Posted 24 July 2013 - 10:33 PM
Posted 24 July 2013 - 10:58 PM
It sounds like either your Red Dot Finder or finder scope(whichever your scope has) isn't properly aligned with the main tube. For alignment at night,use your lowest power eyepiece and locate and center in the eyepiece the star Polaris(The North Star which doesn't appear to move. Without moving the scope,look through the finder and see where the star is,then adjust it accordingly to center the star in the finder. Then Insert the 6mm eyeiece and see if you can see the star anywhere the finders field of view. Adjust again if needed,making sure once again to not move the main tube. Repeat as needed. Once aligned,the finder should hold that for a long time provided it isn't knock out of alignment or removed.
Good luck,it get's easier as you gain experience.
Posted 24 July 2013 - 11:05 PM
Posted 24 July 2013 - 11:10 PM
I understand and what I'm trying to say above is the margin of error is slim at a much higher magnification of having Saturn in the field of view versus the low power 25mm eyepiece,if the finding device isn't properly aligned for the highest magnification eyepiece. Did you first use the finder to locate Saturn,and then was it in the field of view using the 25mm eyepiece? If so,where was it in that view. Near center?
I what I'm trying to say is I had Saturn in the middle of the 25 and I quickly changed to the 6,,shouldn't I see Saturn?
Posted 24 July 2013 - 11:36 PM
I guess what I'm trying to say is I had Saturn in the middle of the 25 and I quickly changed to the 6,,shouldn't I see Saturn?
When you pop in the 6mm after having centered the 25mm Saturn should still be in the field of view if you are quick. Did you also refocus? You will have to rack in the focus quite a bit going from a 25 to a 6mm. An extended object like Saturn at high power AND way out of focus will fill the f.o.v. and be too dim to see. Also, if your scope does not track it will also move out of the f.o.v. very fast.
Practice switching from 25 to 6mm on the moon until you get a feel for it. The moon so big and bright it is hard to miss. Center a smallish, prominent feature in the 25 and switch to the 6mm. Take note of how much off center the feature has become after you refocus. You may solve your dilemma.
Posted 24 July 2013 - 11:51 PM
Posted 24 July 2013 - 11:56 PM
Posted 25 July 2013 - 12:00 AM
Posted 25 July 2013 - 01:44 AM
ugly math... 'cause a Dob'll drift. :dob:
The Earth is round and there's 360° in a circle...
there's 24 hour in a day; so the sky moves 'bout 15° in a hour (KISS)
so 1° of drift takes 'bout 4 minutes.
Now, the XT8's gotta FL of 1200mm; so with a 6mm Plossl you get 200x.
A Plossl's gotta 'bout 50° AFoV, so it's only gotta 'bout 50°/200x or 0.25° TFoV. :iwhat: (True Field of View)
That means it only takes about a minute at most to drift all the way from the middle of one edge all the way ta the other edge. Even if the low power field is really in the middle - Ya Got 'Bout Half A Minute Ta Swap Eyepieces!
un That's why ya wanna nudge yer scope so what yer lookin' fer drifts Inta view, 'steada OUT. :john:
Keep after Saturn, (call it motivation), you'll get the hang of it!
Posted 25 July 2013 - 01:53 AM
Posted 25 July 2013 - 02:56 AM
Posted 25 July 2013 - 04:19 AM
Cool, not bad for first viewing. Yeah no biggie, you will get the hang of switching out EPs in no time. The little nudge/drift thingie works every time. :breakdance:
Posted 25 July 2013 - 04:58 AM
Thanks for the advice guys. I showed my wife Saturn and she was amazed, she can't wait to see it with the 6mm,,she's hooked,
I liked the advice given by Lamba. Btw, ensure your focuser screw is loosened. Sometimes after racking out my focuser, the screw gets tight and focuser does not move but after loosening the screw, I can wiggle out a few more mm. Quite possibly the system in your Dob is same as Z8.
Posted 25 July 2013 - 09:23 AM
Posted 25 July 2013 - 09:37 AM
The same method is used when performing two-star alignments for DSC computers.
Posted 25 July 2013 - 04:35 PM
Posted 25 July 2013 - 04:43 PM
If your 6 mm eyepiece is a Plossl, i would add that short focal length Plossls have tight eye relief. You really need to put your cornea almost on the lens.
As mentioned above, you also have to refocus. A combination of improper eye distance and extreme defocus could be the problem, assuming you're switching EPs quickly enough.
Posted 25 July 2013 - 06:26 PM
Posted 25 July 2013 - 06:55 PM
Posted 25 July 2013 - 07:42 PM
Posted 25 July 2013 - 08:10 PM
Additional suggestion: if the problem is a misalignment of the finder to the main scope, gang up on the problem. Have your wife keep Saturn in the center after you've gotten it there. She will be the tracking mechanism. Obviously, this will take a bit of practice. Just have her keep Saturn in the center of the low-power field for a few minutes. Center it again and have her keep it there while you adjust the red-dot finder to perfection. She has to override any bumps you impart to the scope. After this has been done, switch to the 6mm and repeat. You will have it.
hey there you go, little team work.
Have you also thought of picking up a Telrad maybe? I like using that on my Dob. Also good luck to night, wish it was clear here maybe it will clear out by tonight.
Posted 26 July 2013 - 02:09 AM
Posted 26 July 2013 - 02:17 AM
Well I did what you guys suggested and it worked great, changed ep a lot faster and let Saturn drift right into view. I did what kfiscus said while I had Saturn in the middle my son adjusted the red dot and now it's dead on. Thanks all
Awesome! Did you have time to view anything else this evening?
Posted 26 July 2013 - 10:09 AM
Posted 26 July 2013 - 10:14 AM