telescope alignment
After my so-so experience the night before I spent some time surfing the net looking for alignment issues regarding the Nexstar SE line of telescopes. Here is what I found on the net and also what i found out later by trial and error:
- make absolutely sure that your tripod is level
- adjust the "anti-blacklash" settings of your telescope to ensure better GOTO performance. I'll try to go into the details further down the page
- to get better results, use the two star alignment or three star alignment feature instead of the SkyAlign feature
- if you are only looking at a certain part of the sky, use the sync command to re-sync the telescope at a certain object of interest
I found is a very good description about what this is and how it can be corrected on the the great nexstarsite. Basically it says that you're supposed to do the following:
- point your scope at a distant object. This can be done during the day.
- set the slew rate to 4 or 5 using the RATE button on the hand controller
- press one of the directional buttons and observe if the object starts to immediately move or if it takes a while to move
- the longer it takes the image to move, the more likely you have to put a higher value into the "anti backlash" settings (Azm Backlash corresponds to the left/right buttons, Alt Backlash corresponds to the up/down buttons)
Why did I set it to 20 and 40 ? Well, I had no idea what those values actually meant, I only knew they go from 0 to (I think) 99. So I just guestimated and set two different values in order to see how those values would affect the movement of the scope.
The results were that the scope started to almost immediately react to left/right commands but made a huge jump up or down whenever I pushed the Alt (up/down) buttons. So obviously the setting of 40 was to high.
After about 15 minutes of trial and error i ended up with the following values:
- Azm Backlash positive: 25 / Azm Backlash negative: 25
- Alt Backlash positive: 15 / Alt Backlash negative: 15
Personally I think that the quality of the product should be good enough to not require any additional corrections by the user - but that's probably just the mac user in me speaking his mind....
Important addition: when you attach different gear on your telescope, then the values that you entered will most likely not work as well anymore. I just got back after attaching my digital camera and noticed that due to the added weight my ALT anti-backlash settings of 15/15 made the image "jump" again. I had to set it to a value of 4/4 in order to minimize the backlash. So i guess the more weight you add, the lower the ALT number ? I'll have to give it some more tries...
Addition 09 January 2010: While i was aligning my new finderscope i changed the backlash settings again. I now have got a setting of 10 for the alt negative and positive and a setting of 50 for the azm negative and positive. I changed the values because i felt like there still was alot of pause in the azimutz axis.
...and out on the garage I went again
This time around i made absolutely sure that the tripod was as level as I could get it with the limited tools (small bubble level) I had. I wonder if there are any other more sophisticated levels out there.
I then used the two star auto align by choosing Arcturus and then Altair as the guide stars. Got the "alignment confirmed" message - so far so good.
I then chose Jupiter from the Planets menu and watched the scope slew all the way over to jupiter. While it was moving, I looked through the finderscope and when the scope stopped, the red dot was EXACTLY over the planent. Looking through the eyepiece had Jupiter almost spot on smack in the middle of my 25mm eyepiece.
Bill Cosby voice mode: "Now that's what i'm talking about !"
I then entered M13 and again, ended up with the object almost centered in the eyepiece. That's defenitely good enough for me. And the scope is not even polar aligned ! I guess GOTO performance must be even better if the optional polar wedge would be used.
So I think the combination of not leveling the tripod properly plus a certain amount of backlash in the gears was the reason for my disappointing experience the other night.
Addition 09 January 2010: While i was aligning my new finderscope i changed the backlash settings again. I now have got a setting of 10 for the alt negative and positive and a setting of 50 for the azm negative and positive. I changed the values because i felt like there still was alot of pause in the azimutz axis.
...and out on the garage I went again
This time around i made absolutely sure that the tripod was as level as I could get it with the limited tools (small bubble level) I had. I wonder if there are any other more sophisticated levels out there.
I then used the two star auto align by choosing Arcturus and then Altair as the guide stars. Got the "alignment confirmed" message - so far so good.
I then chose Jupiter from the Planets menu and watched the scope slew all the way over to jupiter. While it was moving, I looked through the finderscope and when the scope stopped, the red dot was EXACTLY over the planent. Looking through the eyepiece had Jupiter almost spot on smack in the middle of my 25mm eyepiece.
Bill Cosby voice mode: "Now that's what i'm talking about !"
I then entered M13 and again, ended up with the object almost centered in the eyepiece. That's defenitely good enough for me. And the scope is not even polar aligned ! I guess GOTO performance must be even better if the optional polar wedge would be used.
