Meade 16" Lightbridge

[TARDIS KINGAROY]

This is my first post-I ask your tolerance of my ignorance of astronomy and my longwindedness. Two years ago my wife and I visited the Maidenwell Observatory (Jim has three Meade LX200GPS) We then didJim's astronomy course which I highly recommend.) I then bought a Meade 8"LX200GPS which for a numer of reasons(mostly work related) I have only started to enjoy since I built a "Roll-off Roof" observatory. My interest is with the Moon and the Planets-particularly Mars. I have a strong desire (obsession?) with seeing Mars via my own eyes (ie,rather than "imaged") and I now realise I will be unlikley to achieve this with the 8" Meade. The 16" Lightbridge seems very good value, but can an unguided Dob be comfortably used to observe Planets? The only astronomical scopes I have ever looked through are Jim's 14"Lx200 and our own 8"- ie,I have never viewed through a Dob. I realise anything is possible, and that long before Schmidt-Cassigrain scopes and computers were heard of, people were recording sketches of detail on Planets;but how practicable is it to do this? I have been enjoying watching Jupiter and its Moons over the last week, and even with a Tele-Vue 32mm Plossl, if the "auto" is turned off, the view does not last long. I am aware that whatever scope I use to achieve my goal, it will probably require hours at the eyepiece, waiting for that magical few minutes (seconds?) of good seeing. Are sensibly priced drives available for large Dobs? As portability is not an issue, are there any other (affodable) large scopes which will let me see Mars as more than a tiny orange blob? [I have just re-read this-by "ignorance" in the first line, I meant "practical Ignorance" -I learnt a lot from Jim's course. DENIS (KINGAROY TARDIS) 26'31'46.42S 151'48 16.33E

[norm]

Welcome to the Forum Denis. :welcome:

I'll let other knowledgeable folk answer your questions.

Just out of curiosity did you have a budget in mind?

Clear Skies. Norm

[ngcles]

Hi Tardis & welcome,

I don't pretend to be the font of all knowledge on telescopes, but here goes.

A 16" 'scope theoretically has much better resolving power and will be capable of resolving more detail more easily than your current 8" -- of that there is no doubt.

You will also get a brighter image of planets and much else. So from that point of view, stepping up in aperture to see more detail _on planets_ at least seems like reasonable advice.

With a really well made dob, it is certainly possible to hand track and enjoy a frustration-free view at powers up to about x250. Commercial drive systems are available for dobsonians but are in truth complex and expensive. For example, on my 18" Obsession clone I have an Argonavis and a Servocat which work together flawlessly and produce excellent "visual grade" tracking. With a bit more tweaking and a field de-rotator, I could do imaging as well. However for that level of performance you will have to outlay about $2,600 on top of the cost of the 16" lightbridge bringing the total cost to $5,500- or thereabouts plus eyepieces.

As an alternative, the Mel Bartels telescope-making site has instructions and what-not for a dob drive for somewhat less outlay, but it is very do-it-yourself. Another alternative is a Poncet platform which provides quite nice tracking and these can be home made for a few hundred dollars but some think they are a bit fiddly. Others love 'em.

Having said that, in practical terms, the increase in aperture and thereby the ability to see increasingly fine detail on planets and the moon is very much limited by our turbulent atmosphere (seeing). Assuming the planet is reasonably high in the sky, on a really good night the 16" will show somewhat more detail on Mars. However, during this coming apparition, Mars be close to aphelion (the furthest point from the Sun in it's orbit) meaning it will be pretty small (as viewed from Earth) even at it's best. And, it will also be quite low (comparatively) in the sky. During this apparition, the maximum altitude Mars will attain in the sky will be about 30 degrees -- that's pretty low and we downunder will all be looking through a lot of air (and consequently moving air) while observing Mars this time.

The combined effect of both these factors means any advantage the 16" might have over and 8" in pure theoretical resolving power, is likely to be much diminished unless the seeing is almost perfect -- rare if not very, very rare in Summer and that low down to the horizon. Sorry to say, but that is the truth _as I see it_. The next reasonably good apparition of Mars as seen from downunder is about 6-8 years away I'm afraid. It won't be impossible to see great detail this time -- just a lot harder and rarer than in say 2003 or 2005.

