need some quick help on columation

[Starforce2]

I have the laser for it and the xt10 dob. SHould I be using the spider vane screws on the outside of the tube or do I use the hex screws for the mirror itself, or both? I can't seem to get it in both the ring on the mirror and where it belongs on the laser target thingy at the eyepeice. DO I need to do anything with the mirror screws under the primary? I have a possible girl scout event tomarrow that Iw as just reminded of today so I don't have much time to get this adjusted. Jupiter turns into a nice long smudge on a 15mm eyepiece and wont focus so it's way screwed up.

[MarkC]

ason

Try watching this. I have an XT12 and columinate it every time I use it.

https://www.youtube.com/watch?v=YAVGcGEBmCE

Center the laser on the primary using the screws on the back of the secondary.

I also use the barlow method of columinating the primary using the screws on the back of the primary. I use a white cap on the inside of the focuser tube for this.

http://www.backyardastronomy.net/collim ... nians.html

Mark

[Dick Jacobson]

If you get it collimated and still have poor images, you might have a problem with the mirror being too warm. If possible, put the scope outside just after sunset and set up a fan blowing at the back of the mirror.

[dwindseth]

Here is a collimating web site to look at. Huggy gave me this when I was collimating. Google: Astro-Baby then click on Astro-Baby guide to collimating. I thought it was very indepth and useful.

[dwindseth]

Another great site for collimating that was given to me is Starizona.com, and click collimating. It shows great detail using an orion lasermate and an orion collimating eyepiece.

Good Luck

[SEmert]

I have the laser for it and the XT10 dob. SHould I be using the spider vane screws on the outside of the tube or do I use the hex screws for the mirror itself, or both? I can't seem to get it in both the ring on the mirror and where it belongs on the laser target thingy at the eyepeice. DO I need to do anything with the mirror screws under the primary? I have a possible girl scout event tomorrow that Iw as just reminded of today so I don't have much time to get this adjusted. Jupiter turns into a nice long smudge on a 15mm eyepiece and wont focus so it's way screwed up.

All the sites listed are good ones. To directly answer your questions, it sounds like you may have to go back to some very basic adjustments before using the laser collimator.

1. The spider vane screws on the outside of the tube... Those are to center the secondary left and right and forward and backward under the focuser. If, even when you have the secondary rotated so it is pointing correctly, the secondary still appears to be off center to the left or to the right when viewing through the focuser using a sight tube, you use the spider vane screws to move the secondary left and right to center it. For up and down (toward or away from the primary), you use the center screw in the secondary's holder. Screw it looser or tighter to move the secondary up and down so it is centered in the focuser. You WILL have to loosen or tighten the three secondary adjustment screws to let that happen.

2. The three secondary adjustment screws... I suggest first adjusting them so they are all sticking the same distance out of the secondary holder (if they stick out the top of the secondary holder, that is easy to see. If they don't, which I believe is the case with the XT10, you will have to look at the spacing between the bottom of the spider's center and the top of the secondary mounting block. A couple years ago, people were just using the laser collimator on the 20" Padre at Eagle Lake and not looking closely at the orientation of the secondary, and as a result it was horribly tilted and miscollimated even though you could get the laser dot centered on the primary. The laser said it was good, but the views were horrible! It was because the secondary was at an incorrect rotation, but the tilt of the secondary compensated for it to get the laser beam to fall on the center of the primary mirror.

It's a combination of making sure the secondary mirror is rotated correctly so that it is square with the focuser, and making sure the secondary mirror is centered under the focuser first with all the secondary screws about evenly extended. *Then* finally you can start using the laser collimator to adjust the tilt of the secondary mirror so that it directs the laser beam directly into the center of the donut in the middle of the primary mirror to collimate the secondary mirror.

3. Finally, after the secondary is collimated, go for the primary mirror. Use the three screws behind the primary to direct the laser beam directly back into the hole in the laser collimator that the beam is coming out of. I think the XT10 has six screws. Three are collimation screws, three are mirror lock screws. Collimate it, and lock the mirror in place with the locking screws. When you tighten the locking screws it usually messes up the collimation a bit, so you have to go back and forth between the collimation screws and the locking screws a few times until it is tight and collimated at the same time.

4. Once you've done that, re-check the secondary. You may have to realign the secondary so the laser beam again lands directly in the middle of the primary mirror. Adjust the secondary to do that, then check the primary's collimation again and adjust as necessary. "Wash, rinse, repeat." In other words, if it was pretty bad to start with, you may have to go back and forth a few times to fine tune it into perfect collimation.

