About sensors' sizes

[Abdul Rahman Jamous]

The whole thing is so confusing, right now I'm literally puling my hair.

 

I was reading about anamorphic lenses so naturally I tackled the topic of sensors' sizes. But the thing is that when it comes to sensors' sizes, the internet is full of scattered information and honestly I don't trust them. So I opened the Arri website and found out that Alexa mini has a super 35mm sensor, but according to the manual of the camera the sensor size is 35mm!

Are super 35mm and 35mm sensors basically the same? or did Arri contradict itself?

[Dom Jaeger]

“35mm format“ is just a generalised description to differentiate from 16mm or full frame or micro 4/3 or whatever. 35mm these days (in a cine or video context) would mean S35.

Unfortunately every camera seems to use slightly different sensor sizes even within the generic S35mm category. Usually they are close enough to a standard that most lenses made for the format cover. A more accurate description of sensor size gives the diagonal dimension, which can then give you an idea of whether a lens will cover it, if you know the diameter of the image circle a lens creates. Different aspect ratios within the sensor recording area, and sometimes different frame rates or recording codecs can also use a smaller area than the full sensor.

The standard size of S35 is often given as 31.1mm diagonal, which is based on the full aperture of a super 35mm 4 perf film gate. But many S35 sensors are smaller than this, especially when shooting a standard aspect ratio like 16:9. For this reason many old lenses designed for standard 35 still cover most modern S35 camera sensors, at least within normal shooting modes rather than Open Gate for example. 

Anamorphic lenses only need a nearly square sensor area of 1.2:1 to achieve a final 2.40 aspect ratio, so the image circle is often smaller again.

See the different sensor areas used for various shooting modes on an Alexa Mini for example:
 

 So for example in anamorphic mode with 2.39:1 as your desired aspect ratio, the diagonal required is 27.55mm. Much smaller than the S35 “standard” of 31.1mm, and easily covered by any anamorphic lens made for 35mm since anamorphic was invented. 
 

[Satsuki Murashige]

The internet is your friend!

https://vmi.tv/training/useful-stuff/Guide-to-Sensor-Sizes-and-Lens-Formats
http://phfx.com/tools/formatCompare/

Traditionally, most cinema and video formats have been smaller than photography formats. If you come from a photography background, then you may consider 35mm format to be 36x24mm (1.50:1 aspect ratio). Digital cinema cameras have only recently caught up to this sensor size: Red Monstro, Alexa Mini LF, Sony Venice, Canon C700, etc.

Most of the earlier digital cinema cameras (like the Alexa Mini) were based on the motion picture 35mm format in order to be able to use the same lenses. Motion picture 35mm film uses the same film gauge as stills but usually runs vertically thru the camera rather than horizontally. Thus, the largest area these motion picture film cameras could use was about 24.89x18.66mm (1.33:1), often called Super35 4-perf, or Silent Aperture.

The 35mm Anamorphic film format actually uses a slightly smaller area horizontally (1.19:1), which when de-squeezed to correct for the anamorphic distortion expands horizontally by a factor of 2x to create a 2.39:1 aspect ratio. 

 

[Abdul Rahman Jamous]

Thank you very much, things started to make sense now

[David Mullen ASC]

In film terms, 4-perf 35mm is the classic standard and “Super 35” just means exposing the entire Full Aperture width rather than the slightly less wide sound aperture width (Academy/anamorphic/1.85 contact print). The difference is only about 2mm, 24mm versus 22mm. 
The Full Aperture of 4-perf 35mm is basically what was used in the Silent Era — 4x3 / 1.33 : 1. If you used all of this for 2X anamorphic photography, you’d have a 2.66 : 1 image once unsqueezed — so the anamorphic format doesn’t use the full width of Full Aperture, it uses the width of a sound aperture like Academy but the height of Full Aperture, more or less a 1.20 : 1 area to end up with a 2.40 : 1 image.  The Alexa sensor at its largest, Open Gate, is even wider than Super-35, but you don’t use it when shooting anamorphic on the Alexa, the area of the sensor used is very close to what is used if you shoot 4-perf 35mm film.

[Abdul Rahman Jamous]

It seems to me that I have to devote a whole day just to get a deep understanding of what has been said.

 

Thank you very much, all of you!

[David Mullen ASC]

Keep in mind that if you are using 2X anamorphic lenses and want a final unsqueezed image to be 2.40 : 1, then you are only going to use a 1.20 : 1 area of the sensor and most cameras have wider sensors than that, so it really becomes about comparing the height used to the 4-perf 35mm anamorphic format and to other sensors to determine things like crop factor / field of view.