Nexstar 8se EQ Wedge Alignment Procedure
Posted 07 October 2008 - 04:59 PM
Here's a link to my photobucket album with more images of the wedge and my other goodies, theres a bit of a description with each image.
Wedge, dew heater and electric focuser images
I must say I didn't do this all on my own, I had help with the wedge design and build from my mates Peter and Jimbo.
Peter came up with a nice design and some cool calculations to get the centre of balance of the scope/mount over the centre of the tripod. Jimbo helped me with the cutting of the wedge with power tools and I did all the measurements and used a paper protractor printed from a website protractor generator to get the plate angles correct to about 1/4 of a degree.
with the Focuser I adapted one design from the internet for the servo/mounting plate side of things but instead of ripping the servo controller out just to get a continuous rotation motor with the servo gears intact I researched the net for a servo speed controller and found many designs all using the 555 timer IC chip.
I built the focuser controller circuit onto a breadboard (much easier than soldering but not permanent) to test it and once I was satisfied that it worked I set about soldering it onto stripboard so that it could be permanently housed.
For the heater controller I spotted some heater circuits for 555 timers while I was researching the focuser circuit, this circuit I built into a bit of breadboard as a prototype and housed in a small Â£1 'really useful box' and handn't intended to keep it permanently as I had a design for an automatic heater that I plan to make at some point.
My weight system is a design I copied from my another friend called James, who also donated the bar and weight which were surplus to his requirements on his lx200r 10".
Posted 07 October 2008 - 09:38 PM
Thanks for posting them and I've got more questions for you coming up. As they say, stay tuned.
Posted 08 October 2008 - 04:04 AM
Posted 14 October 2008 - 12:18 PM
I was happy to see your post as I just recently got the bug and bought my own 8SE and then immediately started looking at astrophotography. I've had pretty amazing success just taking pictures through the eyepiece using my little Canon point and shoot before I started buying any accessories. I even took a few medium length (~15 second) exposures by using a separate tripod to hold the camera in front of the lense.
I bought the universal camera mount, which works pretty well for holding my SD700, but almost immediately turned around and bought my Nikon D90 (FINALLY an excuse to get a DSLR!) and various T adapters and the Celestron wedge. Thus, I was grateful to see your post and the other reference someone mentioned in this thread that discuss the alignment procedure.
So far, I've attempted the alignment a couple of times but am still not satisfied that I'm getting good results. For a long (several minute) exposure, I get small trails with dots at either end, that seems to indicate to me that the scope is jumping. At this point I'm thinking it's a balance issue giving the drive problems. I notice you don't appear to have or mention any counterweights, but was wondering if you've looked at this since. In looking at the design of the 8SE, it's apparent that the typical weight system that mounts to the OTA is NOT the appropriate solution for this.
It turns out that JMI has made a counterweight that mounts to the mounting bar for the OTA, which is where it would need to be to move the CG back over the azimuth axis. What's the chance anyone has used this and can comment on how well it works? Unfortunately it doesn't allow for moving the weights further away from the OTA, so I'm concerned that balancing may require additional weight rather than taking advantage of additional leverage. I'm also a bit concerned about the mount chewing up the bar on my OTA. Thus, I'm trying to decide between spending the $60 to try that out vs. rigging something on my own.
At any rate, Don, the original question I wanted to ask you was if you could post a bit more detail on the steps you took to tighten the bearing assembly on your 8SE. I'm not sure if I want to go for that yet, especially if it's just a balance issue. Of course given that I've now put more money into accessories than into the scope itself, I'm starting to wonder if I shouldn't just trade my new 8SE in for something with a bit heftier drive and a better balance system.
I look forward to hearing from you and anyone else who has a comment and am attaching a pic to give people an idea what I've accomplished so far. This is a through-the-lens hand-held shot of the moon using my DS700 taken last month. Unfortunately it won't let me post the full 2816x2112 resolution! I also have a pretty good stack-up of Jupiter (done manually in Corel PhotoPaint) that I'll post some other time, and a couple of half-way decent shots of the ring nebula.
Posted 14 October 2008 - 01:23 PM
I have been thinking of asking the same question as you have ...
... At any rate, Don, the original question I wanted to ask you was if you could post a bit more detail on the steps you took to tighten the bearing assembly on your 8SE. I'm not sure if I want to go for that yet, especially if it's just a balance issue.
I'll sit back and listen.
Once again, welcome aboard!
Posted 14 October 2008 - 06:11 PM
Posted 18 October 2008 - 03:48 PM
Welcome to the world of AP with a NexStar 8SE. You certainly have jumped right in there and seem to have gotten off to a great start. I myself use a Stellacam astrovideo camera with the 8SE and have found great success.
You mentioned that you are possibly seeing jumps in the scopes movement. What you may be seeing is called Periodic Error or PE. Unfortunately there is no provision on the NexStar for correction of PE, thus no PEC. Where does this error come from, well it's due to the imperfections in the gears and the scope will move to soon or to late as the teeth mess with imperfection. The irregulars will show up repeatly every 8 minutes for the 8SE which is one complete cycle. In Alt-Az you have to deal with this in two axis while in equatorial mode it's just the az axis.
I use alt-az a lot with the Stellacam because it takes almost a minute before field rotaion becomes a real problem, and the camera can only expose for much less than one minute.
My video imaging is live and my particular 8SE there are cyclical movements with the image wandering slightly in the field of view. This isn't a problem over the 8 minute cycle cause it's video and the image is always in view.
Well I hope may have been of some help, lots of continued success with your 8SE.
Posted 19 October 2008 - 04:22 PM
I also bought some knobs to replace the cap screws that hold the diagonal supports, but haven't decided to switch yet. My initial though was to allow removing the bars to allow flattening the wedge for storage, but it's too much trouble to put back together every time. My other thought was that since I had to loosen the cap screws on the arms to open the wedge to begin with that eventually they might work loose, so having knobs would probably be a better solution there. On the other hand, I'm not likely to be changing latitude significantly, so it'll probably be a while before that's an issue!
Posted 19 October 2008 - 10:23 PM
Thanks for the info. That was my guess as well that it was in the gear train. I would suspect that a balanced scope improves that situation at least slightly. I had some pretty good success last night but my best pictures were from using the radial guider and eyepiece to keep it tweaked. I can already tell it's time for an autoguider!
Posted 21 December 2012 - 10:28 PM
In later versions, the Wedge Align option is replaced with the Polar Align option. This allows the use of ANY star to complete the polar alignment.
Does anybody have experience of using the newer Polar Align option? Especially in the Southern Hemisphere.
Posted 23 February 2013 - 12:41 PM
After much searching...I just "found" the Polar Align option...seems very similar to a software program I downloaded called Alignmaster. I made my own wedge but have NOT been able to try either Polar Align or Alignmaster for real. Would have been nice if Celestron updated their owner's manual before shipping. I noticed the manual is dated 2006 !!.....