Size Matters

Size Matters

Approximate 7 minute read

One of the questions I often see posted from Church Tech people, particularly regarding new video camera purchases or recommendations is, “I am thinking about getting new I-Mag or sermon capture cameras for my church auditorium. Will the (insert: large sensor camera model du jour) work well in this application?”

I guess the first question is, how are we defining “a large sensor camera?” For the sake of this article I am defining a large sensor camera as any camera who’s imager is greater than 11mm diagonal (or in other words anything larger than a 2/3” HD video imager, which is historically the de facto HD broadcast multi-camera standard).

Included in the large sensor camera category might be the Black Magic Pocket Cinema Camera (which is 14.32mm diagonal or 30% larger than 2/3”), Black Magic’s Cinema Camera (18.09mm, 64% larger), the Black Magic URSA broadcast (14.98mm, 36% larger however will crop to 11mm in some instances), the Black Magic Studio camera (14.32mm, 30% larger), various Micro 4/3rd cameras like Panasonics AG-AF100 & GH1 (21.64mm, 97% larger),  Super 35mm Digital cameras ranging from Sony’s PMW-F3 or NEX-FS100 all the way up to Arri Alexas & REDs (31.11mm, 183% larger), and photographic full frame DSLR 35mm, like the Canon’s 5D (43.21mm, 293% larger than 2/3”).

So why would anyone want a larger (than 2/3”) sensor camera anyway?

Well for commercials, feature films and some episodic TV – all being scripted content – the reason many Directors of Photography prefer a large sensor camera is that the larger sensor size makes it easier to obtain a shallow depth of field.  Shallow depth of field can be one tool a cinematographer uses to force the viewer to pay attention to certain things in a frame while disregarding other things in a frame.  Shallow DoF along with shooting at 24 (23.98) frames per second, a 1/48th (or expressed differently, a “180 degree”) shutter, and particular gamma curves all help digital cinematographers achieve a “film-ick” aesthetic.

Unfortunately large sensor cameras create substantial challenges when used for single or multi-camera capture of a sermon, live during a church service. There are many reasons why this is so. Here are five important ones:

Shallow DoF is Not Always Our Friend:

As stated, large sensor cameras lend themselves to having a very narrow depth of field which can make them a valuable tool for scripted narrative content however this same capability makes them problematic for live multi-camera uses.

Shallow depth of field shooting, although potentially beautiful is dependent on the talent “hitting marks” so the camera operator, or more typically in the commercial and feature-film world – a First Assistant Cameraman (1st AC) – can pull focus based on the known physical measurements between the “film plane” of the camera and the talent’s known location. In a typical sermon or church application the preacher moves around the stage (or behind a lectern) as they will, making it difficult or even impossible for a camera operator (even a professional one) to maintain razor sharp focus when shooting at wide apertures.

Here is an example: a super35mm sensor camera at 50’ subject to talent distance, shooting a MCU (Medium Close Up) field of view, with (0) no gain, no shutter, and at F4 aperture will have a razor thin depth of field of only 6.7 inches. That means if the subject you are shooting (the pastor/teacher) moves closer or further from the camera by 3.5” they will perceptively go out of focus!

Such a narrow DoF makes it problematic for the camera operator to maintain sharp focus for extended periods of time. This is why on live multi-camera entertainment productions that use large sensor cameras and wide aperture settings achieving a shallow depth of field, there is always a First AC pulling focus for the professional camera operator. That’s two expensive professionals per camera.

Most churches however find it difficult to recruit just one volunteer to operate a camera let alone two. Furthermore, focusing at 6.7” DoF (as in my example above) is well beyond the skill level of most church volunteers even given a second separate person dedicated to only operating the focus barrel on the lens.

So then what do many churches do if using large sensor cameras for live multi-camera production?

Answer: they stop down the aperture to deepen the DoF. For example at F8 the same super35mm sensor camera (at the same distance, FoV, etc.) will achieve a 13.5” depth of field – still difficult – but more manageable for the operator(s) than 6.7” DoF.

That’s better, however in doing so they’ve made their image substantially underexposed (darker) due to cutting the amount of light getting to the camera’s imager by half, and then by half again!  The net result of stopping down in this way is that you will need to either (a) light the stage at 200% higher illumination levels than you would at F4, or (b) you will need to add gain/ISO which increases noise (degrades the image), or (c) you will need to reduce shutter (if you had any dialed in to begin which in my hypothetical example above, there was none), which then may potentially cause motion artifacts and will certainly impact the cinematic aesthetic – the primary justification many cite for shooting with a large sensor camera in the first place.

Most churches can produce only so many lumens on stage to achieve the illumination levels required from stopping down. If the stage light levels increase 200%, projection may also need to become brighter, as may house lighting, to balance the total scene. So then one may rightly ask, why accept a 200% lighting (or noise, or motion aesthetic) penalty just to achieve a meager < 14” DoF, all caused by the decision to shoot with a larger sensor camera?

