I’ve made a few other improvements to my scope over the last year, one of the most significant is the replacement of the cheap Meade plastic focuser. I recently had a chance to get a few JMI gift certificates and decided to splurge and get a JMI NGF2 with the motor. Installation turned out to be quite a chore, not just an easy swap as I had hoped. First the tube has to be stripped down to just the cardboard, I.E. remove the primary, secondary, finder and the old focuser. The major part of the problem is that the focuser has a larger radius than the scope tube. This leaves a gap and if you try to tighten it down it will distort the tube.

I started by cutting a small piece of aluminum sheet metal to match the bottom of the focuser, then bent to match it’s curve. I then marked the screw holes and the center opening and drilled and filed and sanded until everything matched the focuser. I set this on the tube where it was evenly centered on the old focuser hole and put masking tape around it (not touching it) to protect the tube and mark it’s location. I then attached the plate to the tube using some hand moldable epoxy to fill the gaps on the sides. This stuff stays pliable for a while so it is easy to move things around and get them where they belong. Check the radius once or twice by setting the focuser in place to make sure that you don’t over or under correct the curved shape. I found that it is easiest to have a little too much epoxy at the gap and squeeze it out by pushing the focuser down to correct the curve. Once everything is where you want it you can trim the excess that sticks out with a knife or a razor blade. The edge of the epoxy can then be smoothed by wetting your finger and rubbing it until it’s smooth. Now carefully peel off the tape and resmooth the edge and clean up any excess epoxy with a damp rag. Let the epoxy set overnight.

Alternatives to the above approach would be to make a spacer out of hardwood or plastic or whatever or place wedges made from hardwood under the edges of the focuser to take up the gaps. I found out after all this was done that the focuser is too short to focus without an extension tube anyway, so if you end up with a thick spacer it shouldn’t be a problem, at least on this scope.

Next drill the screw holes by starting with one corner. These holes don’t go in to the tube on a radial line so you can’t drill straight into the tube, you have to angle them, so start with a small drill and increase the size and angle as you go until the screw will slide in with the focuser in place. The holes will need to be slightly larger than you think to get this to work. Repeat this process with the other three holes. Now you need to enlarge the center hole to allow the new tube to slide through it. This can be done with a small grinder bit or a rasp in a dremel tool. I used a rougher rasp in my drill and took the hole out to the size of the hole in the plate. It leaves a pretty rough edge on the inside of the tube that I had to clean up with an Exacto knife. Now mount it and make sure everything clears the tube and snug it down.

Reassemble everything else. I won’t get into how to collimate a scope in this article, but collimate it by whatever method you prefer.

This is one smmooooth focuser. Absolutely no trace of image shift even at outrageous powers. It better be good, it lists for $259 with the motor. And another $35 for the extension tube. I just love it, now that it’s all done. I can switch eyepieces and a quick tap or two on the remote brings things to a fine focus. It’s pretty handy at the public nights too, because you can let everybody focus it for his or her own eyeball, without having to reacquire your target every time.

This is a pretty cheap fix and it’s easily done in an afternoon or a cloudy evening and it makes a big improvement in the contrast of your views. It involves darkening the inside of the tube with baffles and black paint. The darkest stuff I could find at the local builders supply was flat black Krylon, I know there is darker stuff out there, but I couldn’t find it when I got the urge to do this, so that’s what I used.

First remove the primary, secondary, focuser and the finder. Then spray the inside with a couple of coats of the flat black paint. This wasn’t too hard to do with the tube from my 10" but it may be trickier with a smaller tube. I’ll leave this part for you to figure out. Let the paint dry. At least for a while.

Next get some black sticky backed weather stripping foam tape. The stuff I used was 1/2" wide 3/8" thick, If I do it over I’ll use 1/2" X 3/4" thick. You want it make a baffle in the tube that still has an inside diameter no less than the size of your primary.

Example: My mirror is ten inches, the inside diameter of the tube is twelve inches. I should be able to put anything up to an inch thick on the wall of the tube without it being in the optical path.

Now figure out the circumference of the inside of the tube. I.E. 12 X 3.1416 = 37.69 Cut five strips this length and stick them in to the tube at even intervals as shown. Now I know there is a scientific way to calculate exactly how to space these and how many should be used, but I don’t know it, so I not going to include it here. If someone would care to provide this information I’ll gladly revise this. I found that the easiest way to place these is to overlap the ends slightly, an inch or so should do, and just lightly stick it to itself, so you have a ring just a little bit smaller than the inside of the tube. Start with the center ring and stick one point to the wall of the tube then go to the point directly across from it and stick this point to the other side. Check your measurements; make sure it is square in the tube. Measure from the edge to the two points that you stuck to the wall. Looking down the tube it should look roughly like the picture on the right. Once you are satisfied with its position start pushing it down on the wall from the point at 9:00 o’clock in the picture and working counterclockwise. When you get to about 6 o’clock loosen the point at 3 o’clock. This is to prevent stretching the tape. Keep working all the way around until you get close to the overlap then detach the overlap and butt the ends together and finish sticking it to the tube. Go around several times and make sure it is firmly attached everywhere. Repeat the above for the other rings.

When all the baffles are all attached spray them with the flat black paint. A couple of light coats should do it.

Reassemble the rest of the scope and collimate it. Now when you look into the interior it will be much darker than it was before and if you look down at the mirror you will see the 5 black shadows of the baffles, this really makes it dark in there.

When I did this I took the scope outside and Jupiter was in a good position, high in the south, when I got my collimation dialed in I swung it over to Jupiter and was treated to the best views of the planet I’ve ever seen, short of the pictures from NASA. The contrast and colors stood out like a busted piston rod. I watched barges and white ovals slide around the bands and the GRS coming into view. I thought I had a speck of dirt in my eyepiece for a moment, because there was a tiny little dark spot on one edge of the planet, it grew as I watched it, and soon I realized that it was a shadow of one of the moons. I sat there and watched for a couple of hours as this perfectly round black dot moved well past the center of the planet.

Not too shabby for about 20 bucks material and a little time.