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New C8SE waiting for First Light; Q's?

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#1 butsam

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Posted 28 December 2012 - 06:39 PM

Hi all! New to the forums, posted once in Beginner but I realized this may be a more appropriate place for a couple of my questions. Of course, the midwest is now getting significant snowfall several days between now and when I go back to work...lol Figures! That said, I'm extremely excited to put this scope to work -- hopefully Sunday, if the weather doesn't clear before then (and the report doesn't change).

First, the list. Got the Celestron 8SE, Power Tank, Celestron Eyepiece Kit, and Dew Shield. I am viewing in the suburbs of a semi-major city.

Eyepieces I have are as follows: 6 mm, 8 mm, 13 mm, 17 mm, 25 mm, 32 mm, and 2x Barlow. I also have filters, but other than the ND-filter I am not likely to use them the first few nights.

A couple questions:

(1) Which alignment method do you recommend, 2-star or 3-star? (Names of stars isn't an issue to me...I know some of them already, and Stellarium on my android can tell me any I don't know at the 'scope even if I don't plan correctly, so no issue. That in mind, any reason not to use the 2-star?)

(2) When aligning, what eyepiece should I bother using?
-- Obviously, it's best to either start at 32 mm or 25 mm (the 25 mm came with the scope) and work down from there, but how far down should I go? I guess what I am asking is, what is the limiting accuracy, assuming I can get fairly precise GPS coordinates (from Google Maps for my backyard), and fairly precise time information (to within a couple seconds)? Does it make sense to work my way down to the 6 mm to align, or should I just call it good with the 25 mm, or somewhere in between? I guess ultimately this is a question of how much error there is in the gears and/or software?

(3) The manual mentions to align with your final alt & az direction adjustments being in the same direction your scope would approach an object from, and gives an example (keeping in mind up/down reverse). Does this mean my scope is programmed to always approach a target with the same final movement (ie, it may overshoot by a bit but then use the same final approach), or does this depend on the targets I choose for the night?

This is my "first" scope...in quotes because my brother had a scope growing up, but I didn't use it much, as at the time I didn't know much about it myself. So, I think this is the first that really counts for me. I do have a very strong theoretical understanding...took Astronomy in High School, and have a Masters in Physics (although not emphasizing astronomy) and working on my PhD...but I don't have a lot of practical experience in Astronomy specifically.

Anyway, what are your thoughts?

#2 Midnight Dan

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Posted 28 December 2012 - 07:36 PM

Hi butsam and welcome to the forum!

Congratulations on the new scope!

1) Auto two-star is the recommended procedure. The 3-star (SkyAlign) is equally accurate, but because it has to figure out where it's pointed, it sometimes fails so it's less reliable.

2) I would just stick with the 25mm. You should b able to get stars pretty close to center without changing to a higher power. And in most cases, the limiting factor for accuracy of gotos is other things like backlash in the gears. One technique many people use is to defocus the star until it is a large donut of light. It's easier to center that way.

3) Yes, the scope is programmed to always approach from a certain direction. That direction can be changed in the menus. For the northern hemisphere, the goto approach direction for azimuth should always be set to positive. For the altitude axis, it depends on on whether your scope is front heavy or back heavy, but there's some controversy on which setting works best. I'd say try it set to positive and negative and see what works best for you. But ... once you've got the goto approach set, you do want to be sure that during alignment, you use the same final approach direction as the goto approach setting.

Good luck and let us know how it goes!

-Dan

#3 Skip

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Posted 29 December 2012 - 02:49 PM

Hi butsam,

WELCOME TO THE COLLECTIVE!!

:borg: Prepare to be assimilated - resistance is futile! :borg:

:grin:
Dan has already covered your questions. So I'll just add the welcome. Enjoy that scope. You will come to love it! :love:

#4 butsam

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Posted 29 December 2012 - 03:07 PM

I did some of the preparations just now, set the scope up for "Positive" Alt and "Positive" Az, which means I think that it is approaching objects with final movements being "Up" and "Right", is that correct? (Meaning, "Down" arrow and "Right" arrow for alignment, since the controls for up/down reverse for the final step of alignment for each star.) At least, that's what it looked like to me visually -- now just waiting for first light!