In summary, this time around, the 16" won't be a big (if any) advantage _on Mars_ over the 8". However, on Jupiter and Saturn next year which are both somewhat if not much higher in the sky, it would be somewhat better than the 8" -- and a lot brighter image.

And then of course there is the vast leap (no, not tempted to say "quantum leap") in performance on deep-sky stuff. A 16" has 4-times the light-gathering power of the 8" meaning everything deep-sky will be 4 times brighter and much, much better resolved. The difference between say 47 Tucanae (NGC 104) in an 8" and a 16" has to be seen to be believed!

The switch to a _truss-tube_ Newtonian over commercial Schmidt Cassegrainian also means you will have to learn to collimate the telescope well (every time you assemble it) to get a really good image (it's not that hard!) and be prepared to do a bit of maintenance from time to time in giving the mirrors a wash to remove dust etc.

I've had experience with two different 16" lightbridges and for the money, they are very nice 'scopes -- not perfect in every way but really very good for the price.

That's my two-bob's worth!

What do others reckon?


Best,

Les D
Contributing Editor
AS&T

[sejanus]

i have been looking at getting tracking going on my 16". So far, www.roundtableplatforms.com have quoted $850 usd to send one here. So it ain't cheap unfortunately.

not sure yet if I'm going to go ahead with it. I'd like to though as at 6mm stuff moves rather quick.

[astronut]

Hi Tardis,
:welcome: to I.I.S
I agree with all that Les spoke about, but I would like to add that an 8" aperture is not small!!
It will still give you excellent views of any of the planets, it's just that the 16" will be a whole lot better!!
Your current scope already has tracking capability, this is a big bonus if you're into sketching your image.
With the dob you will have to nudge it along to keep the image in play.
A tracking platform will help with this.
Whether you stick with your current scope or go to the larger aperture, the images will be very good.:thumbsup:

[Dujon]

Hello, TK, welcome to the good ship IIS.

All the above advice is good and accurate to the best of my (little) knowledge. One thing that I don't think has been specifically mentioned is that as you increase aperture you also increase the effects of poor seeing.

I have only had my current 'scope for about a year or so and, because of back problems, have not had a chance to use it as often as I would like. Nevertheless I have had the opportunity to view the moon - not too hard - and Jupiter. At this stage I haven't chased Mars around the sky. Given that these (Moon/Jupiter) are both bright objects I have tended to use short focal length eyepieces. You are right, the image zips through the field of view at a fair rate of knots.

The inference here is that you need to ensure that your mount is silky smooth in order to 'follow', at high magnifications, whatever it is that you are observing. My beast is but a 10" (252 mm) Newtonian and I've not had the opportunity to 'look through' a 16" monster. At this stage I've merely mucked around with the mount, but it's still a bit jerky at times - presumably something that would be accentuated with a larger aperture device. Perhaps others could comment on this aspect of a large 'Dob'?

By the way: I found I had to use my moon filter when observing Jupiter and even then found myself blind in my observing eye when looking away from the 'scope.

[TARDIS KINGAROY]

Norm,

[TARDIS KINGAROY]

Norm-thanks to you and everyone else for your thoughts and interest. As this next scope will be a "onester" to probably last me until I shake off these mortal coils, I do not have an exact dollar budget. The scope is roughly $3000-I have not costed 2" eyepieces, but lets say $1500 for a couple of top quality items,and $1000 for a "Drive." I am not rich, but I amnot poor either (yet!) and the difference between the standard Meade eyepiece and the Televue I bought recently, is impressive. So that is $5000 to $6000. If there is something out there that will satisfy my lust for MARS which costs say $500 more, I would go for it. DENIS

[Mick]

Don't give up on your 8" SCT TK, as stated no scope is going to compensate for poor seeing. Your scope is capable of stunning views of the planets at the right times and with good seeing. In 2001 Mars was shrouded in a dust storm that engulfed the entire globe making the viewing frustrating and disappointing. 2003 and Mars was at it's closest approach to Earth in a very long time and on the night of 26th of August I was rewarded with some of the best views of this planet that I have ever witnessed. 2005 was almost as good, I haven't viewed Mars yet this year but I will very soon. Your best chance of seeing detail visually on Mars is at or around opposition but you must have good seeing. Good luck and welcome to IIS.

[jjjnettie]

Welcome to IIS Denis.