Focal Length Equivalents

It is common for 35mm photographers to try and compare focal lengths to medium and large format cameras because these are the focal lengths they understand the best and use as their frame of reference.

We want quick and easy answers, but unfortunately it is a little more complicated than most would like.

As you will see in the information below, we can easily calculate an equivalent focal length using a computed crop factor, but as you will see, the field of view will not be the same. Even before I understood the math, I intuitively understood medium and large format images felt much wider than their 35mm equivalents.

I provide the information and tools on this page to help you calculate the equivalent focal lengths to 35mm using a crop factor method. It is simple, effective, and quick. As noted above, the field of view won’t be the same, but it is good enough to accomplish the basic task of comparing focal lengths.

I don’t cover the effective depth of field differences here, but the crop factor that I share how to compute for the focal length can be used to get a close approximation for depth of field.

I hope you find this information useful. If you have any questions, please let me know.

Before You Use The Charts Below

Understanding the difference between angle of view and focal length, especially when comparing various formats like 35mm and 4×5 large format, is essential in photography.

Focal Length
Focal length, measured in millimeters (mm), is the distance from the lens’s optical center (or focal point) to the camera’s sensor when the lens is focused at infinity. It determines the lens’s field of view and influences the magnification of the image. A shorter focal length (e.g., 24mm) provides a wider field of view and a more extensive scene in the frame, leading to a “wider” lens. Conversely, a longer focal length (e.g., 200mm) offers a narrower field of view, magnifies the subject, and is considered a “telephoto” lens.

Angle of View
The angle of view is the extent of the scene captured by the camera’s sensor at a given focal length. It is determined by the focal length of the lens and the size of the sensor. Wider lenses have a larger angle of view, allowing more of the scene to be captured. In contrast, telephoto lenses have a narrower angle of view, focusing more closely on the subject.

Comparison Between Formats
When comparing focal lengths between different formats, such as 35mm (full-frame) and 4×5 large format, the concept of “equivalent focal length” comes into play. Because the size of the sensor or film plane affects the angle of view, a lens with a given focal length will produce a different field of view on different formats.

For example, a 50mm lens on a 35mm full-frame camera is considered a standard lens, providing a relatively natural perspective close to human vision. However, on a 4×5 large format camera, which has a much larger sensor area, the same 50mm lens would act as a wide-angle lens because the larger sensor captures a wider portion of the scene, leading to a broader angle of view.

To compare focal lengths across formats and understand their equivalent field of view, photographers use a “crop factor” or “focal length multiplier.” This factor, determined by the ratio of the diagonal dimensions of the sensors or film sizes, helps to calculate the equivalent focal length that would yield a similar field of view on a 35mm camera. For instance, the crop factor between 35mm and 4×5 large format is approximately 0.2 (or 5x, depending on how you frame it). So, a 50mm lens on a 4×5 camera would have a field of view similar to a 10mm lens on a 35mm camera, illustrating the substantial difference in how focal lengths translate across formats.

In conclusion, while the focal length of a lens is a fixed physical property, the angle of view it provides varies with the sensor or film size of the camera system. Understanding this relationship is crucial for photographers, especially when working with different formats or trying to achieve consistent framing and composition across various cameras.

Crop Factors

The crop factor between different camera formats is determined by the ratio of their sensor or film sizes, particularly the diagonal measurement of each frame. Here’s how it generally works for medium format systems compared to the standard 35mm format, which has a frame size of 24x36mm:

1. 6×4.5 (also known as 645): This format has a frame size of approximately 60x45mm. The diagonal can be calculated using the Pythagorean theorem.
2. 6×6: This square format has a frame size of 60x60mm.
3. 6×7: This format has a frame size of approximately 60x70mm.
4. 6×9: This format has a frame size of 60x90mm.
5. 6×12: This panoramic format has a frame size of 60x120mm.
6. 6×17: Another panoramic format with a frame size of 60x170mm.

To calculate the crop factor, we use the formula:

Crop Factor = Diagonal of 35mm film / Diagonal of medium or large format

The diagonal of 35mm film is √(24² + 36²) which is approximately 43.3mm. Let’s calculate the crop factors for each medium format system based on their diagonals.

