ARRI Tech Talk: ALEXA LF (Large-Format) Explained

ARRI Tech Talk is web-series that is focused on ARRI cameras, workflow, technology, and more cool stuff. The sessions are short, most interesting and yet simple to understand. Take a look at the chapters about the ALEXA LF presented by ARRI LF Product Manager Marc Shipman-Mueller.

ALEXA LF (Large Format) Sensor

This chapter is an introduction to the ALEXA large-format sensor which was developed due to the demand for large format “look” and the success of the ALEXA 65.

It’s important to mention that the ALEXA 65 is a huge sensor (three times big than the super 35 sensors) and thus it’s a rental-only product, but the ALEXA LF (“smaller” sensor) is a sale product if you can afford it for almost $100,000! 

The definition of LF

Take a look at the screenshots below which demonstrate the difference between sensors sizes:

It’s important to note that the LF sensor shares the same type and size of photo-sites, therefore, larger sensors have the privilege of more photo sites which leads to many advantages like cleaner image and lower noise levels. 

The ALEXA LF sensor is a 4K sensor

This sensor is slightly larger than full-frame sensor and can be operated in one of three modes which can be recorded using ARRIRAW or ProRes.

In order to maximize and utilize the whole sensor, one must record in Open Gate mode, which means that you record all that the sensor sees. However, in order to get the entire image, a large format lens must be used, because LF lenses own the abilities to cover the entire sensor. More information about lenses covering the sensor and lenses that have the compatibility with the LF format is in the video below.

The chapter is talking about other modes but we won’t cover them, however, you can explore them in the YouTube videos below.

ARRI Lens Illumination Guide (LIG)

Furthermore, the chapter refers to a cool online tool named ARRI lens Illumination Guide, which allows you to choose the camera, lens, T-stop, and verify how much sensor is covered by the lens. You should definitely check this tool BEFORE you choose your lenses, especially when shooting in the large format with super 35 lenses. This is crucial to eliminate vignetting.

For more info, check out the full video below: 

Large-format image

The other chapter talks about large format imagery, and what it grants us, filmmakers.

Recently, Large Format (LF) has gained significant popularity among filmmakers due to its unique artistic characters.

This chapter focuses on the characteristics of the large format sensor.

The LF sensor is twice the size of the super 35 sensors, but with the same photo sites, it means there are significant advantages regarding noise. It produces less noise but with the same unique image quality that ALEXA cameras own.

LF advantages

• Less noise derived from the larger number of photosites, as explained: ISO 16,000 on the ALEXA LF is equivalent to ISO 800 on the ALEXA Mini.
• More bokeh when using longer lenses.
• For the same angle of view on LF vs super 35 (assuming there is no change in the T-stop, shutter angle and distance), you will have to use longer focal lenses, which means you will get more bokeh  since the factor is 1.5 == > you see 1.5 more in LF than in super 35, thus you will get a shallower depth of field, and faces will look better due to compression.
• LF allows more visual compression (in general – depends on what you would like to achieve visually). You can get closer to your subject without distortion of the faces when using longer lenses.

Watch the relevant chapter below: 

Final thoughts

To sum it up, we can say that a large format is not only about depth of field, compression, and bokeh. It’s also about better dynamic range, better picture quality. It also can be used as an amplification of movements (but this is a discussion for another article).

I am convinced that LF is here to stay. The main disadvantage here is that these sensors are expensive…. VERY expensive.

Have you been shooting LF before? Let us know your insights in the comments section below!