TRO Blog

A Suitable Chariot for the Beast?

Meade LXD600 Mount

“The Beast” on the LXD600 mount with original 2.xx version hand control.

In June 2021 I drove to Phoenix to see my mom. On the way home I went through Tucson heading to Southern New Mexico to visit my son. On a whim I set the GPS to take me to Stellarvison Astronomy shop. Bad idea. When I got there I asked Frank Lopez, the owner, if he had any LXD750 mounts. He said without batting an eye “Yes three of them.”  He also had several LXD650’s and even a few LXD600. This series of mounts are up to30 years old, not an expected find even in a used telescope store!

The mounts were Specifically developed for Meade’s lineup of ED refractors in the 1990’s. It’s very difficult to find information online about these scopes and mounts. Much of the information you do find is very negative. The 7″ ED refractor that uses the LXD750 mount and tripod had a lot of issues and often had to be returned to the manufacturer. This obviously did not set well with customers. However, the mounts were some of the first to use “Goto” technology. They are set up to be similar to the feel of a professional observatory of that day. Big thick “paddle” controllers and lots of numbers to input. The optical tubes are also some of the first commercial “Extra Dispersion” glass color corrected refractors and had the usual teething issues of new products. 

So why in the world did I want an LXD750 mount?

Size and cost, that’s why! Years ago I bought a used Celestron 6″ F/8 refractor (the “Beast” in a parody of David Levy naming his telescopes) and I needed something that could handle it. The first mount used for the 6″ actually came with the scope when I got it. It was an old Orion Skyview Pro with a dual axis drive. It worked, but not well. You could get a 45 second, unguided image if your polar alignment was good, the wind wasn’t blowing, you didn’t touch it and a large truck did not pass by! Then only every other image would have round stars!

After a few months a Celestron ASGT mount was purchased but still not sturdy enough for all conditions. However, with a lot of patience I did get a pretty good image of M 57 with the Celestron ASGT. After a freak 120 mph windstorm demolished the ASGT mount I purchased a used Orion Sirius mount. This was better but it still was not made for a refractor this long. It was not the weight but the long “lever” action of the 1200mm focal length tube that made these mounts unsuitable.

M 57 with the 6″ F/8 achromatic refractor using a Johnson-Cousins V photometric filter and a SBIG ST-7E CCD camera.
The Celestron 6″ F/8 achromatic refractor mounted on a Celestron ASGT at the City of Rocks north of Deming, NM.

Because the LXD mounts are so old the prices are usually pretty low, as well as being massive. A new similar weight mount can cost 5000 dollars and up, and that’s for the low end of the price scale. Plus the mounts can hold a lot of weight, somewhere around 100 pounds. The 7″ refractor was big around, long and heavy.  You needed a substantial mount just to use it visually, much less for imaging.

The motor drives are odd on this series of mounts. They are essentially a “slot car” motor geared down to drive the mount. They actually run over 10,000 rpm but by gearing them down, have pretty good torque. This contrasts to the mount itself which uses heavy metal and even steel bearings on the shafts. No plastic here! If Meade would have made the drives as robust as the mechanical part of the mounts they would still be a mount of choice to this day. However, if the drives ever die I plan on using the mount without them and it will still handle a large telescope well.

Unfortunately, I had a problem in buying the 750. Being on vacation and not having planed on buying a large mount, I had not left room in my car for something this large. So I settled for the next best thing, an LXD650. This is a scaled down version but with an effective weight limit of around 50 pounds. Most forums say it only holds about 30 pounds but those who have used one for years say 40-50 pounds. Especially if it is a shorter tube than a refractor.

When I got home I promptly blew out a capacitor, since it was a 19 volt power supply.  The stock capacitors couldn’t take my ham handed bumbling.  Frank at Stellarvison, was gracious enough to let me send it back and then replaced it with the LXD600 which is the same as the 650 but uses a safer 12 volts instead. The higher voltage was added to the 650/750 models (without any electronic changes by the way) to facilitate a faster slew speed. This created an issue with the capacitors blowing out and sometimes taking a ribbon cable or board out with it. I am not in that big of a hurry!

