Better Mount for LX200 OTA 

       

From: Alan Voetsch <avoetschmail.com> Date: Mar 2001

I'd like to get some feedback on the subject of mounts. I use a 12" LX200 Classic. Add to that a NGF-S, Taurus Tracker, OM1, Meade counterweights, a Losmandy dovetail plate that will soon be holding a TV-85 and you can see there's a potential for trouble.

So, I'm starting to look into replacing the mounting. Another of many subjects I know little of. I know of the G-11, MI 250, AP900, 1200... I'm sure there are others.

What I'd like to find out is: what are you using, how well does it work, how happy are you with it...

------------------------------------------------------------------------

Subject: Best Mount for LX200 --part 2

From: Doc G

This is a very good question. I have studied mounts for about 6 years now. There are several things about them that I feel are mechanical basics. I will try to explain briefly.

Let me first confess that I have used fork mounts (the LX scopes) almost exclusively. I also confess that I generally do not like GEM mounts for the reason that they swing the eyepiece to all sorts of unpleasant viewing positions and they have some problems in passing through the meridian when imaging. Though some of the newest GEMs are quite good in this respect.

Now I will get into trouble. Fork mounts of the size and construction that we (Meade users) have in hand are not as solid and stable as the better GEM mounts you are considering. Of course the GEM mounts alone that you list cost more than the entire LX in most cases. So this is not a completely fair comment.

Still from a purely mechanical design aspect, the GEM mount can be made very strong and stiff because it is very compact. The RA and Dec axes are generally one solid block of metal with both relatively large bearings and large worm wheels. The required equatorial angle can be built into the mount with great mechanical strength since it can be applied very near to the point where the RA and Dec axes cross.

In summary, the mount is compact and mechanically strong. The center of gravity of the OTA is as well near the confluence of the axes. It can easily be balanced with counter weights.

The Fork mount in contrast has a much more spread out structure. In the case of the LX scopes, The entire weight of the forks and the OTA are suspended some 19 inches out from the RA bearing. (in the equatorial mode)

This puts great stress on the bearing structure and requires the bearings to be extremely stiff. Any flexing of the bearings is multiplied by the long lever arm. From basic mechanical considerations, the fork mount is a large mass at the end of a spring. Getting the springiness, which is mainly in the bearings, to be small enough takes large, high precision and thus expensive bearings. Supplying bearings of the required size would make the costs of the fork mount much higher. I actually half completed a fork mount which was strong and solid. But I terminated the project which was getting so costly that I would have just as soon purchased a Paramount or equivalent.

Thus, a very much better fork mount, than that of the LX, could be (and are) built, but again at a cost of more that the whole LX scope costs. Note that mechanically, the fork mount is similar to the English mount used on the Hooker telescope, but in that case the fork is held on both ends. There are many variations of mounts of course. Unfortunately the fork, held at one end, is probably the least stable of them all.

But I have gone on long enough. What this has to do with your question in summary is this.

You have purchased an affordable scope with a mount that is adequate for viewing and somewhat problematic for imaging because of its strength and stability. You are considering mounts that are certainly better, but at a cost that is probably several times the cost of your entire scope.

Thus as with so many things, you need to balance your use and needs against the investment you want to make. This is a personal decision. I would choose if I had unlimited resources, an RC optical tube and put it on a AP1200 mount. That would certainly be better than any LX scope. Of course it would cost a bit more.

------------------------------------------------------------------------

Subject: Best Mount for LX200 --part 3  

From: Michael Gregory

I switched my 10 inch LX200 to an Mountain Instruments MI-250. I normally have two scopes, a camera (sometimes two at the same time), ST 4, upper and lower Losmandy dovetails, and 45 pounds of counterweights. The measured PEC with this setup is about 7 arcseconds (without training the mount's PEC correction).

I think all of the mounts that you mentioned are good with the AP 1200 probably being in the spectacular category.

I have been very pleased with the MI-250, although at times I miss the GoTo capability. DSCs work great with the MI-250 (high resolution encoders are built-in), but it's just an extra step in the process. Mountain Instruments has just released a GoTo mount. Another nice thing about using the MI-250 with the Meade 10 inch is the ease of setup. The mount Dec assembly is easily removed so none of the individual pieces are very heavy. I still use the Meade tripod. The mount will run for two nights of imaging using one small nine-volt battery (one of the advantages of not having GoTo capability).

