Buying Guide
How to Use the AstroEquip Telescope Simulator — Complete Guide
The AstroEquip Telescope Simulator is a live sky map that previews exactly how a target will frame in your camera — for your specific telescope, sensor, and mount — and a built-in sub-exposure calculator that tells you how long to expose and how many subs to stack. This guide is the complete desktop reference: every panel, the calculator, five concrete pre-session workflows, and five gear-upgrade comparison workflows. On a phone? See the mobile guide instead — the UI is laid out very differently.
In this guide
- The sky viewport
- Searching for a target
- Setting up your equipment — autofill or manual
- Rotation modes (FOV / POV / FOV+POV)
- Filter preview modes
- Live readouts & the HUD
- The Stats tab — sampling, trailing, light budget
- The Sub-Exposure Calculator
- Saving setups & sharing
- Pre-session workflow examples (5 scenarios)
- Gear-upgrade workflow examples (5 scenarios)
- Tips, gotchas, & keyboard shortcuts
1. The Sky Viewport
The dark area in the middle of the simulator is a live, deep-zoom view of the real sky, rendered by Aladin Lite from the DSS2 colour sky survey. The teal rectangle overlaid on the sky is your framing rectangle — exactly what your sensor will capture given the focal length and sensor format you've chosen.
- Drag anywhere on the sky to pan. The framing rectangle stays centred as you move.
- Scroll (or pinch) to zoom. The sky survey re-renders seamlessly down to deep-zoom resolution.
- Click a recognised object for a name pop-up.
The rectangle is always at the centre of the viewport. That means the sky moves under it, not the other way around — matching how a real telescope works.
2. Searching for a Target
Type any object name into the search box at the top-left of the toolbar. The simulator resolves it against Simbad and re-centres on it.
| What you type | What it does |
|---|---|
M31, M 31, Andromeda
|
Resolves Messier 31 |
NGC 7000, North America Nebula
|
NGC and IC by number or common name |
Sh2-155, IC 1396, B33
|
Sharpless, IC, Barnard catalogues |
05 34 31 +22 00 52 |
RA/Dec coordinates (also has a dedicated entry in the Stats tab) |
Below the search field, the M / NGC / IC / B catalog pills filter the autocomplete dropdown to objects from that catalog only. Useful when you're browsing rather than hunting.
3. Setting Up Your Equipment — Autofill or Manual
The right-hand Setup sidebar is where you describe your imaging train. There are two ways to do this: type your gear's model name and let the simulator autofill the specs, or set focal length / sensor / mount by hand from the toolbar.
Autofill (fastest)
The Setup sidebar has three cards: Telescope, Imaging Camera, and Mount. Each starts with a text input. Type the model name you actually own — e.g. "Esprit 100", "ASI2600", "AM5", "RedCat 51" — and the autocomplete dropdown shows matching products from the AstroEquip catalogue. Pick one and the simulator fills in:
- Telescope: focal length, aperture, focal ratio, design (refractor, RASA, SCT, Newt), weight.
- Camera: sensor format, pixel size, sensor dimensions, camera type (OSC / mono / DSLR).
- Mount: mount type (EQ GoTo / tracker / Alt-Az), payload, weight.
The framing rectangle, the Stats tab readouts, and the Calculator all update instantly. Click SWAP to change the selected product, or × to clear the slot and return to the autofill input.
Manual entry (for fine control or uncatalogued gear)
The middle section of the top toolbar has explicit inputs you can use without going through the autofill:
- FL — focal length in millimetres. Printed on every telescope and most lens barrels.
- Proj — projection mode. Default for most refractors and Newtonians. Switch only for fisheye lenses or hyperbolic correctors like RASA / Hyperstar.
- Sensor — sensor format. Each option encodes width × height in mm. APS-C is the default since most beginner astro cameras (ASI533, ASI2600, modified DSLRs) use that format.
- Pixel — pixel pitch in micrometres. Drives the image-sampling readout in Stats.
- Mount — Alt-Az / Star Tracker / EQ GoTo. Drives the max-sub-exposure estimate.
- Bortle — local sky brightness, 2 (rural-dark) to 8 (heavy LP). Drives the light-budget estimate. Look up your value at lightpollutionmap.info.
Autofill and manual entry are not mutually exclusive — you can autofill a telescope and then override the focal length manually (e.g. to simulate a focal reducer on the same scope) without breaking anything else.
