Celestron RASA 8 with ToupTek ATR533C
1.94″ per pixel across a 1.62° × 1.62° field, at 400 mm and f/2.0. 12 of the catalogue's 29 equatorial mounts carry the 10.54 kg train within the imaging derate.
Every figure is computed from catalogue rows that link their maker's page. Rows marked provisional have not yet had a second, human check.
Optics
At the native focal length.
Image circle: 22 mm, the telescope's stated figure (Celestron RASA 8). Source
Sampling
Seeing divided by image scale: how many pixels a star's core spans. Each band is a tradeoff, and wide-field work is undersampled on purpose.
At 2.5″ seeing a star’s core spans 1.29 pixels on this sensor. Undersampled; the standard, deliberate wide-field trade.
| Seeing | FWHM | Band |
|---|---|---|
| 1.5″ | 0.77px | badly undersampled |
| 2.5″ | 1.29px | undersampled |
| 3.5″ | 1.81px | practical |
- Badly undersampled: the pixel is wider than the seeing disc, so stars land as blocky squares.
- Undersampled; the standard, deliberate wide-field trade.
- Practical band for typical seeing.
Framing
The 13 catalogue targets against this field, by the fraction of the frame each fills along its tighter axis.
M31 Andromeda Galaxy fills 183 % of the frame and M27 Dumbbell Nebula 7 %. Of the 13, 2 fill the frame, 2 are a tight crop, 3 need a mosaic, 6 are small in the frame.
| Target | Size | Frame filled |
|---|---|---|
| M31 Andromeda Galaxy | 178′ × 70′ | 183%needs a mosaic |
| M45 Pleiades | 150′ × 150′ | 155%needs a mosaic |
| NGC 7000 North America Nebula | 120′ × 30′ | 123%tight crop |
| NGC 1499 California Nebula | 160′ × 40′ | 165%needs a mosaic |
| IC 1805 Heart Nebula | 60′ × 60′ | 62%fills the frame |
| M42 Orion Nebula | 90′ × 60′ | 93%tight crop |
| NGC 2237 Rosette Nebula | 80′ × 50′ | 82%fills the frame |
| M101 Pinwheel Galaxy | 24′ × 23′ | 25%small in the frame |
| M27 Dumbbell Nebula | 6.7′ × 6.7′ | 7%small in the frame |
| M51 Whirlpool Galaxy | 13.7′ × 11.7′ | 14%small in the frame |
| M81 Bode's Galaxy | 22′ × 11.3′ | 22%small in the frame |
| M13 Hercules Globular Cluster | 16.5′ × 16.5′ | 17%small in the frame |
| NGC 4565 Needle Galaxy | 16.8′ × 2.9′ | 17%small in the frame |
Target sizes: OpenNGC by Mattia Verga (tag v20260501), CC BY-SA 4.0. This table is shared under the same license. Source and license
Spacing
The corrector rows this telescope links in the Backfocus Solver's catalogue, with the face each figure is measured from.
No separate corrector is needed. The maker: “Flat field free of optical aberrations like field curvature, coma, astigmatism and chromatic aberration across an entire APS-C sensor.” Source
Mounts
The catalogue's equatorial mounts that carry this train within 60 % of their rated payload, the imaging derate. The sum is the Rig Reality Check's.
On the saddle this train weighs 10.54 kg, 2.25 kg of it assumed. 12 of the 29 equatorial mounts in the catalogue carry it within the derate; the smallest rated is the Celestron CGEM II, at 59 %. 17 more would run it over 60 %.
