First Light: Meade Lightbridge 12" Not So Great Results, Advice Requested, Help!

[pixlgeek]

Ahoy SGL'ers!

First post and first scope purchased myself.

Long time amateur astronomer but have never owned my own scope. For years a I used a borrowed ETX 90 that gave me decent results.

I received a Celestron NexStar 6 SE for Christmas and decided I would exchange it for something a bit larger. I pondered for days about perhaps upgrading to the NexStar 8 SE or go with a Dob to force me to learn the stars and layout of the night sky. After much thought I decided to go with the Lightbridge 12" that I got for a great deal at $800.00 USD. I couldn't pass it up.

So I pick up the scope, drive it home and begin building. After a couple of hours and so much excitement I take her outside, a chilly night probably high 40's to low 50's. I turn on the cooling fan and allow it to run for roughly 45 minutes to an hour, put in the included eyepiece, put Jupiter in my sights and sit down in preparation for what I expect to be leaps and bounds above the quality of that tiny ETX 90 I had been using. I place my eye to the eyepiece and attempt to bring the fuzzy ball into focus. To my utter dismay I cant seem to get the thing into a sharp/crisp focus. There was what I would describe as a coma or ghosting (I could see faint opaque balls mirroring the object forcing me to strain my eyes view any detail in the planet. I barely managed to see the bands across this giant and could only make out one of its' satellites (moons). Needless to say I was quite disappointed.

My first inclination was that the primary was not cool enough yet so I gave it another half hour and to no avail the image was still quite ghostly and slightly unfocused. Clearly not what I was expecting from this giant scope. The scope came with a rebate for the Meade 4000 Eyepiece kit so I have sent off for that and expect that will help magnify the image greatly as the planet was not very large at all, another disappointment. To be honest when I first testdrove the Nexstar 6 SE that I originally was gifted the planet looked fantastic, large, sharp and with tons of contrast. Did I make the wrong decision in opting for the Dob instead of the Nexstar? I sure hope not.

Now, my next thought was that the collimation was off or shifted in transit as I have read that these need to be collimated at each session. I didn't have any collimation tools so went ahead and ordered the Orion LaserMate Deluxe kit which should be arriving in a few days and I truly hope that this fixes my issues and presents me with an image that I can be amazed at.

PLEASE PLEASE SGL posters, if you have any advice or motivating tips as to if my theories are correct, please do tell me. I am a bit down at this point in my decision to go with the LightBridge as opposed to the NexStar 8 SE. Any help is greatly appreciated.

I am glad to be here and hope to be getting to know many of you over the upcoming years.

Best,

-pixlgeek

[Grunthos]

First of all - Don't Panic! (you are posting in the right place for help)

I think (although stand to be corrected) that you are having a small problem with collimation. The larger dobs need to be collimated more frequently than the smaller ones (especially after having been lugged around).

I just bought a 10" dobo (still have my Celestron 6SE) and had some initial issues with collimation (most new reflector owners do).

After having read up on the subject am now looking on it all as a fun part of owning a dob (seriously!)

Have patience and wait until your collimation kit arrives.

Meanwhile you may wish to search for various threads in SGL on the subject of collimation.

Here is a link for starters. (Astrobabys site is highly regarded).

Clear skies.

[swamp thing]

Hi

welcome to the forum.

The 12" lightbridge is a highly rated scope that will easily out perform the 8" SCT.

First off collimation is indeed vital on large newts. Any mirror over 10" should be checked, and adjusted if required, every time the scope is used.

Second, if the lightbridge still comes with that 26mm QX piece of garbage. Do yourself a favour and throw it over the nearest hedge. Possibly the worst eyepiece I have ever looked through.

Regards Steve

[RobH]

I agree, it sounds like a collimation issue.

A word of warning re. laser collimators though.....unless your focuser is absolutely at 90 degrees to your tube, they don't work, and, also being the owner of a 12 inch LB, I can tell you that it won't be.

Also, the laser itself may not be collimated.

I tried collimating mine with a laser and got terrible results.

I would strongly suggest cancelling your order (if you can) for the laser collimator and order a cheshire eyepiece instead...once you get used to using one, you'll get great results very quickly and don't need to worry about focuser collimation etc etc.

Another thing most LB owners do is to replace the springs that help to hold the primary mirror with stronger ones, and replace the secondary mirror adjustment screws with 'Bob's Knobs', which make secondary adjustment much easier.

