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Beware kids and grandkids bearing gifts especially an ETX80.
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Beware kids and grandkids bearing gifts especially an ETX80.
By Mark Stewart
I was given a Meade ETX80 for my birthday by my children (and grandchildren) one year. Over time I have modified my ETX80 to better suit my needs. When first bought, the scope did not track very well. The recorded PE numbers exceeded 680 arc seconds. Even at 400mm focal length any pictures taking would have to be extremely short exposures that would need stacking and processing. When I tried the mount in polar mode the RA axis would jump and jerk and often slip. It would only work in alt/az mode again limiting any astrophotography endeavor. I tried cleaning and adjusting the axis but the plastic bushing used for bearings were just not up to it. Aligning was a pain also with no finder mounted. I tried my Mallincam VSS in the scope but it would not come to focus in the eyepiece and when using the back port one lost a good portion of the sky at zenith with the camera having the potential to hit the base and do damage to the camera or scope.
So in the American spirit of "more better" I started a series of upgrades. First I added a laser finder to the scope. Boy did that help. I pressed the button and slewed the laser to the alignment star. When I would look in the eyepiece there it was. I should have started off with some kind of finder! I added a thumb screw for the on off switch and I got tired of the batteries going dead. Each time I changed them I had to realign the laser with the scope, so I bought a dc transformer for it. I used some dc plugs and wired one into the laser and a jack in the transformer. No more dead batteries and dim laser in the cold, and I could unplug the laser from the power supply for storage. While I was at it I added a 12v dc transformer to power the ETX80 as well (yes the ETX80 can run on 12v). Dew was always a problem so I bought an ETX105 dew shield that I saw on sale for $1 with free shipping. I took some foam and lined the inside at the base to make it snug on the ETX80. It works great as a sliding dew shield.
Next up was cutting off the eyepiece port so the Mallincam camera could come to focus. I took 3/4" off the eyepiece tube. I took the upper ring off and reused it. I spread it open a little, glued it to the top, drilled out three holes for thumb screws, tapped the holes, used epoxy to fill the missing bit of the ring, and finally painted it. The Mallincam video camera could now come to focus and with an eyepiece extension tube the eyepieces worked fine also.
Now the camera worked but alt/az mode just didn't cut it so I bought a used Meade 884 tripod. I added a couple of levels to the tripod so I could set it up level easily. The scope just would not work in polar mode however. The RA would jump or slip. I used my micrometers and calipers to measure everything then poured over a Grangers catalog and found roller bearings, thrust bearings, and off the shelf pvc plumbing parts to add roller bearings to the base. The mount was now free spinning with the clutch undone. I could even balance the scope in RA in polar mode. The Mallincam loved the new bearings and I started to get some live viewing in. The PE still measured in the 180 arc second range but no more jumping or slipping. This was the mod of no return. I spent about 2 hours doing it but a couple of Sunday afternoons planning it. I was sweating like a sinner in church when doing it!
Now for a setback, the DEC knob broke. The plastic knob broke off the threaded shaft. I unscrewed the threaded shaft and used a 1/2" pipe tap to thread the hole deeper (it seems the shaft must be 1/2" pipe thread). I bought a short pipe nipple and a pvc T with a 1/2 female thread in the middle. Great new knob as I can get some real torque on it without the worry of breaking something. I also route my cables through it.
Even with the new bearings in place and doing polar mode I wanted better so I started looking at guiding. I had already taken a Celestron 9x50 finder with quick release bracket and made it into a finder/guide scope. I did this by removing the front objective and rear eyepiece. I cut off the rear of the tube just to the back of the groove for the adjusting screws. I sanded a 2" to 1.25' eyepiece adapter a bit and pressed it into the tube. I took the original crosshair eyepiece and glued it into a 3/4" copper coupler. The copper coupler is just less than 1.25" so it fits in the eyepiece adapter. After replacing the objective cell and mounting it, I now had a guide scope that would still function as a finder. One important thing to note is the way the ETX80 focuses. It moves the front of the ota in and out to focus. The mount for the guide scope cannot be too far forward or it will interfere with the inward movement of the ota during focus. Since there is no room for the laser and guide scope so I mounted the laser on top of the guide scope. When I aligned the finder with the ota I tightened the allen head adjustment screw (spring loaded screw) really tight so the finder scope will not move or flex in its bracket.
With the guide scope made it was time to tackle guiding. I had a Meade DSI pro for a guide camera, the 506 cable, and serial adapter working fine so I installed PHD. No matter what settings I tried the scope would over correct. Changing the slew rate on the hand controller helped some but it was not helping as much as I would have liked. After some emails with the experts on Weasner's Mighty ETX site I opted to replace the 494 with a 497. I patched it with the latest patches off the site and was in business. With guiding the PE was way down. PE measured around 30 arc minutes on the first night and I was able to get that even lower. The mount has a worm period of 900 seconds (15 min) and for most of that time the PE is very good guided. There is one spot on the worm that the guiding can't correct for however. All in all getting 2 minute shots "live" works well now. They do have some trails especially from poor polar alignment, but hey it is an ETX80 just taking snapshots. I have added a patch to allow for PEC on the ETX80 but so far I have not had time to really work on getting this working yet.
One problem the scope has always had is the jiggles when touching the focus knob. It was always hard to get good focus and I tended to say close enough because of the difficulties. I happened to see a sale of the Meade 1244 electric focuser at 29$ with free shipping so I took a chance. It had to be modified but I got it to fit. That is another mod that the scope needed from day one. I also took the alt shaft off the 884 tripod and threaded it with a 7/16 die. I glued a 7/16 nut on an old adjustment knob I had. I now have a stop at the correct setting and can make fine adjustments to the alt settings of the tripod. Meade should have done this one from the factory. Next I need to come up with an az adjuster for the tripod but that is not as critical. One note, when you look at the pictures of the ETX80 setup you will see a Celestron tripod spreader on my Meade 844. I lost the original spreader and Meade refused to sell me the spreader (Shame on you Meade) so I use the one off my Celestron CGEM.
Anyway the modifications to the ETX80 have been fun and they are something I could do when clouded out. While the pictures are not great and are not going to get published anywhere they were fun to do none the less, besides how many deep space unprocessed pictures have you seen with an ETX80 and not piggybacked on some other mount? The scope is light and I can carry the whole thing setup with cameras and all, in one trip outside. It truly is a grab and go. You can see by the pictures it has improved dramatically. The next "upgrade" needs to be a semi-apo type filter.
I only wish Meade would sell parts or part out the returns they trash.
The whole project got started because of the gift so beware of kids and grandkids bearing gifts. As one so aptly put it "there is no such thing as a free puppy".
Mark Stewart Stew57
Pictures taken with the ETX80
Pictures of the equipment
Pictures of the roller bearing modification
Pictures of the Meade 1244 electronic focuser being added
Pictures of modified finder scope
Pictures of the results of guiding