Camera kits

Full Frame and S-35 - Creative and Technical Differences

Introduction

Film making has always had ‘pinch points’ of innovation, some of them more successful than others and in recent history more often than not driven by the retail thrust to sell more TVs- HD, 3D etc.  Mostly these modifications or improvements have an emphasis on an upscale in quality to tempt the consumer to upgrade their hardware or VoD packages and of course this means the origin of the content must also have been ‘upscaled’ to deliver on the retail promise. We have seen the advent of digital sensors replacing film and then HD sensors and then 4K and 8K and so on and whilst the increase in resolution (more pixels-more detail and colour subtleties) has been important, manufacturers have also started to release larger size sensors to not only accommodate the increased pixel counts but to allow the film maker to utilise the benefits of a larger sensor. These larger sensors are known generically as Full Frame (FF) and this article will try and explain the differences between that and Super 35mm size sensors and what the advantages/disadvantages the FF world can offer along with some description of what the different cameras can achieve.

 

Dimensionally Challenged:

Both Super 35mm and Full Frame are not new terms or concepts in fact they are older than most of us and both are derived from film terms. Before we start however it is important to clarify one parameter that will be used a lot on this piece and that is aspect ratio. An aspect ratio does not define the size of a sensor it is the fixed relationship between the horizontal and vertical axis and could be any size physically. And so the most commonly used aspect ratio ( that of our TVs) is 16:9 (1.78:1) but it can be used on any size sensor from 2/3rds size chain cameras up to Alexa 65mm and IMAX-which is a massive postcard size picture (or frame) compared to the B4 cameras but importantly the aspect ratio is exactly the same. Aspect ratio is a means to define the ‘look’ of a piece but sits on top of the actual dimensions of the sensor being used so when you see the term ‘for a given aspect ratio’, it means the pictures match in terms of the framing box but do not necessarily match in terms of area/size of that box and this is an important distinction when explaining FF.

                                                

Super 35mm

A term derived from film that has several parts to understand. Firstly motion picture film has used the same basic principles for nearly 100 years and that is that the film travels vertically downwards through an exposure window called a gate and each picture is moved on by four perforations (Bell & Howell pitch for the geeks). The picture again could be any aspect ratio but it had to be constrained by the fixed width of the film at 35mm and by the need to allow for magnetic soundtrack on the printed film which meant that the optical centre of the film was offset to accommodate the strip needed for the soundtrack. So the more widescreen the aspect ratio used the smaller the physical height of the picture (remember the horizontal is fixed by the size of the film and the soundtrack strip) and as the vertical dimension reduces to create a pleasing aspect ratio then more surface area of film is not being used and therefore the resolution is lowered (effectively less film pixels if you like). The anamorphic process was introduced as a way to counter this reduction in quality whilst delivering a widescreen aspect ratio but more of this later. The ‘Super’ in Super 35mm refers simply to the removal of the soundtrack safety zone and an optical re-centre to the middle of the piece of film. The point of this is that the horizontal dimension increased (more pixels) so ‘for a given aspect ratio’ the physical area used was increased and therefore the quality of the image was greater as more of the vertical could be utilised. Dimensionally there is some variation on 16:9 Super 35mm sensors but they are all essentially derived from the size a 16:9 aspect would be when applied to the four perf 35mm wide, with no soundtrack strip, piece of film.

 

Full Frame

Image result for super 35mm vs full frameNowadays is a bit more of a generic ‘catch all’ phrase but again it does have a fixed dimensional history based on 35mm film. In SLR stills cameras the same 35mm film as movie cameras was (is) used but with one major distinction- the film in an SLR travelled horizontally. The film was pulled along at 8 perfs per shot but because the aspect ratio was laid on East-West as opposed to the North-South, the image size for a given ratio was considerably larger meaning that a far greater area of film (pixels) would carry the image and therefore the quality would be higher. The aspect ratio usually found in SLRs was 3:2 (1.5:1) with an actual measurement of 36x24mm but in DSLRs you have the ability to create a more popular ratio such as 16:9 with the benefit that the image size is greater than that of the movie camera. So Full Frame cameras basically emulate a stills camera size gate (sensor) where the film has enabled a much larger surface area by travelling sideways instead of vertically. There are variations on this theme that need to be considered as they will crop up in the camera section.

