Tuesday, March 15, 2011

Celestron Astromaster 130 | Star Pointer, illuminated Red Dot Finder


Finding objects in the night sky is a challenge with every amateur astronomer. With Celestron Astromaster 130 it becomes even more difficult. The red dot finder is perhaps the most criticized part of a Celestron astromaster 130. I have read approximately 20 to 30 posts and blogs where this item is regarded as completely useless and replacements have been suggested. However, I disagree its that bad. It does the job for me. I am able to point at Moon, Jupiter, Polaris, Betelgeuse, M42 etc at one go. It takes a little getting used and practice. It becomes slightly difficult to find fainter stars with this but some star hopping eventually leads to the desired object. Here are some useful tips to use the red dot finder at its best.

CHECK FOR EXACT ALIGNMENT OF RED DOTS:
As mentioned in my earlier posts I have had lot of difficulty when I had received the telescope and wanted to point at some object in the sky using the red dot finder. Later I discovered the red dot finder was improperly aligned. So instead of helping me out finding a star it was misguiding me. Here’s how you can check if your red dot finder is well aligned.

Note: This activity can only be performed in well lighted area. So I suggest you do it before deploying your telescope for observation.

In your red dot finder or star pointer you will see two circles each of same diameter. You will also notice that there are two thumb screws on the top. Go to the front side of scope, in front of the aperture opening and observe the star finder. You will see the nearer circle enclosing the farther circle within it. Now the thing to observe here is whether these to circles are equally separated all through their circumference or not, as explained in the following diagram:

Alignment Star Pointer - Red dot Finder scope


Another condition to check is whether the front red dot completely covers the rear dot when these circles are equally separated or not. If these above conditions are not true on observance, you will have to adjust the two screws on top to achieve perfect alignment of the circles and the dots. This process requires patience as you might get lucky to get the right alignment at few twists or you might not get it for long, as motion of the transparent panel is quite weird when screws are turned. After this is done your Star Finder/Red dot finder is ready for use.

POSITIONING YOUR EYE:
Initially when I had begun I used to try a lot of positions to see through the finder. I tried going far, near, from the finder, behind the OTA etc. Finally I settled for a position which works best for me. Its about 10- 15 cms behind the finder over the OTA. Now the trick lies here, once you have positioned your eye like this and the two dots are overlapping perfectly, close one eye and do not move. Move your scope as you move along with it as if one. Now see the star through the finder, overlap it over the red dot and you will see it in the ocular too. However if you had moved your eye considerably if u moved the scope you need to realign for perfect alignment of the three, the two dots and the star. See how alignment impacts the view:

Celestron  star pointer mechanism


The above method works well for bright objects, however for faint objects there is another small trick involved, you will notice while pointing to a faint object you are not able to view the object itself through the star finder. Now this gets really irritating. You can eliminate this problem by doing the following.

LOCATING FAINTER OBJECTS:
Fainter objects cannot be seen when viewing through the starpointer. This is a solvable problem. All you need to do is bring the red dots of pointer near to the star and now open one eye to view the star alone. Now make an estimate about the star’s position and move the OTA accordingly after closing one eye and keeping watch that the two dots are aligned along with your eye as you move the Optical Tube Assembly (OTA). Now open the other eye again and repeat the process. See whether you have reached nearer to the star or not. This technique needs some practice especially because the star’s position appears to change in the sky when viewed with both eyes and when viewed with only one. But if you practice for sometime you will know what I am talking about and make this method work for you.

That’s all is required for viewing through the starpointer. If it doesn’t work for you still, you may substitute it with a telrad or something. Happy viewing and clear skies.

5 comments:

  1. Thank you for that!

    I have an AstroMaster 130 EQ and aligning the thing has been grief.

    Using your method I have been able to get to brighter objects quite quickly, but I still cannot get anything in the ocular (even the 20mm) straight away.

    Part of the problem is my eyesight. I have poor acuity in one eye, and am quite short sighted. If I wear my glasses so that I can see the target (star, planet), I cannot focus on the two red dots to see if they are aligned. If I don't wear them, I can see the dots, but not the star.

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  2. I tried this method and it did not work for me.

    The problem I see is that unless you are absolutely dead center in front of the red dot finder then your alignment of it will be off because if you are even slightly off center and set the circles even then is alignment is set wrong and and this is multiplied quite badly when you try and sight an object with it.

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  3. Thats Brilliant and well explained ..thanx

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  4. how much would the extra barlow, eyepiece set cost

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  5. has anyone tried spotting Uranus and Neptune, is that possible?

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