The Problems: Well, the most obvious one is that the tube is finished in a nearly perfect gloss white. Some people actually like this sort of finish, but I do not. I am an observer, and the white finish reflects light (even from a dark sky) right into your face while peering through the telescope. So I decided to paint the tube a darker color. Cobalt Blue was the color chosen, and the paint I used was a heavy duty floor paint, of the sort that would be used on a cement garage or basement floor. I had it mixed at the local hardware, this stuff is very easy to find.
After a few nights of observing, I noticed that the OTA had a little trouble holding collimation - not that there was a serious problem there, but there was something flexing or moving a little more than I wanted it to. I finally traced this to the thin Sonotube (or whatever brand name of rolled forming tube is used). The tube is adequate to resist most creep, except at the points that the mirror cell screws pass through it, where you will note quite a bit of compression of the cardboard-like material. This appears to allow the cell to rock back and forth a little too easily. I also note that the saddle straps will flex the entire tube depending on how tightly you crank them down - the tighter the straps, the more the tube flexes. If you set up your scope on different nights with different tensions on those straps, then that will translate into some miscollimation.
I like the thermal characteristics of Sonotube, and recommend that you keep the original tube material. The thing to do is reinforce these troublesome points, so I decided to use some superglue and fiberglass patching on the weak areas.
I also was not satisfied with the way the tube allowed scattered light into the focal plane. This robs contrast, and is a very easy problem to address in a Newtonian. Again, this is not a huge problem that renders this telescope hard to use, like the mounting problems - this is simply a matter of trying to squeeze every bit of performance out of the OTA that I possibly could. The installation of baffling is the main weapon to combat scattered light, as is the introduction of blacker interior tube paint and, if you choose, roughening of the tube interior.
Finally, the focuser on my scope had serious problems - it had very coarse and rough motions, and more damaging yet was the tendency of the focusing tube to rock back and forth as you turned the focusing knob (this is the Meade #77 Giant 2" Focuser I am talking about here - in my opinion a bad deal at any price). Focuser replacement is definitely in order. I do want to retain a 2" focuser for this scope, with a 1.25" adapter, so I purchased a JMI NGF-DX3 Crayford focuser. Just about any well-made Crayford should do, so scan the ads in Sky & Telescope. This focuser is lower in profile than the Meade focuser, so I had to change the position of the secondary holder and focuser hole in order to use it.
Even if you decide not to replace your focuser, you might discover that the bottom of your focuser (or the secondary mirror) is causing some vignetting. If either of these conditions applies, now is the time to address these. There is a separate section on whether or not your Starfinder vignettes below.
This may seem like a lot of things to do in one fell swoop, but it makes sense to do all these things all at once, while you have the mirrors out and the accessories removed from the tube. If you have not built or done heavy modifications to a scope before, the wisdom of doing it this way might escape you. The thing to do here is to get all ready and pick a period where you anticipate several cloudy days in a row - or, if you are a deep sky observer, use the full moon period - to do the work.
The Cost: I picked up a small can of cobalt blue floor paint, for the outside of the tube, for about $10. I bought a fiberglass repair kit at an auto-parts store that had about a square yard of fiberglass cloth, resin, hardener, and tools, for $7. The best paint for the inside of the tube is Krylon Ultra-Flat Black, a spray paint that is quite dark - properly applied, much darker than the paint job the original Meade has. It runs a few bucks a can, and I got two cans. The baffling material can be pretty much anything - I have used hole-less pegboard (I don't know what it is really called), thin plywoods, and even heavy poster board for baffles in the past. I also bought a small $3 can of putty, to use to fill some cosmetic flaws in my tube - this is optional though. My total expense in money for this part of the project was about $35. Someone who works harder to make this cheap can probably drop that to $20 or so.
The focuser can cost anything you want it to cost - there are 2" focusers on the market from $50 to hundreds of dollars. I chose a fairly expensive and very high quality unit from JMI, which ran me close to $130. If you want a textured tube interior, following my example of using corn cob bedding and Elmer's Glue will cost only about $10 or so. I found this method unsatisfactory, and have since switched my preferences to Protostar brand light-absorbing paper. This paper is seriously dark, and I recommend you use it in favor of any other product (the Protostar product is not the same as Edmund flock paper; it is both darker and cheaper).
