....to expand on what Kirch explained.... Hz is "refresh" cycle per SECOND....what you're seeing is the image through the optic to eyepiece being processed at 30, 50 or 60 times a second. At 30Hz there will always be VERY slight fluidity of motion impairment through the process to the eyepiece.
At 50Hz or 60Hz there should be NO real issue from scope image processing to the human eye.
...but when you throw in the on or off board video/audio recording process that many optics have.. you can have a perceived lag issue-but through the recording process.
I have a Trij MKIII 35 set at 60Hz....a Pulsar Trail XP50...and a Pulsar Axion2 XG35...and have no motion lag issues that have ever caught my attention.
