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#1 Frost55

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Posted 24 July 2013 - 10:33 PM

Got my xt8 and took it out tonight around 10 and locked on to Saturn,could see the rings really clear with the 25mm stock but when I put my 6mm in it was a lot darker and nothing? Shouldn't it be right there? I only had a few minutes to try, wasn't real dark out but that was awesome when I focused to see the rings:-)

#2 KWB

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Posted 24 July 2013 - 10:58 PM

Hello and Welcome

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. :)

#3 Frost55

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Posted 24 July 2013 - 11:05 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?

#4 KWB

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Posted 24 July 2013 - 11:10 PM

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?

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?

Make sense?.

#5 Astrodj

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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?


Hi Frost55,

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. :grin:

#6 Frost55

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Posted 24 July 2013 - 11:51 PM

I tried to align the red dot on Saturn when I had it in the middle but the adjustment would only let me go so far, might have to shim the finder scope, thanks

#7 AngryHandyman

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Posted 24 July 2013 - 11:56 PM

Planets also cross the field of view relatively quickly compared to the moon and stars. If the alignment with the 25mm was off a bit or not really centered, by the time you get the 6mm in it may have already migrated out of the much narrower view.

#8 AngryHandyman

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Posted 25 July 2013 - 12:00 AM

The red dot is susceptible to parallax error as well, moving your eye around can have the dot appear in slightly different positions which is enough to miss what you're aiming at. With practice it can be pretty accurate but I've definitely missed targets at high magnification with a red dot finder often.

#9 Lamb0

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Posted 25 July 2013 - 01:44 AM

:grin: Welcome to Cloudy Nights! :thewave:
:FarmerRon: ugly math... 'cause a Dob'll drift. :dob:

:thinking: The Earth is round and there's 360° in a circle... :doah:
there's 24 hour in a day; so the sky moves 'bout 15° in a hour (KISS) :winky:
so 1° of drift takes 'bout 4 minutes. :ubetcha:

Now, the XT8's gotta FL of 1200mm; so with a 6mm Plossl you get 200x. :idea:

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! :scared:
un That's why ya wanna nudge yer scope so what yer lookin' fer drifts Inta view, 'steada OUT. :john:

:waytogo: Keep after Saturn, (call it motivation), you'll get the hang of it! :bigshock:

#10 youngamateur42

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Posted 25 July 2013 - 01:53 AM

Hi and welcome Frost, you could have bumped the scope slightly,it's also relatively easy to push the scope away when inserting the eyepiece.

#11 Frost55

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Posted 25 July 2013 - 02:56 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,
:-)

#12 AstroTatDad

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Posted 25 July 2013 - 04:19 AM

:rimshot: :banjodance: :rockon:
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:

#13 Maverick199

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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. :lol: 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.

#14 Achernar

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Posted 25 July 2013 - 09:23 AM

Next time you go out with the telescope, sight in on Polaris because it does not move. Center it in the FOV through your low power eyepiece, then switch to the higher power eyepiece and center it again. Adjust the finder so Polaris is centered on the reticle when it is centered in the field of view through the 6mm eyepiece. Then try again on Saturn. You will get a very nice view of the planet at 200X unless the seeing is bad.

Taras

#15 tezster

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Posted 25 July 2013 - 09:37 AM

Another well known trick to more easily align a finderscope is to intentionally defocus the star so it looks like a big circular blob - much easier to make sure the star is centered in the eyepiece this way.

The same method is used when performing two-star alignments for DSC computers.

#16 Billytk

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Posted 25 July 2013 - 04:35 PM

Before you take out the 25mm EP, notice which way Saturn is moving through the field of view. Then put saturn on the edge of the field of view so that it moves to center by the time you have the 6mm EP installed.

#17 Widespread

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Posted 25 July 2013 - 04:43 PM

You have already gotten lots of good advice.

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.

Best,
David

#18 GalaxyCollide

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Posted 25 July 2013 - 06:26 PM

You should get Telrad, or Green Laser so you can be accurate with your target. If you already have a illuminating eyepiece,try to make the object in the cross as close as possible. If you don't have them, then try to move the scope around just a little.

#19 Frost55

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Posted 25 July 2013 - 06:55 PM

Well looks like perfect conditions for tonight not a cloud in the sky.So I'll try out the suggestions on here,,thanks alot. Last night I seen Saturn so clear with the rings and space between them on the 25mm"48x",when I had my tele and eyepiece plugged into Stellarium it showed just a small white dot with the 48?did I see it because conditions were good?To make Stellarium show what I seen, I had to put the 6mm with a 2x at 400x?

#20 kfiscus

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Posted 25 July 2013 - 07:42 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.

#21 AstroTatDad

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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.

#22 Frost55

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Posted 26 July 2013 - 02:09 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

#23 AstroTatDad

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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


:bow: Awesome! Did you have time to view anything else this evening?

#24 csrlice12

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Posted 26 July 2013 - 10:09 AM

I'd get a RACI or even a straightthru optical finderscope (like the 9X50, or even a 6X50 on a smaller scope)and then align the finder on a fixed object. I find using the red lights on top of radio towers work very well for aligning the finderscope. But any object about a mile away should work.....

#25 kfiscus

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Posted 26 July 2013 - 10:14 AM

Excellent! The skies are full of stuff that will blow you away with your 8". I'd recommend M-13 (Great Globular Cluster in Hercules) and M-27 (famous Dumbell Nebula in Vulpecula- below head of Cygnus the swan). Use your 25mm to find them, then switch to the 6mm. Every star map or software will show these objects and 1000's more your scope can show you.






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