ZWO cooled astronomy cameras: sensor sizes and fields compared

The 17 cooled ZWO cameras in our data use eleven Sony sensors in six format classes. Pixel pitch runs from 2.4 µm on the ASI183 Pro to 5.94 µm on the ASI2400MC Pro, yet nine of the 17 bodies share the same 3.76 µm pitch. Sensor width sets how much sky you get; pitch sets how finely it is sampled. Two bodies with the same pitch can differ almost fourfold in field width.

Focal lengths that frame each sensor class

Instead of the field at fixed focal lengths (that table is below), this one gives the focal length at which each sensor’s long side spans 2° or 1°, and where one pixel covers 1″, all computed from pixel count × pixel size.

focal length (mm) = sensor width (mm) ÷ (2 × tan(field ÷ 2))

focal length for 1″/px (mm) = 206.265 × pixel size (µm)

Sensor (ZWO bodies)	Imaging area (mm)	2° wide at	1° wide at	1″/px at
IMX585 (ASI585MC Pro)	11.14 × 6.26	319 mm	638 mm	598 mm
IMX533 (ASI533MC/MM Pro)	11.31 × 11.31	324 mm	648 mm	776 mm
IMX183 (ASI183MC/MM Pro)	13.19 × 8.81	378 mm	756 mm	495 mm
IMX294 / IMX492 (ASI294MC/MM Pro)	19.19 × 13.07	550 mm	1099 mm	955 mm
IMX571 (ASI2600 family)	23.49 × 15.70	673 mm	1346 mm	776 mm
IMX071 (ASI071MC Pro)	23.63 × 15.70	677 mm	1354 mm	986 mm
IMX455 (ASI6200MC/MM Pro)	36.01 × 24.02	1031 mm	2063 mm	776 mm
IMX410 (ASI2400MC Pro)	36.07 × 24.01	1033 mm	2066 mm	1225 mm
IMX366 (ASI4400MC Pro)	36.04 × 24.02	1033 mm	2065 mm	908 mm
IMX461 (ASI461MM Pro)	43.83 × 32.90	1255 mm	2511 mm	776 mm

The last two columns pull apart as sensors grow. The ASI461MM Pro needs 2511 mm to narrow its field to one degree, but its 3.76 µm pixels already reach 1″/px at 776 mm, where the field is still 3.24° wide. The small IMX183 behaves the other way: its 2.4 µm pixels hit 1″/px at 495 mm, where the field is only 1.53° across.

If you assume 2″ seeing and the sampling calculator’s default of 2–3 pixels per star FWHM, the target scale is 0.67–1.0″/px. For 3.76 µm pixels that corresponds to roughly 776–1163 mm; for 4.63 µm it moves to 955–1432 mm. Sampling and seeing explains how to substitute your own seeing.

Duo and Air variants share the ASI2600 field

The ASI2600MC Duo and Air list the same IMX571, 6248 × 4176 pixels and 3.76 µm pitch as the ASI2600MC Pro, so their field-of-view rows are identical. The difference is a second sensor. The Duo page describes a Type 1/1.8 SC2210 guide sensor of 7.68 × 4.32 mm with 4 µm pixels and says the design removes the need for a separate off-axis guider and guide camera. Because that chip looks through the same telescope, its scale follows the main focal length: 2.06″/px at 400 mm.

The Air carries the same kind of guide sensor plus built-in ASIAIR control. Its manual gives main-sensor read noise as 0.84–4.2 e⁻, while the product page (and our table) says 0.9–4.2 e⁻, and it lists back focus as “12.5mm or 17.5mm”.

Back focus as ZWO publishes it

Most bodies list 17.5 mm, but the figure means different things. The ASI585MC/MM Pro manual writes “17.5mm (11mm ring included) / 6.5mm”, and ZWO’s compare page gives the same 6.5/17.5 mm pair for the ASI533, ASI294 and ASI183 Pro bodies. The ASI4400MC Pro manual says 17.5 mm with the tilt adjustment plate and 12.5 mm without. The ASI461MM Pro appears as 17.5/22.5 mm with no note on which setup each number describes. The back focus guide covers how to add up the stack.

Where ZWO’s own numbers disagree

The compare page lists the ASI6200MM-P and MC-P at 1.5–3.5 e⁻, while the current ASI6200 page gives 0.86 e⁻ for the P25 revision; the mono model is sold in both revisions. For the ASI585MC Pro the compare page says 0.8–12 e⁻ and 47 ke⁻, the product page 0.7 e⁻ and 40 ke⁻. The ASI2600 series page states 50 ke⁻ full well, but the P25 page for the same sensor states 73 ke⁻. Our spec table records the product-page value; treat these columns as claims for a specific revision, not fixed sensor properties.