Category Archives: cinematography

Shimming Nikon to Canon Lens Adapters. Helps get your zooms to track focus.

I use a lot of different lenses on my large sensor video cameras. Over the years I’ve collected quite a collection of Nikon and Canon mount lenses. I like Nikon mount lenses because they still have an iris that can be controlled manually. I don’t like Nikon lenses because most of them focus back-to-front compared to broadcast, PL and Canon lenses. The exception to this is Sigma lenses. The vast majority of Sigma lenses with Nikon mounts focus the right way – anti clockwise for infinity. If you go back just a few years you’ll find a lot of Sigma, Nikon mount lenses that focus the right way and have a manual iris ring. These are a good choice for use on video cameras. You don’t need any fancy adapters with electronics or extra mechanical devices to use these lenses and you know exactly what your aperture is.

But…. Canon lenses have some advantages too. First is the massive range of lenses out there. Then there is the ability to have working optical image stabilisation if you have an electronic mount and the possibility to remotely control the iris and focus. The down side is you need some kind of electronic mount adapter to make most of them work. But as I do own a couple of Canon DSLR’s it is useful to have a few Canon lenses.

So for my F3, initially I used Nikon lenses. Then along came the FS100 and FS700 cameras plus the Metabones adapter for Canon, so I got some Canon lenses. Then came the MTF Effect control box for Canon lenses on the F5 and now I have my micro Canon controller with integrated speed booster for the F5 and F55. This all came to a head when on an overseas shoot I got out one of my favourite lenses to put on my F5, but, the lens was a Nikon lens and I only had my Canon mounts (shame on me for not taking both mounts). Continually swapping mounts is a pain. So I decided to permanently fit all of my Nikon lenses with Nikon to Canon adapters and then only use Canon mounts on the cameras. You can even get Nikon to Canon adapters that will control the manual iris pin on a lens with no iris ring.

Now a problem with a lot of these adapters is that they are a little bit too thin. This is done to guarantee that the lens will reach infinity focus. If the adapter is too thick you won’t be able to focus on distant objects. This means that the focus marks on the lens and the distances your focussing at don’t line up. Typically you’ll be focussed on something 3m/9ft away but the lens markings will be at 1m/3ft. It can mean that the lens won’t focus on close objects when really it should. If your using a zoom lens this will also mean that as you zoom in and out you will see much bigger focus swings than you should. When the lens flange back (distance from the back of the lens to the sensor) is correctly set any focus shifts will be minimised. If the flange back distance is wrong then the focus shifts can be huge.

nikon-adapter1-300x225 Shimming Nikon to Canon Lens Adapters. Helps get your zooms to track focus.
Remove the 4 small screws as arrowed.

So what’s the answer? Well it’s actually quite simple and easy. All you need to do is to split the front and rear halves of the adapter and insert a thin shim or spacer. Most of the lower cost adapters are made from two parts. Removing 4 small screws allows you to separate the two halves. Make sure you don’t loose the little locking tab and it’s tiny spring!

 

 

NIKON-ADAPTER3-284x300 Shimming Nikon to Canon Lens Adapters. Helps get your zooms to track focus.
The adapter split in two. The shim needs to fit just inside the lip arrowed.

Split the two halves apart. Then use the smaller inner part as a template for a thin card spacer that will go in between the two parts when you put the adapter back together. The thickness of the card you need will depend on the specific adapter you have, but in general I have found card that is about the same thickness as a typical business card or cereal packet to work well. I use a scalpel to cut around the smaller part of the adapter. Note that you will also need to cut a small slot in the card ring to allow for the locking tab. Also note that when you look at the face of the larger half of the adapter you will see a small lip or ridge that the smaller part sits in. Your spacer needs to fit just inside this lip/ridge.

 

nikon-adapter4-300x273 Shimming Nikon to Canon Lens Adapters. Helps get your zooms to track focus.
The card spacer in place prior to reassembly. Needs a little tidy up at this stage!