Vistavision again is not a new term but has been revived chiefly by RED on its ‘Monstro’ sensor and again was based on process designed to increase the quality of a piece of film by increasing its physical size. So a Vistavision film camera took the East-West travelling concept of an SLR and turned it into a movie camera able to run at 24fps but crucially with an 8 perf pull across allowing for a box of 36x24mm to be exposed. The advantages were a much bigger picture, therefore higher https://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/IMAX_comparison.svg/220px-IMAX_comparison.svg.pngquality as more film grains were used per frame to present a smooth fine grain image which was extremely useful for visual effects and it’s the same advantage in today’s digital cameras. The disadvantage in film terms was that it used twice as much film as a vertical pull down camera and so was relegated to the visual effects world fairly early on in its lifetime.

Other variations to note are the Alexa 65 which is based on a sensor size emulating 65mm film travelling North-South and IMAX which emulates 65mm travelling East- West, both of which are therefore postcard size pictures. So it’s all very well having these big sensors but we haven’t yet looked at the fundamental requirement of these big things, which is a lens that can deliver an image big enough to cover them.

Lens Stuff

We have discussed lenses at length before (ref here) and so will try not to get side tracked too much and stick to the FF bits. All lenses produce an upside down circle of light containing an image of what is in front of them and that image via a set of precise mounts and distances falls onto the sensor. The ‘you had one job’ bit of this for the lens is that the circle has to be big enough to cover the box it is sending an image to. If the circle is not big enough then you will end up with vignetting or a circular shadowing around your image. The reason for the circle being as close to box size as possible means that the lenses can transmit  as much light energy as possible and not dissipate this by having an over large circle. Indeed when the jump from 35mm to Super 35mm occurred, lots of lenses including Zeiss SuperSpeeds or Speed Panchros for example had (have) an exit circle that doesn’t quite cover that new bigger box.

Full frame therefore needs a big circle which is why we need FF lenses to cover but just as with aspect ratio we need a quick de-bunk before we move on. A 25mm lens is a 25mm lens is a 25mm lens. Putting a 25mm lens onto an FF camera does not alter the focal length of the lens, it is still a 25mm lens and it has the same field of view and depth of field that it did when you last put it on a Super 35mm camera because…it is a 25mm lens. Those of us who come from a movie background found that working with a Canon 5D for instance was weird because all the lenses appeared to wider than we were used to and people coming from a stills background found that digital movie cameras were ‘cropping’ compared to the DSLRs they were used to. Both are right. A 25mm FF lens on a Super35mm sensor will ‘feel’ just like any other 25mm because the box is collecting all the image info it needs and is ignoring a significant proportion of the circle. A 25mm FF lens on an FF sensor will provide a wider image because all of the bigger circle of image is now being used. The bigger circle is transmitting a greater quantity of light rays from around the edge of the field of view which is why the image appears wider than on the Super 35mm version.

Anamorphic lenses are (have) generally been designed to output their image oval onto Super 35mm size sensors so you will get strong vignetting if trying to use these on an FF sensor. Some manufacturers are beginning to produce lenses that do cover bigger sensors (Cooke’s 1.8x squeeze for instance) but these are for high end only and specifically for sensors with a 3:2 (1.5:1) aspect ratio to maintain the correct de-squeeze geometry.

Telecentric lenses are those that have two special qualities in relation to FF-telecentric refers to a greater quantity of light rays leaving the back of the lens in a parallel fashion which benefits the picture by allowing more even image illumination (within the image circle) and removing ‘hot-spotting’- where the centre of the picture is brighter than the edges because the light rays are travelling further and therefore slightly dimmer.  The second advantage is that in a telecentric lens the magnification of objects is more even including those outside of the focal plane and this is part of the perspective flattening process previously discussed which means we are now entering into the creative use of FF lenses and sensors so we need a section heading.

