FOV Astro

Telescope brand Telescope model

Custom aperture / diameter (mm)

Custom focal length (mm)

Camera brand Camera model

Pixel size (µm)

X pixels

Y pixels

Sensor diagonal (mm) (optional)

Reducer / Flattener

Seeing FWHM (arcsec): —

Sampling indicator —

Metric	Value

Object

Ready.

Rotation (deg): 0°

Help

Select telescope: Choose your telescope brand/model. To enter your own numbers, select Custom and type Aperture and Focal length. While using Custom, background image loading is paused until focal length is at least 150 mm.
Select camera: Choose a camera model. To enter your own sensor, select Custom and type Pixel size (µm) plus Resolution X/Y. Diagonal is optional; if left blank it is calculated. While using Custom, background image loading is paused until pixel size is at least 1.0 µm.
Reducer / Barlow: Use this to change effective focal length. Reducers widen the field; Barlows narrow it.
Object: Pick a target (RA/Dec). The app loads a square sky background around it.
Rotation: Move the slider to rotate the cyan frame overlay. Match your imaging train/camera angle.
Drag the frame: You can drag the cyan frame on the image to adjust framing. Click/touch inside the frame and drag; release to stop. Dragging does not change your FoV — it only repositions the overlay within the current background.
Center frame: Tap Center frame (under the rotation slider) to snap the overlay back to the middle.
Seeing (FWHM): Typical star size at your site (arcsec). It drives Pixels per seeing and the sampling label.
Sampling: The bar is “GOOD” when your seeing blur spans roughly 2–3 pixels. Under-sampled means stars look blocky; over-sampled means you’re not gaining detail.
Background source: Sky images loads from local cache first. Missing cache falls back to NASA SkyView (DSS & other surveys).

Tip: set your average seeing first, then adjust rotation while keeping the image visible.
Drag limit: the frame can only move within the available background margin.