With the spacer in place offer up the two halves of the adapter. Then use a fine scalpel to “drill” out the screw holes in the card, a fine drill bit would also work. Then screw the adapter back together. Don’t forget to put the locking tab back in place before you screw the two halves together.

 

 

 

nikon-adapter-5-300x269 Shimming Nikon to Canon Lens Adapters. Helps get your zooms to track focus.
Gently widen the narrow slit between these parts to make the adapter a tight fit on the lens.

Before putting the adapter on the lens use a very fine blade screw driver to gently prise apart the lens locating tabs indicated in the picture. This will ensure the adapter is a nice tight fit on the lens. Finally attach the adapter to the lens and then on to your Canon mount and check that you can still reach infinity focus. It might be right at the end of the lenses focus travel, but hopefully it will line up with the infinity focus mark on the lens. If you can’t reach infinity focus then your shim is too thick. If Infinity focus is short of your focus mark then your shim is not thick enough. It’s worth getting this right, especially on zoom lenses as you’ll get much better focus tracking from infinity to close up. Make up one adapter for each lens and keep the adapters on the lenses. You’ll also need to get some Canon end caps to protect you now Canon mount lenses.

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How To Become A Better Camera Operator.

….Learn to edit and grade properly!

OK, so if you already shoot and edit then you’ll know this already. But I’m surprised at how many shooters there are that have no idea of how to edit or have never studied the editing and post production process. Very often I’ll hear comments form people like “I shoot this way because it the easiest” or “they can sort it out in post” with clearly little understanding of exactly what the implications for the poor post people are.

Modern post production workflows can be very powerful with the ability to perform many corrections and adjustments, but very often these adjustments only work well when the footage was shot specifically for those kinds of adjustments. Just because you can adjust one type of shot in a particular way, it doesn’t mean that you can do that to any type of shot.  You should shoot in a way that is sympathetic to the post production process that has been chosen for the project.

The other thing that learning to edit brings is an understanding of how a program or film flows. It teaches the camera operator the kinds of shots that are needed to support the main part of an interview or drama scene. Those all important cut-aways that help a scene flow properly. It’s not just a case of shooting a bunch of random shots of the location but thinking about how those shots will interact with the main shots when everything is edited together. If your shooting drama then it is a huge help if you can visualise how cuts between different shots of different characters, scenes or locations will work. How framing and things like camera height can be used to change the tension or intimacy in a scene. I think one of the best way to learn these things is by learning how to edit and I don’t mean just pressing the buttons or randomly dropping stuff in a sequence of clips. Learn how to pace a sequence, how to make a scene flow, understanding these things makes you a better shooter.

But don’t stop at the edit. Follow the post production process through to it’s end. Learn how to grade with a proper grading tool, not just colour corrections in the edit suite (although it’s useful to know the limitations of these) but things like power windows and secondaries. You don’t have to become a colourist, but by understanding the principles and limitations you will be able to adapt the way you shoot to fit within those limits. It is  a good idea to find a friendly colourist that will let you sit in on a session and explain to you how and why he/she is doing the things being done. There is always the Lite version of Resolve which you can download and use for free. If you don’t have anything to edit or grade then go out and shoot something. Find a topic and make a short film about it. Try to include people, interviews or drama. Maybe get in touch with a local drama group and offer to shoot a performance.

Whatever you do, get out there and learn to edit, learn to grade and then experiment and practice. Try a workflow where you create the finished look in-camera, then try shooting a similar project very flat or with log/raw and take that through the post production process and compare the end results. I think the best shooters are normally also competent editors. By full understand the post process you will keep the editor and colourist happy. If you make their lives easy the director and producers will see this when they sit in on the edit or grade and you’ll be more likely to get more work from them in the future.

One final thing. Even if you think you know it all, even if you do know it all you should still speak to the post production people before you shoot whenever possible to make sure everyone is clear about how they want you to deliver your rushes.

Raw is not log, log is not raw. They are very different things.

Having just finished 3 workshops at Cinegear and a full day F5/F55 workshop at AbelCine one thing became apparent. There is a lot of confusion over raw and log recording. I overheard many people talking about shooting raw using S-log2 or people simply interchanging raw and log as though they are the same thing.