So I think the combination of not leveling the tripod properly plus a certain amount of backlash in the gears was the reason for my disappointing experience the other night.
Posts
thanks for a really handy blog, I have the same telescope and am really get some good information from your writings. I have tried last night to set the back-lash. I don't like the sound of the gears when start playing with the values. I've settled on around 10 for everything, but there is still a"spinning gear" sound before the telescope makes a move in any direction. Not sure if you've experienced this. Keep up the blog, thank again.
ReplyDeleteWayne
Hey Wayne - I also get the spinning gear sound for a little while when I hit the
ReplyDeletedirectional buttons. As far as I understand it, the " better" the anti backlash settings, the shorter the spinning should be noticeable before the field of view starts to move.
Thanks for your comment - it's great to hear that at least one person read my blog :) it's snowing right now and the weather has been really bad for weeks - so I probably won't have anything interesting to write about for some time...
Marc
Marc,
ReplyDeleteI am looking at the 6SE also, for pictures of the moon etc, do you need long exposure times and therefore a wedge for the 6SE or you just using the standard mount and OTA. This would be my first scope and the 5SE has an inbuuilt wedge but I would rather spend the extra on the 6" scope rather than the 5" but the wedge is £300, a little to much expensive
Great Blog
Paul
Hi Paul
ReplyDeleteFrom what i've learned so far, exposures up to 15 seconds or so should be fine with the standard alt-az mount the 6SE has. You can log onto the forums at cloudynights.com and ask around if anyone is using the optional polar wedge for astrophotography. I think that if you're really serious about long exposure photography that you will have to get an alltogether different computerized mount.
I bought the 6SE because it has the same mount the 8SE uses - so if i ever want to get a bigger OTA, i can do that without a big hassle.
I am just starting out with astrophotography but from what i've seen online, if you use a stacking software with alot of short exposure images, pretty good results can be realized.
I hope this helps
Cheers
Marc
I was asking about a price deal 6SE and the guy was saying that the 6SE will only see the planets and a couple of extra nebula etc, but the 8SE will see 20-30 more, yes it will gather more light but I do not believe that the 6SE will not see lots of objects in the sky.
ReplyDeleteHow have you found your viewing so far have you tried for nebula and other galaxies?
Cheers
Paul
Paul - i used to own an 8" Meade LX10 - so far i've not noticed any big differences. I used to look at globular clusters like M13 alot and it looks great in my 6SE as well.
ReplyDeleteI guess it really depends on what you're looking for. An 8" scope is alot bigger than a 6" scope although it does not seem like alot of difference. It would probably be best if you go see a store that has them both on display so that you can see for yourself.
If you only want to look at faint deep sky objects, then i guess the bigger the scope the better. So far i've only used the scope to look at the Moon, the planets (Jupiter, Venus), globular (like M13) clusters and a nebula (the ring nebula, that looks like a donut) and the 6SE worked just fine.
Marc,
ReplyDeleteThats what I plan on doing the only thing is it is in the middle of Glasgow and Edinburgh. Best to go and see and ask a few questions.
The 6SE setup is going to cost just under £1000 but the 8SE would be another £250 on top, it is not much but to shell out £1250 for a first scope is lots of cash!!.
As you say go to a local shop, your blog needs more pictures ;-) Scotland has alots of dark sky about 1 hour from me so hopefully lots of things will be viewable.
Cheers
Paul
Dear Paul
ReplyDeleteI honestly wish i had any pictures to put on the blog : ) But with the bad weather and family it just does not leave me enough time right now.
I've read alot of entries on cloudynights.com where people are asking wether or not they should get a 6SE. It usually boils down to the portability and the budget. If you don't mind the extra cash and if you don't plan on moving the scope alot, get the 8SE.
But I'll do my best and as soon as the sky clears, I'll try to take some pictures : )
great blog
ReplyDeleteHelp!!! I have just bought a Nexstar 6 scope and followed (I think) the instructions to set up the handset. I can get as far as the handset telling me to align to a star but when I use the direction arrows to slew the scope nothing happens.
ReplyDeleteWhat am I doing wrong?
I would be grateful of any advice.
Hello Guy - you need to use the number keys on the keypad. As you will notice these keys also have "up" "down" and so forth written on them. Do not use the direction keys on top of the keypad for this.
ReplyDeleteCheers
Marc