Hi
Happy New Year to everyone. I hope Mars went well
I posted a request in early 2007 for help in collimating my Celestron short tube Powerseeker 127 EQ and got information regarding removing the inbuilt Barlow lens from the focuser when collimating. This was a great help but I still want to try to get better results with the scope especially as I now have a Philips 900 webcam that I want to start using.
So far, I have made the following "improvements". (I have been criticised for spending too much time on a cheap telescope but I'd like to make it as good as it can reasonably be and I have done the work over a year of spare time.) All this work and this post is in spite of the fact that I have a GSO 200mm Dob on the way.
1. Replaced all possible mount and scope screws with stronger hex cap-head bolts.
2. Disassembled and re-greased and adjusted everything.
3. Replaced the focuser bearing strips with ice-cream container strips. Much less slop.
4. Installed an ice-cream container washer between tripod and mount.
5. Made a much more useful and rigid accessory tray out of MDF and square aluminium tube with in built spirit levels and clock and will take 4 eyepieces in their protective tubes. I can post a photo if anyone is interested
6. Filled the 9 aluminium tripod leg sections with steel rods and mortar. Much more rigid and damped. (Messed up the the compass I originally had in my new tray though)
7. Filled tripod top bracket with mortar with aluminium tubing between the leg mounting holes.
8. Green laser pointer to replace finder.
9. Replaced the RA and Dec slow motion cables with simple 1 inch dia knobs. They don't get in the way and work well if scope is balanced and mount is greased/adjusted. You have to have this to use an RA motor anyway.
10. The reason for this post
I am thinking of replacing the OTA tube so I can dispense with the inbuilt focuser lens. The result will be an appreciably longer OTA but a simpler, cleaner optical path and much easier collimation as I won't have to disassemble the focuser every time. I have documentation on how to position everything on a tube when building from scratch but I have the following questions. Note that I am planning on using a 1 metre length of 150 mm PVC storm water pipe from Bunnings for the tube which I have found is an absolutely perfect fit for the Celestron tube end pieces (better than the original in fact). The scope has figures of Primary mirror dia 127mm, Focal length 1000 mm (I will check this) and this gives a focal ratio of 7.87.
1. Does anyone know of any problems in using PVC tubing? It is white but I am planning to line the inside with something black.
2. Will my documentation work given that the original scope was designed around using the inbuilt lens? ie are the focuser, primary mirror, etc going to work in this role?
3. Even if the focuser will work would I need to remove the inbuilt lens mount assembly? It effectively reduces the diameter of the focuser tube but I figure I will have a narrower light cone when it gets to the focuser anyway. Leaving it in will give me the option of using the the scope with both tubes perhaps?
4. Any other problems that anyone can foresee?
Thanks for any help
Regards
Steve