Cheers

Rob

[umadog]

It could also be that the seeing was bad. This, coupled with poor collimation, will easily explain what you saw.

I too suggest a Cheshire/sight-tube combo tool. A cheap laser is more hassle than it's worth. I don't see why the focuser needs to be 90 degrees to the tube for them to work, however, if for no other reason than that the Combo tool measures the same errors as the laser (http://www.cloudynights.com/photopost/data/500/19446collimation_tools_table6.PNG). Don't forget that adjusting secondary tilt adjusts the focuser axial alignment (Telescope Reviews: Useful info about secondary mirror alignment).

[Northern Soul man]

Hi Ya Pixlgeek, The light bridges are a great scope, I have a 12" dob and also an 8" SCT, you find as you increase the size of the scope, the wow factor decreases somewhat. Yes its bigger, but your also magnifying the unsteady atmosphere proportionally more than the 6 - 8" scopes as well. I use my dob mainly for deep sky and find it to far exceed the SCT due to the increased light grasp, but your always battling against light pollution, differences in telescope design (each scope has its pros and cons) seeing conditions, temperature changes, dew to name but a few. I live in a very light polluted part of the country, when the sky transparency isn't there, it doesn't matter what scope you have it becomes a problem to observe the faintest objects, but with this in mind, just get the star charts out and look for a particular galaxy or nebular, and if its not "there", just move on to the next. Yes, large scopes will need some form of filtering for the planets - whether it is just polarising, or coloured to try and extract fine detail, 0III, UHC to increase contrast for deep sky. The next night you go out to observe, conditions may be better, but , to be honest the scope which amazes me the most is the 127 Mak I've got, when you think its only got 5 inches of aperture, on the planets its great. Don't worry you've got a fantastic scope there, just using it under good and bad conditions makes you realise why they put Hubble in orbit - take care and happy observing Paul.

[LeeB]

Hi friend was having similar issues with 10" (second hand) interestingly while setting up for him noticed the vanes on the spider were upside down (and bent slightly) and did not allow secondary to be perfectly central, unsure if problem was at meade or some rebuild failure as scope was second hand. removal and correcting and a good collimation and the scopes a gem. So don't worry all is sortable.

[John]

The secondary mirror is not perfectly central in an F/5 newtonian - it should be offset away from the focuser a little. In most commercial scopes this offset is built into the design of the secondary holder though.

[LeeB]

I know about offsets, 3mm approx in an f4.8, the ofset away from the focuser is normally done within the holder offset. The secondary should still appear to be central,(ie its actual physical centre is offset) the offset shows in the secondary reflection as an offset.

[John]

I know about offsets, 3mm approx in an f4.8, the ofset away from the focuser is normally done within the holder offset. The secondary should still appear to be central,(ie its actual physical centre is offset) the offset shows in the secondary reflection as an offset.

Thats good - I just thought I'd mention it

I used to get quite worried about secondary offset until I realised that the manufacturer had take care of it.

[Peter Drew]

Another thing worth checking on a Lightbridge is whether the primary is too tight in its cell. If you can't turn it easily with your fingers, back off the screws that hold the mirror clips untill you can just slide a piece of paper under them as a gap guage.

[LeeB]

Thats a good point the springs on the lightbridge were quite weak and collimation was hard to hold until stiffer ones were fitted. Try vertical collimation and then at horizontal to see if it moves. If the springs arnt stiff enough its easy to over tighten locking screws to hold it. With the stiffer springs the locking screws arnt even necessary. ps. sorry John I sounded a bit agressive in the last post!!

[John]

Tps. sorry John I sounded a bit agressive in the last post!!

No probs at all mate - my post was a bit short and "to the point" as well

I had a Lightbridge 12" for a while and found it a pretty decent scope once it had had a few mods like the ones that RobH mentions. I just found it too heavy for me to lug around so I downsized to an Orion Optics 10" F/4.8.

[RobH]

I don't see why the focuser needs to be 90 degrees to the tube for them to work, however, if for no other reason than that the Combo tool measures the same errors as the laser (http://www.cloudynights.com/photopost/data/500/19446collimation_tools_table6.PNG). Don't forget that adjusting secondary tilt adjusts the focuser axial alignment (Telescope Reviews: Useful info about secondary mirror alignment).

It does if you're using a laser, as if not, you'll get the wrong adjustment on your secondary as the beam won't be hitting it at 90 degrees.

With a Cheshire though, it doesn't matter....probably didn't make myself clear

Rob