139 replies to this topic

[MikeTahtib]

Do NOT start taking your mirror out or taking things apart just yet.  To see if your mirror is binding, just try to lift the mirror from behind.  A gentle but firm push, slow and steady, on the back of the mirror glass is all that's needed. the mirror should be able to lift at least a tiny bit off its pads, and swing around a bit on its sling.  If it's working properly, you will see how the mirror cell adjusts to support the mirror.  It will shift a bit under the weight of the mirror.  Your mirror is kind of heavy (maybe 12 pounds?), so I recommend doing this with the scope pointing close to horizontally, so you're not trying to lift the weight of the entire mirror.  It should swing away from the pads, supported by a sling that wraps around the bottom half of the mirror. If it can't be pushed away from the mirror cell support pads, it may very well be bound up by the safety mirror clips.  

 

The mirror clips are not really used during telescope use.  They are there to prevent the mirror from falling out of the scope during shipping, transport, or some calamity.  That is why they should be a little bit above the surface of the mirror.  There to catch the mirror if something goes wrong, but to stay out of the way during normal use.  Kind of like a spotter for a gymnast.

 

If you find the mirror is held solidly in place, spend some time studying the mount to understand better how it works.  Also, seek advice on assembly/disassembly from the place you bought the scope from.  Most telescope stores should be helpful with this type of thing.

 

My telescope has felt pads on the cell, and I was having some problems.  Someone showed me this trick, and showed me how the felt had become stuck to the back of the mirror, and was causing a bit of distortion.  

[Playa17bk]

Hi Russell, not that I can remember, I seem to remember the stars being round, just not in focus. I'm going to bring her out tonight and really focus on the shapes of the stars to make sure.

Thanks Mike, I'll try your advice first to see if it moves.

[Russell Swan]

Hi Russell, not that I can remember, I seem to remember the stars being round, just not in focus. I'm going to bring her out tonight and really focus on the shapes of the stars to make sure.

Thanks Mike, I'll try your advice first to see if it moves.

If your stars are nice and round then the clips are not part of any problem. If they were tightened down, they would “pinch” the mirror, creating a slight distortion in its shape. With 3 clips you would see a subtle triangle shape to medium bright stars. If you don’t then leave the clips alone. 
 

Telescopes focus light into a diffraction pattern where most of the light should be centered into a little ball. That little ball is what we regard as being the star. Some of the light will bleed off into rings surrounding the central “star”. They may be barely noticeable. The spikes you see on the stars are additional diffraction caused by the secondary mirror spider intruding on the light path. It is normal in a Newtonian. 

 

If your stars are not perfectly round, in and out of best focus, in the very center of the field of view, then some aberration is going on in the optical train, which includes your own eyes. 
 

Edited by Russell Swan, 28 February 2025 - 11:34 AM.

[Bulldawg54]

One item I haven’t seen mentioned is that the AD12 comes with a 2” 30mm eyepiece, and a 35mm extension for the focuser. The extension is provided to allow focus with 2” eyepieces. Are you removing the extension when using the Plössl eyepiece? I’m not able to get a sharp focus if using the extension with 1.25” eyepieces. Just a thought, I wanted to make sure you have all the bases covered.

[Playa17bk]

Russell, I'm definitely going to focus on the star shapes really closely. I completely agree, if there is no need to, I do not want to remove the mirror.

[Playa17bk]

Thanks Bulldog, yes, I tried that extension tube the first night out, didn't see any difference so its been in my eyepiece case ever since then. But I do like the fact we are thinking of everything we can, good post.

[rrpallechio]

One of the easiest double stars to see is Mizar, the second star in the handle of the Big Dipper. Try it with a pair of binoculars, you should be able to resolve it easily. Then try it with you Dob.

If you can resolve the two stars of Mizar, try Almach next. Not because it is easy (it is) but because it is beautiful.

[JOEinCO]

It still kinda sounds like collimation to me. The "cross shaped glow" sounds like more than just spider vane diffraction spikes, especially if you are seeing it on more than just the planets.

 

You say you've used a laser, but what do stars actually look like? Point the scope at Polaris and tell us what you see. As you slide to either side of best focus, does the cross shaped glow shift back and forth 90°? 

