Camera kits

Capturing 2:1 Anamorphic with Alexa LF and S-35 lenses

In a nutshell, according to ARRI, shooting on 35mm format anamorphic lenses for a 2:1 aspect ratio at 2,880 x 2,880 with Alexa LF is suitable for 4K and has been cleared by Netflix as an acceptable solution.

The reasons for doing this are easy – 2,880 x 2,880 has the same number of pixels as 3,840 x 2160 – try it and you will see that this is correct. 

Nextflix et.al do not specify the native code, whether RAW Prores 4:4:4 etc, suffice to say that this needs to be a qualifying version of Prores, which to my knowledge is most of them

In case you are interested, Netflix has approved ARRIRAW, ProRes 4444 XQ, ProRes 4444 and ProRes 422 HQ for use with ALEXA LF.

This sounds great, as it means that Alexa LF can work with S-35 anamorphic lenses and record 4K, which is exactly what our clients will want to do and shoot in the hallowed 4K format without compromise and without having to choose large format (or full frame) spherical lenses.

So, I wanted to find out whether it might be possible to achieve this using Alexa Mini, Alexa XT open gate or other existing pre-LF variants of ARRI LF…

However, the devil is in the detail, so upon investigation, I found out

Two things.

 

  1. 2880 pixels height is VERY high and that some S-35 anamorphic lenses do vignette a bit. 

Whilst I prefer exacting language and try to articulate myself carefully, the truth is that the widest lenses will compromise the cinematographer, so I don’t think that this is that useful.  See below.

Whilst the longer lenses will fully cover without issue.

 

  1. Next, could conventional Alexas with 3.2K open gate achieve this coverage?  

 

Sadly no, the Alexa 3.4K open gate covers this at the widest point but the height is compromised and ARRI advise me that in their tests, a maximum vertical pixel count of 2,202 is possible.

So in English, this means that whilst 2,880 x 2880 with a suitable set of lenses would satisfy 4K anamorphic capture, this only really works with

1. Acquiring on Alexa LF and using

2. Full frame anamorphics, unless the cinematographer has assured themselves of the suitability of given lenses at all focal lengths at this image size. However, as you can see from the images supplied by ARRI, all Master Anamorphics cover from 28mm onwards, though the 28mm is a bit close.  ARRI have advised me that the Cooke Anamorphic/i lenses have slightly greater coverage, though I have not confirmed this myself.  It is our expectation however, that cinematographers will demand that the desired sensor size is covered adequately and without compromise.

However, if you can find lenses which keep the cinematographer happy, shooting with 2x anamorphics and Alexa LF, you can achieve 4K capture in a 2:1 aspect ratio which satisfies the exacting standards of Nexflix.

Meanwhile, we are all waiting for the next sensor which ARRI will bring to the market with the next generation of 4K/6K/8K Alexa Mini...  Though on this, ARRI have not been too forthright about their plans.

Barry Bassett

VMI, July 2018

 

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