Tag Archives: 4k

The practicalities of fast run and gun shooting with a large sensor camera.

April 21, 2013 alisterchapman 8 Comments

Well I’ve just returned home from NAB and a week of Tornado Chasing in the USA. For the Tornado chasing I was shooting in 4K using my Sony F5. I’ve shot run and gun with my F3 and FS700 in the past when shooting air-shows and similar events. But this was very different. Tornado chasing is potentially dangerous. You often only have seconds to grab a shot which involves leaping out of a car, quickly setting up a tripod and camera and then framing and exposing the shot. You often only have time for one 30 second shot before you have to jump back into the car and move on out ahead of the storm. All of this my be happening in very strong winds and rain. The storms I chased last week had inflow winds rushing into them at 50+ MPH.

The key to shooting any thing fast moving, like this, is having whatever camera kit your using well configured. You need to be able to find the crucial controls for exposure and focus quickly and easily. You need to have a way of measuring and judging exposure and focus accurately. In addition you need a zoom lens that will allow you to get the kinds of shots you need, there’s no time to swap lenses!

For my storm chasing shoot I used the Sony F5 with R5 recorder. This was fitted with a Micron bridge plate as well as a Micron top cheese plate and “Manhandle”. Instead of the Sony viewfinder I used an Alphatron viewfinder as this has a waveform display for exposure. My general purpose lens was a Sigma 18-200mm f3.5-f6.5 stabilised lens with a Canon mount. To control the iris I used a MTF Effect iris control box. For weather protection a CamRade F5/F55 Wetsuit. The tripod I used for this shoot was a Miller 15 head with a set of Carbon Fibre Solo legs.

Overall I was pleased with the way this setup worked. The F5’s ergonomics really help as the logical layout makes it simple to use. The 18-200mm lens is OK. I wish it was faster for shooting in low light but for the daytime and dusk shots, f3.5 (at the wide end) is OK. The F5 is so sensitive that it copes well even with this slow lens. The CamRade wetsuit is excellent. Plenty of clear windows so you can see the camera controls and a well tailored yet loose fit that allows you to get easy access to the camera controls. I’ve used Miller Solo legs before and when you need portability they can’t be beaten. The are not quite as stable as twin tube legged tripods, but for this role they are an excellent fit. The Miller 15 head was also just right. Not too big and bulky, not too small. The fluid motion of the head is really smooth.

Storm Chasing in the USA with the PMW-F5

So what didn’t work? Well I used the Element Technica Micron bridge plate. I really like the Micron bridge plate as it allows you to re-balance the camera on the tripod very quickly. But it’s not really designed for quick release, it’s a little tricky to line up the bridge plate with the dovetail so I ended up removing and re-fitting the camera via the tripod plate which again is not ideal. The Micron Bridge plate is not really designed for this type of application, when I go back storm chasing in May I’ll be using a baseplate that locks into a VCT-14 quick release plate, not sure which one yet, so I have some investigating to do. The VCT-14 is not nearly as stable or as solid as the Micron, but for this application speed is of the essence and I’m prepared to sacrifice a little bit of stability. The Micron bridge plate is better suited to film style shooting and in that role is fantastic, it’s just not the right tool for this job.

The MTF-Effect unit is needed to control the aperture of the Canon mount lens, it also powers the optical image stabiliser. But it’s a large square box. I had it mounted on the top of the camera, not in the best place. I need to look at where to mount the box. I’m actually considering re-housing the unit in a custom made hand grip so I can use it to hold the camera with my left hand and have iris control via a thumbwheel. I also want to power it from one of the camera’s auxiliary outputs rather than using the AA batteries internally. The other option is the more expensive Optitek lens mount which I’m hoping to try out soon. I’m also getting a different lens. The Sigma was fine, but I’m going to get a Sigma 18-250mm (15x) f3.5-f6.5 for a bit more telephoto reach. The other option I could have used is my MTF B4 adapter and a 2/3″ broadcast zoom, but for 4K the Tamron will have better resolution than an HD lens. If I was just shooting HD then the broadcast lens would probably be the best option. After dark I swapped to my Sigma 24-70mm f2.8 for general purpose shooting and this worked well in low light but with the loss of telephoto reach, I need to look into a fast long lens but these tend to be expensive. If you have deep enough pockets the lens to get would probably be the Fujinon Cabrio 19-90 T2.9, but sadly at the moment my budget is blown and my pockets are just not that deep. The Cabrio is very similar to an ENG broadcast lens in that it has a servo zoom, but it’s PL mount and very high resolution. Another lens option would be the Canon CN-E30-105mm T2.8, but overall there isn’t a great deal of choice when it comes down to getting a big zoom range and large aperture at the same time, in a hand-held package. If I was working with a full crew then I would consider using a much larger lens like the Arri Alura 18-80 or Angenieux Optimo 24-290, but then this is no longer what I would consider run and gun and would require an assistant to set up the tripod while I bring out the camera.

