My journey with this telescope began about 3 years ago. I purchased this telescope from Woodland Hills Camera and Telescope.
I thought I knew everything I needed to know about collimation and alignment of a Mak-Newt.
I immediately purchased a Moonlite focuser, the 2” (CR) version. I lined it up with the factory center spot on the secondary mirror and I thought it would be great.
After replacing the focuser the scope exhibited oblong stars. At one point, I thought the scope had astigmatism due to a bad mirror figure or such.
I removed the rear cell and removed the small cork squares in the mirror support structure and put in my own cork to support the primary mirror. I removed the old center spot in the primary mirror, and put in my own (catseye center spot).
Put everything back together and still had the same issues.
I checked everything I could but still always had issues with improper illumination and star shape issues.
The scope sat in the corner gathering dust while I used my 140mm Refractor.
A read many posts here on Cloudy nights and found some great info on offset secondary mirror installation.
Spent some time taking the whole scope apart and found the factory center spot on the secondary mirror was not in the proper place at all!
I removed the factory spot with alcohol and began by looking at the support shaft of the mirror.
I looked at the secondary mirror arrangement and found the easiest way to mark the center spot was to look down the support shaft of the secondary mirror and put the center spot right in the middle of that.
I marked the side centers of the mirror with a white board pen and then eyeballed the center mark with a permanent ink sharpie. (You can remove the mark with alcohol if needed)
The next major thing I did was change from the moonlite 2” CR to the Moonlite 2.5” CRL focuser. I wanted the bigger focuser because I had an APS-C and Full Frame cameras. I used a laser collimator to align the new focuser. The new focuser could rotate a complete 360 degrees.
This really helped me align my focuser by allowing me to rotate the focuser and observe the laser spot on the primary mirror. I adjusted the bearings so the laser would not move at all while rotating the focuser. This ensured my focuser had no angle at all.
I placed a cheshire in the focuser and began working on moving the secondary mirror in and out of the tube to align the mark I made on the secondary mirror. It was off quite a bit. I made sure the secondary mirror mark was in the center of the cheshire cross hairs. Then I put the laser back in the focuser and aligned the secondary mirror, then aligned the primary mirror.
Checked it again with the CatsEye Autocollimator and alignment looked great.
I took some shots last night and had fantastic images.
Conclusion: The SkyWatcher 190MN is a fantastic telescope, HOWEVER; the stock focuser is not good for astrophotography so you will need to be prepared for a lot of work to get alignment right after replacing the focuser.
I recommend using the larger focuser (Moonlite 2.5 CRL) because it does allow you to completely eliminate and angle errors from the focuser to the secondary mirror.
Do not rely on the center spot mark on the secondary mirror unless you verify it is marked properly. My center spot was in the center of the mirror, not on the mirror support shaft.