------------------------------------------------------------------------

Subject: Best Mount for LX200 --part 4  

From: Bert Katzung <katzung1home.com>

My little bit of feedback (but without any experience mounting an LX OTA on a GEM). I have an LX200 8 inch and pretty much abandoned it for photography because of shaky forks and inability to get it to track with an ST-4. (The LX is still my favorite for star-parties.) I switched to a Losmandy G-11 and 5 inch refractor and can highly recommend the mount with this kind of load (including an 80 mm f/11 guidescope on a side-by-side plate). The G-11 is truly rock solid; damps vibrations in less than a second and tracks beautifully with the ST-4, even in moderate winds. I have just taken delivery on a 1200GTO and will be putting a 12.5 inch RC on it. It is another order of magnitude up in solidity (if that's possible) from the G-11 and also tracks perfectly with the ST-4. Depending on your load, you can't go wrong with either of these mounts.

------------------------------------------------------------------------

Subject: Best Mount for LX200 --part 5 of 5  

From: David Bahr

I have a Parallax Instruments HD150C mount and it is wonderful. Great features, great stability, etc. I waffled between the Mountain Instruments and the Parallax and finally selected Parallax because of the AP GoTo features and their excellent machining (they custom built a pier adapter that would fit my observatory). I elected to fix the latitude on my mount which also increased the stabililty.

Subject: Switching from the LX200 Fork Mount to an Equatorial? --part 1 of 3  

From: Emilio Robau <ejrconsult-rwa.com> Date: Nov 2003

-----Original Message-----
Herb HReiheraol.com
> I'm still curious as to what people think about switching
> from a fork to EQ mount, say if I take my 10" LX200 OTA and put it on a
> new or used Celestron CGE 1400 or Losmandy G-11 mount. Would such an EQ
> mount solve the problems we've discussed, and could they handle a
> piggybacked 4" refractor?

A couple of months ago I purchased a Losmandy G-11 with the Gemini GoTo and took the 10" Mead OTA off of my LX50. The difference is like night and day. I am only talking stability not the GoTo function which are excellent on the G11 with the Gemini GoTo. I had a choice to purchase an entire Meade 12" GPS unit and opted out for the Losmandy without the OTA.

When I first got back into observing I remember all of the experienced salts saying spend your money on a mount. A good mount can make a marginal OTA perform. This is not a two way street. A good OTA can not make a marginal mount perform. This is absolutely the best advice I ignored. Of course I went for the most that my money could purchase and in that vein Mead is one of the best. I regret not purchasing the excellent mount first.

I have absolutely no regrets about the switch over to the Losmandy. I am actually thrilled with the performance of the mount from every aspect. The bottom line is you get what you pay for. In my opinion the selling price of a G11 at approximately $3,200 new with the Gemini GoTo without the OTA is a better long term value if you want to do CCD imaging and was worth passing up all that was offered with the comparable 12" Meade GPS with the OTA at about $3,600. I think that GEMs (German equatorial mounts) are inherently more stable than fork mounts.

I think that anecdotal evidence suggesting that the Losmandy is somewhat more steady is kind of an understatement. I think the 10" LX50 has the same basic construction as the 10" LX200 with respect to fork structure. If this is the truth, then I can tell you from experience (anecdotal evidence have not done the study that Doc G would do) that the G11 is far superior with respect to stability. Rock solid mount when matched with a 10" SCT OTA which weighs approximately 28lbs. Matched with the 10" Meade or the 11" Celestron OTA, I think the combinations are the best long term value in the industry today. I think this comes from the fact that the GEM has the load directly above mount, Losmandy sells a great mount and Mead and Celestron have become masters at mass producing good OTAs.

My fork mounted scope hung quite a ways away from the main structural loading point. The forks as a result were more prone to vibration when knocked or worse yet in a small breeze. I looked at the new Celestrone CGE units and after lurking on the user's group, hearing of the problems and realizing that this is a first production run I paid the extra money and went with the tried and true Losmandy.

-------------------------------------------------

Subject: Switching from the LX200 Fork Mount to an Equatorial? --part 2

From: Emilio Robau<ejrconsult-rwa.com>

-----Original Message-----
From: Mark de Regt
I do have a couple of questions:

Can you take pinpoint images at 2500mm focal length, including the ability
to take long-exposure individual images (20 to 30 minutes, which is
necessary at that slow focal ratio when imaging very dim objects like
Stephan's Quintet, or when imaging with a hydrogen alpha filter)? I would
be curious to see such images with that load on a G-11.

Do you have to flip the OTA at or near the meridian? I hear that is
often necessary with GEMs, and that would be a drag in the middle of the
night, in the middle of an imaging session.

I trust that you are not suggesting that a $3200 mount is necessary for
purely visual work, but, rather, for quality imaging.

