Ruined Images

Ok, enough equipment posts for now. Last night I got out to do some imaging. Hurray! Summertime is tough in Florida for decent nights—high temperatures and high humidity mean afternoon thunderstorms pretty much every day, and usually poor seeing at night. The past week or two have seen cloud cover as well, late into the evening. Not last night, though—last night was pretty good, and I took advantage of it.

Now I’m fairly new to CCD imaging—the images I took last night represent only my fourth, fifth, and sixth attempts at LRGB CCD imaging. Two of my targets—M27 and M52 (picked somewhat randomly by the way)-- were one’s I’d never imaged before. The other, M31, is a favorite, although this was my first attempt with the CCD.

Anyways, as it turned out, some of the most interesting occurrences of the night had nothing to do at all with the targets. Now when I’m imaging, sometimes I watch the subs come in, and other times I just look at the sky. I find it ironic that since I’ve started CCD imaging, and the computer is set up to automatically take the subs for me, I actually spend more time just looking up, not less. Wonderful! Anyways, at this point, I was doing luminance subs on M27, and I was watching them roll in, when this popped up on one:

Veteran imagers will recognize this instantly. A meteor, caught on film! Ok, caught on digital at least. Neat! I’ve had this happen before, but not often (when I’m not specifically targeting meteors). Sure, the frame is no use to me now for M27—but I’ve got plenty of others to use!

But even more intriguing was later. I went back to do another set of luminance subs (I thought I had accidentally used the wrong filter on the first set—turned out I didn’t), and I caught this:

What is that? My first thought was a satellite, but it was moving sooo slowly! I mean, you have to realize, these are 10 second subs, and the field of view of my CCD is pretty small—so this thing is moving slow! Here’s a shot of the next few subs:

My next thought was that it’s an asteroid. That would explain it moving so slowly, as it would be much further away. But in that case, it almost seems like it was moving too fast! So I’m not sure. I’m going to do more research. I’m thinking it’s a satellite, but I had the foresight to scribble down the time of one of the subs, so hopefully I can figure out how to check and see if there could have been something else out there.

So quite a few subs got ruined. Perfect! I love ruined images. I was watching the subs come in when the satellite/asteroid/whatever appeared above, and I admit I leaned forward in my seat, awake, alert. I decided I would try to follow the object, I could always come back to M27. Unfortunately, but true at least to my prowess with the telescope, I slewed in the wrong direction, twice, at maximum speed, and lost it completely. Wonderful. Oh well.

And in case you’re wondering, I did get some nice shots. Here’s my preliminary version of M27:

Yeah, my processing skills need a lot of work. But I’m pretty pleased. I had never imaged this object before, in color or otherwise and, well, I’m happy with it, for now. And isn’t that what its all about?

Mounting a Guidescope on a 6” LXD75 Schmidt-Newtonian

Not too long ago I picked up a used Orion Guidescope, which is a 3.1” f/11 achromat. It came with a dovetail plate with holes in all the wrong places and some rings that I could not figure out how to mount. What I wanted was a simple package that had everything I needed to mount the guidescope to the main scope, so I set out on an internet search for just that.

What I came across was the Piggyback Scope Mounting Kit from ScopeStuff. It advertised no drilling required, all hardware included. Perfect. I selected my telescope (6” SN LXD75), placed my order and waited for it to arrive.

When the package came it looked pretty complete. Here’s a picture of the contents (minus the bar):

The rings looked nice. They hinge open, to make removing the guidescope easier. Each ring (the package came with two, only one is shown here) sports three screws to adjust the orientation of the guidescope. The rings came threaded with hex head bolts, each threaded with a washer and lock washer—presumably these are for permanent mounting of the rings. I didn’t use them.

The package also came with the cars and associated hardware—these are on the top right. Each contains a socket head bolt, and threaded onto that is a nut, metal washer, nylon washer, and (I believe) aluminum car. The idea is that you put the car into the metal bar, and tighten the nut down on the washers to hold it tight.

Getting Started

Excited that it appeared to have everything I needed, I got to work. First, size up the bar on my main scopes rings. Uhh, wait a minute. Something’s wrong here:

The holes don’t fit. At all. In fact, they’re pretty far off. I figured I must have been shipped the wrong bar, and emailed Jim at ScopeStuff to get the problem corrected. Well, as it turns out, they only have that bar with the different spacing (presumably for the larger scopes). He told me that he could fabricate a bar with the correct hole spacing, if I could email him what that spacing was.

