Tutorials and Questions
How the gear finder matches - A guide to our logic system
An opening note that sets the tone for the article. Edit this default copy here, or remove the block for posts that should jump straight into the body.
AstroEquip is a free, vendor-neutral gear finder for astrophotographers. When you describe what you have and what you want to photograph, an engine ranks the catalogue and tells you what fits, what to upgrade, and what to skip. This page documents exactly how that ranking works, so you can decide how much trust to place in it.
In this guide
1. What the engine actually is
The engine is a small piece of server code that runs every time you click Find my matches. It does three things in sequence:
- Filters the catalogue to products that can physically pair with the gear you described.
- Ranks the survivors by how well they support your stated imaging goals.
- Annotates them with warnings for non-blocking concerns (payload margins, sampling, autoguiding fit).
No machine learning. No popularity weights. No clickthrough loop. Just a set of rules derived from optics, mechanics, and sky-condition physics, plus a small library of heuristics that experienced astrophotographers would apply.
2. The inputs you give it
Every wizard step funnels into one structured object. These are the fields the engine actually reads:
| Step | Inputs | How the engine uses them |
|---|---|---|
| Goals | Deep sky, planetary, wide-field, lunar, solar (multi-select) | Drives the Phase 2 boost weights for each product category. |
| Telescope | Focal length, aperture, f/ratio, optical design, focuser thread size | Determines compatible cameras, reducers, flatteners, guide scopes. |
| Camera | Type (mono / colour / DSLR), sensor size, pixel size where known | Calculates sampling (arcsec/pixel) and gates filter recommendations. |
| Mount | Type (EQ GoTo / EQ manual / Alt-Az / tracker), payload capacity | Blocks autoguiding on alt-az mounts; warns when telescope weight nears 50% payload. |
| Sky & filters | Bortle scale (1 to 9), filters already owned, optional latitude | Prioritises light-pollution and narrowband filters where they actually help. Latitude (if provided) is used to flag targets that never rise from your site. |
| Budget | Per-category caps in your store's currency | Re-ranks (does not block) over-budget items, applying a clear badge. A product 10% over budget loses ~6 points; 50% over loses ~30; 100%+ over loses up to 40 (the cap). |
| Autoguiding | "Have / Want / Not needed", guide scope focal length, camera pixel size | Suggests guide cameras of an appropriate pixel scale for your imaging focal length. |
| Experience level | "Beginner / Experienced" (optional) | Beginners pay small penalties for demanding rigs (very fast f/<4 optics, RC astrographs, long-FL SCTs for deep-sky, mono as a first camera). Does not block anything — just nudges the ranking. |
Everything else (your IP, your device, your Shopify customer ID for signed-in users) is processed only for security, sync and idempotency, never for ranking. The full data flow is in our privacy policy.
3. The three scoring phases
Phase 1 – Physical compatibility
A product is excluded outright if it cannot pair with your gear. Examples:
- A camera that requires a 3-inch focuser, when your telescope has a 2-inch focuser.
- An off-axis guider that needs a separate adapter that does not exist for your scope's thread.
- A reducer with a back-focus distance incompatible with your imaging chain.
- An ultra-narrowband filter (e.g. 3 nm Hα) against a one-shot-colour or DSLR camera — the Bayer matrix throws away ~75% of the signal, making the combination not usable in practice.
- An off-axis guider or guide scope paired with an Alt-Az mount — autoguiding cannot correct for field rotation.
- A mount whose payload capacity is below the estimated weight of your imaging rig (scope + camera + guide gear).
These are returned with score = 0 and listed in the "Blocked" panel so you can see why they did not make the cut. The block reason is always shown.
Phase 2 – Goal-driven scoring
Each surviving product is scored against your goals. A telescope that is excellent for wide-field Milky Way work gets a positive boost when "Wide-field" is one of your selected goals, and a smaller boost when it is not. A camera that is fast and clean for narrowband gets a boost when "Deep sky" is selected and your Bortle is high (because that is where narrowband actually pays off).
Phase 3 – Warnings
Warnings do not change rank. They flag concerns the user should be aware of before buying.
| Warning | What it means |
|---|---|
| Payload near limit | Adding this scope brings your mount past the safe loading threshold. For imaging goals the threshold is 55% of payload (caution) / 75% (over limit); for visual-only goals it is 70% / 90%. |
| Sampling: over-sampled | Pairing this camera with your scope yields a tighter image scale than typical seeing allows. You may want a focal reducer or 2×2 binning. |
| Sampling: under-sampled | Pixel scale is coarser than ideal. Fine for large nebulae, less good for galaxies and globulars. |
| Bortle mismatch | Recommended filter or technique does not gain you much at your sky brightness. Triggers at Bortle ≥ 6 for deep-sky goals (where light-pollution filters become essential). |
| No autoguiding possible | Alt-Az mounts cannot guide due to field rotation. The product is fine, the workflow is the limit. |
| 1.25″ focuser too narrow | Your focuser will vignette the corners of an APS-C or full-frame sensor (or a DSLR). A 2″ focuser or visual back is the imaging standard. |
| Filter wheel size needed | An APS-C sensor wants 36 mm round (or 1.25″ with mild vignetting); full-frame wants 50 mm round. Smaller filters clip the corners. |
| Back-focus matters | Most refractors and reducers need a precise back-focus distance (commonly 55 mm). The chain of camera + filter wheel + spacers must sum to that within ~2 mm or stars elongate at the edges. |
| T-ring needed | A DSLR cannot attach to a telescope without a brand-specific T-ring (Canon EF, Nikon F, etc.) plus an M48 or T2 nosepiece. |
| Dovetail compatibility | Heavy SCTs and Newtonians (≥ 150 mm aperture) usually need the wider Losmandy (D-style) dovetail rather than the narrow Vixen (V-style) bar. |
| Field rotation (Alt-Az) | Alt-Az mounts impose a sub-exposure limit even with perfect tracking, set by how fast the field rotates at your target's altitude. |
4. What boosts a product's rank
This is the part that decides ordering inside a category. The boosts the engine applies, in rough order of weight:
- Goal alignment. A camera or scope suited to your selected goals climbs the list.