 

Then just barely defocus Polaris and describe the pattern you see. Do not grossly defocus to "the big donut", that's too far. You just want it barely defocused. You should see something like this with the central Poisson Spot bright dot visible and perfectly centered at the highest power you can give it: 

.

[MikeTahtib]

One other thing I just thought of, if you do find the mirror is binding against the clips, you can probably create some distance by backing out all the collimation bolts by some amount, maybe 3/8" each (I hope someone more familiar with the Apertura comments here, though, as I am not familiar with the specifics of this telescope), then recollimate using only 2 of the 3 bolts, if possible.  Once you get collimation, without any of the bolts near the end of their range, you should always be able to collimate using only 2 bolts.  This is assuming the 3d bolt doesn't move at all.  The reason for this is to ensure the mirror stays in the same position, and you don't inadvertently walk the mirror up or down the tube on the collimation bolts.

[Playa17bk]

Thanks rrpallechio, I'm definitely going to put those on the list

[Playa17bk]

JOEinCO, this is great advice, everything I read about the star test told me to de focus all the way big white donut with black in the middle. I'm definitely going to try what you suggested, thank you.

[Playa17bk]

Mike, this was talked about in another post and I tried it, it threw off collamination big time when I did it. I use the barlow laser method for the primary and can get it cenetered easy. When I tried leaving the tightening bolts barley lose or one not tight at all, I couldn't get the collamination to focus. Good thought though.

[Playa17bk]

Literally the day I started this post and got so much amazing info from amazing people, the clouds rolled in. It has been cloudy for three nights now and the weather man says rain is on the way We never have rain, so looks like the astronomy gods have been reading this post too and are messing with me now. I can't wait for things to clear up and try everything suggested. You guys are awesome, keep them coming, I'm really excited now to get back out there under stars, thank you everyone

[MikeTahtib]

Mike, this was talked about in another post and I tried it, it threw off collamination big time when I did it. I use the barlow laser method for the primary and can get it cenetered easy. When I tried leaving the tightening bolts barley lose or one not tight at all, I couldn't get the collamination to focus. Good thought though.

When you drop the primary down on its collimation bolts, the collimation will probably be thrown way off at first.  You should still be able to get it back to collimation, though.  The mirror isn't moving that much compared to the length of the optical tube, and something would have to be seriously bent for it to not be collimatable in the new position.  There may be an issue with focus, though, in that even when collimated in the new position, there may not be enough travel in the focuser to get the eyepiece close enough to the mirror to focus.  Of course, if the mirror isn't binding, this isn't an issue.

 

Also, I am definitely not recommending you leave any collimation screws loose.  I'm sorry if I made it sound that way.  What I'm saying is that once you get a good collimation, and everything locked down, if you need to recollimate the next time you use the scope, leave one of the collimation screws exactly where you left it, and only use the other 2 screws to get back to perfect collimation, then tighten all the locking screws down again.  I don't know if your telescope requires recollimation every time you use it.  My solid tube scope holds collimation extremely well, and yours may also.  My truss tube, on the other hand, requires some adjustment after disassembly and a long drive to a dark site.  By only adjusting 2 of the screws, it prevents me from falling into a pattern, for example, preferring to turn screws in rather than out, which would move the mirror up the tube over time.

 

Also, good for using the barlowed laser method.  I never had much luck with direct laser, but barlowed laser has been good.

[MikeTahtib]

I just watched a video on your telescope.  It looks like the mirror clips may move with the mirror during collimation.  I honestly can't tell.  If they do, then backing the collimation bolts out won't help create space between the clips and the mirror, so if it si bound up, then you will need to remove the mirror.

[Playa17bk]

Now I see what your saying Mike. Makes more sense. Definitely worth a try, thanks.

[Playa17bk]

Yes, some people suggested that. But, we all came to the conclusion to first check the shape of stars then try messing with the mirror clips. I am supposed to focus on the shape of the stars, and if they are not in triangle shapes then it isn't the mirror clips. That is one of my first things to try next.

