M5) Camera selection in Microscopy, based on FOV and resolution

In this article, we use the concepts that were described in the previous article to estimate the Fields-of-View (FOVs) and limiting resolution that can be achieved when specific sCMOS and CMOS cameras are used in conjunction with commercially available microscope objectives.

Note: the selection of sCMOS or CMOS camera technology is usually made prior to the considerations of FOV and resolution. Making this decision first (on the basis of the photonics of the application) can keep users from making expensive mistakes in the selection process.

For details about matching the photonics of an application to the relevant characteristics of different camera technologies, please visit the Scientific Cameras section of our Knowledge Base. Another useful resource is the prioritized selection criteria list that was put together by our experts to help in camera selection.

A key point in the selection of cameras in microscopy is that in order to achieve diffraction-limited imaging the pixel size of a camera must be smaller than a maximum value that is determined by the wavelength and the NA of the objective. During camera selection, it is very useful to know the “max pix size (μm)” number for each objective, at the wavelengths of interest. The tables below help microscope users keep this point in mind while also estimating the FOV for each camera + objective combination. The “max pix size (μm)” on these tables is shown for reference at λ = 550nm, but it can be re-calculated for the wavelengths of interest. Camera + objective combinations that achieve diffraction-limited imaging at λ = 550nm are easily identifiable in the tables below by the green-text used in the “limiting resolution” column for each objective.

Our Knowledge Base article titled “Camera selection – real world examples” shows that all else being equal, a larger pixel size typically gives a camera better photonics characteristics. This figure-of-merit is quantifiable, since one can estimate it in terms of a higher Signal-to-Noise Ratio (SNR) under the conditions that are typical to a particular application. Camera selection in microscopy therefore often involves a compromise that is specific to each application. One must find a camera with a pixel size that is large enough to achieve desirable photonics characteristics while also being small enough to produce diffraction-limited images with available objectives.

Our imaging experts are available to provide information and assistance. Please contact us to discuss the requirements of your specific application.

Lower-magnification microscope objectives: 1x, 2x, 4x, 10x

A lower-magnification is desirable when it is important to capture a relatively large FOV in a single image. Cameras with relatively small pixels sizes (< 5μm) and larger pixel counts are well suited to low-magnification microscopy. FOVs with lower-magnification systems can range from 1mm to a few tens of mm, depending on the objective used. The optical resolution of low-magnification systems can range from a little above 1μm to about 20μm.

– Estimated FOVs & resolution with sCMOS cameras

– Estimated FOVs & resolution with CMOS cameras

The following notes apply to both the low-magnification systems shown above and to the higher-magnification systems shown below.

1) The minimum feature size is estimated using the Rayleigh Criteria at λ = 550nm; it can be re-calculated for other wavelengths. R = 1.22*λ/(2NA)
2) The maximum pixel size is estimated by applying the Nyquist criteria to the minimum feature size as it appears on the imager plane. Maximum pixel size = R*magnification/2
3) Camera and Objective combinations which meet the Nyquist criteria and are therefore diffraction limited are indicated by showing the Limiting Resolution in green font. (*)
4) Values for Working Distance (WD) and Field Number (FN) are shown for reference only. Actual values may vary.
5) Vignetting, a darkening of the image at the corners, may be observed if the Imager Diagonal is larger than the Field Number of the Objective.

Higher-magnification microscope objectives: 20x, 40x, 60x, 100x

FOVs with higher-magnification systems can range from about 0.1mm to ~1mm depending on the objective used. The optical resolution of low-magnification systems can range from a little above 0.24μm to about 1μm.

– Estimated FOVs & resolution with sCMOS cameras

– Estimated FOVs and resolution with CMOS cameras