The cost in time for these improvements is about 8 hours.
What To Do:
Step 1: Prep the Tube: First, remove the primary mirror and cell as one unit. Be careful, this is an expensive part of the system, and you don't want to break it. Store it somewhere safe.
Once the primary is out, remove the secondary, secondary holder, and spider, also as a single unit. To get the spider screws out of the tube, you may have to twist the spider somewhat to gain the needed clearance. Don't worry, mine did not break, and I applied a fair amount of force when getting it out. Don't be concerned if the assembly looks a little twisted up when you have it out - we can fix this easily when we put it back in. Store this assembly in a safe place, perhaps with the primary.
Now remove all the stuff attached to the outside of the tube. The focuser is held on with four nuts and bolts, easily removed. The finder and its holder can be similarly removed.
Now you have a bare tube, except for an upper plastic end ring. On my scope, the lower end ring is loose and easily removable - in fact, it won't even stay on by itself. But the upper one is glued to the tube. You need to get this off. I gently got under the ring with a screwdriver and pried it up at about two dozen locations around its circumference. This separated it from the glue on the outside of the tube, but there was still some glue on the tube edge holding it on. I got the screwdriver under the ring again, and gently tapped it with a mallet all around the tube. This was enough to remove the end ring with no cracks. The key is to be patient and gentle - no great force is needed; a little bit of force all over the place is the key to safely removing this part.
The next step is sanding down the tube. I used a DeWalt random orbital sander for this work, because I happened to have one, but the tube is not so big that you could not easily do it by hand. Use coarse sandpaper - I got good results with no. 60 aluminum oxide paper, but this isn't rocket science - use whatever you have on hand. The goal is twofold. You want to sand off all the gloss from the finish, leaving a somewhat rough surface. You do not want to sand down into the brown parts of the tube, or raise up any paper layers - this will make finishing the tube a little bit harder. I also sanded down all the seams so they were more or less flush with the rest of the tube - those seams are just double thicknesses of the finish layer of the tube, so you can afford to put some elbow grease on them without worrying too much about sanding too deeply.
Step 2: apply superglue and fiberglass:
Figure Four (a): Applying superglue to the holes drilled in the tube. The bolts that attach the primary cell, secondary spider, and other components to the tube will abrade the tube and cause fraying. Saturating these areas with superglue puts an end to this.
Figure Four (b): The tube, sanded and with the first of the fiberglass applied. The fiberglass is used to buttress the weak points of the tube - essentially, anywhere there is a hole. If you set up and take down your scope a lot, put some fiberglass in the area that the saddle straps will cross the tube. This will make the tube less susceptible to flexure from tensioning those straps.
The superglue will be used to stiffen up the sonotube near each hole. You will need a couple small tubes. Simply smear around as much superglue as the sonotube will absorb, concentrating on the insides of the holes. Give this an hour or so to dry - this is a non-standard use of superglue, and I found it benefited from the extra time. This will significantly stiffen the sonotube right near the holes and provide somewhat better wear characteristics.
Remember, I only did the fiberglass reinforcing because of my scope's problems holding collimation. If your scope is holding collimation properly, I would advise you not to worry about this step, just move on to the next one.
Next, cut your fiberglass into various sheets. You will be applying broad fiberglass layers over the tube areas that are drilled for the mirror cells, focuser, and finder. I do not recommend that you fiberglass over the whole tube - if you did this, you might as well have gotten a new fiberglass tube for your telescope in the first place. Just a few square feet of reinforcement is all that is needed. See figure four to take a look at my fiberglassing job.
I discovered that using a disposable paint brush to apply the resin to the cloth was the easiest and most drip free way to go. Make sure the fabric is well saturated with resin, and use drop cloths. Other than that, follow the instructions that came with your supplies and you should have no trouble.