#5 Tel

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Posted 29 December 2012 - 03:50 PM

Hi Butsam,

A very warm welcome to CN and to this forum in particular. Congratulations on your acquisition of the 8SE. It's a very fine 'scope which, I'm sure, will give you many years of viewing and possibly imaging pleasure. :bow::bow:

Yes, if you have set your "Altitude GoTo Approach" to positive, (Azimuth setting also to positive of course), this should take advantage of the balance of the tube (OTA) being offset to give a little back-end heaviness and as such, it will finalise its approach to any object you select, with an upward and "to the right" movement.

This further means, that when centralising your alignment stars, each should be moved to the centre of your chosen eyepiece using a "to the right" and downward movement when said star is viewed in the eyepiece.

Additionally, you may be interested in this synopsis contained (if you page down) on this attached thread, to posting:

#5421776 09-14-12 11:47pm.

http://www.cloudynig...5417848/page...

Finally you may care to view the attachment I have made at the title of my post here, hopefully to assist you in the future to keep your 'scope "on track" !

Hoping this helps,
Best regards,
Tel

Attached Files



#6 butsam

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Posted 30 December 2012 - 10:28 AM

Thanks much :) Very helpful documents, both the attachment and thread. I'll definitely look at fiddling with those settings as I get things going. :)

My scope was, in fact, defaulted to Positive, Negative approach directions as the attachment said, and I switched it to Positive, Positive. I'll remember the gear settings as I mess around with it once I have a star to look at :)

More snow forecast for New Year's Eve and into New Year's Day, but there is a chance that early this evening the clouds may break for a few hours...at least, according to the Android astronomy weather app that I have. Keeping my fingers crossed! (And moved the OTA to the garage for the day so it can cool off to near ambient.) Otherwise, looks like next weekend will be a lot more clear as a backup. I'll be sure to provide the First Light post as soon as the skies cooperate :) I can't wait to see Jupiter, and many of the other objects in the sky this time of year :)

#7 Tel

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Posted 30 December 2012 - 11:15 AM

Hi Butsam,

Yes, the factory release settings for the Altitude and Azimuth GoTo Approach are, I'm sure, Negative/Positive.

A negative setting presupposes that your OTA is fore-end heavy whereas with a positive setting, a back-end heaviness is supposed to dominate.

The idea behind having this slight, (and I emphasise that it should be slight), offset balance, is to ensure that the tube places a small load on the altitude drive in order to minimise backlash between its spur gears.

As I said though in the original posting, experiment with both "Altitude GoTo Appproach" settings, (both positive and negative), to establish in your own mind, which performs better for you, bearing in mind that you must retain a positive azimuth setting for the reason that you dwell in the northern hemisphere.

Also, perhaps see how the tube responds to re-offset balancing in this respect: (i.e. moving the tube forward or back in the dovetail,.

The main thing is to experiment with all of these various settings until you, personally, are satisfied that you have optimised the performance of your individual 'scope ! :waytogo:

Best regards,
Tel

#8 Bob Griffiths  Happy Birthday!

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Posted 30 December 2012 - 12:07 PM

Couple of thoughts ... it makes Absolutely Positively no difference if you run the scope SLIGHTLY (caps intentional) front or rear end heavy.. I happen to run mine rear end heavy and set my GoTo approach to + and + ... IF I ran the scope back end heavy I woudl have set it at +_ and -
Don't start thinking like a future PhD and royally confuse yourself to figure out why the direction buttons reverse at slow slew speeds... Just follow your natural tendency to use the Right button to move the freaken star to your right in the FOV and the Down Button to move the freaked star down lower in the FOV of the eyepiece... end of problem and you do not even have to engage your brain..

With a + and + approach you center using the Right and Down buttons..
With a + and - approach you center with the Right and UP buttons...

I normally use a 25 mm eyepiece to do my alignments BUT I de-focus the star to enlarge it to resemble a HUGE donut that almost entirely fills the entire FOV .. its just easier to center it that way then guessing the center of a small "dot" (the star in focus)

Art Dent wrote an excellent sticky on aligning these scope here on this forum..and FogFire wrote an equally good one over on the Astronomy Forum

Read'em ...

Which Method to use...? Makes no difference what you choose... even the 3 star Skyalign procedure only uses 2 stars (the third is just a conformation star) Just remember to space your first 2 stars close to 80 to 120 degrees apart and avoid using planets or the moon AND do not use any star above say 75 degrees NOR any star lower then say 30 degrees..

Piece of cake.. LOL

Bob G.






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