Focus Convergence -Focusmax
CFZ for a scope can be worked out with this fomula:
CFZ(in Microns) = 2.2 x (Scope_Focal_Ratio²)
My Telescope is a Takahahsi 106ed (530/106)2 having a focal ratio of 5 gives me a CFZ of 55 microns.
Or 1250/250 = 5F x 2.2 = CFZ 55
That sounds tiny in everyday speak, good thing that I have an awesome high resolution stepper motor focuser.
According to FLI focuser manual, the total focusing range is a relatively small (but more than adequate) 0.35 inches , the Atlas manages to make an incredible 105,000 precise steps over that range – resulting in each step being only 3.33 millionths of an inch, or 0.085 microns.
.
| Focus Convergine Calculation | ||||||
| FLI - Distance Steps | 105000 | |||||
| CFZ mircon | 55 | 0.055 mm | ||||
| mm travel | 8.89 | 8890 mircon | ||||
| mircons | 0.085 | |||||
| sec trave drawtube | 105 | |||||
| Steps per sec | 1000 | 105 x 1000 steps | 105000 | |||
| Method: = CFZ / (Steps / length of travel distance in Mircon) | ||||||
| 105000 /8890mircon | 11.81102 | (1 miron=11.81 steps) | ||||
| 55/11.81 steps | 4.66 | |||||
This leave my CFZ to a 4.66 (5) steps to focus, so the step width in the Focus Convergence setting, Now we need to change the setting in Focusmax focus convergence, start with approximately 1/4th of the CFZ step value:
4.66 x 1/4 = 1.16
1 step and 5 samples
Check the focus accuracy if not prefect increase the steps to 1/2th
4.66 x 1/2 = 2.23
2 steps and 5 sample