Scope Calculators
Is the rig matched to the sky? Sampling & drizzle, critical focus zone, dither scale, guiding-RMS bloat, alt-az field rotation, and polar-alignment drift — all from your rig's real image scale and f-ratio.
Scale vs seeing
undersampled — too coarse — drizzle×3 recovers detail (needs many dithered subs).
Focus tolerance
At f/3.9, the focuser resolves the CFZ (8.1 steps). Refocus about every 6.8°C of temperature change.
RMS → star bloat
Guide scale 6.45″/px → RMS 3.22″ (1.2 main px). Loose vs the 2.77″/px scale — stars bloat 2.0″ → 7.85″.
Main ↔ guide
15 main px = 41.5″ = 6.4 guide px. Enough to walk hot pixels / fixed-pattern off frame to frame.
Equatorial mount
ZWO AM5 is equatorial — tracking cancels field rotation, so subs aren't length-limited by it (polar-alignment drift applies instead, right). Tap alt-az to model an alt-az setup anyway.
Alignment → unguided
3′ polar error drifts 0.79″/min (worst-case) → 211s unguided before a 1-px trail. For 120s unguided you need ≤ 5.28′ alignment.
Focus shift per filter
Offsets relative to L, in focuser steps at 5µm/step. The 25µm spread exceeds half the 41µm CFZ — a full refocus (or autofocus) is needed across the big jumps. Seeded by family; refine from autofocus history.