Raw and Log are completely different things!

Raw simply records the raw, unprocessed data coming off the video sensor, it’s not even a color picture as we know it, it does not have a white balance, it is just digital “1’s” and zeros coming straight from the sensor.

S-Log, S-Log2, LogC  or C-Log is a signal created by taking the sensors output, processing it in to an RGB or YCbCr signal and then applying a log gamma curve. It is much closer to conventional video, in fact it’s actually very similar, like conventional video it has a white balance and is encoded into colour. S-Log etc can be recorded using a compressed codec or uncompressed, but even when uncompressed, it is still not raw.

So why the confusion?

Well, if you tried to view the raw signal from a camera shooting raw in the viewfinder it would look incredibly dark with just a few small bright spots. This would be impossible to use for framing and exposure. To get around this a raw camera will convert the raw sensor data to conventional video for monitoring. Many cameras including the Sony F5 and F55 will convert the raw to S-Log2 for monitoring as only S-Log2 can show the cameras full dynamic range. At the same time the F5/F55 can record this S-Log2 signal to the internal SxS cards. But the raw recorded on the AXS cards is still just raw, nothing else, the internal recordings are conventional video with S-Log2 gamma (or an alternate gamma if a look up table has been used). The two are completely separate and different things and should not be confused.

UPDATE: Correction/Clarification. OK, there is room for more confusion as I have been reminded that ArriRaw uses Log encoding. It is also likely that Sony’s raw uses data reduction for the higher stops via floating point math or similar (as Sony’s raw is ACES compliant it possibly uses data rounding for the higher stops). ArriRaw uses log encoding for the raw data to minimise data wastage and to squeeze a large dynamic range into just 12 bits, but the data is still unencoded data, it has not been encoded into RGB or YCbCr and it does not have a white balance or have gain applied, all of this is added in post. Sony’s S-Log, S-Log2, Arri’s LogC,  Canon’s C-Log as well as Cineon are all encoded and processed RGB or YCbCr video with a set white balance and with a Log gamma curve applied.

How big a compromise is using a DSLR zoom on a 4K camera?

This came up as a question in response to the post about my prototype lens adapter. The adapter is based around an electronic Canon EF mount and the question was, what do I think about DSLR zooms?

There is a lot of variation between lenses when it comes to sharpness, contrast and distortions. A zoom will always be a compromise compared to a prime lens. DSLR lenses are designed to work with 24MP sensors. A 4K camera only has around 9MP, so your working well within the design limits of the lens even at 4K. While a dedicated PL mount zoom like an Angenieux Optimo will most likely out perform a similar DSLR zoom. The difference at like for like apertures will not be huge when using smaller zoom ratios (say 4x). But 10x and 14x zooms make more compromises in image quality, perhaps a bit of corner softness or more CA and these imperfections will be better or worse at different focal lengths and apertures. At the end of the day zooms are compromises but for many shoots it may simply be that it is only by accepting some small compromises that you will get the shots you want. Take my storm chasing shoots. I could use primes and get better image quality, but when you only have 90 seconds to get a shot there simply isn’t time to swap lenses, so if you end up with a wide on the camera when a long lens is what is really needed, your just not going to get the shot. Using a zoom means I will get the shot. It might not be the very best quality possible but it will look good. It is going to be better than I could get with an HD camera and a very slightly compromised shot is better than no shot at all.
If the budget would allow I would have a couple of cameras with different prime lenses ready to go. Or I would use a big, heavy and expensive PL zoom and have an assistant or team tasked solely with getting the tripod set up and ready asap. But my budget isn’t that big. I could spend weeks out storm chasing before I get a decent shot, so anything I can do to minimise costs is important.
It’s all about checks and balances. It is a compromise, but a necessary one. It’s not a huge compromise as I suspect the end viewer is not going to look at the shot and say “why is that so soft” unless they have a side by side, like for like shot to compare. DSLR zooms are not that bad! So yes, using a DSLR zoom is not going to deliver quality to match that of a similar dedicated PL zoom in most cases, but the difference is likely to be so small that the end viewer will never notice and thats a compromise I’m prepared to accept in order to get a portable camera that shoots 4K with a 14x zoom lens.

