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Astrophotography & Cameras

Full-Well Capacity & Dynamic Range Calculator

Compare full-well charge with read noise, express the result as a ratio, stops and decibels, inspect peak-pixel headroom, or solve a target specification.

Astronomy & Space · model workbench

Keep sensor charge capacity, read noise, entered usable headroom and ADC code depth distinct instead of treating them as interchangeable camera specifications.

Private calculations in your browser · explicit inputs and model boundaries
Example preview · Cooled-camera specificationSensor range and digitizer depth in stops
Noise-limited sensor range13.6502825 stops
Entered ADC depth16 bits

Noise-limited sensor range comes from usable charge divided by read noise. ADC depth is the entered nominal bit count; the smaller limit can constrain recorded tonal separation under ideal mapping.

  1. 1EnterProvide the known values
  2. 2CalculateResults update automatically
  3. 3VerifyReview the details and units
Try an example

Enter values in e⁻/pixel.

Enter values in %.

Enter values in e⁻ rms/pixel.

Enter values in bits.

Calculation result

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Enter valid values to see the result.

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Understand the relationship

The reasoning behind the result

Full well and read noise define a specification ratio

DR = Qusable / σread

Full-well capacity is a per-pixel charge capacity associated with a sensor operating mode. Read noise is an rms uncertainty per pixel from that same mode.

Dividing compatible electron quantities produces a dimensionless maximum-to-noise ratio. The entered usable fraction can reserve headroom below the listed capacity without claiming a measured linearity boundary.

Stops and decibels re-express the same ratio

stops = log₂(DR); dB = 20log₁₀(DR)

A stop doubles the ratio. The decibel expression uses 20 times the base-10 logarithm for this signal-amplitude to rms-noise ratio.

Neither representation adds information or predicts scene contrast; they make specification comparisons easier.

Bit depth is not dynamic range

nominal ADC levels = 2^bits

Bit depth counts nominal digital code levels. Sensor noise and analog gain determine whether those codes capture useful distinctions across the charge range.

The displayed ideal electrons per level divides usable charge by every nominal code. Real offset, system gain, clipping, nonlinearity and encoding may produce a different mapping.

Headroom belongs to a peak pixel

headroom = Qusable − Qpeak

Saturation and linearity are local pixel concerns. An aperture sum or whole-image electron total cannot be compared directly with a per-pixel well capacity.

A predicted peak charge still depends on source profile, focus, seeing, sampling, exposure and calibration; this workflow accepts the charge rather than deriving it.

Follow the numbers

Express a 50,000-electron camera specification

  1. Apply the entered 90% usable fraction: 50,000 × 0.90 = 45,000 electrons per pixel.
  2. Divide 45,000 by 3.5 electrons rms read noise to obtain a usable charge/noise ratio of about 12,857:1.
  3. Take log₂(12,857) to obtain about 13.65 stops.
  4. Take 20log₁₀(12,857) to obtain about 82.18 dB.
  5. A 16-bit ADC has 65,536 nominal levels; ideal full-scale mapping would average about 0.687 electrons per level.

The sensor ratio is about 13.65 stops while the entered digitizer has 16 nominal bits; this does not establish the camera's actual linearity, gain map or scene-level range.

Quick guide

How to use this calculator

  1. Use full-well capacity and read noise from the same camera gain, readout-speed and sensor operating mode.
  2. Enter 100% only when the listed full well is the maximum charge you intend to use. A lower fraction creates an explicit planning ceiling; the calculator does not infer detector linearity.
  3. Use headroom with a relevant peak-pixel electron estimate, not a whole-image total. Values beyond listed full well cannot be reconstructed by this arithmetic.
  4. Treat ADC bit depth as a separate digitizer property. The ideal electrons-per-level result assumes full-scale mapping and is not a substitute for the camera's measured system gain.

Calculation method

Calculation and interpretation

Keep sensor charge capacity, read noise, entered usable headroom and ADC code depth distinct instead of treating them as interchangeable camera specifications.

Usable maximum charge = listed full well × entered usable fraction; dynamic range = usable maximum charge / rms read noise; stops = log₂(range); dB = 20log₁₀(range). Inverse solves listed full well = target × read noise / usable fraction or read noise = usable fraction × full well / target.

Worked example

Express a 50,000-electron camera specification

The sensor ratio is about 13.65 stops while the entered digitizer has 16 nominal bits; this does not establish the camera's actual linearity, gain map or scene-level range.

Usable maximum charge = listed full well × entered usable fraction; dynamic range = usable maximum charge / rms read noise; stops = log₂(range); dB = 20log₁₀(range). Inverse solves listed full well = target × read noise / usable fraction or read noise = usable fraction × full well / target.

Supported inputs

Precision and limits

One operating mode

Full well, read noise, bit depth and any peak-pixel charge must refer to compatible camera settings. Mixing high-gain read noise with low-gain full well creates a fictional ratio.

Entered usable ceiling

The usable fraction is a visitor-supplied planning assumption. It is not a measured linear-full-well value, anti-blooming limit or manufacturer guarantee.

Specification range, not image SNR

The ratio excludes source shot noise, sky background, dark current, fixed-pattern noise and stacking. Use the separate SNR workbench for an entered observation model.

No saturation recovery

Headroom arithmetic cannot recover clipped charge or certify an exposure. ADC clipping, analog-chain saturation and per-channel behaviour can occur before or after the sensor well limit.

No camera recommendation

The inverse mode rearranges an entered target. It does not rank products, choose gain, guarantee detectable contrast or determine an appropriate exposure.

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