[RickylMcc53]

I have read through this post, and agree with everything I read. Not sure how long most of the people posting have been doing this, but I am still new to this hobby as well. I started in 2021 with a 6 inch dob. I read on this site that you needed experience to actually see more details. They are correct. I see more now on the same objects that I viewed in 2021, knowing what to expect and look for. keep at it and don't give up hope. I have ordered the AD12 that you just bought, not here yet,  but I am telling myself not to expect objects to look like the ones in the books. The only way I have seen more detail in Nebulas and galaxies, is with my EEA, electronically assisted setup. A ZWO camera paired with my 8 inch sct, or a 2 or 4 inch refractor. But I enjoy being out at the eyepiece so much, especially for star clusters, that I am buying the 12 inch to compliment my 6 inch dob. As far as the planets, I have been frustrated many times by Jupiter, but reading on here that can be expected , and seeing is come and go on the planets where I live in Middle Tennessee. Keep us posted on your dob adventures and have fun !

[TPyxidis]

Scale back expectations a bit, your not going to get the CGI images presented on TV. Begin with planets and moon and then move on to other large objects like clusters and nebula. Slow and steady just don't give up hope!

[PKDfan]

Quickly reading through here there is some very good advice, if not a few being somewhat premature, the real issue with a large aperture mirror for it to work right all the little things also need to be right.

Collimation.
Cooling.
Conditions.
Quality of the mirror is far down the list IMO.

Local seeing and user error of unrealistic expectations are the most problematic.

Dial in the collimation of a cooled mirror in still conditions will help you find the mirrors quality.


CSS
Lance
Edit grammar & punctuation

Edited by PKDfan, 02 March 2025 - 08:42 AM.

[Russell Swan]

Yes, some people suggested that. But, we all came to the conclusion to first check the shape of stars then try messing with the mirror clips. I am supposed to focus on the shape of the stars, and if they are not in triangle shapes then it isn't the mirror clips. That is one of my first things to try next.

When you say that you can’t seem to reach a clean focus on stars that means something is off somewhere in the optical train. It really becomes a process of elimination to determine where the problem resides. It is not necessarily with the telescope either. 

 

The discussion evolved to the matter of the primary mirror retaining clips. If tightened down there could be “pinched optics”. If that’s the problem there will be deformed star shapes since the fine curvature of the mirror will be ever so slight altered. 
 

That said, the issue could be from any of a whole host of things:

Collimation which you have covered. 

Astigmatism with your eyes.

Astigmatism induced by the eyepiece in a low focal ratio scope. Unfortunately, large FAST optics require more complex, more expensive eyepieces for off axis views to be clean.

Telescope and eyepiece not both at thermal equilibrium with the environment.

Local atmospheric turbulence. General atmospheric turbulence (seeing). A large 12” being quite susceptible. Do not view over rooftops or sun warmed concrete/asphalt. 
 

It takes some experience to recognize the tell-tale signs of any one in particular. Chances are the telescope is just fine, but may need to be tweaked. Your understanding will improve with time and you will get there. Having someone experienced look at it for you would save you a lot of frustration however. 

 

 

[Playa17bk]

Thank you for everyone who is suggesting to keep going and not lose hope. I wanted to be clear, I didn't start this thread as my swan song. I don't quit when things get difficult, I push and push. I started this thread because I known my scope has a lot more to give me than what I am getting. I know a lot of this has to do with my lack of experience. I knew a lot of great advice would be given and has. I truly appreciate everyone who has chimed in and provided incredible advice. I can't wait to try everything suggested and post what my results have been, now if only the skies would participate. 

[Playa17bk]

Russell, I can honestly say all the things I have read and all the advice given here, I have never heard of acclimating the eyepieces. Mirrors definitely, but eyepieces need acclimation too? I mean they are outside with me, but in a hard case that I keep closed. Do I need to acclimate eyepieces too?

 

While we are on eyepieces. I know mine aren't that great (Orion Plossl). How big of a difference would better eyepieces make? I'm thinking of grabbing one or two top tier, TV if I can find a good deal (not likely) or maybe some Astro techs? Just don't want to put money into things that won't make a huge difference. 

[Spile]

I’d just keep practicing and starting with less difficult targets. Head off to the Orion Nebula and give the Trapezium a look.

Edited by Spile, 03 March 2025 - 04:09 PM.

[Astro_In_Tampa]

I've got an AD12 and the first double I found was Albireo in the Cygnus constellation. Absolutely gorgeous! I know Cygnus is low on the horizon this time of year, and your best chance to see it is early in the morning before sunrise. But if you can make it fit your schedule, you will really thank yourself.