4. Rotation Modes — FOV / POV / FOV+POV
The rotation control on the right of the toolbar has three modes. The distinction matters because they answer different planning questions.
| Mode | What rotates | Use it when… |
|---|---|---|
| FOV | Just the framing rectangle, on top of a fixed sky | You want to see how the target fits with the camera rotated. The sky stays the same; the rectangle pivots. |
| POV | Just the sky, framing rectangle stays axis-aligned on screen | You want to preview what you'd actually see on your monitor — rectangle fixed, sky underneath rotates to match the camera's orientation on the mount. |
| FOV+POV | Both, together, as one unit | You want to slew across the sky in your imaging position — relationship between frame and sky stays fixed as both rotate together. |
The reset button (curved arrow) next to the rotation input returns to 0° = celestial north up, the convention every published reference image uses.
5. Filter Preview Modes
The Filter dropdown changes how the sky is rendered. These are approximations based on the bandwidths of common filters and are useful for planning ("would dual-narrowband help me here?") but they aren't photometrically accurate.
| Mode | Simulates | Best for |
|---|---|---|
| Visual (no filter) | Natural DSS2 colour | Default. Most flexible for framing decisions. |
| L-eNhance / dual-band | Hα + OIII (~8nm each) | OSC cameras under Bortle 5+ on emission nebulae. |
| Hα only | Hα narrowband (~6nm) | Mono cameras building SHO / HOO palettes. |
| OIII only | OIII narrowband (~6nm) | Planetary nebulae, supernova remnants. |
| SHO (Hubble palette) | SII / Hα / OIII → R / G / B | Classic Hubble look. |
| HOO | Hα → R, OIII → G+B | OSC-friendly bicolour. |
| Broadband LP | Light-pollution suppression | Galaxies and clusters under urban skies. |
When you pick a narrowband mode, a second toolbar slides in with intensity sliders for each band — drag them to see how the image responds to different channel weightings. This is the closest you'll get to previewing a processed image before collecting a single frame.
6. Live Readouts & the HUD
Two HUDs float over the sky viewport:
Target HUD (top-left)
Shows the current target name and the field of view in degrees (width × height). The small ◎ Field toggle next to the name switches between Field mode (auto-picks the most notable DSO inside your current view as you pan) and Locked mode (stays on whatever you last searched for). Field mode is invaluable while exploring — you can pan over an area and instantly see what notable objects you're passing over.
The ⓘ button opens a search for the current target — the fastest way to find imaging examples and historical context.
Nearby HUD (bottom-left, when applicable)
When you're framed near a notable deep-sky object that isn't your primary target, the nearby HUD names it. Useful for spotting opportunistic neighbours — "M81 is right next to my M82 frame, I could mosaic them" — which is the kind of insight a real plan benefits from.
7. The Stats Tab — Sampling, Trailing, Light Budget
The right sidebar has three sub-tabs: Setup, Stats, and Calc. The Stats tab is where most of the planning happens.
Image sampling (arcsec/pixel)
Your focal length and pixel size combined into one number. Tells you how much sky each pixel sees and whether that resolution matches typical atmospheric seeing.
| Sampling | Verdict | Meaning |
|---|---|---|
| < 1.0"/px | Over-sampled | Too fine for typical seeing — consider a reducer. |
| 1.0–1.5"/px | Excellent | Ideal for high-res deep sky in good seeing. |
| 1.5–2.5"/px | Good | Well-matched to typical atmospheric seeing. |
| 2.5–4"/px | Coarse | Fine for large nebulae and wide-field targets. |
| > 4"/px | Very coarse | Better suited to very wide-field targets only. |
Star trailing limit
Maximum sub-exposure length (in seconds) before stars start to streak at your current focal length and mount combination. EQ GoTo with guiding is effectively unlimited; a star tracker at 600mm is around 60s; alt-az at 1000mm is essentially unusable for deep sky. A planning estimate — your specific tracking, polar alignment, and seeing will push the real number around.
Light budget
Suggested total integration time given your target, your Bortle value, and your filter choice. A galaxy under Bortle 6 with no filter needs roughly 3–5 hours; the same galaxy under Bortle 3 needs 1–2 hours. Narrowband targets need 3–5 hours per channel even under good skies because the filters discard ~99% of the incoming light.
Go to coordinates
An RA/Dec entry pair at the bottom of the Stats tab. Useful when you've found a target in a planetarium app or paper plan and want to centre the simulator on its precise coordinates without name-resolving.