After that, it should only take minor adjustments the next time you bring it out. But please do check it every time you bring the scope out. Newtonians, including Dobsonians, are notorious for needing a slight tweaking quite often.

Finally, if you are a perfectionist, you can use the Nils Olaf Carlin "Barlowed Laser technique" I highly recommend it. You could Google for the article either on his web site or on the S&T web site (it was an article in S&T quite a few years ago), or you can download the copy of the S&T article that I posted on the BSIG forum. Also, for real perfection, you can use an autocollimator (Google it). But for 98% of the people out there, the procedures I listed are just fine.

[SEmert]

I have the laser for it and the XT10 dob. SHould I be using the spider vane screws on the outside of the tube or do I use the hex screws for the mirror itself, or both? I can't seem to get it in both the ring on the mirror and where it belongs on the laser target thingy at the eyepeice. DO I need to do anything with the mirror screws under the primary? I have a possible girl scout event tomorrow that Iw as just reminded of today so I don't have much time to get this adjusted. Jupiter turns into a nice long smudge on a 15mm eyepiece and wont focus so it's way screwed up.

All the sites listed are good ones. To directly answer your questions, it sounds like you may have to go back to some very basic adjustments before using the laser collimator.

1. The spider vane screws on the outside of the tube... Those are to center the secondary left and right and forward and backward under the focuser - in other words, to center the secondary mirror in the middle of the optical tube assembly. If, even when you have the secondary rotated so it is pointing correctly, the secondary still appears to be off center to the left or to the right when viewing through the focuser using a sight tube, you use the spider vane screws to move the secondary left and right to center it. For up and down (toward or away from the primary), you use the center screw in the secondary's holder. Screw it looser or tighter to move the secondary up and down so it is centered in the focuser. You WILL have to loosen or tighten the three secondary adjustment screws to let that happen.

2. The three secondary adjustment screws... I suggest first adjusting them so they are all sticking the same distance out of the secondary holder (if they stick out the top of the secondary holder, that is easy to see. If they don't, which I believe is the case with the XT10, you will have to look at the spacing between the bottom of the spider's center and the top of the secondary mounting block. A couple years ago, people were just using the laser collimator on the 20" Padre at Eagle Lake and not looking closely at the orientation of the secondary, and as a result it was horribly tilted and miscollimated even though you could get the laser dot centered on the primary. The laser said it was good, but the views were horrible! It was because the secondary was at an incorrect rotation, but the tilt of the secondary compensated for it to get the laser beam to fall on the center of the primary mirror.

It's a combination of making sure the secondary mirror is rotated correctly so that it is square with the focuser, and making sure the secondary mirror is centered under the focuser first with all the secondary screws about evenly extended. *Then* finally you can start using the laser collimator to adjust the tilt of the secondary mirror so that it directs the laser beam directly into the center of the donut in the middle of the primary mirror to collimate the secondary mirror.

3. Finally, after the secondary is collimated, go for the primary mirror. Use the three screws behind the primary to direct the laser beam directly back into the hole in the laser collimator that the beam is coming out of. I think the XT10 has six screws. Three are collimation screws, three are mirror lock screws. Collimate it, and lock the mirror in place with the locking screws. When you tighten the locking screws it usually messes up the collimation a bit, so you have to go back and forth between the collimation screws and the locking screws a few times until it is tight and collimated at the same time.

4. Once you've done that, re-check the secondary. You may have to realign the secondary so the laser beam again lands directly in the middle of the primary mirror. Adjust the secondary to do that, then check the primary's collimation again and adjust as necessary. "Wash, rinse, repeat." In other words, if it was pretty bad to start with, you may have to go back and forth a few times to fine tune it into perfect collimation.

After that, it should only take minor adjustments the next time you bring it out. But please do check it every time you bring the scope out. Newtonians, including Dobsonians, are notorious for needing a slight tweaking quite often.

Finally, if you are a perfectionist, you can use the Nils Olaf Carlin "Barlowed Laser technique". I highly recommend it. It definitely helps. It especially helps if you have a rack-and-pinion focuser that has a little slop in it, making it difficult determine when the secondary is properly collimated. You could Google for the article either on his web site or on the S&T web site (it was an article in S&T quite a few years ago), or you can download the copy of the S&T article that I posted on the BSIG forum. Also, for real perfection, you can use an autocollimator (Google it). But for 98% of the people out there, the procedures I listed are just fine.

[Ricola]

Barlowed laser article from sky &telescope