What about DSLR primes and why have I chosen the Canon Mount?

This is where the image performance gap gets even narrower. A high quality DSLR prime can perform just as well as many much more expensive PL mount lenses. The difference here is more about the usability of the lens. Some DSLR lenses can be tiny and this makes them fiddly to use. They are all All sorts of sizes, so swapping lenses may mean swapping Matte boxes or follow focus positions etc. Talking of focus, very often the focus travel on a DSLR lens is very, very short so focussing is fiddly. If the lens has an aperture ring it will probably have click stops making smooth aperture changes mid shot difficult. My prime lenses are de-clicked or never had clicks in the first place (like the Samyang Cine Primes). It’s not so much the issue of requiring a finer step than the one stop click, but more the ability to pull aperture during the shot. It’s not something I need to do often, but if I suddenly find I need to do it, I want a smooth aperture change. That being said, one of the issues with using Canon EF lenses with their electronic iris is that they operate in 1/8th stop steps and this is visible in any footage. Ultimately I am still committed to using the Canon mount lenses simply because there are so many to choose from and they focus in the right direction unlike Nikon lenses which focus back to front. For primes I’m using the excellent and fully manual Samyang T1.5 Cine Primes. I really like these lenses and they produce beautiful images at a fraction of the price of a PL mount lens. My zoom selection is a bit of a mish-mash. One thing about having a Canon mount on the camera is that I can still use Nikon lenses if I fit the lens with a low cost Nikon to Canon adapter ring. If you do this you can only use lenses with an actual iris ring, so generally these are slightly older lenses, but for example I have a nice Sigma 24-70mm f2.8 with a manual iris ring (and it focusses the RIGHT way, like most Sigmas but unlike most Nikon mount lenses). In addition I have a 70-300mm f4 Nikon mount Sigma as well as an Old Tokina 28-70mm f2.6 (lovely lens, a little soft but very nice warm colour). One thing I have found is that most of the Nikon to Canon adapter rings are little bit on the thin side. This prevents any zooms from being Parfocal as it puts the back focus out. Most of the adpaters are made in two parts and it’s quite easy to take the front and back parts apart and add shims made out of of thin plastic sheet or even card between the two halves to correct the back focus distance.

So there you have it. Overall DSLR lenses are not a huge compromise. Of course I would love to own a flight case full of good quality PL mount, 4K ready, glass. Perhaps one day I will, but it’s a serious investment. Currently I use DSLR lenses for my own projects and then hire in better glass where the budget will allow. For any commercials or features this normally means renting in a set of Ultra Primes or similar.  I am keeping a close eye on the developments from Zunow. I like their 16-28mm f2.8 and the prototype PL primes I saw at NAB look very good. I also like the look of the Zeiss 15.5 to 45 light weight zoom. Then of course there is the excellent Fujinon 19-90mm Cabrio servo zoom, but these are all big bucks. Hopefully I’ll get some nice big projects to work on this year that will allow me to invest in some top end lenses.

Choosing the right gamma curve.

One of the most common questions I get asked is “which gamma curve should I use?”.

Well it’s not an easy one to answer because it will depend on many things. There is no one-fits-all gamma curve. Different gamma curves offer different contrast and dynamic ranges.

So why not just use the gamma curve with the greatest dynamic range, maybe log? Log and S-Log are also gamma curves but even if you have Log or S-Log it’s not always going to be the best gamma to use. You see the problem is this: You have a limited size recording bucket into which you must fit all your data. Your data bucket, codec or recording medium will also effect your gamma choice.

