Medium Format Cameras

Phase One A/S is known as market leader in the area of medium format cameras. But what does medium format actually mean and where does it come from?

Phase One has a long and rich history in Professional Photography, where 'medium format' is widely adopted, but I like to explain in a nutshell for non-photography experts in my network. Especially since we are addressing more markets and industries outside of photography.

***Note that this is just a high-level overview and there is a lot more to it***

Medium format camera's go back to the early 20th century and use film to capture scenes. As the name suggest, it relates to the size of the film being used. It is everything between 35mm (Full Frame) and 4x5 inch (Large Format).

In the below comparison you see several sensor sizes compared, varying from a standard FHD (motion video) sensor, to APS-C, Full Frame and Medium Format from Phase One.

In analogue times, medium format (and smaller) was done with film rolls, while for most large format imaging, sheet film was used (i.e. 1 new sheet per image).

The company Leaf (now Phase One A/S) was the first company in 1991 to introduce a commercially available, digital scanning device (digital back), to replace the film roll on the backside of a 'system camera'. A system camera has exchangeable lenses, bodies and backs, which allow a person to upgrade the camera without the need to invest in a complete new camera.

In the early days Phase One A/S primarily focused on the innovation of digital backs, but through a series technology breakthroughs and iterations, later also introduced own digital (medium format) system cameras.

Today Phase One produces 2 different cameras (XF and XT), which are known for being worlds best cameras and are used by the most renowned photographers of the world.

So how did Phase One started making dedicated aerial cameras?

The past 2 decades there was a highly increasing demand for creating digital maps e.g. for navigation systems. Phase One cameras were used because of their efficiency and combination of a large sensor, high resolution and overall image performance.

Geospatial Mapping or Digital Cartography is (and I quote) “the process by which a collection of data is compiled and formatted into a virtual image”. This eventually result in a 2D or 3D map.

Again a series of innovations have changed the standard digital back of a photography camera, into a medium format camera specifically designed for airborne platforms (think of radiometric lens calibration, input for GNSS & IMU for high precision geotagging, synchronizing a multi camera setup, local storage and special imaging workflows).

So while you maybe are not aware, but when you use your navigation system or look up a location in an online search engine, it is likely you are using data that was created using Phase One camera technology.

At the moment we provide complete aerial mapping solutions (PAS series) as well as the core imaging camera components (iXM series) to other leading companies, who build their own systems for mapping or security applications.

Given their compact form factor, iXM cameras are also a great fit for many drone platforms.

So… Medium Format…

The essential benefit of medium format digital sensors are its large size, which is beneficial for 2 main things:

- High resolution

- Large pixel size

When using a medium format sensor for aerial imaging, you are able to cover a much larger ground surface compared to smaller sensors.

At a fixed flying altitude and using a fixed focal length lens (i.e. no optical zoom), the ground surface will be fixed.

The higher the resolution of the sensor, the smaller the pixel size on the sensor, the smaller the pixel size on the ground (known as Ground Sample Distance or GSD)

In summary: a smaller GSD will allow for greater details and greater digital zoom capability, while the large sensor still allow for a large ground coverage. This is beneficial for a lot of things like; more efficient mapping & inspection, increased situational awareness, documentation, improved actionable intelligence, larger and faster search and rescue missions, etc.

Contrary to smaller traditional motion video sensors using optical zoom, where you always have to chose between large ground surface (no details visible) or small GSD (but small ground surface).

?While pixel size on the ground (GSD) and pixel size of the sensor are related, they are not the same.

We may want a small GSD for greater detail, we like a bigger pixel on the sensor. Because the smaller the pixel size, the more we sacrifice in image performance in terms of sensitivity, signal to noise ratio (SNR) and dynamic range.

Sensitivity is primarily a function of 3 factors:

- Quantum Efficiency (how well photons can be transformed into electrons)

- Low noise (lower noise allow for higher analogue gain of the sensor)

- Most important: pixel size (imagine trying to capture rain drops (photons) in a large or small cup)

Also very important is that a larger pixel result in a larger full well capacity (the amount of charge that can be stored in a pixel before it is saturated). This is a very important aspect as it is essential for a higher dynamic range. A high dynamic range allow to capture more details in dark and bright area’s in the same image.

If you fly your mission during a sunny day, there will likely be a lot of bright areas, as well as darker shaded areas. It is important to be able to see detail both areas.

Phase One iXM cameras output raw images in 14-bit with a dynamic range of up to 84 dB.

?So in summary: Medium Format cameras provide the best of both worlds: a large ground coverage with small GSD for greater detail but without sacrificing in image performance.