Now, I’ll admit, at this point I was pretty frustrated. I mean, like I said at the beginning of this post, what I was looking for was a turnkey solution that required zero fiddling on my part… ok, maybe some fiddling (this is, after all, astrophotography) but no serious work. And the site didn’t say it wouldn’t work for my scope—under LXD75, it just said not AR-5, the refractor, but nothing about reflectors. And I was able to select my scope on the list! So you think they’d have checked to see it didn’t fit.

Well, they didn’t, and once I got myself out of too-high expectations mode and back into the land of aint-nothin-ever-works-out-of-the-box mode, i.e., reality, I set to work making it work.

Ok, Jim can fabricate me a bar. I could have him do that, and get the result in a week or so. Or I could just drill a hole myself, and have it today. So that’s what I did. And of course, this project provided a perfect excuse to go buy a new set of drill bits. No, you don’t need to run out and buy a new set of bits just for this one hole—but no one’s saying you can’t.

Now the bar that ships with the ScopeStuff kit has two holes—a regular hole, and one that is elongated, presumably to account for small discrepancies in ring distance. So if you’re going to drill a new hole, make sure you use the elongated hole as the one you ‘keep’, and that way, you don’t need to be too concerned about getting your hole exactly right. I marked the location in pencil and clamped my bar to a piece of wood:

The original hole size is ¼”, so this is what I aimed for. I started small:

And drilled out to the final size:

Now the observant among you will note that I didn’t do a particularly good job keeping the hole in the center of the rail. It’s a little tough to start the hole with a regular drill, and it kept moving about. If I had a drill press this would have been easy. That said, I wasn’t too concerned if the hole wasn’t exactly dead center, since I could easily take care of any difference when I aligned the guidescope using its rings’ three screws.

There was one other problem—the rail itself is not wide enough to allow the heads of the socket head bolts down into it without the top being widened; the pre-drilled holes all come with this complete. I didn’t have an easy way to do this so… and I’m not sure I’d recommend this, in fact, I probably wouldn’t, although it worked fine for me. Please be careful! Absolutely wear eye protection! Anyways, I took my ¼” bit, put it in the hole I drilled, pulled the trigger, and slowly angled it into the top of the rail. It bit away chunks, slowly, and I only had to do one side for a moment to make a gash big enough to get the bolt head in—here, take a look. This picture is a little out of sequence (I had another problem mounting which I’ll get to presently) but it shows the gash nicely. Not pretty, but it works:

Now it's just a matter of...

Ok. Perfect. Now, like I said, the image above was a little out of sequence, because it shows the bar successfully tightened down onto the main scope rings. Surely, now that the holes are in the correct spots, it’s just a matter of using the supplied hardware to tighten down the rail? Au Contraire, Mon Frère. The supplied hardware is all metric (M6 I believe). Through a happy coincidence I happened to have a pair of hex head bolts that were ¼-20 thread, and they fit the holes. So it appears that hardware type is issue #2 with the ScopeStuff kit. Ahh, well, no biggie, another excuse to go to the hardware store—which I did, for some ¼-20 socket head bolts. You see, the hex heads are too large to tighten down on the rail—you need socket head. I returned home triumphant, only to encounter this:

Argh! They wouldn’t thread in. They would go just a little bit, and then get stuck. I was afraid to force them too much, for fear that I had somehow misjudged the threads. Enough of this. I went back to the hardware store with everything—the socket head bolts, the hex head bolts, the scope rings, everything. Now perusing the hardware store, and trying pretty much every screw and bolt they had in the holes, that the only thing that fit were the ¼-20 hex head bolts. Nothing else. I noted that a lot of the ¼-20 stuff was marked as USS Coarse, which refers to the threads. I also noted, however, that there appeared to be a section of socket head bolts all marked SAE fine—which I reasoned were smaller threads, and would fit. Unfortunately they didn’t have any ¼-20 (although they did have sizes larger and smaller). Hmm. Time for some assistance.

I showed the hardware guy my dilemma, and he began the same procedure of trying every screw and bolt in the store in the holes. Once he was convinced it was actually ¼-20 thread, he began forcing some of them much harder than I dared, and I believe he saw me cringing. Ahh well, no harm, no foul. He asked me if the scope rings were a scuba tank holder. No, it’s for a telescope. Ahh, I had one of those as a kid, he says. Only got it out a few times. Some neat stuff up there, he says. Sure is buddy. Be happy to show you sometime. Now find me a gosh-darned solution!