If your shooting and recording with an 8 bit camera, anything that uses AVCHD or Mpeg 2 (including XDCAM), then you have 235 bits of data to record your signal. A 10 bit camera or 10 bit external recorder does a bit better with around 940 bits of data, but even so, it’s a limited size data bucket. The more dynamic range you try to record, the less data you will be using to record each stop. Lets take an 8 bit camera for example, try to record 8 stops and that’s about 30 bits per stop. Try to extend that dynamic range out to 11 stops and now you only have about 21 bits per stop. It’s not quite as simple as this as the more advanced gamma curves like hypergammas, cinegammas and S-Log all allocate more data to the mid range and less to highlights, but the greater the dynamic range you try to capture, the less recorded information there will be for each stop.

In a perfect world you would choose the gamma you use to match each scene you shoot. If shooting in a studio where you can control the lighting then it makes a lot of sense to use a standard gamma (no knee or knee off) with a range of up to 7 stops and then light your scene to suit. That way you are maximising the data per stop. Not only will this look good straight out of the camera, but it will also grade well provided your not over exposed.

However the real world is not always contained in a 7 stop range, so you often need to use a gamma with a greater dynamic range. If your going direct to air or will not be grading then the first consideration will be a standard gamma (Rec709 for HD) with a knee. The knee adds compression to just the highlights and extends the over-exposure range by up to 2 or 3 stops depending on the dynamic range of the camera. The problem with the knee is that because it’s either on or off, compressed or not compressed it can look quite electronic and it’s one of the dead giveaways of video over film.

If you don’t like the look of the knee yet still need a greater dynamic range, then there are the various extended range gammas like Cinegamma, Hypergamma or Cinestyle. These extend the dynamic range by compressing highlights, but unlike the knee, the amount of compression starts gradually and get progressively greater. This tends to look more film like than the on/off knee as it tends to roll off highlights much more gently. But, to get this gentle roll-off the compression starts lower in the exposure range so you have to be very careful not to over expose your mid-range as this can push faces and skin tones etc into the compressed part of the curve and things won’t look good. Another consideration is that as you are now moving away from the gamma used for display in most TV’s and monitors the pictures will be a little flat so a slight grade often helps with these extended gammas.

Finally we come to log gammas like S-Log, C-Log etc. These are a long way from display gamma, so will need to be graded to like right. In addition they are adding a lot of compression (log compression) to the image so exposure becomes super critical. Normally you’ll find the specified recording levels for middle grey and white to be much lower with log gammas than conventional gammas. White with S-Log for example should only be exposed at 68%. The reason for this is the extreme amount of mid to highlight compression, so your mid range needs to be recorded lower to keep it out of the heavily compressed part of the log gamma curve. Skin tones with log are often in the 40 – 50% range compared to the 60-70% range commonly used with standard gammas.  Log curves do normally provide the very best dynamic range (apart from raw), but they will need grading and ideally you want to grade log footage in a dedicated grading package that supports log corrections. If you grade log in your edit suite using linear (normal gamma) effects your end results won’t be as good as they could be. The other thing with log is now your recording anything up to 13 or 14 stops of dynamic range. With an 8 bit codec that’s only 17 – 18 bits per stop, which really isn’t a lot, so for log really you want to be recording with a very high quality 10 bit codec and possibly an external recorder. Remember with a standard gamma your over 30 bits per stop, now were looking at almost half that with log!

Shooting flat: There is a lot of talk about shooting flat. Some of this comes from people that have seen high dynamic range images from cameras with S-Log or similar which do look very flat. You see, the bigger the captured dynamic range the flatter the images will look. Consider this: On a TV, with a camera with a 6 stop range, the brightest thing the camera can capture will appear as white and the darkest as black. There will be 5 stops between white and black. Now shoot the same scene with a camera with a 12 stop range and show it on the same TV. Again the brightest is white and black is black, but the original 6 stops that the first camera was able to capture are now only being shown using half of the available brightness range of the TV as the new camera is capturing 12 stops in total, so the first 6 stops will now have only half the maximum display contrast. The pictures would look flatter. If a camera truly has greater dynamic range then in general you will get a flatter looking image, but it’s also possible to get a flat looking picture by raising the black level or reducing the white level. In this case the picture looks flat, but in reality has no more dynamic range than the original. Be very careful of modified gammas said to give a flat look and greater dynamic range from cameras that otherwise don’t have great DR. Often these flat gammas don’t increase the true dynamic range, they just make a flat picture with raised blacks which results in less data being assigned to the mid range and as a result less pleasing finished images.