- Compatibility tightness. A product that fits your gear with no adapters or compromises ranks above one that needs a stack of adapters.
- Shopping intent. If you left the telescope field blank, the engine assumes you are shopping for one and boosts telescopes.
- Sky-condition fit. Narrowband filters get a big boost above Bortle 5 where they actually move the needle. The same filters get a smaller boost at Bortle 2 because broadband work is already viable.
- Autoguiding fit. If you indicated you want a guide setup, guide scopes and cameras are surfaced. Their pixel scale is matched to your imaging focal length so you don't end up with mis-scaled guiding.
- Experience-level adjustment. If you flagged yourself as a beginner, the engine applies small soft penalties (−4 to −8 points) to gear that's known to be demanding for first-time imagers: very fast f/<4 optics that require sub-millimetre back-focus precision, RC astrographs that need precise per-session collimation, long-focal-length SCTs for deep-sky, mono cameras as a first camera. Nothing gets blocked — just nudged down.
Things that do not boost rank: brand popularity, our catalogue size for a brand, price, our ability to source the product, any commercial relationship.
5. Warnings vs. blocks
A block means we believe the product cannot work with the gear you described, full stop. Blocked items appear in a separate "Why these don't fit" panel with the specific reason. We show them so you can see what the engine considered and rejected, not just what it returned.
A warning means the product can work but there's a caveat you should know. The product still appears in your match list with the warning badge attached. The warning never lowers the score by enough to bury the product; it informs the click.
6. Bundles
Bundles are pre-curated combinations of gear that work well together, hand-assembled by us. They are a separate ranked list shown alongside individual products. A bundle is recommended when:
- You are shopping for two or more of telescope, camera and mount.
- Your stated goals match the bundle's intended use.
- Your budget cap (if set) does not put the bundle far out of reach.
Bundles are useful when "tell me one good starter setup" is what you actually want. They are not advertised in any priority over individual products. If you have specific gear already, individual products will outrank bundles for you.
7. The simulator and where the sky data comes from
The Telescope Simulator is a separate tool, reachable via the Preview my setup button. It uses your gear specs to draw a framing rectangle over real sky-survey imagery so you can see what a given target looks like through your setup.
Data and software credits.
- Aladin Lite, developed at the Centre de Données astronomiques de Strasbourg (CDS), Strasbourg Observatory, France. Cite as: Bonnarel et al. 2000, A&AS 143, 33; Boch & Fernique 2014, ASPC 485, 277.
- Simbad object database, also operated by CDS. Cite as: Wenger et al. 2000, A&AS 143, 9.
- HiPS (Hierarchical Progressive Survey) sky tiling standard, Fernique et al. 2015, A&A 578, A114.
- DSS imagery (Digitized Sky Survey) used for the default broadband view, produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The plates were obtained at the Palomar Observatory and the UK Schmidt Telescope.
Queries to Aladin and Simbad are anonymous; no personal data is sent to CDS. None of this software or imagery is owned by AstroEquip. We display it under their public-use terms with full attribution.
8. Editorial independence and future affiliate links
AstroEquip is free, ad-free, and vendor-neutral. To make the rules explicit:
- The scoring rules above are the only inputs to ranking. They are not influenced by any commercial relationship, donation, sponsorship, or click incentive.
- We do not accept payments from manufacturers in exchange for inclusion, ranking, or favourable copy.
- We do not currently use affiliate links. We may add them in the future. If we do, every affiliate link will be visibly tagged as such on the storefront, and the presence or absence of an affiliate relationship will never change a product's rank.
- The catalogue itself is sourced from each manufacturer's own public product pages. Where a spec is uncertain we mark the source as such and welcome corrections.
- Voluntary Ko-fi donations support continued development. They confer no special status, rights, or product favouritism.
If a recommendation feels off, write to us. The engine is rules-based, so any bias is a bug we can fix in code, not a "model" we hand-wave at.
9. What the engine deliberately does not do
- It does not score your skill, experience, or knowledge level. It scores compatibility, full stop.
- It does not push you toward expensive gear. Over-budget items still show, ranked lower, with a clear badge. You can also hide them.
- It does not personalise based on which products you previously viewed. We do not track that.
- It does not run A/B tests on individual users. The ranking rules are the same for everyone.
- It does not call out to any external "recommendation API". All scoring runs on our own server with the catalogue we maintain.
10. Spotting an error
Most of what the engine returns is mechanical. If something looks wrong:
Check the inputs first
A wrong focal length or sensor size cascades through every downstream rule. Click "Edit setup" and verify.
Open the "Blocked" panel
If the product you expected isn't appearing, it is probably in the blocked list with a stated reason. The reason tells you whether it's an input error or a real incompatibility.
Read the warning text on the card
Warnings explain themselves. "Payload at 78%" is a real concern; "Sampling: 0.9 arcsec/pixel" is a number you can decide about.
If the ranking still looks wrong, write to us
Either we have a bug, or our catalogue entry for that product has a stale spec. Both are fixable. Email alvesastrofotografi@gmail.com with the setup you entered and the product you expected to see ranked differently.
Ready to try it?
Tell the Gear Finder what you have, what you photograph, and how dark your sky is. It will rank the catalogue against those inputs and explain every recommendation.
Open the Gear Finder →