Tonight is clear and not breezy, so I decided to try out my Surplus Shed Wollensak 127mm based refractor for the first time. I have been working on this for past 3 weeks and finally got it completed last week.
I aimed for the moon. Right away I noticed the first problem - I could not achieve focus until I had the focuser racked all the way in (I designed it to be at focus at the mid-range of the draw-tube). Even then the focus was not good. The moon was mushy and showed a distinct second outline. I removed the diagonal to give me more room to focus. When I finally attained focus, the image was quite poor. Although I could see small craters, it was not a sharp image and was very sensitive. If I defocussed by a just a 1/4 turn it was enough to go out of focus. I measured the focal length, and it came out to be 1140 mm, not the specified 1200 mm.
I know that my collimation is not perfect but this is my 5th telescope and I have gotten better at it. With all my previous telescopes of similar focal lengths I found the images of the moon very sharp and clearly defined outer edge.
Next, I looked at Arcturus. At my best focus, it looked like a bright small disc in the middle surrounded by a perfectly symmetrical and big halo. The halo covered 1/2 the FOV of my 26 mm ep. I have never seen a star image like this. I tried a few fainter stars and they also showed a halo but the halo was not very bright.
This was quite unexpected because I was expecting nice sharp stars as in my previous builds. So I am confused. Only explanation I could think of was that the Objective could have been incorrectly assembled like crown and flint elements flipped or even backwards. Another clue is that the measured focal length is 1140 mm instead of 1200 mm.
Thanks for reading and for any suggestions!