8. The Sub-Exposure Calculator
The Calc sub-tab is a full-featured sub-exposure and SNR calculator that pulls live values from your current simulator setup. It answers the most common planning question: how long should each sub be, and how many subs do I need to stack?
What you set yourself
| Input | What it is | Typical values |
|---|---|---|
| Camera preset | One-click load of read noise + dark current for common camera classes. | Cooled ASI (2e⁻), Cooled CCD (3.5e⁻), Color CMOS (5e⁻), DSLR (8e⁻). |
| Read noise (e⁻) | Electronic noise added every time a sub is read off the sensor. Lower is better. | ASI2600/ASI533: 1.5–3e⁻ · Modern DSLR: 4–8e⁻ · Older DSLR: 8–12e⁻. |
| Dark current (e⁻/s) | Thermal electrons accumulating per pixel per second. Lower with cooling. | Cooled CMOS at -10°C: ~0.001e⁻/s · Uncooled DSLR: ~0.05e⁻/s. |
| Sub length (s) | Your target individual exposure time. | 30–300s typical for deep sky; the calculator suggests an optimal. |
| Number of subs | How many you plan to stack. | 30–200 typical depending on session length. |
What's pulled from your simulator setup
- Bortle scale — from the Bortle dropdown in the toolbar.
- Pixel scale — from your focal length × pixel size (the Stats sampling number).
- Sky background brightness — derived from Bortle + pixel scale.
- Narrowband filter on/off — divides the sky-background contribution by ~20 when on, reflecting the filter's light rejection.
What the calculator gives back
Sky-noise-limited target length
The sub length at which sky noise dominates read noise by roughly 10×. Shorter than this and your stack is read-noise-limited (longer subs would help more than more subs). Longer is fine for tracking convenience but gives diminishing returns and risks more saturated stars.
Sub length × number of subs
How long the session will run if you actually capture every sub. Real sessions lose ~15-25% to dithering, meridian flips, focus checks, and clouds — round up.
R / √n and SNR vs. single sub
Effective read noise in your final stack. Halving it requires 4× more subs (or longer subs). SNR gain is shown vs. a single sub — going from 25 to 100 subs only doubles SNR.
Noise breakdown bar
The horizontal bar at the bottom shows, per sub, what fraction of total noise comes from each source: read noise, dark current, sky-background shot noise, and target shot noise. Use it to diagnose:
- Read-noise-dominated bar? Your subs are too short for your sky brightness. Lengthen them until sky noise overtakes read noise.
- Sky-dominated bar? Welcome to the optimal-sub regime. More subs help; longer subs help less. This is what you want.
- Dark-current significant? Either you're shooting at warm sensor temperatures or your subs are much longer than they need to be.
9. Saving Setups & Sharing
Saving your setup
The Save button in the toolbar captures a PNG screenshot of the current framing — sky, framing rectangle, and any filter rendering all baked in. Right-click to copy or drag to save locally.
Below the Setup tab, the Save this setup button stores your gear configuration to your AstroEquip account (signed in) or to local storage (signed out). Saved setups sync across devices once you sign in, so you can plan on desktop and pull up the setup on your phone at the imaging site.
Sharing a link
The Share button copies a URL that re-creates the current view. The URL includes target, focal length, sensor, pixel size, mount, Bortle, rotation, and filter mode — anyone who opens it sees exactly what you see. Useful for asking forum questions or coordinating with an imaging partner.
10. Pre-Session Workflow Examples
Five concrete walkthroughs for using the simulator before a session. Each one takes 2–5 minutes and answers a specific planning question.
Workflow 1 — "It's clear tonight, what's worth shooting?"
Open the simulator and autofill your gear.
Type your telescope, camera, and mount into the Setup sidebar. The framing rectangle takes its true shape.
Set Bortle to your local value.
Your Stats tab will now show realistic light-budget estimates for any target.
Click ◎ Field on the target HUD to enable Field mode.
The HUD will name whatever notable object is at the centre of view, automatically, as you pan.
Pan across tonight's visible sky.
If you don't know what's up, type a known reference (M31, Cygnus, Orion) and pan from there. Field mode will surface neighbours you didn't think of.
Open the Stats tab on each candidate.
Check the light-budget number. If it says 1–2h and you have 3, that's a great target. If it says 6h+ and you have 2, look for something easier or commit to a multi-night project.