| Mount | Rated | Used | Band |
|---|---|---|---|
| Celestron CGEM II | 18kg | 59% | Workable; more sensitive to wind, little room to grow |
| iOptron CEM40 (with tripod) | 18kg | 59% | Workable; more sensitive to wind, little room to grow |
| iOptron HEM44 | 20kg | 53% | Workable; more sensitive to wind, little room to grow |
| Pegasus Astro NYX-101 | 20kg | 53% | Workable; more sensitive to wind, little room to grow |
| Sky-Watcher EQ6-R Pro | 20kg | 53% | Workable; more sensitive to wind, little room to grow |
| WarpAstron WD-20 | 20kg | 53% | Workable; more sensitive to wind, little room to grow |
The other 6 mounts that carry it
| Mount | Rated | Used | Band |
|---|---|---|---|
| ZWO AM7 | 20kg | 53% | Workable; more sensitive to wind, little room to grow |
| Losmandy GM811G (LW tripod) | 22.7kg | 46% | Comfortable |
| Celestron CGX | 25kg | 42% | Comfortable |
| iOptron CEM70 (iPolar) | 31.8kg | 33% | Headroom for a future upgrade |
| Sky-Watcher CQ350 Pro (with tripod) | 35kg | 30% | Headroom for a future upgrade |
| Sky-Watcher EQ8-R (head with counterweights) | 50kg | 21% | Headroom for a future upgrade |
What the 10.54 kg is made of
| Component | Mass | Basis |
|---|---|---|
| OTA: Celestron RASA 8 | 7.71kg | maker’s figure |
| Rings and dovetail | 0.90kg | assumption |
| Camera: ToupTek ATR533C | 0.58kg | maker’s figure |
| Filter drawer and filter | 0.20kg | assumption |
| Guide scope and guide camera | 0.80kg | assumption |
| Cables, dew strap, focuser motor | 0.35kg | assumption |
| Total | 10.54kg |
Assumptions are the Rig Reality Check’s round placeholders, not measurements; replace them with your own figures there.
Run the Rig Reality Check with the ToupTek ATR533C as yours, then give it your budget, sky and targets.
Sub length
The shortest sub at which read noise adds no more than 5 % to the stack's noise, from the Exposure Planner. Each figure opens the planner with the same inputs.
At gain 15000 (the lowest published read noise, 0.66 e⁻ read noise), 203 mm at 400 mm. Under a Bortle 6 sky it is 0.2 s with no filter and 3.6 s through a 7 nm dual-band filter.
| Sky | No filter | 7 nm dual-band |
|---|---|---|
| Bortle 421.00 mag/arcsec² | 1.2 sbelow the 30 s floor | 23 sbelow the 30 s floor |
| Bortle 619.00 mag/arcsec² | 0.2 sbelow the 30 s floor | 3.6 sbelow the 30 s floor |
| Bortle 817.90 mag/arcsec² | 0.1 sbelow the 30 s floor | 1.3 sbelow the 30 s floor |
- This design has a central obstruction, which the catalogue holds only in prose. The figures are computed unobstructed, so each is a floor: the obstruction lowers the sky signal and lengthens the shortest sub. The planner takes the obstruction as an input.
- Under 30 s, download and dither time dominate, so the planner raises shorter results to 30 s. The dual-band column uses the reference’s approximation: Dual narrowband 7 nm (Ha + OIII).
Prices
Dated readings from the maker's store or a major US retailer, with the page each came from. A first-year total needs a mount and the essentials, which the Rig Reality Check adds.
| Part | Price | Read |
|---|---|---|
| Telescope: Celestron RASA 8Provisional | $2,199 | manufacturer, 2026-09-27OTA with CGE dovetail; included items per page: '42mm (1.65") T-thread camera adapter | C-thread camera adapter | Fan battery pack'. In stock 2026-09-27. |
| Camera: ToupTek ATR533CProvisional | $769 | manufacturer, 2026-09-27 |
Provisional rows have not yet had a second, human check against their source. The Rig Reality Check prices whole builds, essentials included.
How this is computed
scale["/px] = 206.265 × pixel[µm] / focal length[mm]
field[°] = 2 × atan(sensor side[mm] / (2 × focal length[mm])) × 180/π
sampling = seeing FWHM["] / scale["/px]
frame filled = max(major axis / field width, minor axis / field height)
utilization = Σ imaging mass[kg] / rated payload[kg]
shortest sub = R² / (e_sky × ((1 + p)² − 1)), p = 5 %Focal length is the telescope’s, times a corrector’s factor only where its maker states one. The image scale and field use the exact forms; the worked example shows the arithmetic. The sampling bands are the physics reference’s presentation choice, and every band is printed so the tradeoff can be read in full.
The payload sums every part on the saddle, the way the Rig Reality Check does, and the bands encode the 50 to 60 % imaging derate, which is forum practice rather than a maker’s figure. Spacing figures are the Backfocus Solver’s rows; sub lengths are the Exposure Planner’s.
Source: docs/03-physics-reference.md §§ 1, 3 and 4. Implemented in packages/physics (optics.ts, payload.ts, exposure.ts, scoring.ts), each with the reference's worked examples as unit tests.
Last updated Computed from the catalogue when the site is builtEvery camera on the Celestron RASA 8