Meade Lightbridge 12" first light and comparison with my Celestron Omni XLT 120

[gustavo_sanchez]

At last, I was able to mount my Lightbridge outside for some action. Yesterday, I practiced collimation, so I was more or less confident on doing it right tonight without wasting a lot of time. I do not have a lot of open sky where I live, so I had to place the dob on two places during the course of the night to see as much as I could. First note: I had to collimate the scope every time I moved it. Not very nice, but at least with my laser collimator it was no big. The first obvious mod is to add Bob's knobs for the secondary; primary does not need them. The primary mirror held collimation very well; I do not know if Meade improved the springs on the lock knobs, but I only had to collimate the secondary.

Later, I brought out my Omni refractor, and set it up side to side so I could compare views using the same eyepieces. I used the following EPs during the comparison: a Celestron 8-24mm, an Orion Ultrascopic 5mm, Hyperion 10mm, Hyperion Aspheric 31mm, and the stock Meade QX 26" Wide Angle.

To accept the 2" EPs, I installed a recently purchased 2" dielectric quartz diagonal on my refractor, which improved the viewing greatly from the stock 1.25" diagonal. In addition, I attached a Baader Planetarium 2" Fringe Killer filter to the front end of the diagonal to suppress CA and make the "fight" between the scopes a little more even.

I started with Jupiter on the Lightbridge, and noticed Great Red Spot almost instantly, something I was not able to do before with the 1.25" EPs and diagonal on the refractor for some reason. I was almost completely blinded by Jupiter on the LB; it was too much light to see, and there were some "sun rays" coming from Jupiter, something I have never seen before on the Omni. I understand that those are diffraction spikes caused by the spider vanes. So, this is my first conclusion: on the Omni I have chromatic aberration (fixed nicely with the FK filter) and on the Lightbridge I have these spikes. How I can get rid of them?

Using 2" EPs for the first time is something to behold. I can see almost all of my 1.25" Plossls collecting dust from now on.

Obviously, there was better resolution on the Lightbridge when I saw Jupiter than on the Omni, but the difference was not abysmal. The refractor held its own very well (the addition of the filter, 2" diagonal and 2" EPs definitely had something to do with that) but the dob has the edge.

Regarding stability of the scopes, tonight's odds were against the Lightbridge, since it was breezy (there were remnants of a hurricane that passed two days ago) and the Lightbridge side-to-side movement was notable (how can I fix that?) Contrary to some opinions, I continue to find the CG-4 mount that came with the Omni as the just match for the OTA. It was very stable, even with the addition of the 2" accessories.

I find the red dot finder included on the Lightbridge just okay. It's not that it is bad, I'm just not a fan of it. I prefer optical finderscopes, so that's added to the wish list. The method that I used tonight was to find the object with the optical finder of the Omni, center it on the refractor EP, swap the finderscope for a mounted laser, and follow the laser beam with the Lightbridge. I need an optical finderscope fast .

The next object was Andromeda, and on this galaxy the Lightbridge obviously had the edge. I was more defined and bright than on the refractor. Very nice view. I did not spend a lot of time on this, because I encountered an issue with the 10mm Hyperion.

I just noticed that you took the 1.25" adapter from the EP to use as a 2", it did not magnify as supposed. I was almost the same magnification as the stock 26mm Meade! I then noticed that there is a extra lens on that adapter, so my guess is that's the reason of the lack of magnification. Somebody can explain that?

The last object I observed during the night was the Orion nebula, which I looked from both scopes. On both of them it was beautiful and clearly defined, and the Trapezium stars inside were clearly visible. I was using the 31mm Hyperion on the Omni and the 26mm Meade on the dob. Again, the dob offered a better view, but this time the difference between the two scopes was greater than for the Andromeda Galaxy. On the Omni, it looked like a clearly defined grey patch of light, but on the Lightbridge the edges were a lot more refined and it had a greenish tint. For clarification, there were no filters on the Lightbridge at any time.

In conclusion, the two scopes fared very well, with the dob having the noticeable advantage (duh!) on the DSOs. I sometime thought of selling the Omni, but now I think they make a great complement. The Omni supplies the refinement of the refractors (and the Fringe Killer filter does wonders on this scope) and the Lightbridge supplies the raw power. Also, I spend almost the same time mounting the Omni as collimating the dob, so they are balanced on that matter too.

I hope you like this, since this is my first comparison ever. Sorry it is so long! . Comments and suggestions are welcomed!

[John]

Sounds like a very successful 1st light

I'd agree about your refractor complimenting your Lightbridge. Sometimes, especially on planets and double stars, the refractor will show detail more readilly that the larger scope so it's well worth having both.

