A thin Schmidt plate lets a spherical mirror work at f/4
A spherical mirror is easy to make but focuses its edge and center at different points. Bernhard Schmidt's thin aspheric corrector plate, placed at the front of the tube, bends the incoming light just enough to cancel that error. In a Schmidt-Newtonian the plate also holds the diagonal flat, so, as in a Maksutov-Newtonian, there are no spider vanes or spikes.
The corrected field is flatter and freer of coma than a plain f/4 Newtonian, but the plate is thinner and less forgiving than a Maksutov meniscus, and the design still shows some coma at the edge of a large sensor.
No major maker builds a Schmidt-Newtonian today
Meade's SN-6, SN-8 and SN-10, sold on the LXD55 and LXD75 mounts, were the best-known Schmidt-Newtonians. Meade closed in 2024, and we found none in current production from a major maker in November 2026. The same Schmidt corrector idea lives on in two places:
| Replacement | Maker | Aperture | Focal length | Price |
|---|---|---|---|---|
| Quattro 200P plus coma corrector | Sky-Watcher (Synta, China) | 200 mm | 800 mm (f/4) | $925, tube only |
| Quattro 250P plus coma corrector | Sky-Watcher (Synta, China) | 254 mm | 1,000 mm (f/4) | $1,325, tube only |
| RASA 8 | Celestron (made in China) | 203 mm | 400 mm (f/2) | $2,199, tube only |
Prices are US list prices checked in November 2026. Special-order instruments are quoted by the dealer.
A used Meade SN-8 is worth buying for the optics if the corrector plate is clean and the diagonal is still glued firmly to it. Parts and support are gone. The RASA is the Schmidt idea taken to its limit: no diagonal at all, with the camera at prime focus.
An 8-inch f/4 Schmidt-Newtonian frames the larger galaxies and nebulae
On an APS-C camera with the Sony IMX571 sensor (23.5 x 15.7 mm, 3.76-micron pixels), a Meade SN-8 at 812 mm gives a field of 1.66 x 1.11 degrees at 0.96 arcseconds per pixel. 100 of the 110 Messier objects fit in the frame, and 28 of them fill at least a quarter of its short side, among them M22 (Sagittarius Cluster), M67 (King Cobra Cluster), M101 (Pinwheel Galaxy) and M20 (Trifid Nebula).
Most backyard skies blur stars to 2 to 3 arcseconds. Image scales below about 0.7 arcseconds per pixel record no extra detail, so cameras on long focal lengths are usually binned 2x2.
A used Schmidt-Newtonian is a capable rich-field visual telescope
At f/4 it gives wide, bright deep-sky fields, but eyepieces show their own edge flaws at such fast focal ratios, and the planets need a Barlow lens. A visual observer who does not already own one is better served by a solid-tube Dobsonian of the same aperture at a fraction of the price.