So how does this antiquated piece of technology work?

Quite well actually! Like a lot of these older mounts it has it’s quirks and oddities that you have to work around. All first generation telescopes have these problems. If you don’t believe it, read “The Perfect Machine” about the Palomar telescope. An engineer discoved a fish weight scale in the mirror structure after many years of operation and removed it thinking it shouldn’t be there. Turns out when it was removed the mirror image went bad until they put it back in. After a few generations and lots of observer feedback, these type of “kludge” fixes are no longer needed in new telescopes. But until then you just come up with work arounds.

The LXD600 sat in my garage over the winter. I had used it for some planet and moon images in the fall of 2021 but really did not do more than set it up and take pictures through the 6″. The reason for this was the cold as well as recovering from a serious heart condition. It was difficult in the fall of 2021 to get the energy to do more than just uncover and run my actual science imaging set up, much less polar align, use the antiquated star numbering system, learn the quirks and heave the 6″ onto the mount.

It is “common knowledge” that you can’t take good color images through a short focal ratio achromatic telescope (F/5-F/10). Obviously, this is false. Using a Celestron Minus V filter stacked with a IR/UV cutoff filter eliminates most ( but not all) the effects of Chromatic Aberration with a camera. What remains is easy to deal with. I use Lightroom but there are numerous other software that will do the job. The Celestron Minus V filter, which is a rebranded Baader filter, has a significant light leak in the infrared which can degrade pictures. Adding the UV/IR filter stops this leak and gives an image with less false color. However if you don’t mind a little purple fringing the colors on the disk are terrific without a filter at all!

Jupiter taken through the Celestron 6″ with a ZWO 120 MC camera.
Here is an image of Mars in the fall 2020 taken with the 6″ mounted on a Meade LXD-75.

Last month an Ebay a dealer listed a pair of EPROM chips for sale for the LXD600/650/750. For 25 dollars delievered I thought it was worth taking a chance that these were some of the long sought after, seldom found, chip upgrade sets for these mounts. Meade’s early versions (ver2.xx) had a 780 object database and limited menu options. The version 3.xx and above chips had 64,000 objects and a much more productive menu. Meade made a few of these upgrade kits but finding one is rare. Since I had the old 2.xx version I was excited to try out this upgrade.

The biggest issue was that the old v2 Handset was not compatible with the v3 chipset. So after the chips came in they were installed in the old board. The boards had obviously been made for this new chip but the version 2 chips had 4 less pins. Not sure why they would put in smaller EPROMs but they did. After installation of the new chips the motors initalized but the handset never “shook hands.”

Clearline Technology provides a new updated replacement handset for 150 dollars. This replaces the old handset with a brand new contoller with capacitors that can handle the extra voltage of 19 volts, though it still works fine for the 12 volt systems. Clearline promptly sent out the handset and when it came in, it was of course sprinkling outside. Eager to see if this upgrade worked I went outside, raised the tarp cover enough to plug in the handset. After powering up the mount it didn’t work! I went in and sent off an email telling Clearline that the handset would be sent back. After the sun came out I went outside to bring in the mount head to replace the old chips on the board and saw that the RA cord was not plugged in. So I plugged in the RA cord and then the handset, powered it up, and it worked great. Now the handset reads Version 7.2! Success, it is a miracle!

The Clearline Technology Handset.

The alignment system is a bit kludgy. To align the scope you have to set the scope in home position, then use the HC to move the RA to 90″ east of where home position is. There is a 2nd mark to indicate when it is in the correct position. If you don’t follow this exact procedure, the optical tube will hit, the tripod. When you press enter and begin the align, the tube will move to where polaris should be. You then use the manual adjustments to center polaris in camera or eyepiece then hit enter again. It will take you to a bright star where you use the handset to center it, then hit enter again. This brings you back to the Telescope and object menus. To get a fair polar alignment you need to do this process multiple times at least 15 minutes apart. Once you get it polar aligned, experienced users have said that you just don’t bother to center Polaris in the center of the field of view and just click enter to go to the next star to align.