So the key points to consider are:

Where you can control your lighting, consider using standard gamma.

The bigger the dynamic range you try to capture, the less information per stop you will be recording.

The further you deviate from standard gamma, the more likely the need to grade the footage.

The bigger the dynamic range, the more compressed the gamma curve, the more critical accurate mid range exposure becomes.

Flat isn’t always better.

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

Supercell-panorama-1024x232 The practicalities of fast run and gun shooting with a large sensor camera.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.

DSC02074-300x199 The practicalities of fast run and gun shooting with a large sensor camera.
Storm chasing with a PMW-F5

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.

DSC01122-300x199 The practicalities of fast run and gun shooting with a large sensor camera.
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.

F5-with-rainbow-300x199 The practicalities of fast run and gun shooting with a large sensor camera.
Rainbow under a severe thunderstorm.

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.

LP-storm2-300x168 The practicalities of fast run and gun shooting with a large sensor 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.

chase3-300x168 The practicalities of fast run and gun shooting with a large sensor camera.
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?

 

The obsession with using Shutter Angle on an electronic video camera.

I’m not sure I fully understand the obsession with using the shutter set in degrees on video cameras. For years video cameras have used fractions of a second to display the actual shutter speed. Very simple, tells you exactly how long the shutter is open no matter what your shooting frame rate. Basic film cameras use a fixed rotating shutter. This is a disc that will have half of it cut away to allow light to fall on the film. If a full circle is 360 degrees then half of this is 180 degrees, hence the commonly used 180 degree shutter. As these basic shutters are fixed then if you changed the film cameras frame rate then the shutter speed changes too. The shutter speed will always be half of the frame rate. More advanced film cameras have shutters where you can adjust the amount angle of the shutter opening, sometimes to as much as 270 degrees, but often only to an angle less than 180 degrees.

When you use degree’s your having to continually make a mental calculation of your shutter speed in fractions of a second to ensure that you don’t run into phase issues with your lighting etc. Why do this? With a video camera, if you use fractions of a second you know exactly where you are. I know of many film cameramen, myself included that found degrees to be a nuisance with the shutter speed changing all over the place depending on frame rate and angle. Fractions of a second are far easier to work with. For example, to avoid flicker from artificial lights (in particular florescent office lighting) when shooting in 50hz areas use a shutter speed that is a multiple of 1/50 and in 60hz countries use a fraction of 1/60, no matter what your frame rate. Try figuring out what angle you need to shoot 24p in a 50hz country (the answer is 1/172.8). Degrees is a hangover from film days that is seen as fashionable because it make you sound like a cinematographer, but this is fashion for the sake of fashion, not because it makes sense or is a better way to work. There is no difference in the way the shutter functions within an electronic video camera whether you use degrees or fractions, it’s just a different way of describing the same thing (unless you have a high end camera like the f65 with a mechanical shutter). If you want to mimic a film camera with a 180 degree shutter then all you have to do is halve the frame rate, so 24p = 1/48, 25p = 1/50, 30p = 1/60. Very simple.  Then if you need to match the local mains frequency simply use the next highest mains multiple. So if shooting 24p in a 50hz country use 1/50th or shooting 24p in a 60hz country use 1/60th, much easier to figure out than degrees.

Exposing Skin Tones, getting the movie look.

This post was inspired by a discussion on another forum. One of the things that tends to differentiate the movie look from a typical video look is exposure range. When you watch a typical TV soap, documentary or news programme the pictures are normally bright and vivid. Most TV is watched in rooms with daylight coming through windows or artificial lighting giving at least moderate ambient lighting, so when you sit down to watch a documentary you don’t want too dark an image. In addition a lot of television “action” takes place in daylight. As a result most television programming is exposed to give a bright image.