Workflow 2 — "I have 3 clear hours. What fits?"
Set up your gear and Bortle value.
For each candidate target, search by name and check Stats → Light budget.
Targets where light budget ≤ 3h will produce a clean image. Targets where it's 4–6h will produce a usable but noisier image. Targets where it's 8h+ are not worth attempting in one night unless you're doing a project.
Check star trailing.
Stats → Star trailing limit tells you the longest sub you can take. Divide your session time by that number + 30s (dither + download) for a rough sub count. If you get fewer than ~30 subs, your stack will be noisy regardless of light budget — consider a closer/easier target.
Cross-check in the Calculator.
Switch to the Calc tab. Set your camera preset, type the sub length and count from step 3. The optimal-sub number will tell you whether you can shorten the subs (helpful if your tracking isn't perfect) or whether you need longer ones.
Workflow 3 — "Planning M31 in late autumn from a Bortle 6 site"
Search for M31, set your gear, Bortle 6.
Switch Filter mode through your options.
Visual: lots of light pollution gradient. LP filter (broadband): better. Narrowband: bright in Hα regions only — M31 is a galaxy not an emission nebula, so narrowband is the wrong tool here. The simulator visually confirms what theory says: use a broadband LP filter on M31 from a polluted site, not narrowband.
Frame the galaxy at your sensor size.
If you're on APS-C at 600mm, M31 fits snugly. On full-frame at 600mm it has breathing room. On APS-C at 1000mm it overflows — at least one half of M31 will be cropped. Switch to FOV rotation and try a 30° or 45° angle if you want to fit the full Andromeda + M32 + M110 system into the frame.
Check the light budget for a broadband LP filter under Bortle 6.
Typical estimate: 3–4h per session. M31 is bright; you don't need crazy integration times. A clean image is achievable in one good night.
Save the setup.
Now your phone at the imaging site will have this exact framing and rotation pre-loaded.
Workflow 4 — "Comparing two framings via Share links"
Set up framing A — say, the Rosette Nebula on APS-C at 530mm.
Adjust rotation and target centring until it looks right. Copy the Share link.
Open a second browser tab. Paste the Share link.
You now have two tabs showing identical framings. Modify one — say, switch the focal length to 400mm with a reducer. The framing balloons; you now have the Rosette plus more sky context.
Copy the second Share link and side-by-side them.
Drag the windows next to each other and decide which framing you actually want before you commit a clear night to the wrong choice.
Workflow 5 — "Multi-target field plan in Ursa Major"
Search for M81 and enable Field mode.
Pan slowly around the region.
The HUD names M81, M82, NGC 3077, and others as you cross them. With a wide-field setup (≤500mm on full-frame) you can fit several galaxies in one frame.
Frame for a mosaic.
Try centring between M81 and M82. Use FOV+POV rotation if you need to align the long axis of the frame with the line connecting them.
Save this framing as one setup.
Repeat for any second tile you want, save those, and you have a multi-target night plan all in one place.
11. Gear-Upgrade Workflow Examples
The simulator is the cheapest way to test whether an upgrade is worth it. Five common upgrade questions and how to answer them in 5 minutes:
Upgrade 1 — "Should I go to a faster scope (lower f/ratio)?"
Autofill your current scope. Note the focal length and sampling.
Autofill the faster scope you're considering — e.g. swap an f/7 Esprit 100 for an f/5 Esprit 80, or an f/5 6" Newt for an f/2.8 RASA 8".
Compare on the same target.
Search for a representative target (say IC 1396). Note the field of view, sampling, and star trailing limit in each case.
Run the Calculator on both.
Faster scopes need shorter subs to reach optimal exposure. A RASA 8 might let you stack 30s subs on an unguided EQ — your tracking budget becomes much easier. That's where the value of a fast scope actually shows up.
Decide.
If the upgrade gives you significantly more usable subs per session at your tracking precision, it's worth it. If sampling becomes coarse (over 4"/px), you've gone too fast — beautiful for wide nebulae, less ideal for galaxies.
Upgrade 2 — "Should I go from APS-C to full-frame?"
Same focal length, just swap the sensor.
Search for M31 or NGC 7000 at your current focal length, autofill an APS-C camera (e.g. ASI2600MC), note the framing. Swap to a full-frame body (e.g. ASI6200MC). Same scope, but the frame is roughly 70% bigger in area.
Check image circle compatibility.
