clear sky chart

Job 9:9

Job 9:9-10
9 He is the Maker of the Bear and Orion,
the Pleiades and the constellations of the south.
10 He performs wonders that cannot be fathomed,
miracles that cannot be counted.

Tuesday, March 22, 2011

Experiences With 127mm Refractor

As promised yesterday, I'm going to tell you a little about my experience with the 127mm homebrew refractor.  The first item I went to look at was a semi-bright star.  Not certain which one, I think it was one of the belt stars in Orion.  As I recall, it was a yellowish star.  I noticed right away that if the star was focused in the center of the eyepiece, as it drifted, it got progressively blurrier as it went off center.

Then I went after M42, as its easy to find and I was in the neighborhood anyway.  It was quite bright, compared to the 70mm and 114mm scopes I have.  Of course, M42 is much brighter in the 8 inch Dob, which is to be expected.  A quick peek at Sirius showed a blue star, pinpoint and bright  when focused.  From there, I attempted M51, Canes Venatici, but couldnt locate it.    After spending some time searching, I proceeded to Saturn which was higher in the sky.  There was thin cloud cover, more like a haze, the moon, low on the horizon illuminated the haze, and could be why I was unable to locate M51.

The home made focuser has no side to side slop that I could see.  However, it was not square with the tube, which I corrected today.  This is probably the cause of the focusing issue I was seeing.  I was not able to focus on Saturn as well as I have experienced with the 70mm refractor, but at the time I attributed it to the hazy sky.

Knowing that the telescope needed some more work and some fine tuning, I brought it back in after looking at Saturn.  Today, I re-seated the objective and squared up the focuser as best I could.  I used a laser flashlight and found the laser was off to one side of the objective.  I rotated the laser to make sure it was aiming straight, which it wasnt, but as I rotated it in the eyepiece holder, I saw the dot on the lens, rotate in a circle.  I then adjusted the focuser so that the circle was centered approximately equal from the outer rim of the objective as I rotated it around inside the holder. (the laser flashlight fit fairly well in the 1 1/4 inch focuser with very little slop).  I believe I have the focuser much closer to being true.

Now we need clear skies again to test the scope again.


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