How the Phase One IQ4 XT Saved the Technical Camera
Though the DSLR-styled XF has always been the intended “primary” body for Phase One digital backs since its release, technical camera bodies from 3rd party manufacturers like Alpa, Sinar, Arca Swiss, and Cambo have also been available for years. These cameras are often favored by architectural and landscape photographers because of their parallax-free stitching and movement capabilities, as well as their arguably unmatched potential for image quality thanks to their use of remarkable large format style lenses from Rodenstock and Schneider Kreuznach. Exceptional though most are in terms of build quality, usability, and potential image quality, essentially all technical camera bodies share a fatal flaw: their lack of built-in communication between the digital back and lens.
The Need for Communication
Phase One digital backs rely on a “sleeping architecture” to reduce heat buildup which in turn reduces noise. This means that the sensor is receptive to light only when an exposure is about to be taken, and so it needs to know when an exposure is imminent to activate itself as well as how long the exposure lasts so it can shut itself down. In the past, CCD sensors were made available with a “zero latency” option which made the sensor active all the time. This allowed only a single signal to be sent to the digital back (duration of exposure), but in doing so greatly reduced battery life and increased heat/noise since the sensor was on all the time, and so was not a particularly good solution.
Cambo WRS 1600
Digital backs also require a “black frame” after almost every image, though this has been made somewhat optional and at the very least vastly improved in the IQ4 line. With a traditional non-stored black frame, after the initial capture the back will take a second exposure of a closed shutter. The amount of noise in the black frame is measured and used to reduce noise in the final photograph, improving image quality. The black frame is exposed for an equal amount of time as the initial exposure, thus doubling the time commitment for any given capture, (at least for the first capture; subsequent captures use the initial capture’s black frame until heat changes substantially or shutter speed or ISO is adjusted). More on this later.
Communication regarding exposure as mentioned above to the digital back is performed in the background when using a digital XF body, but in a traditional technical camera system this lack of communication creates problems and must be rectified by connecting at least one cable between the digital back’s multi port and the PC port on the technical camera lens’s Copal shutter. This makeshift method for allowing the shutter and sensor to speak to each other was effective, but cumbersome. Some cables required a two-step process (called two-shot cables), while other “oneshot” cables required a slow depression of an attached cable release to wake the back up. Pushing the plunger too quickly or forgetting a step while using a wakeup cable would result in an error which would need to be cleared on the digital back before taking another image. This additional work to simply capture an image was bad enough, but the cables would often get in the way during operation or get lost in transport, and were another point of failure during a shoot.
The Copal Shutter Problem
Electronic Shutter as Primary Capture Method
To further complicate matters, it was recently announced that the stock of new copal shutters, the shutters required for large format style lenses, has run out and new lenses would not include them in shipping. New lenses from Rodenstock would have to be paired with an aperture-only mount without a shutter at all, completely relying on the electronic shutter found in the IQ3 100MP and IQ4 digital backs, or the complicated/cumbersome Rodenstock eShutter which for many is a non-starter. Though for most uses the electronic shutter in the IQ3 100MP and IQ4 digital backs works just fine, it still is limiting in its inability to work in all situations since it can’t be used with a strobe and exhibits a substantial rolling shutter effect due to its ~1/60s readout time, preventing the static capture of large fast moving objects and creating issues for handheld capture. Even so, the electronic shutter in the IQ3 100MP and IQ4 line of digital backs did well to solve the issue of requiring communication between the lens and back since shutter speed is determined by the back already, but the issue of the black frame persisted.
Rodenstock Aperture Only Mockup
The Black Frame Problem
After a typical capture in an IQ3 or legacy digital back the black frame would occur automatically. When using a copal shutter in a technical camera this wasn’t an issue since the shutter would automatically close after any exposure and naturally pave the way for an automated black calibration. With aperture only mounts, there would be no darkness for an automatic black frame after an exposure. The electronic shutter still requires a physical object to prevent light from hitting the sensor to create a proper black calibration, and so it would be required to physically cover the lens and give the back the command to execute a black calibration after almost every capture. The black frame was necessary after almost every capture prior to the IQ4 line, and though a fast pre-recorded black frame is available in the IQ4 to prevent longer than necessary shooting times, creating black frames is still recommended for exposures longer than 1/10 as per the IQ4 manual to prevent single pixel noise.
Lens Cast Calibration
A third act to technical camera use involved LCC (Lens Cast Calibration) creation. Part of what makes large format style lenses able to render such fine detail across the frame is the close proximity of the rear element to the sensor. Unfortunately this close proximity creates a significant angle at which the light has to travel from the rear element in order to cover the entire sensor. When a digital back is used that employs micro-lenses over its pixel wells with such a lens, only part of the light is directed into much of the sensor’s pixel wells, particularly at the corners. The rest of the light is scattered creating sometimes significant color cast and vignetting.