For comparison purposes, with the same exact shooting details as that above including distance between the camera and talent, lower stage lighting levels, field of view and aperture (f/4), a 1/2” sensor camera will produce a depth of field of almost thirty inches! Even a 2/3″ camera would achieve a twenty inch DoF.  Both of these would be manageable for the average volunteer camera operator while still being shallow enough that the background set in the scene may be slightly out of focus directing the viewers attention to the preacher/presenter who is continually in sharp focus.

Availability of Cost Effective Long Focal Length Lenses:

As discussed, the large sensor format was originally created for content that is scripted. On these (feature films, shorts, commercials) the camera is generally much closer in distance to talent than the average church which prefers to put cameras in the back of the house as not to impede sight-lines for the congregation. It is often difficult to find cost effective lenses with adequate long focal lengths to achieve tighter fields of view for use in live church service environments.

For many churches looking for cameras for live multi-camera production, streaming, Imag; a tight-follow camera at 50’ (or more) from talent is now quite common. However to achieve a MCU (medium close up) with a super35mm camera at this distance will require a whopping >420mm lens!!! The majority of PL mount digital cinema zoom lenses max-out at about 290mm focal length and even then can cost upwards of $75,000 USD! There are some greater than 290mm focal length PL mount zoom lenses manufactured, however costs increase dramatically even over that described.

One option sometimes employed at churches with large sensor cameras is to opt instead for still photography lenses, however none of these have adjustable back focus which means they cannot track (meaning, stay in) focus during a zoom or a truck move. Each time a still photography lens focuses, that focus is accurate for only one focal length.  Additionally, still photography lenses have innate design limitations which cause them to be less than easy or inexpensive to accommodate professional rear operator zoom/focus controls to.

Zoom Ratio:

The third consideration is that most zoom lenses manufactured for larger sensor cameras, whether originally manufactured for DSLRs or $100,000 dollar PL mount digital cinema cameras, is they have relatively small zoom ratios. That means the zoom range – from maximum wide to maximum telephoto (compared to broadcast lenses) – is very small.  While this makes perfect sense for scripted content where you can change lenses in between takes to achieve various focal lengths that may be needed, most church-techs cannot halt shooting to change lenses in the middle of a sermon.

Here are some examples: a Canon EF 24-70mm has a zoom ratio of only 2.9x. A Canon EF 70-200mm also has a zoom ratio of 2.85x. Even PL mount cinematography lenses like the $75,000 Angenieux 24-290mm (a powerful lens by cinematography standards) has a relatively small zoom ratio of 12x, compared to 2/3” or 1/2” “standard” lenses which are now offered as 20x, 22x, or 24x. The relative value of broadcast lenses becomes apparent. Even the least expensive broadcast lens models for 1/2” sensors have 14x – 16x zoom ratios. And you always have the option (if money is no object) to buy a 2/3” lenses all the way up to 107x!!! That means you have more choices if not shooting with a larger sensor camera, and choices coupled with readily available sales and rental inventory can result in improved economies day to day and for special events at your ministry.

Accessories:

Fourth, larger sensor cameras and their associated lenses typically do not allow you to easily or inexpensively use standard broadcast lens accessories. Some lenses made for larger sensor cameras do not have servo zoom motors and therefore there is no easy and inexpensive way to connect camera operator rear zoom (or focus) controls. For example, a Preston Microforce zoom control and Heden motor (commonly added to a PL mount cinematography lens) can cost more than a whole Black Magic Cinema camera!

CCU Functionality:

Fifth and lastly, many (but not all) of the larger sensor cameras in this class do not have basic multi-camera functionality: (i) remote iris, (ii) remote live paint/detail/gamma/pedestal control, (iii) CCU/RCP/MCU capability, (iv) remote power from a base station, (v) two-wire RTS/Clear-com compatible communications via the camera cable, (vi) tally, (vii) return video and (viii) prompter.

Because (many) of the larger sensor cameras do not have traditional remote paint capability, color matching them (in a live multi-camera production environment) is problematic or expensive. Some camera manufacturers address this deficiency by opting instead for using a color corrector in the switcher however this is not the same thing as having a camera with remote paint capability.  In general, color correction (not built into the camera) may induce noise and/or latency.

If a larger sensor cinema camera has a remote paintbox spigot, it may be able to be used with a 3rd party CCU fiber system like Multidyne’s Silverback or Telecast’s (now Grass Valley’s) Copperhead, however these type of systems tend to cost about $20,000 USD (each camera) in addition to the cost of the camera head, viewfinder, lens, camera operator controls, tripod, and video shader’s controller, etc.

Summary:

Despite the foregone conclusion that I am just “anti” larger sensor or cinema cameras, the truth is quite different.  The fact is that at least on a professional level, I shoot with large sensor or a mixture of larger/smaller sensor cameras for live multi-camera capture quite often.  It is exactly this experience which makes me cautiously pessimistic about shooting with large sensor cameras in a church live multi-camera environment.  For many churches, the technological sweet-spot for multi-camera Imag or broadcast will be with 2/3″ – 1/3″ sensor cameras.

The original version of this post was published December 20, 2013.  It has been updated and reposted here.

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