Well, the guy decided that there was some gunk gunking up the top of the holes. Upon closer inspection, he was right—it was all black on the top, but silver down below. Looks like when they sprayed the anodizing on, they just sprayed it right into the holes as well. Can you believe that? How did I miss that? Sometimes all a problem needs is a new set of eyes. He hooked me up with a tap, which is what they use to put threads in holes:

Usually I guess you need a special tool to keep these straight and everything, but he said I’d be fine with just pliers if I were careful, since the hole was already threaded, and I was just cleaning it out. I was careful:

The first few turns were tough, then it threaded right on through. In five minutes my holes were clear, and the ¼-20 socket head bolts I had bought went right in. Hurray!

Rings

With the bar successfully mounted, it was time to try out these cars for the rings. Here’s one mounted on the rail:

Now here’s the problem as I see it. When you tighten it all down, per ScopeStuff’s instructions, the ring can still spin on the bolt! There’s nothing holding it in place! Now, I guess you can make the argument that once both rings are on, and there’s a scope tightened down, that it won’t matter, since the scope itself will hold the rings in place. But that just didn’t sit well with me. What if I removed the scope? Then the rings could spin (easily, I may add) and get out of whack. Furthermore, even with a scope in there, I reasoned that they could shimmy just a little bit back and forth—enough to potentially mess up autoguiding. So why take the risk? All this setup needs is one more nut to tighten the ring down as well. I tried it out using the nut from the other car assembly, but the bolt was just a little too short to comfortably get everything on.

So off I went to the hardware store to get more 6-1.00 nuts, 6mm washers, and slightly longer (6-1.00 x 30) socket-head bolts. What I did was thread the bolt and a washer down through the ring, and tighten it fast with a nut on the other side:

The washer takes care of the fact that the hole isn’t quite large enough to tighten the socket-head bolt down completely. I would have liked another washer on the bottom, but, alas, I only bought two. Ah, well. I plan to keep an eye on it to make sure it doesn’t loosen—although if it does, I’ll be no worse off than I would have with the original kit.

Next I threaded on the second nut, another washer, the nylon washer, and finally the aluminum car, and mounted the whole thing to the rail in the normal fashion, tightening it down with a pair of vice grips since my pliers were too thick to avoid loosening the first nut:

And that was that! Here’s the whole assembly back on the mount:

The Final Verdict

So how would I rate the kit? The rings are great. As I said, however, the kit was not at all a turnkey solution for my scope. The holes didn’t line up and the supplied hardware didn’t fit. That said, though, I’m pretty pleased with it, although in retrospect I’d go with something simpler. There’s a bit of play since the scope itself is held so far off of the rail by relatively thin bolts. Supposedly the cars are a more convenient solution than permanently mounted rings, but honestly, how often are you going to be moving the rings up and down the rail? And when you factor in the fact that the cars themselves are unable to slide past the socket-head bolts that hold the rail down, the convenience factor is lost—you have to remove the rail to reposition a ring in the center. The instructions that come with the kit have a second picture that supposedly shows you how to permanently mount the rings to the rail, but it doesn’t appear that their method works. They show a bolt threaded through a washer directly into the aluminum car, and tightened down—but when you try that, the thing ends up getting snug only when the ring itself is at crazy angles to the rail (i.e., not straight). Their solution is to say that the ring base must have the hole drilled out to ¼”. Ugh. The heck with that.

I will say this, though. Now that I have it all set up and everything, it seems to work great. Haven’t had a chance to try any auto-guiding through the setup yet, though, so the real test remains...

… but dang it, don’t it look sweet!

Links:
Piggyback Scope Mounting Kit

LXD75 Mount Tune-up

Out observing the other day, I noticed a little more play in the RA axis than I was comfortable with. The problem had been building for awhile, and the play in the axis had now reached that magical point of frustration where I had to do something about it.

Now, up until this point, I had avoided taking the mount apart at all, for fear of messing something up so badly that I had to send it back to Meade-- and be scopeless for a month or longer. A search of the web, however, revealed a wonderful site all about eliminating backlash from an LXD75. Reviewing the directions, complete with pictures, I decided the job was manageable with minimal risk. And of course, you never really understand how something works until you tinker with it, so it was time.

I won't reproduce the instructions here in their entirety. I will, however, expound on a few issues I ran into as a first-timer opening the mount, so hopefully you can avoid making the same mistakes I did.