A feature film on the other hand is often watched in a dark cinema or at home in the evening where light levels may be lower. As a result you can use lower brightness images with fewer issues. In fact it does seem to me sometimes that the term “Blockbuster” means a movie where the story will take place almost entirely in the dark. What’s interesting is to look at faces and skin tones. We know how bright faces normally appear to us in real life so they make a good exposure reference. In television it’s quite normal to expose faces somewhere in the region of 60-70%. Many video camera operators will use zebras set to 60-70% to expose faces. If you look at a typical movie though you will find that faces are generally exposed a little lower.

skin-tones-comp Exposing Skin Tones, getting the movie look.
Blockbuster Skin Tone Exposure.

Looking at the image above you can see that for the day time shots faces are falling between 45 and 60%. Now before you all rush out and shoot everything a stop or two  lower than perhaps you would normally, you need to put this in to some context. Movies have big lighting budgets and they get extensively graded so they will generally have tight control over the contrast ratios of the entire shot, a luxury you may not have when shooting for news and docs. You probably don’t want faces at 55% if the rest of the scene has lots of much brighter areas. But what it does show is that you don’t always have to follow the video convention of skin tones at 60-70% and this might help in a difficult lighting situation where dropping skin tones a little may help with highlights. If you are looking for that movie look a lower overall exposure may help you achieve it. As always with conventional video it is highlights that that give the biggest problems as if you clip them they are gone forever and no amount of grading can get them back. On the other hand a little bit of under exposure can normally be recovered without too much of a problem. For night scenes and low key scene exposures may be a little lower still, but not by that much, you don’t normally want faces getting so dark that you can’t see them.

Contrast and Resolution, intricately linked.

This is one of those topics that keeps coming back around time and time again. The link between contrast and resolution. So I thought I would take a few minutes to create some simple illustrations to demonstrate the point.

contrast1 Contrast and Resolution, intricately linked.
Best Contrast.

This first image represents a nice high contrast picture. The white background and dark lines have high contrast and as a result you can “see” resolution a long way to the right of the image as indicated by the arrow.

contrast2 Contrast and Resolution, intricately linked.
Lower contrast.

Now look at what happens as you slowly reduce the contrast in the image. As the contrast reduces the amount of resolution that you can see reduces. Keep reducing the contrast and the resolution continues to decrease.

contrast4 Contrast and Resolution, intricately linked.
Low Contrast.

Eventually if you keep reducing the contrast enough you end up with no resolution as you can no longer differentiate between light and dark.

Now look at what happens when you reduce the resolution by blurring the image, the equivalent of using a less “sharp” lower resolution lens for example. What happens to the black lines? Well the become less dark and start to look grey, the contrast is reducing.

contrast5 Contrast and Resolution, intricately linked.
Reduced resolution.

Hopefully these simple images show that contrast and resolution are intrinsically linked. You can’t have one without the other. So when choosing lenses in particular you need to look at not just resolution but also contrast. Contrast in a lens is affected by many things including flare where brighter parts of the scene bleed into darker parts. Flare also comes from light sources that may not be in your shot but the light is still entering the lens, bouncing around inside and reducing contrast as a result. These things often don’t show up if you use just a simple resolution chart. A good lens hood or matte box with flags can be a big help reduce stray light and flare, so in fact a matte box could actually make your pictures sharper. They are not just for pimping up your rig, they really can improve the quality of your images.

The measurement for resolution and contrast is called the MTF or modulation transfer function. This is normally used  to measure lens performance and the ability of a lens to pass the light from a scene or test chart to the film or sensor. It takes into account both resolution and contrast so tells you a lot about the lens or imaging systems performance and is normally presented as a graph of contrast levels over a scale of ever increasing resolution.

Why Nailing Your Mid Range Will Make Post Production Happy. Even with Cingammas and Hypergammas.

