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Cgem 800 alignment problem

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#1 juand731112

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Posted 05 January 2013 - 08:57 AM

First night viewing with my new CGEM 800 HD. Had a great night viewing. Orions neubla, jupiter and andromeda. Just some questions for the pros. The telescope takes me to my destination with no problem, but I'm trying to do photography, as I tried to even do a 5 second picture of Sirius last night it came out blurry. I did the two star alignment. So I don't think it's tracking the stars right. Also I'm having problems understanding the polar alignment. My latitude in rhode is 41 degrees so do I set my initial polar alignment to that angle?

FYI initially the scope was facing south but than I moved it roughly facing north and tried realigning, it would roughly take me to Sirius or Rigel, I than centered and align but my pictures still came out blurry.

If anyone has a set up for dummy tutorial for this mount that would be great. Tonight's conditions are suppose to be even better and I want to get some images. Thanks everyone.

#2 RTLR 12

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Posted 05 January 2013 - 10:58 AM

First thing you should do is to go back and read the manual. The mount must be polar aligned for AP. You have the "All Star" alignment routine in the hand controller to do this, but it's accuracy is dependent on an accurate initial 2 + 4 star alignment.

You want to point the mount as close to the NCP as possible when first setting up. I use a compass for this when I am not sure where the NCP is. Then you need to do a very careful and accurate 2 star alignment followed by at least 2 or more calibration stars. When this is done you need to do a polar alignment using the All Star procedure. If you follow the prompts in the hand controller this is easy. Just take your time and align your stars in the very center of the eyepiece every time.

Stan

#3 Maverick199

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Posted 05 January 2013 - 11:22 AM

What Stan suggests. I do the two star plus four calibration star. I then use the manual alt/az knobs to do Polar alignment and in my case its much more difficult as my latitude is below the required 20 deg N. In your case, I can only assume it would be easier.

Btw, even though accurately pointed towards Polaris, the first two alignment stars may be outside the FoV of finderscope. Not to worry, just do the alignment and then start the four star calibration. By the time you get to the second calibration star, it should be right in the eyepiece.

After that, do the Polar Align routine by following instructions and you should be good for 30 secs or more with a Focal reducer.

#4 Tel

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Posted 06 January 2013 - 08:11 AM

Hi Jo,

I'm not at all familiar with the CGEM mount but in essence I'm sure it's similar to my Skywatcher HEQ5 set-up, in which case, perhaps consider what it says in your manual with regard to mount settings/calibration (page 27/29) and periodic error correction, (page 30).

These settings are particularly important when contemplating astrophotography using 'scopes placed on GEMs, while any errors within them are likely to go unnoticed when one merely views at the EP, as your description above indicates.

The basics associated with all GEMs though, are essentially the same.

Place one leg of the tripod, (nominated to be the "North Leg"), on a drawn North/South line, (e.g. chalk or paint), with the OTA pointing in the same, North direction. The two other legs of the tripod must sit parallel straddling this North/South line.

If it is possible therefore, start by drawing a single line by either using a compass and straight edge, or along the shadow produced by the midday Sun from an upright pole, on the surface of your viewing area for what ever length you think appropriate, and then another parallel to it at a width conducive of how far apart you require your tripod legs to be.

The whole assembly is then placed on both lines, the "North leg on one line and one of the rear legs on the other. The mount unit is then elevated to your latitude, ( ca.41 degrees) and the fine polar adjustments can begin.

Hoping these comment may help you a little with your initial set-up. If you think I can help you further based on my experience with a Skywatcher HEQ5, then please let me know.

Best regards,
Tel

#5 hopskipson

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Posted 06 January 2013 - 10:08 AM

Wow Tel, I'm so glad I have a direct line of sight to Polaris! My head is aching :love: trying to digest your set up. Even w/o the polar scope if you look through the hole where the polar axis scope should go and center polaris you should be "in the ball park". If you don't have a direct sight to polaris, set the mount to the home position. Use a GPS device or compass to find true north(not magnetic north) and align the centerline of the mount to this position. If you have drawn a line to indicate true north and placed the "north" leg on this line, then the other 2 legs should be equidistant to the true north line. I haven't done this since I can see Polaris, but in my mind :crazyeyes: I think this would work?

James

#6 RTLR 12

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Posted 06 January 2013 - 10:55 AM

I have tried the procedure described by Tel and it is very easy to do and surprisingly accurate.

Stan :waytogo:

#7 Tel

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Posted 06 January 2013 - 12:02 PM

Hi James,

I think I've understood your point correctly but if not, please excuse me ! :idea:

Let me see if I'm right.

Assumingly therefore, if you, (personally), align the "North Leg" of your tripod with Polaris and look through the vacant polar 'scope "hole": in viewing it, (i.e. Polaris), you are claiming to be in a position to proceed with your alignment ?

If so, this is of course true.

However, if you are a little "off" from night to night resulting from a non-premarked position of your mount with the ground or placing it on only a single "North/South" line thus invoking adjustments to the mount particularly in azimuth but outside the mount's individual adjustment capability, I'd assume you have no alternative but to keep re-positioning the tripod legs until Polaris appears visible through the polar axis "hole". (?)

But, (and again assuming this to be the case), if you were to have a set of parallel lines with the distance between them set to that of the leg spread of the tripod which gives you the most comfortable object viewing height, then you should not only be able set up your 'scope/mount asssembly to locate Polaris that much quicker and easier, but additionally : (depending on the length of the parallel lines one draws): be able to set the whole assembly, (where appropriate) along the drawn N/S line in order where necessary, to gain viewing access to objects which otherwise might well be obscured due, say, to tree, fence or wall obstruction.

Does this make any sense ? I hope so ! If not let me know ! :idea:

Best regards,
Tel

#8 hopskipson

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Posted 06 January 2013 - 03:47 PM

Now that made more sense. I think the pole and midday sun threw me off! I also read your post before my morning coffee. After re-reading it now I got it.

James

#9 Arctic_Eddie

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Posted 06 January 2013 - 04:26 PM

You can determine a N/S line by using a shadow cast by a vertical pole at solar noon.

http://www.solar-noon.com/






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