|TMB130SS focuser with MoonLite stepper drive||
The drive position can be changed by loosening the set screw
and rotating the housing.
|Focuser with drive housing vertical.||Focuser with drive housing horizontal|
|Focuser mounted on OTA||
Closeup of stepper drive mounted on OTA
Top OTA is an Orion ED80 with the stepper drive
|Though not part of the stepper drive upgrade I had the rear 4"- 2" adapter plate drilled for 3 screws instead of one. The screws are longer than the stock one to make tightening easier and more secure when a camera is used.|
Positioning accuracy must be repeatable for reliable automated focus operations. Three passes of V-Curve measurements using FocusMax and with full equipment weight were performed to test the accuracy of the MoonLite stepper drive and also measure the profile characteristics of the stock TMB focuser draw tube. The images below show a very repeatable and consistent profile.
Physical step measurements were conducted using a Mitutoyo caliper with .001" gradients. The stepper drive ASCOM interface was set to use full steps (vs. half steps). A total of 10 passes were made to verify consistency. A group of 20 steps measured .005" or 127 microns. This breaks down to 1 step equaling .00025" or 6.35 microns. To determine the critical focus zone (CFZ) the numbers applied to the formula CFZ= focal ratio (squared) X 2.2 the TMB 130's F/7 CFZ = 107.8 microns. This equals 16.9 steps of the Moonlite focuser. The Focus Max V-Curve measurements display the Position Intercept difference of 17.X counts so the math and physical measurements fall within the CFZ area.
|FocusMax V-Curve run #1||FocusMax V-Curve run #2||FocusMax V-Curve run #3|