Sometimes you press enter and nothing happens. The hand control is fairly sensitive and a long push or too short of push will not work. You have to at times, press enter multiple times before it responds. Not sure why, but these are some of the quirks refered to above. The clutch knobs also need to be tightened good or the scope slips. This is easy to overlook.

One of the other quirks is that the original setup used a built in cradle for each size refractor in the Meade lineup. So you have to buy 2 adaptors to use a common dovetail of today. Mine came with a Farpoint adapter on an ADM assembly that works very well for the standard Vixen style dovetail. However, the ADM assembly that holds the adapter was actually a little loose and caused the adapter to be “off” a little when you goto an object. When that was tightened down it became much more accurate on the slews and centering.

The Farpoint and ADM adapters.

The # 1697 Manual, part 1&2, will be your best friend! This is the name of the goto system that was added during or after purchase. The mounts orignally came without the goto feature and had to be added to the early models. It was easy to install and most mounts today have this system. I suspect if you were going to spend all the money you had to spend for the telescope and mount you might as well spend a bit more and get it with the goto feature. The stars and objects in the #1697 system are given numbers that you enter in the the appropriate menu. Messier objects use their regular numbering but the stars have 3 digit numbers that you have to memorize or look up in the manual.

There is a “CCD port” on the mount that uses a standard ST-4 cable though you can pulseguide with a modern ASCOM driver. PHD2 guides it quite well but you have to have the ST-4 cable in place for it to pulse guide. The manual gives you instructions on making your own cord which tells you this was a pioneer feature of the mount. This is just another quirk of the system.

There is also a RS232 port that uses the Meade 507 or LX200 Classic cable. Unfortunately, the one that I originally bought for this scope got trashed when I stepped on it one night testing it. Before this accident it was driving the mount through TheSky 6 Pro, so this means it should run under other planetarium programs. There are several drivers that you can get on the ASCOM website.

I recieved another equivalent Meade 507 cable from Ebay for 20 dollars delivered. This time I am reinforcing the serial cable end with permanent “Gorilla Glue” brand Duct tape. The telescope end is already reinforced. It is just too easy to step on a cable in the middle of the night and tear a wire loose!

Generic Meade 507 cable with Gorilla Tape.

When the mount was purchased it came with one weight. For all but the 6″ refractor it is all you need since the shaft is extra long. For the “Beast” you need slightly more weight, especially with a camera attached. Problem is, the shaft is an inch in diameter which is wider than all my other weights. When I found a weight that would fit, it cost too much.

So I made one! Using a 2.5 and 5 pound weight I bought 1.25″ shaft collars from Grainger and superglued it to the weight. In the first efforts to do this the glue would hold for a week or so then it would come off. The trick is to use alcohol to wipe off the dirt and grease on both surfaces before applying glue. I used a hammer on the shaft collar and it would not come off the weight. Also replaced the set screw with a slightly longer one. In the future I plan on using Alum Bond, especially for a heavier weight. Alum Bond advertises a holding power of 25,000 pounds and it seems to work well with metals. It fixed the broken spreader plate and it is now stronger than what it was before it broke.

Walmart weight with a Grainger shaft collar.

For the money this is quite a mount. It holds the 6″ refractor steady and points accurately. Spent an hour or two in totally wretched conditions the other night going to different deep sky objects with the 6″ telescope. Even with the marginal conditions and 10+ mph winds it held the scope steady and slewed to the target in a wide field eyepiece. Users report that if you fix the cone error mechanically the LXD mounts are quite accurate. With the Smart Drive feature you can correct for irregularities in guiding (PEC).

My plan is to use T-Point under TheSky 6 to correct for cone error and an auto guider for imaging. The 6″ refractor will be used primarily for planets but will occasionally be used for deep sky work. Recently I purchased a 6″ TPO Ritchey-Chretien optical tube. The “Mini-Beast” will be placed on this mount to finish a study of the Central Stars of Planetary Nebula study. It is also fun to use a Orion ST-80 to deep sky image with the mount. Defintitely a case of mount overkill!

Orion ST80 refractor (F/5), no filters, NEX-3N camera.