The crop factors between 35mm and the various medium format systems are approximately as follows:

1. 6×4.5: 0.58
2. 6×6: 0.51
3. 6×7: 0.47
4. 6×9: 0.40
5. 6×12: 0.32
6. 6×17: 0.24

These values indicate that medium format systems have a larger sensor size compared to 35mm film, resulting in lower crop factors. The lower the crop factor, the larger the sensor size, and the wider the angle of view for a given focal length.

Large Format Crop Factors

The crop factors for large format cameras when compared to a 35mm camera are approximately as follows:

1. 4×5: 0.27
2. 5×7: 0.20
3. 8×10: 0.13
4. 8×20: 0.08
5. 11×14: 0.10
6. 12×20: 0.07
7. 16×20: 0.07
8. 20×24: 0.05

These numbers reflect the relative size difference between the 35mm format and large format cameras. A smaller crop factor indicates a larger film size, which results in a wider field of view for a given focal length. Therefore, these large format cameras can capture much wider scenes than a 35mm camera, explaining their popular use in landscape and architectural photography where capturing expansive scenes with great detail is crucial.

On a side note, I use an old micro four-thirds camera as a compositional tool, and I need to understand the crop factor between the MFT sensor and the 4×5 large format. The diagonal of the Micro Four-Thirds sensor is approximately 21.64mm. The crop factor for a 4×5 large format camera compared to a Micro Four-Thirds camera is approximately 0.13.

How To Use Crop Factors

To compare the focal lengths between different formats using the crop factor, think of it as a way to translate the field of view from one camera system to another. Here’s a step-by-step explanation aimed at beginners:

1. Understand Crop Factor: Crop factor is a number that shows how much smaller or larger the digital sensor is compared to a full-frame 35mm film sensor. A larger number means a smaller sensor, and a smaller number means a larger sensor.
2. Know the Crop Factors: Each camera format has a specific crop factor. For example, if the crop factor of a medium format compared to a 35mm format is 0.5, this means the medium format sensor is twice as large as the 35mm sensor.
3. Compare Focal Lengths: To compare focal lengths, you use the crop factor to find the equivalent focal length that would give you the same field of view on different formats. For example, if you have a 50mm lens on a 35mm camera, and you want to know what lens on a medium format camera (with a crop factor of 0.5) would give you the same field of view, you multiply the focal length by the crop factor: ( 50mm x 0.5 = 25mm ). So, a 25mm lens on the medium format camera would give you a similar field of view to a 50mm lens on a 35mm camera.
4. Apply It Both Ways: This calculation can go both ways. If you know the focal length you use on a medium format camera, you can find the equivalent for a 35mm camera by dividing by the crop factor. So, using the previous example, if you have a 25mm lens on the medium format camera, you would get ( 25mm / 0.5 = 50mm ) as the equivalent focal length on a 35mm camera.

By using the crop factor in this way, you can better understand how different lenses will behave on different camera formats, helping you achieve the desired field of view or composition in your photographs.

To compute the equivalent focal length of a 50mm lens on a 6×9 medium format camera compared to a 35mm camera, follow these steps:

1. Determine the Crop Factor: The crop factor is the ratio of the diagonal of the 35mm frame to the diagonal of the medium format frame. From our earlier calculation, the crop factor for 6×9 medium format compared to 35mm is approximately 0.4.
2. Understand the Meaning: This crop factor means that the 6×9 medium format sensor is larger than the 35mm sensor. A lens on a 6×9 camera will have a wider angle of view compared to the same focal length lens on a 35mm camera.
3. Calculate the Equivalent Focal Length: To find the equivalent focal length for a 35mm camera, multiply the focal length on the medium format camera by the crop factor. If you are using a 50mm lens on a 6×9 medium format camera, you calculate the equivalent focal length for a 35mm camera as follows: Equivalent Focal Length = 50mm x 0.4 = 20mm.

This calculation shows that a 50mm lens on a 6×9 medium format camera provides a field of view similar to what a 20mm lens would provide on a 35mm camera. Therefore, the 50mm lens appears “wider” on the 6×9 format than on the 35mm format due to the larger size of the 6×9 sensor.

Real Example

I use Fuji GW690 II and GSW690 II cameras with 90mm and 65mm lenses respectively. If I wanted to know the approximate focal lengths of these cameras as compared to a 35mm camera, I would perform the following:

To find the equivalent focal lengths on a 6×9 camera compared to a 35mm camera, we use the crop factor we previously calculated, which is approximately 0.4 for the 6×9 format. This crop factor helps us understand how the field of view compares between the two formats.