A Supercell thunderstorm looking like a flying saucer.

From an operating point of view one thing I had to do was to keep reminding myself to double check focus. If you think focus is critical in HD, then it’s super critical for 4K. Thunderstorms are horrid things to try and focus on as they are low contrast and soft looking. I had to use a lot of peaking as well as the 1:1 pixel function of the Alphatron viewfinder, one of the neat things about the Alphatron is that peaking continues to work even in the 1:1 zoom mode. As I was shooting raw and using the cameras Cine EI mode to make exposure simpler I turned on the Look Up Tables on the HDSDI outputs and used the P1 LUT. I then exposed using the waveform monitor keeping my highlights (for example the brighter clouds) at or lower than 100%. On checking the raw footage back this looks to have worked well. Quite a few shots needed grading down by 1 to 1.5 stops, but this is not an issue as there is so much dynamic range that the highlights are still fine and you get a cleaner, less noisy image. When shooting raw with the F5 and F55 cameras I’d rather grade down than up. These cameras behave much more like film cameras due to the massive dynamic range and raw recording, so a little bit of overexposure doesn’t hurt the images as it would when shooting with standard gammas or even log. Grading down (bringing levels down) results in lower noise and a cleaner image.

Frame grab from the F5 of a Supercell storm with a grey funnel cloud beneath.

So you can run and gun in an intense fast moving environment with a large sensor camera. It’s not as easy as with a 2/3″ or 1/2″ camera. You have to take a little more time double checking your focus. The F5 is so sensitive that using a F3.5-F6.5 lens is not a huge problem. A typical 1/2″ camera (EX1, PMW-200) is rated at about 300 ISO and has an f1.8 lens. The F5 in Cine EI mode is 2000 ISO, almost 3 stops more sensitive. So when you put an f3.5 lens on, the F5 ends up performing better in low light, even at f6.5 it’s only effectively one stop less sensitive. For this kind of subject matter you don’t want to be at f1.8 – f2.8 with a super 35mm sensor anyway as the storm scenes and shots involved work better with a deep focus range rather than a shallow one.

Having watched the footage from the shoot back in HD on a large screen monitor I am delighted with the quality of the footage. Even in HD it has better clarity than I have seen in any of my previous storm footage. This is I believe down to the use of a 4K sensor and the very low noise levels. I’d love to see the 4K material on a 4K monitor. It certainly looks good on my Mac’s retina display. Hopefully I’ll get back out on the plains and prairies of Tornado Alley later in May for some more storm chasing. Anyone want to join me?

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Convergent Design Odyssey 7Q To Work With FS700 Raw!

April 8, 2013 alisterchapman 5 Comments

Waveform and measurement options on the Convergent Design Odyssey7Q

Hot off the press from NAB is the announcement that the Convergent Design Odyssey 7Q will be able to work directly with the FS700 to record 4K and 2K with from the FS700 with 2K raw going up to 240fps. This is really great news. I’ll be posting a video blog about this later in the week. for now here is an extract from the official press release

LAS VEGAS, NAB Booth C11001, April 8, 2013 — Sony is announcing that its affordable 4K production camcorder, the NEX-FS700, will support a direct connection to Convergent Design’s new Odyssey7Q. The combination will allow recording of 2K RAW at up to 240 frames per second, with 4K video enabled via a single 3G connection.

The NEX-FS700 can achieve a high frame rate of up to 240 fps recording in 2K RAW while recording to the Odyssey 7Q. The 240 content fps is recording continuously, without windowing the imager or line doubling the signal. This assures full resolution at all times without windowing artifacts.
The direct connection to Convergent Design’s new Odyssey 7Q complements Sony’s own newly announced recording solution using the AXS-R5 RAW recorder and the new HXR-IFR5 interface unit. Now professional users have even more flexibility in choosing a workflow that meets their needs for today’s diverse client requirements.

“The addition of RAW and 4K recording unleashes the full power of the FS700’s state of the art 4K imager, vastly increasing the potential applications for the camcorder and resulting in tremendous flexibility in post-production,” said Peter Crithary, marketing manager for large sensor technology at Sony Electronics. “Now, interoperability with the exciting Odyssey 7Q in addition to our own recording technology gives users a wide range of cost effective choices when working with diverse workflows.”

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Sony PMW-F55 raw samples for download.

April 3, 2013 alisterchapman 2 Comments

I have uploaded a couple of short F55 raw sample for you to play with. The exposure was deliberately pushed to it’s limits on these clips so you can have a go at grading them. Resolve Lite (free) can be used with the footage.
http://www.alisterchapman.com/samples/f55-raw-samples.zip

If you find the footage useful please make a small donation to go towards the cost of hosting the files or buy me a coffee. All donations no matter how small gratefully received.

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When is 4k really 4k, Bayer Sensors and resolution.