Overall the LXD600 is a suitable chariot for the the “Beast!”

The New Mini Beast: 6″ TPO RC

TPO 6″ RC on the Orion Sirius mount. Not the “low cost” strapping and C-clamp for a counterweight.

Recently I purchased a used TPO 6″ f/9 Ritchey Chretien optical tube. What has been surprising is the lack of reviews or any other information on this TPO branded RC. In fact, there is very little at all on 6″ RCs or RCs in general. TPO doesn’t have an instruction manual, so you have to use the one for Astronomics or Orion.

The first thing that I noticed was that the TPO back focus is not the same as Orion or Astronomics. It comes with 2 one-inch rings and 1 two-inch ring that attaches between the optical tube and focuser. If you use a diagonal and eyepiece, you can’t use any rings at all and my Sony NEX-3N camera only uses a one inch ring. Turns out the ATIK 414EX camera that will normally be used needs one and a half inch rings. The Orion instruction manual lists a much different setup for using the visual and camera modes.

The other thing that surprised me was how easy it was to collimate. Several years ago, I struggled with an 8″ F/4 Newtonian that never got completely collimated. Then I broke a corrector plate on my 8″ trying to shim the corrector perpendicular to the (custom) graphite tube. Being dyslexic, collimating is not my favorite thing to do! However, it took me less than a half hour to get this scope spot on!

Being able to reach around and tweak the Allen screws while looking through the Cheshire eyepiece made it a quicker process. Though I suspect that most buyers would opt for an 8″ scope there are definite size and weight advantages of a 6″ vs 8″ or bigger and this is one of them. Somehow the process seemed much more intuitive than my other experiences. What few reviews you can find often talk about the difficulties of collimating these kinds of scopes. I did not have any of those issues and it had to be collimated a second time after a car ride.

Another oft stated remark is that you will be “disappointed looking through one of these visually.” My experience was just the opposite! The view blew me away. Clear, crisp, very sharp views really dazzled me. First light visually was Sirius, and it was quite stunning. Though I don’t think this would be my first choice for a visual scope it was much much better than advertised.

Because of the mirror, focuser and camera being on the back of the tube, weight needed to be added to the front. So, I used two pieces of strapping metal and a heavy C Clamp to hold them onto the dovetail. Worked great and the tube balanced very well. Having a “beautiful” scope is not as important to me as making it work well so a C Clamp holding on weights works well.

The image below is “first light” with a camera. In this 30 second image, the dimmer stars are a bit out of focus, but the collimation is good and the star Sirius striking.

First light: Sirius with the TPO 6″ RC and a Sony NEX-3N mirrorless camera on a Meade LXD-75 mount.

In this reduced image it is hard to see “the Pup” but it is there. This alone shows the quality of the scope.

Disaster?

After transporting the scope home from where the first light images were taken the collimation was way off…I mean way off! So I collimated it again which only took a couple of minutes. Then it was carried down the steps from my upstairs office and put on the mount. One last check revealed that it was way out of collimation again! So after messing with it for an hour I took it back inside and promptly stripped 2 collimation screws on the secondary.

My first thought was I must really be frustrated. Then logic took over. Just thinking about the design would say that it should not get out of line so quickly if it was all working correctly. My conclusion after testing the remaining screw with the hex wrench was that the other two screws were already cross threaded and probably not seating correctly on the secondary.

So after taking the secondary assembly off of the scope and removing the secondary mirror from the assembley it was time to figure out what to do. I ordered a 5 mm heli-coil kit from Amazon. It came the next day. I drilled out the 2 bad screw holes and inserted the heli-coils. Since the coils were longer than the holes I used a dremel cutter to trim the excess. This took 5 minutes! It took me longer to figure out where my dremel tool was than to fix the issue.

Worked perfectly. Not longer do you have to use brute force to move the adjustment screws. It took about 30 minutes to attach the secondary mirror back to the assembly and put the assembly back on the tube. The screws that came from the stripped holes had aluminium on them so it was easy to pre-adjust them to where they were when they stripped. This allowed me to adjust the secondary back to where it was before it had to be removed. Saved a lot of time fiddling with getting the right spacing on the secondary.