Getting Started

First, as suggested, I removed the OTA from the mount and placed the mount in the polar home position. Next I removed the declination axis motor assembly and the RA axis motor assembly. They are each attached via a single socket head bolt. The declination motor assembly was easy-- the bolt is easily accessible with the OTA off, and its short. The RA motor assembly is a little trickier-- the bolt is installed way up in the inside of the equatorial head. My allen wrench was just barely long enough to reach up and in and loosen it. When removing it, I was worried about whether or not I would be able to get it back in with the same tool-- as it turned out, reinstallation was easier than I imagined it would be. I placed the two motor assemblies aside for safe keeping.

With the motor assemblies removed, the worm gears are visible, as well as the the adjustment bolts. Here's a closeup of the dec worm gear:

On the left is the drive gear. In the middle are the three allen head bolts used to adjust the worm gear, and on the right there is the nut that holds the retainer collet. In any event, the next part is where I made my first mistake. The instructions say to lock down the axes using the manual clutches (the little black tab things), and attempt to move the counterweight bar against the clutches, to check for end play.

The instructions read:
Take hold of the counter weight bar and gently work the axis in both directions, if everything is perfectly tight & there are no backlash or end play issues the axis will not move. You shouldn't be pushing or pulling so hard on the axis via the counter weight bar you can move it against the clutches, just enough pressure to determine if there is any looseness or play in the axis. If you cannot get your clutches to tighten down enough to resist some light pressure against the axis without slipping we are going to need to fix that now. This is a simple fix, there is a Phillips head screw in the top of each black clutch lever, remove it pull the clutch lever off & reposition it so you can get the clutch tight enough on the axis to resist the light pressure needed to check the worm gears. Put the Phillips head screw back in the clutch handle head and secure it, your done with that!

Now because my RA clutch didn't feel like it was tightening as much as my dec clutch, I thought it needed adjusting. I mis-interpreted these instructions thinking that the endplay I was experiencing was caused by this looseness, when in fact it wasn't. I realized later that they're saying that you shouldn't be able to force the axis with the clutch engaged, with a moderate amount of pressure. So I set about attempting to remove that Phillips screw. Let me tell you, I'm glad this wasn't the issue, because I never did get that screw out. I couldn't separate it from the black tab, and the screw began to strip. In between searching the web for screw extractors, I re-read the instructions above again, and realized that my clutch was functioning just fine. Oops.

Adjusting the Retainer Collet

Ok, time to move on to the next step. The next step is to adjust the the worm shaft retainer collet to eliminate any endplay. Wha? Yeah, that's exactly what I was thinking. I read this paragraph quite a few times. They say to put your finger on the end of the shaft, and jiggle the counterweight bar. Yep, I could feel it, so that's what endplay is-- the shaft moved freely in and out of the collet what felt like, oh 1/16" or so. It was easy to notice. Ok. So the instructions say to use a 17mm wrench, and remove the lock nut from the retainer collet, hand tighten the retainer collet, and re-fix the lock nut. Now having never opened a mount before, I didn't know what any of these pieces were, so let me explain it quick. The worm shaft passes through the mount. The retainer collet is a small round threaded piece that screws into the mount and (I believe) tightens down on the shaft as it goes in. It has two cuts in the end, so you can use a flat-head screwdriver on it (but you shouldn't-- read the instructions!). Finally, the lock nut threads onto the retainer collet, and locks it in its desired position. Here's a picture of the retainer collet on the left, and the lock nut on the right:

Unfortunately, I didn't understand the parts, and my lock nut was stuck to my retainer collet-- so when I removed the lock nut, the retainer collet came with it, in one piece. I thought they were one piece. This turned out to be a big oops, because the next step says to hand tighten the retainer collet back down, and check to see if the endplay is removed. I hand tightened the retainer collet/lock nut assembly, but it had no effect (presumably because the lock nut was preventing the retainer collet from screwing in far enough). So I used the wrench, and tightened just a little more. Nothing. So I tightened harder. Ok, that did it! I was ecstatic. Problem solved. Unfortunately, when I tried to turn the shaft via the drive gear, it wouldn't budge. I had over tightened. Ok, loosen it up some. Except when I loosened, just the lock nut came. The retainer collet was locked in. Oh look, they are two separate pieces. Oops.
Now I had a problem. The retainer collet was stuck, and it was in so far that I couldn't use a screwdriver to remove it-- the worm shaft protruded too far. What I needed was some kind of screwdriver with a notch cut out in the middle. I slept on it, and it came to me overnight-- a washer has a hole in the middle. If I found a washer with the right size hole, and cut it in half, I could use that to back the retainer collet out. Excellent! The next morning I measured the shaft and collet. The shaft has a diameter just shy of 1/4". The collet has an inside diameter of 5/16", and an outside diameter of 7/16". Perfect. Off to the hardware store I went.