Once your fiberglass work has had plenty of time to set, sand it down until it makes some nice, smooth edges with the sonotube. Fiberglass is very hard, which makes it kind of tedious to sand by hand. For this project, carefully use an electric sander (borrow one if you have to). USE LUNG PROTECTION! You don't want to be breathing in any fiberglass residue.
Step 3: prime outside of tube: This step is a pretty easy one. Simply prime the outside of the tube. I used primer that I bought with my paint, and brushed two coats to the outside of the tube in a total of about an hour and a half.
This step may seem tedious, when we are almost ready to paint - but it is quite necessary. Your paint is going to soak into the porous sonotube rather easily, but won't soak in at all to the fiberglass reinforcing. This will result in an uneven appearance to the final paint job, even after several coats. I am known for allowing my telescopes to look pretty ugly, but even I am not willing to let my telescope look that bad! So, bite the bullet, be patient, and prime the outside of the tube before you go any farther.
Don't forget, if you want your finder and tube to match, sand the paint off the finder and prime it as well.
Reader Suggestion: Robert Haler of Lymax suggested that Kilz Total 1 or Kilz 2 primer is an excellent product to use on sonotube.
Figure Five: The telescope tube, primed and ready for painting.
Step 4: Painting: After the priming is done, you can then paint the outside of the tube with whatever color you chose. I don't know much about painting, but I simply painted two coats onto the tube, letting each dry overnight. Don't forget to paint your finder!
Step 5: Does your Starfinder vignette? Newtonian telescopes, if not properly made, can suffer from a flaw called "vignetting". This is nothing more than some part of the telescope cutting off part of the light cone on its way to the focuser. It might be caused by an undersized secondary mirror, or a correctly sized one placed too close to the primary. Or it might be that the bottom of the focuser tube cuts off some light all by itself. The kind of vignetting we are concerned about here is the kind that results in a zero-size, 100% illuminated field of view. This condition is also known as "aperture vignetting".
The effects of this are simply that the telescope performs like one smaller than 10". You lose light grasp and resolution when there is vignetting, and this is usually an undesirable condition. The only time it could be beneficial is when the primary mirror has a turned-down edge or some other edge-related optical defect. I've run across several Meade Starfinders, both Dobsonians and Equatorial models, which vignette in this way at this point, so I recommend checking it out.
The easiest way to determine if your Starfinder vignettes or not is by using a computer program for the IBM PC called Newt, by Dale Keller. In his readme, Dale says if we like the program we should give it to a friend - so, since I can't find a download site to link to, I am hosting a copy here. (If Dale sees this and wants to give me a pointer, I will link to his site.) In the copy of Newt that I am hosting, I have added a file called "10inch.nwt" that you can load which closely approximates the conditions of most 10" Starfinders I have seen.
Download NEWT (80k)
A somewhat better program for dealing with diagonal size issues and vignetting is available from Mel Bartels:
Check DIAGONAL.ZIP on this page
The cure for these kinds of vignetting is fairly simple - you have to increase the distance of the primary from the secondary. This will also lower the focal plane, bringing it closer to the secondary mirror, so some account must be taken of the effect that this will have on the ability to focus eyepieces. The ideal solution to this problem is to purchase a low-profile focuser to replace the Meade unit. This allows you to drop the focal plane by an inch or so and still bring your eyepieces to proper focus.
Note that any of the 10" Starfinders will vignette if the primary mirror cell is mounted in the photographic (forward) position. This should never be done; using a low profile focuser will also allow your cameras to focus, under normal circumstances.
Step 6: re-install tube parts: This step can go two ways depending on whether your Starfinder vignettes or not, or whether you chose to go with a low-profile focuser or not. It is at this point that I recommend you have some familiarity with basic ATM principles. If you need to, read some books by Texereau or Berry before continuing here.
I chose to add a low-profile Crayford focuser to my Starfinder, so these comments apply to that decision.
First, I needed to drop the focal plane by about an inch and a half. The primary mirror is already very close to the back end of the tube, so there is no room to move it back farther - this is unfortunate, since this would be the easiest thing to do by far. Instead, I will have to move the secondary holder, spider, and focuser forward by an equivalent amount.