In another 30 minutes it was collimated. So I did something that I should not have done! I picked up the tube and shook it as hard as I could. It was still collimated! Success on this repair!

The next clear night ( or what passes for clear in the midwest United States in April) I set it up again, spaced out the ATIK 414 EX camera correctly and shot images of M 42. There were high clouds, bright moon and no calibration frames so it is not a very good image.  It did however,  tell me all was well with the collimation and the problem was truly fixed.

M42 with the 6″ TPO RC, ATIK 414 EX ccd camera and the orion Sirius Mount controlled with EQASCOM. A 60 mm guidescope with a ZWO 120 MM camera was used with PHD2 multi star tracking. 20×60 second stack using a photometric V filter.

It is unfortunate that these little scopes often get a bad rap. Getting everything lined up correctly and collimated can be challenging but I suspect that most who buy one of these are not really ready for this advanced design. It is not a beginners scope. In fact the increased focal length alone makes it difficult to guide accurately and puts a lot of pressure on a mount to track well.

M 97, the Owl Nebula through the 6″ RC. There were thin clouds and this image has no flats, darks or bias frames subtracted.

I got this scope to replace my 8″ LX200 that I broke the corrector plate on. The 6″ RC  was purchased primarily to do imaging of the Central Stars of Planetary Nebula. You need a longer focal length for this type of work to get a good enough signal to noise ratio on these faint CSPN. An RC design is excellent for this kind of work.

PHD2 Test Shot

PHD2 Beta came out a while back with a spiffy new feature. It can now track up to 12 stars at the same time. It is supposed to even out the tracking errors. I wanted to test this claim against reality.

So I updated my PHD2 to the beta version and “let er rip.” The Telescope is a lowly 102 Achromatic refractor from Explore Scientific with a ATIK 414 EX CCD camera using a photometric v filter. The guidescope was made out of a 70 mm binocular objective with a cheap Ebay helical focuser glued on. The mount is an Orion Sirius mount controlled by EQASCOM.

Temple 10

The image of the Andromeda galaxy is a mosaic of two 100×60 second images and one 25×60 (shortened due to clouds) stictched together in Microsoft ICE. They were stacked in Maxim DL5 and tweaked with RawTherapee 5.8.

The PHD2 really worked well. The stars are round and the image is pretty stunning for a monochrome one with a 4″ telescope! The tracking was way better with the muiltiple targets. This version of PHD is a real winner

M 31 with a 4″ refractor.

“The Beast”

In June, while on a trip to Arizona I made the mistake of stopping at Stellar vision. It is like a telescope and accessory mall with a very knowledgeable owner, Frank Lopez. I was looking around and asked Frank “Do you have any Meade LXD-750’s?” “Sure” he said, I have 2 and a couple of 650’s and 600’s as well. Wow, he really had a collection. I recognized right off that the 750 was going to be to big for me to handle or even fit the tripod in my car. It is massive.

So I settled on a LXD-650. After getting it into my overstuffed car I headed home with my treasure. To make a long story short I kind of toasted the 18 volt electronics somehow. Back it went to the shop by mail and it was replaced by an LXD-600. the only difference is a 650 is 18 volts and the 600 is 12 volts. This mount was made around the early 90’s so is a bit outdated.

I bought the mount to handle my Celestron 6″ achromatic refractor. It does this very well. Tracks ok and even pulse guides. Just recently added a 60 mm guide-scope to the 6″ and will give that a shot the next clear night.

The bar that the guide scope is mounted on was made from iron stock and a drill press.

I really like the 6″ refractor. It has done some outstanding work on planets and deep sky objects. All it needed was a solid mount. It has found it in the LXD-600!

The Return of the King…

It’s alive, it’s alive…  Temple 28, the 11″ Celestron CPC Schmidt-Cassegrain telescope is back working again. The North-South autoguiding function still does not work but if it is polar aligned well that won’t matter!