Let me digress a moment to talk about hardware stores. Here in Central Florida, we basically have the big box stores (Lowe's, Home Depot) and the somewhat smaller Ace Hardware. I think there might be a True Value or something around, and maybe a family owned shop or two, but not near me. I usually go to Lowe's, since they generally have what I need. But for hardware, I realized that Ace is far and away the better choice. At Lowe's, all of the smaller hardware is packaged somehow-- so that you can't test fits without breaking a package open (which I'm sure they frown on), and if you need one washer, well, tough-- you have to buy four. At Ace, they have the hardware all loose, and you can test as much as you want and buy only what you need. Their selection is much larger to boot. From now on, for hardware, I'll go to Ace.

Back to the mount. They make what are called fender washers, which looked plenty strong for what I needed. I bought (four... this was before I had the hardware revelation above, and I was at Lowe's) 1/4" x 1-1/2" fender washers. This means a washer with a 1/4" diameter hole, and a total diameter of 1-1/2". Perfect size. I clamped a washer to the table and grabbed my trusty hacksaw. Here's the cut started:

I was having a little trouble getting the washer to stay put on my table, which has rounded sides, so I clamped it to a piece of wood instead, and finished the cut, giving me two halves. As it turned out, I needed them both. Alright! Perfect. Time to remove that pesky collet. Wait a minute. What's going on here. Oh bother. The washer didn't fit in the slots on the retainer collet-- it was just a little too wide. I grabbed the file, and started filing. Boy was that slow going. About twenty minutes later I looked up and saw this:

Oh yeah. That's what this job needs, power. I knew I'd find a use for that bench grinder eventually. I fired it up, donned my safety goggles, and started grinding the end. Unfortunately, I over ground the first half on one side, so it was no longer straight-- and I couldn't engage both sides of the retainer collet. Luckily I still had the other half, which I ground down more carefully. The finished product:

Note the flat side-- I had to grind off one side of the tool to allow it to turn past one portion of the mount. Now, finally, time to remove that collet:

Worked like a dream. Collet came right out. Perfect!

I continued now with the original instructions, hand tightening just the retainer collet this time. I found I had to tighten just ever so slightly past hand tight (I used my tool) to get it to mostly eliminate the end play. There was still a little bit of movement, but that will be taken care of in the next step. For now, it was just tight enough to remove most of the movement, and I could still turn the shaft with the drive gear easily by hand. Time to put on the locknut. I chose to take the plumber's ring route, and put a #9 plumber's ring on the retainer collet. And I threaded the lock nut on and tightened. The first time I over-tightened it. It pushed the o-ring out of the way on one side, looking quite odd, and tightened down the retainer collet itself. So I had to loosen everything up again properly, and re-tighten. This time I only tightened the lock nut until it was fairly tight, but before it distorted the o-ring. I believe this is correct-- everything felt solid, the shaft turned easily. I'll keep an eye on it and make sure it doesn't loosen up-- if it does, it should be fairly obvious; I'll start experiencing end play again.

Finishing Up

Ahh, through the rough stuff. The last part was easy for me-- adjusting the three allen head screws to eliminate that last bit of backlash. I followed the instructions, loosening the middle one 1/8 turn, and tightening the outside two 1/8 turn. This proved to be to much tightening-- I could no longer turn the drive shaft-- so I loosened the outside ones just ever so slightly. This eliminated the remaining motion when I tried to jiggle the counterweight bar. Perfect!

All that was left to do was to reattach the two motor assemblies. I made sure the gear on the shaft and the gear on the motor made good contact, and reattached the socket head bolt holding the motor assembly. I only needed to adjust the RA axis-- my dec axis had no discernable motion, so I left it alone. With the drives reattached, I attached the handbox and powered up the mount and-- the moment of truth-- slew! It slew just fine. Fast, slow, RA, dec-- everything sounded smooth and good. Excellent!

Hopefully this sheds a little more light on this simple tune-up procedure for those of you out there who are getting to that point where you think it might be time to get in there and tinker, get your mount working like new again. I say go for it! I learned more about my mount in a day than I had in the past few years of just observing.

Links:
LXD75 Maintenance 101

Launch!

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