Can't focus a 2nd hand 14" LX200 (Please help!!)

[RealTimeShepherd]

Hi

Apologies, this is my first post and it is a plea for help!

I really hope someone can help me. I have had a Helios (Now Skywatcher) 200P for ten years which I bought 2nd hand which has served me very well. For my 40th birthday, I decided to go for a permanent setup with a Meade LX200. I found a 14" model on eBay with a ton of accessories and purchased that. The seller lived near my Dad, so he was able to go round on my behalf and check out the scope. The seller seemed totally genuine and the scope looked in good condition.

It has taken me months to set up the observatory, but I finally have in place a roll off roof shed from Ian King Imaging and everything looks perfect. In fact it looks so good that my obs is used on the website: http://www.iankingim...hp?category=184

Only one of those pictures (The second one down) is not my shed...

I really wanted to use the scope for planetary viewing, but I am unable to focus the image, especially at higher magnifications. I have collimated the scope OK I think using an unfocussed star, but I do notice that the image of the secondary mirror is only centralised on one side of the focus and not the other. I have bought 2 eyepieces, the Baader Hyperion 68 degree eyepieces, a 24mm and an 8mm which I am able to attach my HD camcorder to so I can show you exactly what I can see.

I've uploaded 2 videos to YouTube, one where I use the coarse focusser through the 24mm eyepiece:

and one through the 8mm eyepiece where I am using the micro-focusser going back and forth across best focus which is never better than a boiling ball:

These are both extremely close to what I see visually

Additionally, there are some flaws I have identified in the optics. There are four mildew spots on the primary mirror, the two largest of which are shown below. I don't think that these are likely to be a problem. More worryingly, there are chips in the corrector plate, only a few mm in size and I have covered them with a small piece of paper to prevent light scattering (also shown). These I find more worrying, as they suggest some kind of tinkering with the corrector plate, and done badly.

I wouldn't be concerned at all if I could get a good image, but with the 8mm eyepiece Saturn never looks focussed. An 8mm eyepiece should provide 444x magnification which ought to be well within the limits of the scope. I'm aware of the problems with seeing (Saturn is quite low this year), especially with a large scope and the problem is that I have no experience at all of a scope this size. But frankly something doesn't seem right.

Here's a photo I took of Saturn in 2003 which was taken just by holding a camera to the eyepiece of the Helios 200P, so no stacking or anything, just a single frame.

Here's a picture of Saturn from a couple of nights ago where I shot 20,000 frames and stacked the best 1000 and it is worse than the single frame through the eyepiece of the smaller scope...

Anyone reading with more experience than me, could you please give your opinion on what has gone wrong? I've basically upgraded my very fine 8 inch scope at considerable expense to a 14 inch, and I'm pretty disappointed. Any help is gratefully received.

Regards

Shep

[DirkSteele]

I am concerned that the chips may indicate that the corrector has been removed, possibly dropped (certainly damaged), before being re-attached the OTA and possibly not in the correct orientation. With all SCT scopes, all the optical elements (primary, secondary and corrector) require a specific orientation to perform as expected. I am only familiar with Celestron SCT corrector which have numbers etched into the components which must be aligned. I would think Meade would have a similar system. However, I am not advocating removing the corrector just yet.

The first video you have posted is interesting because a correctly collimated SCT, should show broadly similar diffraction ring patterns and central shadow inside and outside of focus. In all the times I have collimated my SCT, I have not seen such an extreme move in the central shadow from one focus position to the other. Before we can identify possible problems with the optics and their orientation, we should check the scope really is correctly collimated. Are you familiar with a Duncan Mask? They can be made from cardboard and they are an excellent and simple solution to achieve good collimation with a SCT. Also be advised that you should avoid having the secondary screws too tight as that can cause warping of the corrector plate which can impact the view.

The link below includes all the instructions to make a Duncan Mask and how to use it.

http://www.astrovox.gr/forum/download.php?id=17658&sid=646453d99bbd6eef6845f3d3254b6ff9

Once are confident you have the scope well collimated, would you be able to post another video of a star in an out of focus (both sides) as before, but at a higher magnification? Something around 300x if possible, and ideally with good seeing conditions. Then perhaps we can think about next steps.

And as an alternative path, I assume you have no recourse to the originally seller, or at least ask if the corrector and secondary assembly has been removed and reattached?

[RealTimeShepherd]

Dirk

Many thanks for your response! I will construct a Duncan Mask and use that to confirm the collimation. I'll then post the results and another video as suggested.

The Meades definitely do have the same system where the corrector plate is paired with the primary mirror and the orientation is important. All the advice about cleaning the corrector plate on a Meade refers to marking the orientation before you remove the plate, so I must admit it did occur to me that possibly it had been replaced out of orientation.

If you think that sort of problem could be responsible for an inability to achieve focus, then that is a positive step as it may mean that I might yet improve my view. I was beginning to despair!

Thanks again for taking the time to read the post and respond with some steps I can take. I am extremely grateful

[steppenwolf]

When you took the videos, are you sure that the telescope was fully cooled to the ambient temperature? I feel that part of this focus issue is to do with tube currents although the possible incorrect orientation of the corrector doesn't help!

[John]

Cooling was going through my mind too. A really big SCT can take a long, long time to reach thermal equilibrium. Sometimes they never quite keep up with the changing outside temperature I reckon !

The seeing conditions have been very variable of late and Saturn is a lot lower in the sky than it was in 2003 (when the OP's 1st photo was taken) and this might be making a difference too. I had my best ever views of Saturn in 2003 and I recall it was really high in the sky then.