One of the concepts that’s sometimes hard to understand is why mid range exposure is so critical with most video cameras, even cameras with extended dynamic range. Cameras that use Cinegammas, Hypergammas  may give you great dynamic range and extra latitude but it’s still vital that you get your mid range exposed correctly. In many cases, the greater you cameras ability to capture a wide dynamic range the more critical mid range exposure becomes. I’ve often heard comments from users of XDCAM cameras complaining that they find it harder to work with cinegammas and hypergammas than the standard REC-709 gamma.
So why is this, it seams counter intuitive, surely a greater dynamic range makes exposure more forgiving?

exposure1 Why Nailing Your Mid Range Will Make Post Production Happy. Even with Cingammas and Hypergammas.
Typical Standard Gamma

First lets take a look at a standard gamma curve. These graphs are not accurate, just thrown together to illustrate the point. The standard gamma for HD, REC-709 can be considered to be near linear. Certainly in terms of “what you see is what you get” the idea behind REC-709 is that if the camera is set to 709 and the TV or monitor is 709 compliant then we will get a linear 1:1 reproduction of the real world. However REC-709 is based on the gamma curves used at the very beginnings of television broadcasting where TV’s and cameras had very limited dynamic range. True REC-709 only allows for about 6 stops of dynamic range and as a result the version of REC-709 used in most video cameras is tweaked somewhat to allow a greater dynamic range in the region of 8 to 10 stops while still producing a pleasing image on most TV’s. Another way of increasing dynamic range is to introduce some form of signal compression. The simplest form of this in common use is the cameras knee circuit. This simply takes anything above a certain brightness level (typically between 80 and 95%) and compresses it. We normal get away with this compression because it’s only affecting highlights like clouds in a bright sky or a bright window or lamp in the shot. Our own visual system is tuned primarily to mid tones, faces, plants and things like that so we don’t tend to find highlight compression overly obtrusive.
When considering your post production workflow and grading in particular, it’s important to remember that in most cases whenever anything is compressed then some of the original data is being discarded. In addition if the amount of compression is non-linear (increases or decreases with amplitude) then when we add a linear function to that, like adjusting the signal gain the non-linearity is also increased.
Based on these assumptions, you should be able to understand that anything exposed in the linear part of a gamma curve will grade very well because there is no extra compression and gain adjustments will behave as expected. Now if you look at the graph of a typical standard gamma curve (as above) you can see that everything below the knee point is pretty linear, so anything exposed in this range will grade easily and well (assuming it isn’t actually overexposed). For this reason standard gamma can be very forgiving to small over exposure problems as a slightly bright face should still be in the linear part of the curve. However overexpose to the point where the face starts to enter the knee area and all is lost, you’ll never make it look natural.

exposure2 Why Nailing Your Mid Range Will Make Post Production Happy. Even with Cingammas and Hypergammas.
Typical Cinegamma or Hypergamma

Now look at the curve for a typical Cinegamma or Hypergamma. You can see that this curve starts to become more curved and less linear much earlier than a standard gamma. This is how the extra latitude is gained. Compression is used to allow the camera to record a greater brightness range. This extra compression though comes at a price and that is linearity. The further up the exposure range you go the less linear the response (it’s actually becoming logarithmic). The result is that even though you have more dynamic range, if you do overexpose faces and skin tones by even just a small amount they will start to creep into the non linear part of the curve and this makes them harder to grade naturally. You may be less likely to get those ugly blown out highlights on a shiny face typical of video knee compression with cine/hypergammas, but you must still be very careful not to overexpose.

So there you have it. Greater dynamic range does not necessarily equate to more exposure tolerance. In fact it’s often the opposite. You might get better highlight handling, but you may find you need to be even more careful with how you expose. As we go forwards (or sideways at least) and linear raw becomes more common place then you will be able to shift you mid tone exposure up and down with a lot more flexibility as with a linear raw camera the last stop of exposure has the same linearity as the first, so in theory your mid tones can sit anywhere in the exposure range. Sony’s F65 is a great example of this. It has 14 stops of linear dynamic range. A face lit with a 3 stop range could be placed in stops 11-14 and would grade down to wherever you want just perfectly.