Leroy’s LX200 tips

by Leroy W. L. Guatney

• [G] Generally all telescopes
• [L] LX200 only
• [S] SCTs in general

Directory Sections Advice for New/Soon-to-be Owners | Definitions | History | Statistics | More to come | Topics 10" vs. 12" | ALTAZ | Burn-in | Collimation | Declination Cord Wrap | ENTER key | Focus backlash | Focus shift | Hot-plugging | Limiting Magnitude | Keypad submenus | Mirror flop | Mirror shift | OTA Cool-down | OTA/Fork weights | POLAR | SCT size modeling | Slewing Speed | SYNCing | Updates |

10" vs. 12" [L]

First a word on 10 vs. 12 comparisons, synthesizing past discussion. If you already have a 10" LX200, you might not want to upgrade given what you already have. I upgraded from a 10" LX5, so I got much more than just 2" of aperture. My personal opinion here though, if you might want a 12", I wouldn't listen to other people's reasons to buy yourself a 10", I would just buy the 12".

In just 11 months, I've already traveled with, and used my 12" more than 12 years of ownership of my 10" LX5. Of course, the first six months after graduating from working and going to school over the previous five years probably doubled my 10" LX5's use too. :-) I describe my LX5 as "near new" condition, plus a little dirt. <G>

Like I said before, the 12" drags me out observing with it.
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ALTAZ [L]

For LX-200 ALTAZ operations, I always use a GPS to determine my latitude and longitude, and to set the onboard clock of the LX-200. I set DEC=0, point the base toward North, level the tripod/base, and pick two alignment stars using bestpair, freeware available at:

ftp://ftp.halcyon.com/pub/users/burrjaw/

Some tips for an express alignment are:

• set scope date/time and SITE
• power off and back on after doing the items in the paragraph above
• set scope SLEW speed to 3
• GOTO the first alignment star (the position will likely be off)
• ALIGN (ALTAZ, 2-star)
• manually slew the short distance to the first star and ENTER it
• after selecting second star from list, hit GOTO
• manually slew the short distance to the second star and ENTER it

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Balance [L]

Balance is an issue for any SCT, but this entry is LX200-specific. If you add 2" eyepieces, and any significant accessories to your LX200, you should have a set of balance counterweights. Another solution is the Meade dew shield because it is metal and heavy enough, you can use it to balance the load on your telescope.

You will place unnecessary load on your drives and gears thus bringing on mechanical problems. It doesn't have to be perfect, but it should be close. Piggybacked telescopes for guiding and/or photography will pretty much necessitate a 2-D counterweight system.

Follow the reference link below for a good explanation in the list archives of balancing with a 2-D counterweight system.
Top   Reference: 30cmSCT mailing list (Yahoo group membership required)

Burn-in [L]

The following applies to any LX200, but probably should be done while still under warranty. It is designed to stress the electronics. I have done this for every computer that I own. Once, a Dell 386 had a power supply failure just about 24 hours out of the box. This failure so soon after the purchase allowed me to take it back to the place I had bought it, rather than deal with the manufacturer.

My 12" is going on 11 months old. It is optically sharp, and mechanically solid. I did a "burn-in" on the electronics of my telescope as soon as I got it. Not one lick of problems since.

Brand new, unpacked, I plugged it in in my living room. Faked a star alignment, pointed at an object on the East horizon. I did an imaginary GOTO, but now I realize you could also just slew it there.

I would go to work, and when I returned it would be near the West horizon. Then I would goto objects across the sky back toward the East horizon. This gave me quite a bit of practice with the operations of the scope to, but it may be harder if you don't know the sky that well.

I did all of the above for 72 hours. At one point, everything seemed to overheat and got sluggish. It was July and hot (no A/C in the house). I powered it down overnight. All was well the next morning, and went right back at it to complete the 72 hours.
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Collimation [S]

I have owned Schmidt-Cassegrain telescopes since 1978. I currently own four models of three different manufactures. Two have been collimated, but not for reasons of observational deficiency. Once was re-collimated by a local telescope shop after they cleaned packing foam out of the OTA for me. (I know!) The other was bought used from the same telescope shop, and it is their custom to collimate telescopes before they go out the door.

Having said all of that, neither my 10" LX5, purchased in 1987, or my 12" LX200 purchased in 2000, have been collimated.

I still think it is a good idea to check one's collimation, however, I have never seen the need to collimate one of my telescopes. I recently did remove the corrector plate of my 8" Criterion Dynamax 8 for maintenance work (will eventually be a link here!). I will definitely check the collimation on it when I have the chance to since it's corrector was removed.

If you are a hard-core imager, this advice may not be for you.

I believe that you are best off to leave your collimation to the factory set alignment. A friend of mine said that his was fine until he had to collimate after his corrector plate was removed to check for damage after the wind had blown his over. Now he has to collimate frequently, and he is an imager.

I believe that people who do collimate frequently, end up collimating to the seeing, and that is fine for imaging purposes, because it will improve your results on any given night where the seeing is better than it was the last time you collimated.

I believe that the act of collimating takes you irretrievably down the path of re-collimation in the future. You do not want to overtighten the collimation screws, naturally, so it then is easier to loose your collimation when you handle the telescope, or it is taken on a rough ride someplace.

