IMX455 full-frame cameras: image circle, file size and the seven bodies compared

Seven cameras in our data use Sony’s IMX455: two ZWO ASI6200 bodies, two QHY600, two Player One Zeus and the ToupTek SkyEye62AM. Six of them publish 9576 × 6388 pixels; ToupTek publishes 9568 × 6380. At 3.76 µm that is a 36.0 × 24.0 mm frame, the size of a 35 mm film negative. Two practical questions follow from that size before any spec comparison: can the telescope cover it, and can your computer keep up with it?

The sensor needs a 43.3 mm image circle

The diagonal of the imaging area is 43.28 mm. For the corners to fall inside the region a telescope maker specifies, its corrected, illuminated circle must be at least that wide. An optic designed around APS-C (28.3 mm diagonal) leaves the outer part of a full-frame sensor outside that region, and cropping those corners away discards pixels you paid for.

Celestron’s RASA 11 V2 page is an example of a design sized for this format: it states a 43.3 mm optimized image circle and describes performance for sensors up to 52 mm diagonal as still excellent. Our telescope data lists smaller circles for other tubes, such as 42 mm for the EdgeHD series and 22 mm for the RASA 8, while many Petzval astrographs list 44–55 mm. Check the figure on the telescope’s page and how its maker defines it before pairing it with one of these cameras.

What one frame weighs

A 16-bit FITS image stores 2 bytes per pixel, and the FITS Standard packs header and data into 2880-byte blocks. For 9576 × 6388 pixels:

9576 × 6388 × 2 B = 122,342,976 B → padded to 2880-byte blocks + 2 header blocks = 122,351,040 B ≈ 122.35 MB

That is 2.34 times an IMX571 frame (52.19 MB). One hundred light frames are 12.24 GB. Processing multiplies it: a calibrated 32-bit float copy of one frame is 244.7 MB, and 734.1 MB if a color frame is debayered into three channels. At 300-second exposures with no overhead, one hour of lights alone is 1.47 GB; at 120 seconds, 3.67 GB. The session storage calculator adds darks, flats and processing copies to the total. Binning 2×2 in the camera cuts a frame to 4788 × 3194 pixels and 30.59 MB.

Sampling

With 3.76 µm pixels the image scale is 1.94″/px at 400 mm, 0.78″/px at 1000 mm and 0.39″/px at 2000 mm, the same as any IMX571 or IMX533 camera at those focal lengths. Full frame changes the field, not the sampling. On long-focal-length tubes, 2×2 binning doubles the scale to 0.78″/px at 2000 mm.

How the seven bodies differ

• Revisions: ZWO’s ASI6200 page lists 0.86 e⁻ read noise for the P25 revision and offers the mono camera as both ASI6200MM-P and P25, while ZWO’s compare page still lists 1.5–3.5 e⁻ for the older version.
• Back focus: ZWO and Player One list 17.5 mm (Player One 12.5 mm without its tilt plate). QHY’s QHY600 page gives 23.5 mm for the standard PH (17.5 mm with a 6 mm CAA added) and 14.5 mm for the short-back-focus SBFL model. ToupTek’s SkyEye62AM switches between 17.5 and 12.5 mm by removing a 5 mm ring. See back focus and spacing.
• Pixel arrays: QHY states 9576 × 6388 effective and 9600 × 6422 with overscan and optical-black areas. ToupTek’s 9568 × 6380 makes its field 0.1′ narrower at 1000 mm (123.66′ vs 123.77′), well inside any framing margin.
• Full well as published: ZWO 51.4 ke⁻, QHY above 51 ke⁻ (above 80 ke⁻ in its extended mode), Player One 71.6 ke⁻, ToupTek 51 ke⁻ (111 ke⁻ in LCG mode).
• Color: ZWO, QHY and Player One sell color and mono versions; the ToupTek SkyEye62AM in our data is mono.