 

 

 

 

 

Creative Use of FF Lenses and Sensors:

So now we have cameras with larger sensors and a bunch of lenses that can cover them and we understand how and why it works so the next question must be what are the benefits and what if any are the disadvantages? The creative arguments for using FF should maybe start with most obvious and technical. If you are using a larger sensor then you will be acquiring images beyond the VoD 4K benchmark, so for example the Sony Venice will be in 6K, the RED Monstro/Ranger in 8K and the Alexa LF scraps in at 4K. So you already have an upscale in terms of resolution and detail and even if there is a downscale to HD later on there will be a latent extra quality to the picture and of course future proofing of the material. The downside (depending on the codec used) will be an increase in storage requirements and some NLE platforms and hardware may struggle to play back in full res but that will soon solve itself as it always does. However the biggest difference (and why we have created some images to demo this) is the change in perspective and therefore depth of field. We have seen that ‘for a given aspect ratio’ and the same focal length lens and iris setting, the image will be wider on an FF sensor and as it’s not ever about just being wider, what does this mean in practice? You don’t want to be wider you want the same image you had in your head so the aforementioned 25mm is too wide so you have to change lens to a 35mm or even 40mm to give you the picture you wanted. So by doing that, two things have happened-firstly if your iris setting is the same then your depth of field has shrunk ( if you had changed to a 50mm it would have halved) and secondly the perspective on the image has flattened-objects in the distance will feel a bit closer and a bit softer because of the longer focal length. Now this is sort of the same argument as for using anamorphic lenses because using a 2x squeeze system requires double the focal length for the horizontal squeeze so a 25mm image on Super 35mm ‘for a given aspect ratio’ would be 50mm on anamorphic to match shot size. So the upshot is that your lens grammar needs to shift upwards by one or two focal lengths in order to achieve parity with what you are used to in Super 35mm terms and therefore shallower depth of field and flatter perspectives will be the benefits. The potential downside is as usual with shallow depth of field in that there will be a struggle to hold onto focus. And so as you can see from the images below, the FF versions seem to involve the space around the subject in a more engaging way-it’s a subtle but telling shift in storytelling and it may be for you.

Creative uses inevitably involve the manipulation of technical parameters to achieve the desired effect and using FF as a base increases this relationship to ‘11’.

 

What Camera Does What?

 

 Arri Alexa LF and Mini LF: Provides a 36.7x25.54mm (1.43:1 aspect) sensor that is 4K (4448 pixels in the horizontal plane) when being used in LF mode. Lenses that cover FF are required to shoot in this mode and indeed Arri have created the LPL mount with a 44mm depth for some of their lenses but you can use an adapter that brings it back to PL with a 52mm depth. The LPL mount allows for a more telecentric design of lens as the back elements of LPL lenses can be physically wider to facilitate more parallel light beams therefore reducing hot spotting and increasing even magnification. Any other mode other than full LF on this camera is the same as a normal Alexa or Mini.

 

RED Monstro (Ranger) & Gemini:  The Monstro sensor is 40.96x21.60mm (1.9:1 aspect) and is at 8K resolution in that format. As you can see from the size of this sensor that it is possible to cover a myriad of aspect ratios and resolutions including maintaining a VoD qualifying 4K whilst shooting 2x squeeze anamorphic. The Gemini sensor was built to have special low light capabilities and whilst it is not FF, coming in at 30.72x18mm (1.7:1) it is slightly larger than Super 35mm when being used in full 5K mode and therefore has a potential need for FF cover lenses particularly at the wider end.

 

Sony Venice: Is a true 36x24mm (1.5:1 aspect) size sensor when in 6K mode. It is truly versatile as the 4K mode is Super 35mm size and will therefore accommodate any vintage or anamorphic lenses whilst qualifying on the usual VoD specs…in Sony’s words it is ‘aspect ratio agnostic’.

 

Canon C700 FF: Has a sensor that is 38x20mm (1.9:1 aspect) in 5.9K mode..A slightly overlooked camera platform as it was a bit late to the 4K party and didn’t really move on from C300mkII spec so folk just carried on using that instead. It has a new FF guise now so may well be a channel to consider in conjunction with some medium cost lenses (Canon Sumire’s for instance) for a cost effective foray into the FF world.

Sony A7s & Canon 5D MkIV: Are both 36x24mm FF sensors but reduce the size according to the video codec needed, but if you have been using these camera you are well aware of what FF looks and feels like.

Canon C500 Mkii

Is a new addition to the FF range an promises much

 

FF Lenses:

High End: Zeiss Supreme, Arri Signature, Leica Leitz (primes & zooms), Cooke S7, Fuji Premista.

Mid Range: Sigma Cine, Tokina VV, Celere, Canon Sumire.

Entry Level: Any Canon EF lens.

 

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