There is another, much less expensive, alternative for many, which I lucked
into because my first CCD camera was a used SBIG camera. The SBIG AO-7,
which I bought used for $1000 (it's $1200-$1300 new), when used with an SBIG
dual chip camera, solves all of the shortcomings of the LX200 mount. If one
is just making the decision to get into CCD imaging, for not much more than
the price of the G-11 with GOTO, one can buy a sensitive, large-chip CCD
camera with built-in internal guider and small pixels (the ST-2000XM) and
the AO-7. This certainly is a less expensive alternative than buying a
mount, and then still having to buy a camera, and gets you a great camera in
the bargain. In fact, right now, one can buy an ST-7ME for $1295, and color
filter wheel for $1000, and an AO-7 for $1300, and have a wonderful
combination for just about the same price as the G-11 with GOTO. I find the
convenience of the fork mount very nice, and the combination of the SBIG
camera/AO-7 to be a superb match for the LX200. I have had a great deal of
fun, and success, imaging with that combination.
-----End of Original Message-----

The responses to your questions are as follows.

I can not take pinpoint images at that long of a focal length. I am not sure anyone can. That is a tall order at that focal length. Maybe someone else can but I can't. Some of this is due to my lack of experience and need to tweak the set up further. I am a not a beginner but certainly not ready to publish anything. More importantly I think that the limitation of the equipment, even with the good performance of a G11, will ultimately govern the ability to take the type of images you are talking about at 2500 mm. When you ask that question my initial reaction is no way. I think flexure and other issues will play havoc with the pinpoint goal. Judging from what I have seen others do, it may be possible but very difficult to achieve. I have gained great respect for those who have mastered imaging. Take a look at Philip Perkins and his migration to better equipment which included a switch to a GEM. He and many others end up with GEMs as they progress in the hobby There is an abundance of examples of work done with the G11. I think you can judge for yourself. At the end of the day I think your probabilities of achieving what you are referring to are enhanced with the G11 or better stated a quality GEM.

I am not sure that I would replace good structural design provided with the gem with electronics such as the adaptive optics you are referring to. I think again that it is better to start with a good foundation and build from that. I will never purchase a fork mounted scope again. I don't have any problem with flipping at the meridian. I just plan for the flip. In my short time with this scope It has not been an issue. When I looked at the 12 " Meade one drawback was the inability to have the scope swing fully through the mount.

In the could have, should have, would have, done category here is how I feel. I should have not purchased the LX50 when I could have purchased the G11 and an OTA without the Gemini GoTo for a few dollars more.

The only reason I chimed in was that I made mistakes and the gentleman that is asking should consider my opinions. I will go out on a limb and state my opinion absolute terms and get back to work. The LX 200 is the best most versatile innovative (at the time it first came out on the market) and has probably had the biggest impact on amateur astronomy since the invention of the GEM. With all that said if you want to get deeper into imaging............Herb, go out and buy yourself a quality GEM. You won't be disappointed. It will outperform a fork mounted scope hands down. Spend the extra money on the mount platform. You will never regret it. All of the pros advise accordingly. You can even add all of the adaptive optics and such and get even better results at the end of the night.

-------------------------------------------------

Subject: Switching from the LX200 Fork Mount to an Equatorial? --part 3 of 3  

From: Glen Sharp <dernedidinsightbb.com>

I went to a G 11 with my 7" Mak with a 4" Vixen f/9 piggybacked and I find it way more stable than the LX200 fork. BUT as I have learned, there are just as many tracking issues present with the G11 as there were with the LX mount. And the added inconvenience of no GoTo, and the ever present meridian flip needed with the G11. Also with the 7" OTA, 4" OTA, finder, camera, ST6 for CCD or autoguiding, and the needed counterweighting on the OTAs I have the G11 Close to 46 lbs of it's 60 lb max rated capacity. As such the balance issue seems to be even more critical with the G11 than it was with the LX fork. Would I make the change again...no. IMHO I didn't gain enough for the extra investment I made.

Subject: Other Mounts for Large OTAs --part 1 of 2  

From: Scott Oates <SOates4616aol.com> Date: Jan 2003

...Gary, since you've decided on to find an AP1200, might I suggest you also take a look at the new Losmandy Titan mount. Initial reports show a PE of 4 arc sec and the mount is rated for a 100 lb. load. It also comes with Gemini LVL 3 Goto. The link is: <http://losmandy.com/hgm-titan.html>

----------------------------------

Subject: Other Mounts for Large OTAs --part 2 of 2

From: Alan Chen

I posted a PE plot of the Titan on my website in the equipment section (maybe this is what Scott is referring to). Without any major adjustments, I'm getting approximately +1.8/-1.5 arc-seconds of PE out of the box. I haven't yet attempted any PEC, but just allow my guider to correct the PE! There isn't much in the way of "high frequency" error (large transient spikes), so my guiding is no longer a limiting factor.

<http://www.heavenlyview.com/>