Hi Martha, Point #2 as calculated is technically correct... however, I don't believe it (from a sanity check perspective).

From my calcs, your CFZ is 71.1 um @ 10% focus tolerance, and 87.1 um @ 15% tolerance. This seems right to me for f/7. If you're getting 2 arcsec seeing, I'd constrain to 10% tolerance or better...you don't want to waste good seeing with poor focus!

Now, about that travel measurement.... I'm having a hard time believing the measurement (unless I didn't understand what you said). I would have expected you to have at least 3-4 hundred motor counts for a CFZ that size, but you've measured 94400 um / 25992 motor counts or 3.632 um/motor count (only 0.27 motor counts/um). Are you sure you did that measurement right? You might want to measure again (or tell me what I didn't understand). In the end, I'd expect to find for f/7 something on the order of 300-400 motor counts per CFZ, and a corresponding step size of 250 or so (educated guess). How about a 2nd measurement of your focuser travel and EAF motor counts. Make sure you push one direction with the EAF for at least 100 counts (to negate backlash), and then start your test in the same direction, noting your starting EAF motor count, travel distance, and final motor count. I'd be curious to hear the result. Cheers, Doug

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