January 20, 2011 alisterchapman 8 Comments

When is 4k really 4k, Bayer Sensors and resolution.

First lets clarify a couple of term. Resolution can be expressed two ways. It can be expressed as pixel resolution, ie how many individual pixels are there on the sensor. Or as TV lines or TVL/ph, or how many individual lines can I see. If you point a camera at a resolution chart, what you talking about is at what point can I no longer discern one black line from the next. TVL/ph is also the resolution normalised for the picture height, so aspect ratio does not confuse the equation. TVL/ph is a measure of the actual resolution of the camera system. With video cameras TVL/ph is the normally quoted term, while pixel resolution or pixel count is often quoted for film replacement cameras. I believe the TVL/ph term to be prefferable as it is a true measure of the visible resolution of the camera.
The term 4k started in film with the use af 4k digital intermediate files for post production and compositing. The exposed film is scanned using a single row scanner that is 4,096 pixels wide. Each line of the film is scanned 3 times, once each through a red, green and blue filter, so each line is made up of three 4K pixel scans, a total of just under 12k per line. Then the next line is scanned in the same manner all the way to the bottom of the frame. For a 35mm 1.33 aspect ratio film frame (4×3) that equates to roughly 4K x 3K. So the end result is that each 35mm film frame is sampled using 3 (RGB) x 4k x 3k, or 36 million samples. That is what 4k originally meant, a 4k x 3k x3 intermediate file.
Putting that into Red One perspective, it has a sensor with 8 Million pixels, so the highest possible sample size would be 8 million samples. Red Epic 13.8 million. But it doesn’t stop there because Red (like the F3) use a Bayer sensor where the pixels have to sample the 3 primary colours. As the human eye is most sensitive to resolution in the middle of the colour spectrum, twice as many of these pixel are used for green compared to red and blue. So you have an array made up of blocks of 4 pixels, BG above GR.
Now all video cameras (at least all correctly designed ones) include a low pass filter in the optical path, right in front of the sensor. This is there to prevent moire that would be created by the fixed pattern of the pixels or samples. To work correctly and completely eliminate moire and aliasing you have to reduce the resolution of the image falling on the sensor below that of the pixel sample rate. You don’t want fine details that the sensor cannot resolve falling on to the sensor, because the missing picture information will create strange patterns called moire and aliasing.
It is impossible to produce an Optical Low Pass Filter that has an instant cut off point and we don’t want any picture detail that cannot be resolved falling on the sensor, so the filter cut-off must start below the sensor resolution. Next we have to consider that a 4k bayer sensor is in effect a 2K horizontal pixel Green sensor combined with a 1K Red and 1K Blue sensor, so where do you put the low pass cut-off? As information from the four pixels in the bayer patter is interpolated, left/right/up/down there is some room to have the low pass cut off above the 2k pixel of the green channel but this can lead to problems when shooting objects that contain lots of primary colours. If you set the low pass filter to satisfy the Green channel you will get strong aliasing in the R and B channels. If you put it so there would be no aliasing in the R and B channels the image would be very soft indeed. So camera manufacturers will put the low pass cut-off somewhere between the two leading to trade offs in resolution and aliasing. This is why with bayer cameras you often see those little coloured blue and red sparkles around edges in highly saturated parts of the image. It’s aliasing in the R and B channels. This problem is governed by the laws of physics and optics and there is very little that the camera manufacturers can do about it.
In the real world this means that a 4k bayer sensor cannot resolve more than about 1.5k to 1.8k TVL/ph without serious aliasing issues. Compare this with a 3 chip design with separate RGB sensors. With a three 1920×1080 pixel sensors, even with a sharp cut-off low pass filter to eliminate any aliasing in all the channels you should still get at 1k TVL/ph. That’s one reason why bayer sensors despite being around since the 70s and being cheaper to manufacture than 3 chip designs (with their own issues created by big thick prisms) have struggled to make serious inroads into professional equipment. This is starting to change now as it becomes cheaper to make high quality, high pixel count sensors allowing you to add ever more pixels to get higher resolution, like the F35 with it’s (non bayer) 14.4 million pixels.
This is a simplified look at whats going on with these sensors, but it highlights the fact that 4k does not mean 4k, in fact it doesn’t even mean 2k TVL/ph, the laws of physics prevent that. In reality even the very best 4k pixels bayer sensor should NOT be resolving more than 1.8k TVL/ph. If it is it will have serious aliasing issues.
After all that, those that I have not lost yet are probably thinking: well hang on a minute, what about that film scan, why doesn’t that alias as there is no low pass filter there? Well two things are going on. One is that the dynamic structure of all those particles used to create a film image, which is different from frame to frame reduces the fixed pattern effects of the sampling, which causes the aliasing to be totally different from frame to frame so it is far less noticeable. The other is that those particles are of a finite size so the film itself acts as the low pass filter, because it’s resolution is typically lower than that of the 4k scanner.