I have a question about the in focus star image created by my ETX 125. The scope was new this holiday season and has the new UHTC coatings. I understand from reading posts on Weasner's ETX web site that it is not possible to judge the alignment of some Mak optics based on the out of focus star images. I have been concentrating on studying the star images of my scope when they are in focus. I have been looking at stars at or near the zenith on calm nights with stable optics. In each case, I attempt to put the source in the center of view.
In addition, I have been using a few Christmas tree ornaments mounted across the street on a power pole to try to create an artificial star. The results look consistent to me in all the eyepieces and with the different light sources. I have also tried flipping the mirror a few times and rotating the eyepieces to see if there were some other variable(s) affecting the image.
I have been using my:
15 mm TV Plossl 126x
8mm TV Plossl 237x
5mm Takahashi LE ED 380x
What I see is a round tight star image with a bright first diffraction ring. Next, several faint diffraction rings are visible. If the light source is a star, I will see one or two rings. If the source is an artificial star, lit by the bright sun, I see more rings.
Here is where things get interesting… The diffraction rings in focus do not make a complete circle around the star point in the middle. The rings cover about 45% of the area around the point and they are visible across the top half of the star. The bottom 55% of the image has little or no diffraction rings. If rings show up on the bottom half of the image, they are very, very dim.
I see a consistent pattern of incomplete (weak) or non-existent diffraction rings in a sweep clockwise from three o’clock to ten o’clock around the focused star image.
For a practical example, I have been able to split the left pair of stars in the Double-Double, but I struggle to split the right pair very cleanly using my 8 mm TV EP.
Is my in focus image correct for an ETX 125? What do you think?
Many thanks in advance for any analysis you can provide.
Sincerely, Paul G.
In addition, I have been using a few Christmas tree ornaments mounted across the street on a power pole to try to create an artificial star. The results look consistent to me in all the eyepieces and with the different light sources. I have also tried flipping the mirror a few times and rotating the eyepieces to see if there were some other variable(s) affecting the image.
I have been using my:
15 mm TV Plossl 126x
8mm TV Plossl 237x
5mm Takahashi LE ED 380x
What I see is a round tight star image with a bright first diffraction ring. Next, several faint diffraction rings are visible. If the light source is a star, I will see one or two rings. If the source is an artificial star, lit by the bright sun, I see more rings.
Here is where things get interesting… The diffraction rings in focus do not make a complete circle around the star point in the middle. The rings cover about 45% of the area around the point and they are visible across the top half of the star. The bottom 55% of the image has little or no diffraction rings. If rings show up on the bottom half of the image, they are very, very dim.
I see a consistent pattern of incomplete (weak) or non-existent diffraction rings in a sweep clockwise from three o’clock to ten o’clock around the focused star image.
For a practical example, I have been able to split the left pair of stars in the Double-Double, but I struggle to split the right pair very cleanly using my 8 mm TV EP.
Is my in focus image correct for an ETX 125? What do you think?
Many thanks in advance for any analysis you can provide.
Sincerely, Paul G.