I simply measured an inch and a half forward from the previous holes for the spider and the focuser, and drilled new holes. The focuser required a new 2.2" cutout to accommodate the focusing tube, of course; fortunately the fiberglassing from step 2 covered over the older focuser cutout. I made this new cutout using a hand-held saber saw, and it overlapped by about a half inch with the old cutout. That's no big deal.
Then, I re-installed the parts, starting with the focuser. Exactly how to install the focuser will depend on what focuser you are installing, of course. In the case of the JMI-DX-3, I simply drilled four holes corresponding to the mounting points and bolted it on.
Reader Suggestion: Andrew Hinks of Sydney, Australia, has offered a suggestion on how to go about salvaging the existing Meade focuser, rather than replacing it with a new one. He has removed the rack from the focusing tube, and placed some paper shims underneath it before reinstalling the rack. This raises the rack some into the pinion, and makes for a somewhat more stable focuser that does not tend to rock as much. Unfortunately, not all Starfinders have removable racks, so not all can benefit from this suggestion - but maybe yours can!
The finderscope and mount go on next. I used the same mounting holes for this part.
Next, re-install the spider. In step one, I never took the secondary holder off the spider, so they go back in as a unit. Don't forget you may have to use a little elbow grease to get it in the holes. Once it is in, tighten up the nuts that hold it on, and bend out any kinks in the vanes by hand.
Those who don't mind spending a few dollars might want to think about getting a replacement secondary holder and spider as well. The leader in secondary holder and spider technology today is Protostar, and that is the only spider I would buy. The Protostar unit will have several advantages over the Meade unit. Among them, you can get a three-vane Protostar unit, which will offer less diffraction than a four-vane spider. Also, the Protostar offers mechanical secondary mirror mounting, while the Meade appears to glue the secondary onto its holder using a rather solid glue. The Meade method can result in thermal deformations of the secondary that degrade optical quality, and eventually the secondary might fall off - hopefully not on to the primary. Finally, Protostar units can come with a built-in offset, insuring evenness of field illumination; some Meades seem to have offset but others don't.
Once the spider and secondary are back in place, replace the primary mirror in its cell.
Step 7: Baffles for the Primary and the Focuser Tube: If you peer down your low-profile focuser, you will find that you can almost certainly see in the secondary the reflection of things behind the primary mirror. This is a contrast-robber in telescopes, allowing light from the ground behind the telescope to make it into the eyepiece. This light needs to be blocked. What I did to block it was to cut out a circle of foamcore, and glue it to the plastic tube end ring at the primary mirror end of the scope. After painting it with the Krylon, its good and black, and no light sneaks in from behind the primary anymore.
I also made a simple double baffle from painted posterboard that fits below the focuser drawtube. The dimensions of these baffles can be calculated using another program from Mel Bartels, called BAFFLE.BAS.
The inner portion of the tube was first covered in corn cob pet bedding, and painted black with a sponge, but this method proved to be unsatisfactory. Instead, I recommend using Protostar black light-absorbing paper to cover the inside of your tube.
Step 8: Primary Collimation Retaining Bolts: If you have a look at your primary cell, you will see the collimation adjustment bolts, and also some threaded holes in the cell. These threaded holes are perfect for some retention bolts. Go to the hardware and get some 1/4-20 thumbscrews (confirm this is the right size for your cell first), and put them in these holes. They will but up against the other part of the cell. When you need to make collimation adjustments, loosen these. When you are done collimating, tighten them evenly. This will help hold the primary in a fixed position when your scope is not in use, and is a big improvement if you take your scope in the car with you.
Realistic Expectations at this Point: Your collimation stability should improve dramatically, though very critical observers might still find sources of flexure. The focuser will no longer be a source of horror. The tube interior, now darkened, and the drawtube baffles under the focuser, will result in a much darker field for deep sky observing, and a much more aesthetically pleasing view for planetary observing. Since the outside of the tube has also been repainted a dark color, there is no more skylight reflecting into your face while using the telescope.
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