16" lightbridge

[AG Hybrid (Adrian)]

I wanted a LB16. Then I learned the base is nearly 30" wide... and then I didn't want one any more.

Wont go through doors. Wont fit in my car! Mind you I only drive a Corolla. The 12" fits with plenty of room to spare.

[PSALM19.1 (Shaun)]

Once again, THANKS ALL for some very valuable advice! Yes, no good having a big scope if it won't fit through a back door! I measured my garage back door (can't go through front) and it's 35 inches; so, in theory, if the base of the LB is 30, then it would fit, but not if anything was "jutting out"!
I saw a pic of a guy with this scope and wow, she's big! That is perhaps an issue for me: I'm sort of a sit down kind of observer; the thought of having to stand on a step and view is not a fun one for me! I still have a good few months to really make up my mind: a trip into Bintel will help too, so I can look at both of them....the 14" is out due to the size of the base and it's a little too much money I think for only two extra inches of aperture....look, guys, I've really found your comments useful...! So for the time being it's back to the 8" and considering that about two years ago I had a Celestron Firstscope and a 60mm refractor up until August, I've come a long way!
PS: here's what got me into Astronomy in the first place, with encouragement from my wife, God bless her!

[astronut (John)]

I had the chance to use both the 12" & 16". Whilst the 16" will give approx 1 mag more.

I had to compare that with the weight, size and bulkiness of the 16".

I chose the 12" and am very happy I did...7.5 years later.

[PSALM19.1 (Shaun)]

Thanks John; could you just confirm what 1 mag means? (Scuse' the newbie!)

[sn1987a (Barry)]

Just on the Lightbridge base, a lot of that 30 inches is unnecessary. You can remove the two base circle pieces and instal a squarish piece to pick up the alt supports and a roughly 24 - 26 (from memory) inch circle baseboard. The lazy Susan bearing is a lot smaller than that and does all the work. A couple of wheelbarrow handles and wheels and no worries you're through the door and observing before you can say " sweet ".

My Lightbridge I replaced the entire base with a plywood one. Not very hard to do a cheap handheld router will do most of the work if you use the original pieces as a template. Much lighter and easy to set up. I just wheel it in and out of the back door.

[astronut (John)]

Shaun, I mag of difference is not a lot.

The brighter DSO's won't look much better in the 16" over 12"

The 16" may allow you to perceive the dimmer galaxies, but again, not by much.

For the nebula's, I prefer to use an O111 and/or HB filter to enhance the view.
Remember, in it's current form the 16" lightbridge is BIG, HEAVY and AWKWARD.

Other designs, like the SDM, Obsession type scope are better designed so you don't suffer those problems, but they are more expensive.

If you have the opportunity to view through both scopes, you'll see what I mean.

My two cents.

[PSALM19.1 (Shaun)]

Thanks very much John; am I correct that planets would be better viewed through a 16" or is there also little difference there as well?

[astronut (John)]

The planets are best viewed with the secondary being as small as possible.

This will give the least amount of loss of resolution of the image.

The 16" has approx 30% obstruction compared to 25% for the 12"
But the 16" has greater resolving power, so it's a trade off, BUT you still have the BIG size and weight of the 16" to contend with.

If you are happy to enjoy the greater resolving power of the 16" over the 12" and put up with the greater weight, bulk & size, then go for it.

But, there are no free lunches with the choice.

PM sent as well.

[Satchmo]

I would still go for a 12" if you are into planetary. There is much less glass mass in the 12" and they are high expansion glass compared to Pyrex- I have both looked through and tested a number of 16" GSO's and not seen anything that floated my boat , but the 12"s generally have a typically better figure.

[astronut (John)]

I agree with Mark.

[glend (Glen)]

I have both the 12" GSO and 16" GSO dobs so I think I can give some perspective on relative performance.
In relation to test figures,
I will give you this thread on Cloudy Nights to consider,

http://www.cloudynights.com/ubbthrea...9/Main/5559050

which includes a link out to a German translation of a full test of a 16" GSO mirror; and these 'old specs' from Andrews Comms.

The 12" Optics: 1/12 surface wave error (now claimed 1/16 RMS), BK7 mirrors (primary and secondary)
Resolving power; 0.38 arc second.
Limiting magnitude; 14.9

The 16" Optics: 1/12 wave surface error (now claimed 1/16 RMS, BK7 mirrors (primary and secondary),
Resolving power of 0.29 arc seconds.
Limiting magnitude of 15.5 .


If you would like to really dig into the whole world of mirror quality, then have a read through this article:

http://www.bbastrodesigns.com/ratemirrors.html


In recent times they have changed their stated minimum criteria to 1/16th wave RMS, or better, as RMS is gaining wider acceptance amongst the astronomy community."

Here is what GSO has to say about their minimum mirror criteria:

http://www.gs-telescope.com/content.asp?id=142

The 12" GSO maybe the best value in the production scope market right now (at $749). When you add some good eye pieces it might last you the rest of your life and never bore you.
If your just starting out, buy the 12 and you won't be disappointed. See how you go with that, it's a good scope, the only drawback is that the 12 needs a few mods (like a spring upgrade).

[Allan]

1/12 wave surface error is nothing to get excited about. Don't confuse that with p/v wave error. There would not be a premium mirror maker still in business who makes mirrors to 1/12 wave surface error. But that's only part of the story. Mass produced mirrors are renowned for turn down edges and various other faults that you mostly don't see in premium mirrors. Plus, BK7 is cheap and not as suitable for telescope mirrors as other glass.

You keep bringing up planetary viewing, so I sense that is important to you. The best way to observe planets is with premium optics, which allows you to detect contrast in the surface detail. A 12" mirror made by Mark (Satchmo) or most other premium mirror makers will reveal more detail than a 16" mass produced one. Plus you will have the bonus of a smaller, and more manageable telescope.

Most everyone here are steering you toward the 12" and for good reason.

[PSALM19.1 (Shaun)]

Guys, awesome advice and some new stuff to learn! (All your techo' talk!) I guess, owning a 8" dob, I am more drawn to planetary viewing because DSO aren't quite as exciting (don't get me wrong, they are fun...!). Also, anyone own an Orion 12" with the tracking ability? (12T?). This looks like a good scope, the tracking is a real plus too (goto doesn't matter to me, I like to TRY and find stuff, but to track an object would be great for me and friends and family to get a good long looksie)....thanks again all you experts!

[Satchmo]

The 1/12 wave RMS surface accuracy they claimed on the 16" works out to around 0.66 ( 2/3 ) wave P-V wavefront accuracy which is around what the three 16" GSO mirrors I tested came out to. Not bad for a fairly thick ( 1.75" ) mass produced plate glass / BK7 that would be fairly hard to figure with any more accuracy .

It is simply 'wave inflation' to put specs in such a way that the average person will of course just lock eyes onto the 1/12 or 1/16 wave ....its an obvious marketing strategy that has been around for 50 years -. People will always want to believe that they can get everything for nothing. Most of these mirrors will never get debonded from their cells , make it back to a coater for recoating when the coating fails in a few years , to get a quality coating that might cost them $600 .

That being said a complete 16" scope is outstanding value if you're expectations are realistic for what you are getting . These results applied to the 16" that I looked at . The 10" and 12" I have seen in the field have been somewhat better.