I found this interesting:

... First note: I had to collimate the scope every time I moved it. Not very nice, but at least with my laser collimator it was no big. The first obvious mod is to add Bob's knobs for the secondary; primary does not need them. The primary mirror held collimation very well; I do not know if Meade improved the springs on the lock knobs, but I only had to collimate the secondary...

To me this indicates that your primary mirror cell is NOT holding collimation. The secondary collimation generally should not need adjusting often wheras the primary is the "fine tuning" device. I'd definately plan on replacing those primary collimation knobs and springs. but it's up to you I guess.

[russ]

Losing collimation so often doesn't sound quite right. I have the GSO 12" dob which is basically the same scope with an identical mirror cell and while it does need collimating quite often, it's only like once a session. And that's with the original soft springs. Have you lightly applied the locking bolts after collimation?

[oldfruit]

Very good comparison. Interesting read, especially for anyone wanting to purchase either of the scopes you were using.

[Revs]

Nice report, Gustavo. Cheers

[gustavo_sanchez]

Sounds like a very successful 1st light

I'd agree about your refractor complimenting your Lightbridge. Sometimes, especially on planets and double stars, the refractor will show detail more readilly that the larger scope so it's well worth having both.

I found this interesting:

To me this indicates that your primary mirror cell is NOT holding collimation. The secondary collimation generally should not need adjusting often wheras the primary is the "fine tuning" device. I'd definately plan on replacing those primary collimation knobs and springs. but it's up to you I guess.

Thanks for the feedback. I'm a first time dob user, so I maybe I was wrong. I moved the scope once, and on that time, I did put the primary OTA standing on the floor, resting (supposedly) on its plastic stubs (not the knobs). It could have happened that the primary lost the collimation at that time. But how it could be possible that losing collimation on the primary made the laser from the collimator to be very off center the next time I tried it? That's not "responsibility" of the secondary? Maybe I am confused .

[gustavo_sanchez]

Losing collimation so often doesn't sound quite right. I have the GSO 12" dob which is basically the same scope with an identical mirror cell and while it does need collimating quite often, it's only like once a session. And that's with the original soft springs. Have you lightly applied the locking bolts after collimation?

Hi Russ,

I am not sure I applied correctly the locking bolts. Those are the ones with the springs or the ones without them? And what I am supposed to do with them? Tighten them by hand after the scope is collimated? Sorry for all the questions, but I found the manual lacking on this topic.

[John]

Hi Russ,

I am not sure I applied correctly the locking bolts. Those are the ones with the springs or the ones without them? And what I am supposed to do with them? Tighten them by hand after the scope is collimated? Sorry for all the questions, but I found the manual lacking on this topic.

If you use the locking bolts (the ones wihout the springs) only do them up very gently. The mirror cell on the LB 12" is quit thin and will bend if the locking bolts are too tight - putting the scope out of collimation

After I'd upgraded the primary springs on my LB 12" I found that I did not need the locking bolts at all for normal moving around and it stayed in reasonable collimation, needing only fine tuning at each use.

[russ]

Sorry, i should have explained better. The locking bolts are the ones without the springs. Just apply them gently to take the weight of the cell, as John says. After you apply them just check the collimation again. I find lightly applying them doesn't affect the collimation and stops the cell moving around.

But again as John said, changing the springs to the Bob's Knobs heavy duty springs does away with the need for the locking bolts.

I forgot to say, great observing report

[dph1nm]

I just noticed that you took the 1.25" adapter from the EP to use as a 2", it did not magnify as supposed. I was almost the same magnification as the stock 26mm Meade! I then noticed that there is a extra lens on that adapter, so my guess is that's the reason of the lack of magnification. Somebody can explain that?

This is correct. There is a table somewhere on the Baader site which gives the effective focal lengths with the 1.25" bit removed. I think most of the series end up at ~22mm. You can buy fine-tuneing rings which screw on to the 2" bit and give you different focal lengths.

NigelM

[pvaz]

The loosing collimation part is a bit strange.

I only got an 8" solid tube but my secondary holds for months without adjustments and my primary can hold a fare amount of sessions. I check it about once a week with the laser and start test it at the beginning of every session. More often then not, I don't need to adjust anything. In between it gets used as often as possible, I would say an average 2 or 3 sessions per week depending on weather.

[pvaz]

PS-> I noticed Collimation changes as you change the scope inclination. I collimate the primary at about 55 or 60º from horizontal so the shift will be minimal when I point at zenit or to around 25º above the horizon.

You can observe a little change if you collimate with a laser and when it's done you move the scope up and down, the laser should come a bit outside the dot.