If you primarily use your SCT visually, my advice is to check, but collimate only when you must. To do the best job, it should be done on those nights when you have extraordinary seeing conditions, i.e. very stable images at high power. The telescope should be cooled down too.

The best reference I have found on the collimation is:

Thierry LeGault's Collimation page

You may also find some images which simulate what one may expect to see:

Startest Images Gallery

In the first eleven months of owning my telescope, I have had two or perhaps three nights of excellent seeing, and the factory collimation proved to me that these nights held for me exceptional views. I've never seen so many bands on Jupiter as I did in my 12", except in a 22" classical cassegrain. As a consequence, I am very happy that I have not tweaked the collimation on my 12".

The way I deal with seeing-limited viewing is to use the highest power that the night's conditions will allow. I then occasionally check for improvement of seeing with higher power eyepieces.

This has given me very satisifying results, and most of all, I'm not wasting time second-guessing my telescope and its alignment.
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Declination Cord Wrap [L]

The LX200 by itself will not wrap your declination cord around the base any further than approximately a half wrap. To really foul things up requires a human.

When properly setup with the control panel pointing to the North, the proper starting Declination for your mode (ALTAZ or POLAR), and all other values set (SITE, DATE, TIME, etc.), the LX200 firmware will pick directions to slew in, based upon where it is currently pointed.

If the operator/user of the LX200 uses the keypad keys (N S E W) to slew the telescope, and moves it in a direction that causes the cord to wrap further around the base, then the LX200, next time it is instructed to slew to an object, will further wrap the cord around the base.

The solution to this problem is to pay attention to the way the LX200 slews and if you need to manually take the controls, if you need to return to the earlier part of the sky that the telescope was pointed at, reverse the slew direction that the LX200 chose, and your cord will never completely wrap around the base.
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ENTER key [L]

There are two ways to use the ENTER key on the LX-200: press or press and hold. Getting confused between these two is quite easy even after you have become familiar with the firmware.

Press: this requires just a short press of the ENTER key. Some uses of the press are: selecting items on a menu, accessing keypad submenus after pressing the STAR or CNGC keys, or ENTERing to confirm that an alignment star is in the center of the field of view.

Press and hold: this requires that you press the ENTER key, and hold it down until the LX-200 beeps or otherwise responds. Some uses of the press and hold are: changing the system time, updating a SITE, or SYNCing.
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Hot-plugging [L]

You can DAMAGE your hardware by unplugging the keypad while the LX-200 is powered on. DO NOT hot-plug the keypad. I have not made this mistake myself, but I have heard this from others. Also I am told that a sudden unplugging of the power cord from the LX-200 control panel can cause problems with the motherboard.

I am also told that you can hot-plug the declination cord. But the control of the declination is obviously severed. I don't know if the encoders can get out of sync if this happens.

I can tell you that it should be safe to hot-plug the reticle eyepiece, and the Field De-rotater instruction sheet says it is safe to hot-plug it into the RS-232 port. Other devices that use the RS-232 may not be safe to hot-plug into the RS-232 port.
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Keypad submenus [L]

I am sure this is mentioned in the manual, but it is easy to overlook.

If you press either the STAR key, or the CNGC key, and then press ENTER, you are given useful submenus:

CNGC

• NGC
• IC
• UGC

STAR

• NAME
• STAR
• SAO
• GCVS

This is how you switch between the catalogs, and the STAR/NAME combination is particularly nice, in that you can pull up a star by its name. Thank you JOHN.
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OTA Cool-down [S]

Being a closed tube, the OTA (Optical Tube Assembly) of an SCT is subject to thermal distortions if the air inside the tube has not come to thermal equilibrium with the air on the outside of the tube. If your OTA is exposed to moderate to stronger breezes or winds, this will happen much faster. If the air outside the tube is relatively calm and undisturbed, it can take a lot longer.

Note that I used equilibrium. This is not a propensity for big words but rather an important distinction. It could be that the OTA needs to warm up instead of cool down.

The images through a telescope that has not reached thermal equilibrium seem like the more distorted images of a corrector plate heater that has been set at too high of a temperature for cool or cold weather.

Some people like the SCT cooling fan available at lymax.com but I have no experience with them. In Colorado, our air is usually pretty breezy.
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POLAR [S]

For now, this entry will contain only a link to my favorite polar Drift aligning web site. It is clear and concise. You'll only need it if you are undertaking astrophotography with your LX200 or other SCT.

http://www.maarten.vanleenhove.yucom.be/drift_alignment.htm

Also, this entry is categorized for SCTs in general. It will become more LX200-specific over time.
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Slewing Speed [L]

Set your slewing speed to 3 (or 4 if this is too slow for you) and it will save your motors, as well as quiet the LX200 down a little.

Try to think of it as a contribution to preventative maintenance.
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SYNCing [L]

You SYNC on an object if you wish to revise your LX-200 pointing information. To do this, locate an object in the center of the field of view. Make sure that the OBJECT LIBRARY entry for the object is displayed on the keypad. Press and hold the ENTER key. You will get a beep and a message.