This is exacerbated by using any rise or shift movements since the light from the rear element will have to travel even further at an even greater angle to reach the sensor’s photosites. To counteract this, technical camera users would create a reference image by placing a calibrated piece of translucent plexiglass over the front element and capturing an LCC image. This LCC reference file could then be processed through Capture One and would apply its complement to the final image, removing all but the most significant casts and vignettes. A new LCC would have to be created with every change to the aperture or any rise or shift movement, as these have direct relationships with the lens’s image circle. Again, the work to capture an image with a technical camera increased.
Though still feasible for those that deemed the extra work in capture worth the arguable gold standard of image quality these systems provided, the already niche field of technical cameras and their operators seemed to be on the precipice of evaporating altogether.
Enter the Phase One XT.
The Phase One XT Technical Camera
The XT elegantly solves all of the above baggage related to technical camera use mentioned above. First, in addition to the IQ4’s electronic shutter, the XT’s native Rodenstock lenses all feature Phase One’s new X-shutter which is electromagnetically controlled and powered by the IQ4 digital back. The X-shutter is made of carbon fiber materials and is an adapted version of the shutter found in Phase One’s industrial camera solutions. The X-Shutter has been tested to over 500,000 actuations which, for a camera that currently has a maximum capture rate of 2 fps, will take some significant time to get to. The X-Shutter also adds a stop of speed for a minimum exposure time of 1/1000s.
Look Ma’, No Cables
Second, unlike 3rd party technical cameras that require exterior cables to send information between the shutter and digital back, the XT and its native lenses have built in electronic contacts which allow the IQ4 to become the “brain” of the XT camera system and electronically control the lens’s shutter speed and aperture, removing the need to fiddle with small physical aperture and shutter speed dials as well as the risk of jostling the camera in doing so. The XT takes further advantage of these electronic contacts by recognizing and communicating the digital back’s location on the X and Y axis when employing rise or shift movements, sending them to the IQ4 to be recorded in the image’s metadata. The coordinates are even shown in real time while in live view to help keep track of the stitching process and improve efficiency.
IQ4 150MP mounted to XT in live view showing X and Y coordinates
No LCC No Problem For The IQ4 150MP
Third, the design of the BSI sensor in the IQ4 150 prevents the color cast associated with the same angle of light that would have created absurd color cast in other digital backs, effectively removing most if not all practical need for LCC creation. The Rodenstock 23mm HR was particularly known for having significant color cast due to its extremely wide focal length and small image circle. In our testing with the XT and the IQ4 150 we applied the most extreme movements the XT could provide while using the XT-Rodenstock 23mmHR. The results were astounding. There is essentially zero color cast right up until we meet the edge of the 23mm’s image circle, at which point there is no more light left to gather. No LCC required.
The XT and 23mm RodenstockHR at maximum movements stitched for reference without any LCCs applied. The only slight color cast exists at the transition of the image circle; an immense improvement. The image circle of the 23mm cannot fully cover the XT’s full movement range, so vignetting is clearly visible. Image for illustration purposes.
The XT’s physical design further eases the capture process by incorporating a built in orientation slider, letting the photographer switch from horizontal to landscape orientation without ever being removed from the tripod and while maintaining the optical center. Also for the first time in a technical camera we see a DSLR-style shutter button, the half press of which is customizable, though its default task of initiating live view on half-press is extraordinarily satisfying. Further, the incorporated Arca-Swiss style foot can be removed for a more pleasing hand hold-able experience. To further brag on the body design, since the XT was designed in partnership with Cambo, the XT also accepts Cambo WRS lens plates and many accessories/adapters made for the WRS line of technical cameras, including adapters for the use of Mamiya and Canon lenses, as well as Cambo lenses in Tilt/Swing panels, though capture is reliant on the IQ4’s electronic shutter.
Future Forward Infinity Platform
The IQ4 digital back itself also provides far more than a simple capture medium and control apparatus. The IQ4’s infinity platform allows for new computational photography techniques like Frame Averaging and the current Phase One Labs function Dual Exposure + which is an extremely promising tool. Live view is also the best its ever been in a full frame medium format digital back, allowing for capture during live view as well as exposure simulation, live RAW histogram, focus masking, and much more. Further imaginative features are expected via firmware updates, as Phase One’s model for feature implementation to the Infinity Platform via firmware update over hardware replacement is a breeding ground for innovation.
The IQ4 XT’s digital solution to a traditionally analog process removes the unnecessary operational burdens of traditional medium format technical cameras and lets photographers focus on photography while still delivering everything that makes technical cameras desirable. The XT serves as far more than a frame for the IQ4 digital back and Rodenstock’s quality optics to connect to, but contributes its own feature set. It is for these reasons that the release of the XT is a game changer for current and would-be technical camera users, and in my mind, is the savior of the technical camera as a capture device overall.
Want to know more about the Phase One XT or schedule a private demo? Get in touch.