The big issue is the dirty mirror! Having holes for ventilation is hard on a mirror.  I did not want to ruin the good collimation so I used 91% alcohol in a spray bottle to spray on the mirror through a ventilation hole and clean it off. It helped a little but didn’t clean it off like it should. so I added a drop of liquid detergent to the alcohol and that did the trick…as long as you then wash it off with distilled water. There was a streak under the focusing tube so I resprayed it with the alcohol/soap mix. Then promptly forgot to spay it with distilled water. So there is a film of dried soap on it. Now I have to do it all again when I get home from a trip.

It is good enough to plan to resurrect the scope. Have to set up a new 32 bit computer to run the SBIG ST-8E. The old parallel port camera won’t work with a 64 bit computer. However, a single core computer runs mount and camera just fine so my dual core desktop should work well. I also purchased a PCi parallel port card that has reviews showing it uploads 3x faster than a built in port. When it takes 70 seconds to upload one image this is important!

Hope to get this bad boy back up and running in the next month or so!

Zoomed…

Mid-America Regional Astrophysics conference or MARAC met April 23-24.  In the past MARAC was at KU, Linda Hall Science Library or UMKC. The meeting was canceled altogether last year and was done in Zoom this year. Zoom and the “Gathering.”

The Gathering was a game like set up where you could walk around, talk to people and look at things. Once you got used to the avatar and crude graphics it was kind of cool. I was able to meet and talk astronomy with another participant. Though doing PPT on zoom is kind of odd compared to a live experience it worked well.

A screenshot of Maxim DL 5 photometry. Notice the flat comp stars and the definite curves of SS Cyg.

My talk was on the micro-variability of SS Cyg. The AAVSO was asked to help cover observations for a Japanese researcher who is trying to study the accretion disk around the white dwarf star.  Using a 4″ refractor I was able to see very definite signs of micro- variability. This has been noted elsewhere but seemed to deserve a talk on it’s own.

I did full nights of observing using a Johnson V filter. 15 second exposure with a 45 second delay. There was also about a 7 second upload and check the guide star. Started in July and went until November.

The talk was well received and caught the attention of a nearby college. I have been invited to visit their observatory and talk about their research. Looking forward to summer and more opportunities to explore the light curve of SS Cyg.

Light curve for SS Cyg taken on September 4 2020. This is a whole nights worth of observation.

A New Hope…

Temple 10 with ATIK 414ex

The American Association of Variable Stars Observers has been having a Saturday series (2020) of online events highlighting each observing section. Last week was the section highlighting short pulsating stars. Some of the stars change brightness significantly over the course of an hour or two! Instant result, no patience needed! The techniques used to capture a light curve of these stars is very helpful to me in my Central Stars of Planetary Nebula project.
We had clear skies at dusk so opened Temple 10 (AR102 refractor). I put in my old Celestron apochromatic 2x Barlow and got it focused. Just when I finished the alignment the clouds came over and lightning on the horizon said it was time to close. Two hours later it was clear as a bell, but I digress.
In using a 2.5X Barlow earlier I had obtained a decent image of M 57 with this 4″ telescope by stacking 60 or so 9 second images in v. This was also with an almost full moon. If I use a 2X Barlow instead of the 2.5X it should still give good enough resolution to have an acceptable signal to noise ratio with a shorter integration time but still provide a cadence that will work.

AR102 Refractor
ATIK 414 EX CCD
Orion Sirius mount
Johnson-Cousins V filter
2.5X Barlow       

ZZ Ceti (DAV class) stars include the central stars of PN. Also called PNN stars. Part of the problem in studying these stars is the nomenclature. There are numerous names for these objects, but this class was not finalized until a few years ago.  So, when you tried to find articles on Planetary Nebula Central Stars all you got were thousands of descriptions of the nebula itself or articles on white or red dwarf stars. Having a real classification makes the process of research much easier. Up until the 1980’s it was thought that they weren’t variable at all. 

