Many here on CN have noted that the focal length of their 127Mak is greater than what is advertised. I recall reading a particular post where the user noted that his 127Mak's focal length was in the 1700mm range as opposed to the listed 1540mm.
I therefore decided to do a very informal analysis of my own 127Mak using the Telescope view in Stellarium. I have a 2012 Skywatcher with a 2" diagonal. I used polaris (because it doesn't move) and centered the star as best as I could in the EP. I then compared the view with the Telescope view option in Stellarium using the same EP as in my scope. I then changed the focal length of the scope in Stellarium until I got a very close match at the EP. I used a 20mm 70 degree EP as well as a 15mm 66 degree EP. What I found is that a 1750mm focal length in Stellarium most closely resembled the view at the EP. I expected a longer focal length because my scope used a 2" diagonal, but I was surprised at the 14% increase in focal length. This may also explain why some claim that the sky is darker with better contrast when using their Mak. The extra magnification is darkening the sky.
Anyway, I found this little analysis of mine interesting. I'm curious if anyone has done a more rigorous analysis using star drifting.