Celestron C8 OTA with QHY600M (standard, with CAA)
0.61″ per pixel across a 1.61° × 1.07° field, at 1280.2 mm and f/6.3. 15 of the catalogue's 29 equatorial mounts carry the 8.89 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 1280.2 mm, with the Celestron Reducer/Corrector f/6.3 for SCTs (#94175).
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 4.13 pixels on this sensor. Oversampled: lower per-pixel signal and tighter guiding; binning recovers most of it. Binned 2 × 2 it spans 2.06.
| Seeing | FWHM | Band |
|---|---|---|
| 1.5″ | 2.48px | practical |
| 2.5″ | 4.13px | oversampled |
| 3.5″ | 5.78px | heavily oversampled |
- Practical band for typical seeing.
- Oversampled: lower per-pixel signal and tighter guiding; binning recovers most of it.
- Heavily oversampled: the atmosphere limits resolution long before the pixel does.
Framing
The 13 catalogue targets against this field, by the fraction of the frame each fills along its tighter axis.
M45 Pleiades fills 233 % of the frame and M27 Dumbbell Nebula 10 %. Of the 13, 3 fill the frame, 3 are a tight crop, 3 need a mosaic, 4 are small in the frame.
| Target | Size | Frame filled |
|---|---|---|
| M31 Andromeda Galaxy | 178′ × 70′ | 184%needs a mosaic |
| M45 Pleiades | 150′ × 150′ | 233%needs a mosaic |
| NGC 7000 North America Nebula | 120′ × 30′ | 124%tight crop |
| NGC 1499 California Nebula | 160′ × 40′ | 166%needs a mosaic |
| IC 1805 Heart Nebula | 60′ × 60′ | 93%tight crop |
| M42 Orion Nebula | 90′ × 60′ | 93%tight crop |
| NGC 2237 Rosette Nebula | 80′ × 50′ | 83%fills the frame |
| M101 Pinwheel Galaxy | 24′ × 23′ | 36%fills the frame |
| M27 Dumbbell Nebula | 6.7′ × 6.7′ | 10%small in the frame |
| M51 Whirlpool Galaxy | 13.7′ × 11.7′ | 18%small in the frame |
| M81 Bode's Galaxy | 22′ × 11.3′ | 22%small in the frame |
| M13 Hercules Globular Cluster | 16.5′ × 16.5′ | 26%fills 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.
This telescope needs a corrector. The maker: “Due to the design, the Reducer/Corrector lens does diminish a small amount of field curvature common to all Schmidt Cassegrain telescopes but does not eliminate it.” Source
Celestron Reducer/Corrector f/6.3 for SCTs (#94175)
- Backfocus
- 105mm
- Measured from
- rear threads on the camera side of the reducer (Celestron knowledge base)
- Focal length
- 0.63x, 1280.2 mm
- Image circle
- not published
Solve the spacer stack with this cameraSourceRow not yet verified
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 8.89 kg, 2.25 kg of it assumed. 15 of the 29 equatorial mounts in the catalogue carry it within the derate; the smallest rated is the Sky-Watcher HEQ5-R Pro, at 59 %. 14 more would run it over 60 %.
| Mount | Rated | Used | Band |
|---|---|---|---|
| Sky-Watcher HEQ5-R Pro | 15kg | 59% | Workable; more sensitive to wind, little room to grow |
| Sky-Watcher Wave 150i | 15kg | 59% | Workable; more sensitive to wind, little room to grow |
| ZWO AM5N | 15kg | 59% | Workable; more sensitive to wind, little room to grow |
| Celestron CGEM II | 18kg | 49% | Comfortable |
| iOptron CEM40 (with tripod) | 18kg | 49% | Comfortable |
| iOptron HEM44 | 20kg | 44% | Comfortable |
The other 9 mounts that carry it
| Mount | Rated | Used | Band |
|---|---|---|---|
| Pegasus Astro NYX-101 | 20kg | 44% | Comfortable |
| Sky-Watcher EQ6-R Pro | 20kg | 44% | Comfortable |
| WarpAstron WD-20 | 20kg | 44% | Comfortable |
| ZWO AM7 | 20kg | 44% | Comfortable |
| Losmandy GM811G (LW tripod) | 22.7kg | 39% | Headroom for a future upgrade |
| Celestron CGX | 25kg | 36% | Headroom for a future upgrade |
| iOptron CEM70 (iPolar) | 31.8kg | 28% | Headroom for a future upgrade |
| Sky-Watcher CQ350 Pro (with tripod) | 35kg | 25% | Headroom for a future upgrade |
| Sky-Watcher EQ8-R (head with counterweights) | 50kg | 18% | Headroom for a future upgrade |
What the 8.89 kg is made of
| Component | Mass | Basis |
|---|---|---|
| OTA: Celestron C8 OTA | 5.67kg | maker’s figure |
| Rings and dovetail | 0.90kg | assumption |
| Corrector: Celestron Reducer/Corrector f/6.3 for SCTs (#94175) | 0.12kg | maker’s figure |
| Camera: QHY600M (standard, with CAA) | 0.85kg | 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 | 8.89kg |
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 QHY600M (standard, with CAA) 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.
Not computedThis camera has no sensor profile (read noise against gain) in the catalogue.
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 C8 OTAProvisional | $1,399.95 | manufacturer, 2026-09-27OTA with CGEM-style dovetail, 25mm eyepiece, 6x30 finderscope, star diagonal, 1.25" visual back. In stock 2026-09-27. |
| Camera: QHY600M (standard, with CAA)Provisional | $4,599 | retailer, 2026-10-12QHY600M-PH, the Photographic version QHY specifies at 17.5 mm + 6 mm CAA (SKU QHY-QHY600M-PH); in stock, 1 left |
| Corrector: Celestron Reducer/Corrector f/6.3 for SCTs (#94175)Provisional | $189.95 | retailer, 2026-09-27SKU CE-94175; unavailable at OPT on the day read |
| $199.95 | manufacturer, 2026-09-27#94175, in stock at Celestron | |
| $199.95 | retailer, 2026-09-27in stock | |
| $212.95 | retailer, 2026-09-27SKU CEL-94175 (above Celestron's own price on the day read) |
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 C8 OTA