[Abb]

Interesting comparison - thanks! It tells me just how powerful my 120 really can be - I've only had it out once so far & that was for less than a hour because of weather

Does going to 2" really make that much of a difference??? I thought I read somewhere I can go to 2" without buying additional hardware. And perhaps that Baader fringe killer you mentioned may come sooner rather than later

Have fun!

[gustavo_sanchez]

Hello to all,

Tonight I was able to get the scope again out, and noticed that the collimation was almost spot-on. Some minor tweaks and it was ready to go. I know that the collimations that I have performed to the scope are not completely perfect, but I am getting the hang of it. When I focus a star the best I can, it shows some very short light rays coming from the center, but only one side of the star, not symetrically, so I think that is an imperfect collimation. I need to continue practicing with the laser collimator and the scope to get a perfect collimation.

Abb,

Don't question it, the Omni 120 is a great refractor, and has very good features for the price. The stock focuser already accepts 2" eyepieces, but you will want a 2" diagonal for comfort in addition to the 2" eyepieces. The fringe killer filter just sweetens up the package.

I am a refractor guy, no doubt about it. I'm getting over the difficulties of collimation (a completely new thing to me); and I am sufficiently open minded to enter into dobsonian territory. After all, all those dob users love their howitzers for a reason, right?

[Abb]

Now you really have me going! I was actually thinking of dumping my 114 newton for an 8" Dob but I thought I'd wait until I got some time with the new 120. But after reading your report, there's no 8" Dob in the near future for me. And I don't want to collimate every time I take a scope out.

Which diagonal do you have??? Celestron has a few of them, none of which is specified for the 120. What sizes are your 2" lenses?? I still may hold off on these for now....maybe.....and maybe not

BTW, I have a Sony Alpha 350 DSLR

Many Thanks!

[John]

Which diagonal do you have??? Celestron has a few of them, none of which is specified for the 120. What sizes are your 2" lenses?? I still may hold off on these for now....maybe.....and maybe not

BTW, I have a Sony Alpha 350 DSLR

Many Thanks!

Any 2" push fit diagonal should work with the 120XLT - it does not have to be branded Celestron. 2" eyepieces are generally used for low power, wide angle viewing - you can continue with 1.25" ones for medium to high power. With the 120mm F/8.3 Omni XLT a 40mm 2" wide angle eyepiece can give stunning views

[Abb]

How does this Fringer killer look to you???

Baader Planetarium Semi-APO Filter - 1.25" - OPT Telescopes

[gustavo_sanchez]

How does this Fringer killer look to you???

Baader Planetarium Semi-APO Filter - 1.25" - OPT Telescopes

I think that one is great. You could get a 2" filter, but chromatic aberration is not very great on low power eyepieces (the ones that will want to be of 2" size), so maybe you do not need it.

[gustavo_sanchez]

Any 2" push fit diagonal should work with the 120XLT - it does not have to be branded Celestron. 2" eyepieces are generally used for low power, wide angle viewing - you can continue with 1.25" ones for medium to high power. With the 120mm F/8.3 Omni XLT a 40mm 2" wide angle eyepiece can give stunning views

I actually have an inexpensive OPT-branded quartz dielectric diagonal. You could find some other good ones (I love that carbon-fiber William Optics diagonal...).

[gustavo_sanchez]

Now you really have me going! I was actually thinking of dumping my 114 newton for an 8" Dob but I thought I'd wait until I got some time with the new 120. But after reading your report, there's no 8" Dob in the near future for me. And I don't want to collimate every time I take a scope out.

Which diagonal do you have??? Celestron has a few of them, none of which is specified for the 120. What sizes are your 2" lenses?? I still may hold off on these for now....maybe.....and maybe not

BTW, I have a Sony Alpha 350 DSLR

Many Thanks!

I just started by 2" eyepiece collection. I have the 10mm Hyperion, 31mm Hyperion Aspheric, and the supplied Meade 26mm QX (which I intend to replace soon).

[Abb]

I ordered that filter, but he's out of stock so it'll be about 1.5 weeks before I get it - many thanks! The 2" diagonal will have to wait.....for now

Just out of curiosity, with your solar filter, do you see more than just sunspots - I'm really tempted to get one???

[gustavo_sanchez]

I ordered that filter, but he's out of stock so it'll be about 1.5 weeks before I get it - many thanks! The 2" diagonal will have to wait.....for now

Just out of curiosity, with your solar filter, do you see more than just sunspots - I'm really tempted to get one???

The solar filter is a nice addition, but I found out it is not receiving a lot of attention lately (that could change). You should really focus on getting that diagonal; it will open for you a new world of possibilities (the world of 2" eyepieces, that is).