Edmund Optics Lens Calculator: How to Use It

The Edmund Optics lens calculator is a free online tool that helps you determine key parameters for imaging systems, such as field of view, focal length, and magnification. You enter details like sensor size, working distance, and object size, and it returns the required lens specifications or the resulting image properties. This article explains the calculator’s background, how to use it, and how to interpret its results.

Formula

The core formula used by the Edmund Optics lens calculator (and most basic lens calculators) relates focal length (f), working distance (WD), sensor width (w_sensor), and field of view width (FOV_w):

f = (WD × w_sensor) / FOV_w

Where:

• f = focal length of the lens (mm)
• WD = working distance from the front of the lens to the object (mm)
• w_sensor = width of the camera sensor (mm)
• FOV_w = width of the area you want to capture (mm)

Magnification (m) is simply the ratio of sensor width to object width: m = w_sensor / FOV_w. The height of the field of view is then FOV_h = h_sensor / m, where h_sensor is the sensor height.

Worked Example

Using the default values from the calculator block:

• Sensor width = 6.4 mm
• Sensor height = 4.8 mm
• Object width (FOV) = 100 mm
• Working distance = 300 mm

Step 1: Calculate magnification: m = 6.4 / 100 = 0.064 (or 0.064×).

Step 2: Calculate focal length: f = (300 × 6.4) / 100 = 19.2 mm.

Step 3: Calculate object height: FOV_h = 4.8 / 0.064 = 75 mm.

So a 19.2 mm focal length lens at 300 mm working distance will capture a 100 × 75 mm area on a 1/2.5″ sensor.

What the Calculator Does (and Doesn’t) Do

The Edmund Optics lens calculator is a paraxial (first-order) approximation. It assumes a thin lens and ignores real-world effects like distortion, lens thickness, and the location of the principal planes. It is ideal for initial selection: you get a starting focal length, then you refine it with actual lens data.

It does not calculate depth of field, resolution, or illumination. Those require additional inputs like aperture, pixel size, and lighting. The calculator also assumes the object is perpendicular to the optical axis; if you tilt the object, the working distance varies across the field.

How to Choose the Right Lens

Follow these steps when using the calculator for a real project:

1. Determine your sensor size from the camera spec sheet (e.g., 1/2.5″ = 5.7 × 4.3 mm, 2/3″ = 8.8 × 6.6 mm, 1″ = 12.8 × 9.6 mm).
2. Measure the object area you need to capture (width and height).
3. Decide on the working distance available in your setup.
4. Enter these values into the calculator to get the required focal length.
5. Choose a lens with a focal length close to the result. If you need a 19.2 mm lens, you might pick a 20 mm or 25 mm model, then adjust the working distance slightly to match your exact FOV.

Remember that lenses are sold in standard focal lengths (e.g., 12 mm, 16 mm, 25 mm, 35 mm). You may need to iterate: pick a lens, recalculate the working distance, and see if it fits your space.

Common Mistakes and Misconceptions

One frequent error is mixing up sensor dimensions. A 1″ sensor is not 1 inch wide; it is about 12.8 mm wide (the “1 inch” refers to an old vacuum tube standard). Always use the actual dimensions from the datasheet.

Another mistake is using the diagonal field of view when the calculator asks for width. The calculator uses width and height separately, so be consistent. If you only know the diagonal FOV, you must compute the width and height using the sensor aspect ratio.

Also, the working distance is measured from the front of the lens, not from the camera body or the sensor plane. If you measure from the sensor, you’ll get a slightly different focal length because the lens has physical length.

Finally, the calculator assumes the object is in focus at that working distance. If your lens has a minimum focusing distance longer than your working distance, you won’t be able to focus.

Limitations of the Paraxial Approximation

The thin-lens formula works well for moderate angles of view (up to about 30° half-angle) and for lenses with low distortion. For wide-angle lenses (focal length shorter than the sensor diagonal), the formula becomes less accurate. In such cases, you should use a more advanced optical design tool or consult the lens manufacturer’s data.

Also, the formula ignores the effect of the lens’s principal planes, which can shift the effective focal length by a few percent. For critical applications like machine vision metrology, use a lens with known distortion data and calibrate the system.

For macro photography (magnification > 0.1×), the working distance changes with magnification. The simple formula still works, but you must use the effective focal length, which may be different from the nominal focal length.

Alternatives and Related Tools

Edmund Optics provides other calculators on its site, such as the “Field of View Calculator” and “Lens Focal Length Calculator,” which are variations of the same math. Other manufacturers (e.g., Thorlabs, Opto Engineering, Basler) offer similar online calculators with different interfaces.

If you need more advanced calculations, consider using optical design software like Zemax or OSLO, but those require training. For quick estimates, the Edmund Optics calculator is a good starting point.

Frequently Asked Questions

What is the difference between the Edmund Optics lens calculator and a simple FOV calculator?

They are essentially the same. The lens calculator solves for focal length given working distance and FOV, while a FOV calculator solves for FOV given focal length and working distance. Both use the same thin-lens equation rearranged.

Can I use the calculator for a smartphone camera?

Yes, but you need to know the sensor size and lens focal length of your phone camera. These are often listed in the phone’s spec sheet or on websites like GSMArena. The calculator will give you the FOV for that lens.

Why does the calculator ask for sensor size in millimeters?

Because lens focal length and working distance are typically expressed in millimeters. Using the same unit for all dimensions avoids conversion errors. If you have sensor size in inches, convert to mm (1 inch = 25.4 mm).

What is a good working distance for a machine vision inspection system?

It depends on your space and the object size. A typical working distance is 100–500 mm. The calculator will tell you the required focal length for your chosen distance. If the focal length is too short or too long, adjust the working distance.

Does the calculator work for telecentric lenses?

No. Telecentric lenses have a constant magnification over a range of working distances, so the simple formula does not apply. For telecentric lenses, use the manufacturer’s specified working distance and FOV.

Related

• Degrees Minutes Seconds Calculator Subtract
• Calculator Topics GCSE Maths Foundation
• GCSE Maths Higher Calculator Topics

in sensor_w | Sensor width | mm | 6.4 | 0
in sensor_h | Sensor height | mm | 4.8 | 0
in fov_w | Object width | mm | 100 | 0
in wd | Working distance | mm | 300 | 0
out fl | Focal length | mm | (wd * sensor_w) / fov_w | 1
out mag | Magnification | - | sensor_w / fov_w | 3
out fov_h | Object height | mm | sensor_h / (sensor_w / fov_w) | 1