According the Arri Press release:

“At the 2018 BSC Expo in London, ARRI has unveiled a complete large-format system that meets and exceeds modern production requirements, delivering unprecedented creative freedom while also being backwards compatible with existing lenses, accessories and workflows.

Featuring a large-format sensor slightly bigger than full frame, ALEXA LF records native 4K with ARRI’s best overall image quality. Filmmakers can explore a large-format aesthetic while retaining the ALEXA sensor’s natural colorimetry, pleasing skin tones and proven suitability for HDR and WCG workflows. Different sensor modes cover any deliverable requirement and versatile recording formats-including efficient ProRes and uncompressed, unencrypted ARRIRAW up to 150 fps-provide total flexibility.

Accompanying the ALEXA LF camera are 16 large-format ARRI Signature Prime lenses, ranging from 12 mm to 280 mm and fitted with the new ARRI LPL mount. While the Signature Primes exemplify state-of-the-art optical precision, they render organic, emotional images, gently softening and texturizing the large format. A fast T-stop of T1.8 facilitates shallow depth of field and the smooth focus fall-off gives subjects heightened presence in the frame.”

Arri LPL Mount
The LPL Lens Mount. A PL to LPL adapter is available to mount all your PL lenses.

The lenses intrigue me the most, so much that, I’m hoping there is a technical way RED can develop an LPL lens mount for DSMC2.  I can’t wait until NAB where I can see these lenses in person.

Arri LPL Signaure Series Lenses

The Arri Alexa LF uses the same sensor tech in the ALEV-III sensor.  We all know how amazing that sensor is, shooting a majority of motion pictures today.  This new camera takes the dimensions of two of those sensors and flips them 90 degrees to come up with the larger sensor.

As a Large Format camera, the Alexa LF sensor is larger that Full Frame, your S35 lenses won’t cover the whole sensor.  I’m not 100% on this bandwagon towards full frame.  Back when the Red One came out in 2007, it was a major breakthrough in both large sensor size but also resolution.  When the Canon 5D MK II came out, we had the ability for anyone to finally get a large sensor look.  However, I quickly found out that too many producers and directors were pushing for shooting on long lenses at shallow depth of field.  This created a look where focus constantly shifted in and out as DPs fought with the shallow depth of field and a small low resolution screens without focus tools.

I personally, love the S35 sensor size.  It allows me to use the lenses I love without fighting five inches of depth of field.  I suppose I shouldn’t hold that period against large format cameras, but instead embrace the ability to use new (and vintage) lenses designed for large sensors.

I still think the sweet spot for indies will be S35 for a long time to come, but each story has it’s own unique requirements.  That might be S16 film, s35, Vista Vision, or even 65mm.  With all of these amazing options available to us, it’s most important that we focus on the right tools to tell each story.