You need to SYNC if you are in POLAR and you had previously shutdown with your LX-200 mounted on a permanent pier. When you power back on, all that is necessary is to SYNC on a star, and you have the benefit of the original polar alignment.

In ALTAZ mode, doing a 2-star alignment may not be possible. You can further refine your alignment by SYNCing on other objects. Bear in mind that when you SYNC in this fashion, it is better to pick Messier objects as their coordinates are better known than the CNGC objects are.

SYNCing on the Moon or planets can be done, but you need to cause the LX-200 to recalculate positions. This is done by re-entering the time and date. The longer that time passes after a recalculation, the less accurate will be your position data, and therefore the less accurate will be your SYNCing from such objects.
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Focus backlash [S]

When rotating the focusing knob of an SCT, you will sometimes need to reverse the knob to gain a better focus, one more pleasing to the eye. When changing the direction of rotation of the knob, there is some lagtime before the SCT focus knob begins to move the mirror, this time in the opposite direction. This is focus backlash.
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Focus shift [S]

See Mirror shift.

Mirror flop [S]

When moving an SCT from one side of the sky to another, gravity may cause the mirror to change its rest position against the baffle tube. This is due to the design of the SCT focus mechanism. The mirror rides on a baffle tube, and because it slides up and down that tube, it naturally has some give. This is seen in the form of mirror flop, and requires a small amount of re-focusing the image through the eyepiece or camera, or by locking the mirror in place and using an alternate focusing method.
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Mirror shift [S]

When rotating the focusing knob of some SCTs, you will sometimes see the image in the eyepiece move generally back and forth (left to right, or right to left) in an oval or circular fashion. This is due to the design of the SCT focus mechanism. The mirror rides on a baffle tube, and because it slides up and down that tube, it naturally has some give. This is seen in the form of mirror shift.
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SCT size modeling [S]

Why do present-day SCTs come in the sizes they do?

I attribute it to competetion and gradual saturation in the SCT market. When Meade went up against Celestron with the 2080 and 2120 (8"/10") models, Celestron had already pretty much established their own 5", 8", 11", and 14" models (note the 3" graduations).

Meade went direct against them with the 8", and I see the 10" as attempting to undercut the share for the 11". It's always easy to rationalize getting a little smaller scope, i.e. "Almost as much aperture, not as heavy, not as expensive, ..."

Afterall, Celestron used to produce a 10" and a 16" of their own, along with the 22" (note the 6" graduations). Also note that the 16" and 22" were what I would call institutional telescopes as well, i.e. small colleges/universities, etc. It may well have been the success of the 22" that did in the 16". Grant recipients thinking, "Hey, we've got this $100,000, we can afford a little more bang for our bucks besides a domed or roll-off roof building", so only a few 16" scopes were ever sold.

Meade further bracketed the Celestron market share with their 12". This was pretty smart. A key factor in my not buying a C11 last year, besides the lack of forks (on new scopes), was the singular 1" increase in aperture from my 10". Hence my purchase of the 12" (note the 2" graduations).

With a 14" firmly established by Celestron, and their leaving the 16" relegated to history, naturally Meade came along and secured that aperture size as well.

I think the 9.25 is probably an optimization of maximal baffle for minimized obstruction given the primary's size. And, when you fit it in to this model, the 9.25 is the only place Celestron had left to go without direct competition with Meade.

Celestron's first graduations were 6". Market demand halved that to 3". Meade started and expanded by 2". Together they have saturated the market down to 1" (counting the C9.25 as a 9")—8, 9, 10, 11, 12, and then jump to 2" on the upper end—14, 16.

Below 8", it doesn't pay to drop in increments of 1". Criterion competed against Celestron with their own Dynamax 8 (D8"), and then a D6" to go against the C5". After Bausch & Lomb took over, they decided to bracket the other side of the C5", with their 4" model. Meade also did this with their 2045 4" model.

For whatever reason, 7" has been left to Maksutovs - Meade and Questar. Maybe figuring it was the best way to compete against an 8" SCT.
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Limiting Magnitude [S]

Clear Aperture (D)	Manufacturer	Limiting Magnitude (m)
5"	Celestron	13.2
8"	Various	14.2
9.25"	Celestron	14.5
10"	Meade	14.7
11"	Celestron	14.9
12"	Meade	15.1
14"	Celestron	15.5
16"	Meade	15.7
22"	Celestron	16.4

Formula: m ~ 7.7 + ( 5 * log(D) ) where D is in cm. This also requires magnification equal to ten times the diameter in cm.
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OTA/Fork weights [S]

Clear Aperture	Manufacturer	Weights
9.25"	Celestron	OTA	20 lbs.
10"	Meade	OTA	27 lbs.	Fork	31 lbs.
11"	Celestron	OTA	28 lbs.
12"	Meade	OTA	30 lbs.	Fork	40 lbs.
14"	Celestron	OTA	48 lbs.
16"	Meade	OTA	113 lbs.	Fork	112 lbs.

Top   Reference: 30cmSCT mailing list (Yahoo group membership required)

Updates

I have plenty more to add here, so bookmark this page, and check back from time to time.
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