[RealTimeShepherd]

Hi Steve and John

My assumption is that because the scope resides outdoors in the shed, that it is pretty much always at the ambient temperature. On top of that, the terrible picture of Saturn was taken over two hours after rolling the top off the shed. I am aware though that it is very low this year and that might be the reason. My biggest problem is that I have never looked through a scope this big and I don't know what to expect

The star I was shooting was Arcturus at about 10PM, which I would guess was 45 degrees, but that was moments after rolling the roof off

I am kind of hoping that the problem is due to incorrect orientation as so far the high magnification views are not what I was expecting, and I tried very hard not to have high expectations...

I am also toying with taking the scope to Telescope House to have it overhauled, I don't know if anyone has any experience with them?? Anyway, for the moment I intend to take Dirk's advice and build myself a Duncan Mask for collimation.

Cheers everyone for taking an interest, having some assistance has certainly brightened my mood!

[cgarry]

I wouldn't be concerned at all if I could get a good image, but with the 8mm eyepiece Saturn never looks focussed. An 8mm eyepiece should provide 444x magnification which ought to be well within the limits of the scope. I'm aware of the problems with seeing (Saturn is quite low this year), especially with a large scope and the problem is that I have no experience at all of a scope this size. But frankly something doesn't seem right.

I have a C14 scope and would never dream of putting an 8mm eyepiece on it, 444x magnification is far to much for UK skies. I doubt you will be able to use any more magnification with your 14" scope than you did with your 8" scope in the UK.

Cheers,

Chris

[John]

Have to agree with the above re: magnification. My 12" dob has optics which are probably better than most SCT's plus a smaller central obstruction but 300x is about the max I've been able to use on Saturn this year and 267x has been crisper and more contrasty.

[RealTimeShepherd]

OK, well I guess that's quite helpful and exactly why I came on here, I want to know if I'm doing the wrong thing!

So I was under the impression that magnification was 40-50x per inch, but I guess that breaks down at larger apertures unless I move country...

[Odd Thomas]

50x per inch of aperture is the very max. for perfect seeing conditions (which we never have in the UK) Have a look here http://starizona.com/acb/basics/equip_magnification.aspx for an explination of mags.

Tom

[John]

40x - 50x per inch assumes perfect optics used under perfect conditions I believe. In practice around half those figures seems to be much more realistic, with apertures over around 6 inches or so.

[RealTimeShepherd]

OK, I appreciate all of the responses, and it makes me think that maybe my scope is not as broken as I was thinking, which is a good thing!

Out of curiosity, has anyone else imaged Saturn from the UK this year? How did it turn out?

[Zakalwe]

The scope is definitely not cooled down. You can see the sir "boiling" in the first video at 34 seconds. A big scope like that will take hours to cool if it has been in the warmth. In fact, it will probably never get to ambient in an evening. This will prevent you getting any decent image (I remember the first time that I used my C11 on Mars....it had been out less than 40 minutes and the planet was a shimmering mess. Impossible to achieve focus).

I am also intrigued about the shift in the central obstruction as you move in and out of focus. I've never seen the central shadow shifting like that. before panicking though, I'd be sticking the scope in the garage during the day and letting it cool.

Seeing the chips in the corrector isn't good though. The scope could have taken a knock and something could be out of alignment.

[Zakalwe]

I hope that you get it sorted BTW.

This isn't the correct place to ask (my apologies) but I'm VERY interested to hear your thoughts on the IKI observatory....

[RealTimeShepherd]

hehe, mate your avatar pic is fantastic

The scope is permanently mounted in the shed so, should I be rolling the roof off earlier to cool the scope down? Or am I just going to have to wait until much later in the evening before I put it to use?

When you say you'd be sticking the scope in the garage to cool down, well I only have the shed or the house, and I can't move the [removed word], it's extremely heavy! Is there anything else I could do?

WRT the IKI observatory, I was all geared up to buy an Alexander's observatory, but it was this site that alerted me to the fact that people were having to wait up to a year. So I decided against that, in the end I thought I would have to buy a SkyShed instead so I phoned IKI. I spoke to Ian and he said they had just started with the roll off roof sheds.

Anyway, I am extremely pleased with it, the roof slides off easily and I can just fit my whole setup underneath, I can be up and running in minutes. The guys who assembled it were very dedicated and really put the work in to perfect the finishing touches. I'm quite pleased that my shed features so prominently on their site now!

Still, I do think there is something up with the optics somewhere, have you noticed that one side of focus, there is a bright dot within the shadow of the central obstruction? I need to know if it needs professional attention. I'm very grateful to everyone for their input anyway. I might have set my expectations too high (despite my best efforts) but it is impossible for me to know what to expect and therefore whether anything is wrong!

Shep

[DirkSteele]

Still, I do think there is something up with the optics somewhere, have you noticed that one side of focus, there is a bright dot within the shadow of the central obstruction? I need to know if it needs professional attention. I'm very grateful to everyone for their input anyway. I might have set my expectations too high (despite my best efforts) but it is impossible for me to know what to expect and therefore whether anything is wrong!

Yes, there should be a small dot of light at the centre of the shadow in the defocused image of a point source.

[Davey-T]

When you say you'd be sticking the scope in the garage to cool down, well I only have the shed or the house, and I can't move the [removed word], it's extremely heavy! Is there anything else I could do?

Read a few posts on other forums of folks drilling holes in big SCTs and fitting fans, may be worth a bit of research.

Dave