


#21 EEBA

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Posted 27 February 2020 - 08:19 PM

Asbitec, I agree. Sooner or later i have to learn and collimate my scope. The man in the store said that the piece of the telescope not fitting properly was causing the diagonal mirror to be misaligned qnd caused the problem. His analogy was ' it is like you are driving your car with one flat tire. I will have to wait a few days to test it
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#22 Don W

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Posted 27 February 2020 - 08:29 PM

I agree that people should know how to collimate their scopes. I disagree that it's the first thing a new owner should do.


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#23 Asbytec

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Posted 27 February 2020 - 09:02 PM

I agree that people should know how to collimate their scopes. I disagree that it's the first thing a new owner should do.

I can agree with that. 


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#24 Asbytec

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Posted 27 February 2020 - 09:11 PM

The man in the store said that the piece of the telescope not fitting properly was causing the diagonal mirror to be misaligned qnd caused the problem. His analogy was ' it is like you are driving your car with one flat tire. I will have to wait a few days to test it

Yes, it sounds like it may have been causing some 'misalignment', which is ironic because that is what 'collimation' is. So, I'm a bit confused. lol.gif

 

On a deeper level, I am not sure how a tilted flat mirror can cause misalignment. We simply collimate to compensate for any tilt deviation, I think anyway. Maybe it can, need to think that through. But, now if the diagonal mirror, itself, was in bad shape, then you can get "fuzzy" rings. 

 

So, just have to wait and see because it apparently was not a collimation or alignment problem, yet it was fixed by better alignment. Weird. I'm kind of stumped on that one. The flat tire analogy doesn't help...me. smile.gif  


Edited by Asbytec, 27 February 2020 - 09:12 PM.


#25 aa6ww

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Posted 27 February 2020 - 11:32 PM

I wonder if he just replaced the 1.25" visual back? I don't recalling if the threaded back with the SCT threads is even removable. What else could he have replaced so quickly, a defective diagonal? Maybe so? The issue doesn't sound like the visual back was cross threaded.

 

Hopefully it all works but this sure is confusing, especially of star tests looks good.

 

...Ralph


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