Full-frame sensors are ~43mm diagonally. Most APO refractors have a 30–44mm image circle; many small refractors won't cover full-frame. The simulator shows the framing but doesn't show vignetting — check your scope's spec sheet for image-circle figures. The AstroEquip catalogue includes this for every catalogued telescope.
Re-run the Calculator.
Full-frame pixels are often physically larger (e.g. ASI6200 = 3.76µm pitch, ASI533 = 3.76µm — same — but ASI2600 = 3.76µm so it's the size not pitch that matters here). Pixel-area scales surface flux; bigger pixels collect more signal per sub. The Calculator's optimal-sub may shrink.
Upgrade 3 — "ASI533 vs ASI2600 — which dilemma am I in?"
Autofill the ASI533MC. Note the field, sampling, and read noise.
1" square sensor, 3.76µm pixels, ~3e⁻ read noise. Smaller field, same sampling, very low read noise.
Swap to ASI2600MC. Same focal length.
APS-C, 3.76µm pixels, ~1.5e⁻ read noise. Bigger field, same sampling, even lower read noise.
Compare in the Calculator.
The ASI2600's lower read noise lets you stack shorter subs without becoming read-noise-limited — useful if your tracking caps you below the ASI533's optimal sub length. The ASI2600 also covers more sky per sub, so you finish wide targets faster.
Decide on framing.
If your most-shot targets fit cleanly on ASI533 (small nebulae, galaxies), the smaller sensor's centre-only image circle is forgiving on cheap optics. If you want big nebulae (Heart, Veil, North America), the ASI2600 gives you breathing room you'd otherwise need a wider scope for.
Upgrade 4 — "Will a 0.7× focal reducer help?"
Autofill your current scope.
Multiply the focal length by 0.7 manually in the toolbar.
An Esprit 100 at 550mm becomes 385mm with a 0.7× reducer. The framing rectangle grows by ~2× area.
Check sampling.
The Stats tab will show the new (coarser) arcsec/pixel. Make sure you're still in the "good" or "excellent" band for your target — galaxies want fine sampling, nebulae are happier coarse.
Re-run the Calculator.
The faster f/ratio (~30% faster light) lets you cut sub length by ~50% while collecting the same signal — a significant tracking-budget win.
Upgrade 5 — "From a Star Tracker to an EQ GoTo mount"
Autofill your scope, camera, current mount (Star Tracker).
Stats → Star trailing limit might be 30–60s at your focal length.
Swap to an EQ GoTo (HEQ5, EQ6-R, AM5, etc.).
Star trailing limit jumps to "unlimited" assuming you add guiding. The Calculator's optimal sub becomes achievable — typically 120–300s at most focal lengths.
Look at total session efficiency.
Going from 30s subs to 180s subs is 6× fewer dithers and downloads. That's an extra 15–25% of your total session time recovered as actual on-target integration. The mount upgrade is rarely just about deeper exposures; it's about not wasting clear sky.
12. Tips, Gotchas, & Keyboard Shortcuts
Use Field mode while panning.
Click ◎ Field in the target HUD. As you drag, the HUD will name whatever notable object is in view. Fastest way to discover targets you didn't know existed near your planned framing.
Compare two framings with Share links.
Set up framing A, copy the share link. Set up framing B in another tab, copy that. Side-by-side comparison becomes trivial.
POV before you take the shot.
POV mode shows you what your screen will look like with the camera in its actual orientation on the mount. Catching framing surprises here is much cheaper than catching them after a 4-hour integration.
Calculator first, then plan.
It's tempting to "just shoot all night and stack later." But if you're read-noise-limited (subs too short), you'll learn this only after processing. The Calculator catches it in 30 seconds before you set up.
Filter previews are guidance, not gospel.
The narrowband renderings are based on bandwidths and target spectra in published catalogues. Real results depend on your filter brand, camera QE curve, and sky transparency. Use them to compare options, not to predict pixel-level output.
Keyboard shortcuts
| Key | Action |
|---|---|
| → | Next tutorial step (when tutorial is open) |
| ← | Previous tutorial step |
| Esc | Close the tutorial |
| Mouse scroll | Zoom the sky in/out |
| Drag | Pan the sky |
Open the simulator and plan a session
The fastest way to learn the simulator is to open it with a target you care about and walk through your gear. The Gear Finder will pre-fill the simulator with whichever rig it recommends for you.
Open the Telescope Simulator →