Here’s how you can calculate the equivalent focal lengths:

1. For a 65mm lens on a 6×9 camera:
   Multiply the focal length by the crop factor to find the equivalent focal length on a 35mm camera.
   [ 65mm x 0.4 = 26mm ]
2. For a 90mm lens on a 6×9 camera:
   Similarly, multiply the 90mm focal length by the crop factor.
   [ 90mm x 0.4 = 36mm ]

So, on a 35mm camera, a 65mm lens on a 6×9 camera is equivalent to about a 26mm lens, and a 90mm lens on a 6×9 camera is equivalent to about a 36mm lens. These calculations show how the larger sensor of the 6×9 camera affects the perceived field of view of lenses when compared to a 35mm camera.

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Why do my medium and large format images feel wider than the images on my 35mm camera?

There are several reasons why images from a medium and large format cameras feel wider than their equivalents taken with a 35mm camera, even when comparing lenses with equivalent focal lengths:

1. Larger Sensor Size: Medium and large formats have a significantly larger image area compared to a 35mm camera. This larger size captures more of the scene for the same focal length, resulting in a wider field of view. Therefore, a lens on a 6×9 camera shows a broader perspective compared to the same focal length lens on a 35mm camera. I will stick with the 6×9 medium format vs. 35mm for the rest of the explanation for illustration purposes.
2. Crop Factor Effect: The crop factor between 6×9 and 35mm formats (approximately 0.4) indicates that the medium format’s field of view is wider. When you use a lens with a given focal length on a 6×9 camera, it yields a wider angle of view than on a 35mm camera. Thus, a 50mm lens on 6×9 medium format behaves like a much wider lens on a 35mm camera, making the image feel wider.
3. Perspective and Composition: The larger format encourages a different approach to composition and perspective. Photographers might get closer to their subjects or choose different angles, enhancing the sense of width and space in the images.
4. Depth of Field: Larger formats also have a shallower depth of field compared to smaller formats at the same aperture and field of view. This can make the background more blurred, emphasizing the subject and making the space feel more expansive.

In summary, the larger sensor of the 6×9 medium format camera captures more of the scene at the same focal length compared to a 35mm camera, resulting in images that feel wider and often more dramatic in terms of spatial representation.

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Angle of View Calculation

Yes, the angle of view (AoV) for each format can be computed using the focal length of the lens and the sensor or film dimensions.

The formula to calculate the angle of view is:

where:

• ( d ) is the dimension of the sensor or film in the direction of interest (width, height, or diagonal),
• ( f ) is the focal length of the lens,
• ( arctan ) is the arctangent function.

This formula gives the angle of view in radians, which can be converted to degrees.

To compute the angle of view for each format, you need to specify a focal length. For simplicity, we could use the same focal length for each format to see how the angle of view changes with the size of the sensor or film.

Let’s calculate the angle of view across the diagonal of each format, assuming a focal length of 50mm as an example.

Using a 50mm lens for comparison, the angles of view across the diagonal of each medium format are approximately as follows:

1. 6×4.5: 73.74 degrees
2. 6×6: 80.63 degrees
3. 6×7: 85.35 degrees
4. 6×9: 94.49 degrees
5. 6×12: 106.60 degrees
6. 6×17: 121.97 degrees

These calculations show that as the size of the film or sensor increases (from 6×4.5 to 6×17), the angle of view also increases for the same focal length. This means that a 50mm lens provides a wider field of view on larger formats compared to smaller ones.

Focal Length Equivalent Chart

This chart helps you quickly compare the horizontal angle of view of lenses with focal lengths from 35mm to 1200mm format from 6×4.6 through 12×20. The focal lengths are not perfect, but serve as a quick reference when you need to compare focal lengths between various formats.

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Angle of View Chart

The angle of view was measured from the actual exposed aria of the negative whenever possible. This is why a 6×12 and a 4×5 have the same position. (120mm is the actual exposure with of a Fidelity cut film holder).

Please note that while a lens may cover the horizontal angle of view given in the chart, coverage is necessary for the diagonal angle of view. These charts are intended to aid in lens focal length selections. The coverage of the lens and the movements available with any given lens are entirely different matters that I hope to address in the future.

This chart helps you compare the horizontal angle of view of lenses with focal lengths from 35mm to 1200mm and formats from 6×4.5 through 12×20 ULF to that of a 35mm camera.