The biggest issue in trying to image these stars is the needed cadence. The hotter the star the faster the pulsation, so it is thought. In looking at light curves for 50 pulsating white dwarfs several years ago, there was an apparent temperature to pulsation connection. Hotter is faster. So, using an AAVSO 11″ telescope (2010) to record the PNN in M 57 there was some small evidence of a sinusoidal Light Curve. However, with a 30 second integration time, then a 30 second upload time, the light curve was not complete. Since ZZ Ceti stars in the 20k-30k degrees Kelvin, have a period of 2 minutes to an hour, you will obviously need to shoot in seconds to get a light curve of a star that is 125k+-5k degrees Kelvin if there really is a connection.

The ATIK 414 camera is much more sensitive (about 10%) and has an upload speed of slightly less than 2 seconds. So instead of 60 seconds I will image for a total of 13 seconds with a 2 second upload. This gives a cadence of 4 images per minute. Hopefully, this will capture a true light curve. However, 4″ aperture may not be enough to get a good signal to noise ratio.

If this is not enough aperture, then will try it again with the 11″ after it is rebuilt. I had an hour run from a 24″ telescope at the University of Wyoming but the software (multiple) that I was using refused to read the images. My HDD crashed and took those images with it!  So much of Citizen Science type research is trial and error with techniques. It has taken years to get to this place in my research, but it is what I find “fun.”

Kind of Weird…

Meade 90 mm on Bresser mount

With haze from high winds and the moon I did not open up Temple 10 awhile back. Temple 28 was awaiting a new power supply. So I got out the Celestron Firstscope 80mm F/11 and a generic F/8.8 Meade 90mm I bought on ebay about 8 years ago and a Meade 70 mm. I am working on doing a telescope review of my 70, 80 and 90 mm scopes.

After looking at the moon I decided to try something. If you put on the Star Analyzer (diffraction grating) you can actually see the amount of Chromatic aberration in the shape of the spectra. Since an achromat normally only brings 2 wavelengths (green and red) of light to focus you see what is called a fishtail at the blue end. This is a cone shaped smear of violet and blue light. The spectrum is clean and tight in green/yellow and depending on lens makeup and quality of manufacture often has a slight widening of the spectra in deep red.

Celestron 80 mm Firstscope.

The 80 mm Firstscope has a fishtail in blue which extends to the edge of green, which is common to achromats but goes nice and smooth right to the near infrared region before it widens a bit. So it indicates that using a Minus V filter would probably negate a lot of the bad effects of CA but not all. The 70 mm Meade F9 had a very similar spectra to the 80mm except that it showed signs of pinched optics.

This is what is weird. My assumption going into this testing was that out of the 3 telescopes I tested the 90 MM F/8.8 Meade would be the worst. I bought it off of a vendor on Ebay and paid about 40 bucks for the Optical Tube Assembly. Turns out it is the best. When looking at the moon or Venus there is only a hint of purple and you have to look for it. So I tested this scope with the grating and found a fishtail in violet but not blue. This means that it has much less CA than my other scopes! The red end looks like the 80mm and is better than my 6″ achromatic refractor. Over all there is substantially less visual CA in the 90mm than the 80. Yet the 80 mm is an F/11 and should have better color correction. That very small shift in the wavelength makes a lot of difference. So a Minus V filter would really reduce the CA in this scope.

Meade 90mm scope F/8.8 with Solar filter on it. 

In the 3 telescopes I tested in and out of focus the Meade was also the best. The 80 and 70mm both have about 1/2 wave of spherical aberration. The Meade is at a 1/4 wave.

So after writing most of this I went out and did the tests with the grating again and then just looked at some bright stars with a homemade 26mm eyepiece. The Meade 90 mm really does have a nice view. In fact I put a 4mm planetary eyepiece on it with the almost full moon and saw just a tinge of blue but really nice crisp views of the partially illuminated craters. When a 90 mm F/8 can look this good I think I got the luck of the draw on this telescope!

So a 40 dollar telescope that I have had for years turns out to be the best of the 3 refractors I am testing, go figure!

It’s an Addiction!

