Simulate and compare sensor and eyepiece field of view against major deep-sky objects like M31, M42, and the Orion Nebula.
Pick a deep-sky target from the catalog, then enter your camera's pixel size, sensor resolution, and telescope focal length, plus an eyepiece focal length and apparent field if you also observe visually.
The simulator converts pixel scale into sensor sky coverage and computes the eyepiece's true field, then draws both against the target's cataloged angular size — the Andromeda Galaxy M31 spans 190 arcminutes, over three degrees of sky.
Compare framings before buying gear: the Ring Nebula M57 is only 1.4 arcminutes across and rewards long focal lengths, while the North America Nebula NGC 7000 at 120 arcminutes overflows most sensors on anything but short refractors.
M31 spans about 190 arcminutes — more than 3 degrees — so it overflows many long-focal-length setups. A sensor field of 2.5° × 1.7° captures only the core and inner disk; short refractors and camera lenses frame it fully.
Sensor field of view comes from pixel scale times pixel count and is rectangular; eyepiece true field is the apparent field divided by magnification and is circular. The simulator computes both so you can compare imaging and visual framing of the same target.
Ten popular deep-sky objects with cataloged angular sizes, from the 1.4-arcminute Ring Nebula M57 up to the 190-arcminute Andromeda Galaxy M31 — including the Pleiades M45 (110'), the Orion Nebula M42 (65'), and the North America Nebula NGC 7000 (120').
Compact targets such as the 11-arcminute Whirlpool Galaxy M51 or the 6-arcminute Crab Nebula M1 need longer focal lengths or smaller pixels for useful image scale. Try candidate focal lengths in the simulator until the target occupies a reasonable fraction of the frame.