The ideal focal length range for a target — long enough to resolve detail (min FL), but short enough to fit the object on your sensor (max FL). Shown as a gradient bar in the results.

How many arcseconds each pixel covers. Smaller values mean higher magnification. Calculated as 206.265 × pixel_size / focal_length.

When an object is too large for a single frame, you need multiple overlapping panels (a mosaic) to capture the entire target. The app calculates how many panels are needed (with 20% overlap).

In Telescope Finder mode, target cards appear faded when the object is too small to meet your resolution requirement with even the longest focal length telescope in the database. Faded objects are still selectable.

The telescope's focal length falls within the Goldilocks Zone — the object fills enough pixels and fits on the sensor.

The telescope's focal length is too short — the object won't fill enough pixels to meet your resolution requirement.

The telescope's focal length is too long — the object won't fit on the sensor in a single frame (mosaic needed).

When you select multiple targets, the ranking shows a soft Fit Score for every telescope — not just binary pass/fail. Each telescope gets a per-target score from 0.0 to 1.0 based on:

• Resolution credit: How much of the desired pixel resolution the scope achieves. A focal length that's slightly short still gets partial credit.
• Mosaic penalty: No penalty up to 4 panels. Above 4, the score decreases softly (4÷panels).

Per-target scores are summed, then multiplied by two small tiebreak factors:

• Sharpness bonus: Telescopes with higher star ratings (★) get a slight edge.
• Aperture bonus: Larger apertures get a tiny logarithmic advantage.

The bar is normalized to the top-scoring telescope. The #1 telescope always shows a full bar; others show their score relative to the best.

Each ranked telescope still shows which targets are perfect fits (in the Goldilocks zone) and which are outside range. This binary status is separate from the continuous Fit Score.

Each telescope shows a colored badge with its optical design type (e.g., Triplet APO, Ritchey-Chrétien, Standard SCT). Hover over any type badge for a tooltip explaining:

• Pros and cons of the design
• How well it suits astrophotography
• Ease of setup and use

Each type badge includes a 1–5 star rating for astrophotography ease of use:

• ★★★★★ — Grab-and-go: minimal setup (camera lenses, Petzval APOs, smart scopes)
• ★★★★☆ — Easy: no collimation, may need a flattener (APO refractors)
• ★★★☆☆ — Moderate: some accessories or cooldown (SCTs, Maksutovs, RASA)
• ★★☆☆☆ — Advanced: regular collimation, correctors required (Newtonians, RCs)
• ★☆☆☆☆ — Expert: not designed for AP, needs heavy modification (Dobsonians)

A focal reducer is an optical accessory that shortens a telescope's effective focal length, widening the field of view and making the optics "faster" (lower f-ratio = shorter exposures). Many telescope manufacturers sell reducers designed specifically for their own scopes.

The app includes 116 telescopes with manufacturer-specific reducer data. When a reducer improves a telescope's fit score, you'll see a purple-tinted row showing the improved score, reduced focal length, and new f-ratio.

In the Telescope Ranking, a purple row like → with 0.76x Reducer: Fit: 100% appears when using that reducer would give the telescope a higher Fit Score. Only the best reducer is shown.

In individual target results, a reducer hint appears when a reducer would change a telescope's match status — for example, turning an ❌ "Object Cropped" into ✅ "Perfect Fit" by shortening the focal length enough to fit the target on the sensor.

Only manufacturer-specific reducers are included — no third-party alternatives. This ensures the data reflects tested, recommended combinations. Telescopes without a dedicated reducer (Newtonians, camera lenses, Petzval astrographs, etc.) show no reducer hints.