Meade DS90

When I woke up this morning I didn’t expect to buy another! I just can’t seem to help it. It’s an addiction!
We finally got our stimulus check…note to self…use automatic deposit next year. So I had intended to buy a small apochromatic refractor with some of the money. You know, make sure we spread it around a bit and not spend it all in one place. That idea sounded good until I took a look at some bills and my wife decided to use most of it for the kitchen remodel. So only had 300 dollars left and that would not get what I had in mind. So I noticed while perusing astromart that a guy was selling a fully functional Meade LXD-75 mount  and after some negotiations it is on the way to my house.

Meade LXD-75

So why another mount? I’m glad you asked me that question! I currently have 7 achromatic refractors, two 60 mm, a F8.8 and an F12, 70 mm F10, 80mm F/11, 90mm F8.8, 102mm F6.5 and the 150mm F/8. I have 4 Alt/Az mounts for the smaller telescopes, an Alt/AZ for the 80mm, the AR102 is mounted on the Orion Sirius mount and the 6″ resides in it’s blue carry bag on the shelf only to be taken out for planets once in a while.
I would like to do some testing and imaging with each of these scopes. One of the projects is taking spectra of stars to show the Chromatic Aberration of each telescope.  Actually being able to measure the CA would be interesting.
I am almost finished with “Choosing and Using a Refracting Telescope by Neil English. In that marvelous book it gives a delightful history of the different types of refractors. It is hard for today’s amateur observer to realize that a cheapo Meade or Celestron (read trash scope to many) is as good or better than the most expensive telescopes of yesteryear. In fact a 90mm F/11 would have been considered to be a large quality telescope to people of the 1800’s. We are really spoiled!
So this new mount is to use for the refractors. Primarily visual but you can pulse guide with this mount. Astrobin has a lot of high quality images taken with an LXD-75 so it is suitable for these smaller refractors. Before I bought the Celestron ASGT in 2010 I almost bought the LXD-75. The lack of an ST-4 port to autoguide the internal chip of the ST-7E was the deciding factor on purchasing the ASGT. So I believe The LXD-75 will work even for the 6″.
Many people thought the LXD-75 was too light to image with the 6″ scopes when they first came out. Virtually every review trumpeted that “fact.” However, I did quality imaging with the ASGT mount and the 6″ scope along with the ST-7E. The LXD-75 had just as good of reviews as the Meade mount except for the missing ST-4 port. So I know it will work for the kind of imaging I have in mind.
Ok so what happened today? Well, I bought another telescope! Big surprise. I saw a lady in Kansas City had a Meade DS-90 advertised for sale for 100 dollars. I offered her 75 and she took it. I used to have a DS-2090 that featured a 90mm F8.8 telescope but gave it to a kid when I got the Celestron 6″.

New Meade 90

However, I was not really interested in the mount as much as the scope. It is a 90mm F/11 telescope. If the optics are just ok, it should give very good views. The color should be much better than my other telescopes, except the 60 mm F12, and I am looking forward to getting to play with it. Of course it is raining tonight and all day tomorrow. In fact it has been raining on and off since May 10 and it is still raining on May 16.
The 2 eyepieces that come with this telescope are not bad just not real good. A 25mm Modified Achromat and a 9mm Huygens. They work but I would not call them good. Still great discoveries were made with much worse eyepieces than this! I have 2 new eyepiece adpators on the way from a guy in Ariaona so that my Meade 90 F/8.8 and the new Meade will both accept 2″ eyepieces and diagonals. A quality dielectric diagonal and good eyepieces really help the performance.
The couple I bought it from indicated that they had never figured out how to even put it together. Most of the parts were still in the original unopened bags. They won it in a contest then couldn’t figure out what to do with it. The only issue that I have found so far is 2 of the 3 tripod legs won’t stay extended without some kind of help. I remember having this issue with my old DS 90. Finally took off the crappy levers and just added small c-clamps, that worked better anyway.

Some of the pieces had never been taken out of the bag!

After reading the book on refractors I am really pumped about achromats! They are relatively cheap and a lot of fun. With the premium refractor bias of many observers today the achromat is a great deal!
So now that we have pretty much spent all of our stimulus money I won’t be buying anything else real soon, err, unless you know someone that has a real cheap Meade LXD-750 mount…