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Shutter, shutter speed and shutter angle.

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So you have your nice camcorder, EX1, EX3, AF100, F3 or whatever and it has a function called the shutter. This function may have different ways of being set, fractions of seconds or angle. What is it that the shutter does and what’s the difference between angle and fractions. Also why is it important to know what the frequency of the local mains electricity?

180 degree film shutter

Lets start by looking at the difference between shutter speed expressed in fractions of a second and shutter angle. Shutter angle comes from film camera days when the film cameras shutter was a simple spinning disc with one half of the disc cut away to allow the light to pass from the lens to the film. The other half of the disc would rotate around, blanking off the film so it could be advanced to the next frame. If you consider that a full circle is 360 degrees, then half of a full circle is 180 degrees. So for each frame cycle with a 180 degree shutter, light is allowed to pass from the lens to the film for half of the frame rate (180 being half of 360).

Taking a frame rate of 25 frames per second, each frame lasts 1/25th of a second. Half of that is 1/50th, so with  a 180 degree shutter the exposure at 25P is 1/50th of a second. There is no difference in the way the shutter works, it is just a different way of expressing the shutter timing.

Film camera 90 degree shutter

If we take that and look at a different angle, this time 90 degrees we can see from the picture that this is now one quarter of a full circle (90 is one quarter of 360 degrees). So at 25 frames per second the exposure is one quarter of 1/25th which is 1/100th and so on.

So why use angle instead of a fraction of a second? Well here’s the thing. If you set you shutter speed to 1/50th, then no matter what your frame rate the shutter speed will be 1/50th. The Sony EX and XDCAM cameras can shoot at various frame rates (as can many other cameras). It is traditional when shooting progressive, trying to create a filmic look to mimic the way a film camera behaves, so for this you would use a shutter that is open for half of the frame rate, ie. 180 degrees. When you set the shutter speed using an angle, when you change the frame rate the shutter speed will also change. Set to 180 degrees it will always be half of the frame rate. So going from 25P to 30P will change the shutter speed from 1/50th to 1/60th. Which neatly brings me on to the next bit….

Why it’s important to know the local mains frequency.

We normally take it for-granted in our home countries, shooting at our home frame rates that the pictures will be OK. But if you travel to a country where the mains frequency no longer matches the cameras base frequency then you may experience problems with flickering or strobing pictures when shooting under artificial lighting. Sometimes you will see light and dark bands slowly rolling up and down the picture. This happens because if you take your camera, lets say set to PAL (50i/25P) to the USA, the US mains frequency of 60hz will drift in and out of sync with the camera from one frame to the next. As many artificial lights brighten and dim in sync with the mains electricity you can appreciate that for one frame the lights may have one brightness and then the next frame the brightness may be different. You will possibly experience problems when the mains frequency cannot be evenly divided by the cameras shutter speed. For example shooting 30P will give problems when the mains is 50Hz as 30 will not divide evenly into 50.

So how do you counter this? Well you need to change your shutter speed to an even fraction or even multiplier of the mains frequency. So shooting 30P in a 50hz country you can use: 1/50th, 1/100th, 1/200th etc (mains frequency, frequency multiplied by 2, multiplied by 3 etc). Note that when shooting 60i you can’t normally have a 1/50th shutter so your limited to 1/100th or higher. When shooting 25P or (50i) in a 60Hz country you should use 1/60th, 1/120th, 1/240th etc. For 24P (23.98) you will often have to use the shutter when using consumer or industrial lighting using the same shutter speeds as give above, dependant on the local mains frequency.

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PMW F3 Picture Profile Smorgasbord.

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I’ve been working some more on picture profiles for the PMW-F3, mainly matrix settings. You can download the full set by clicking here: ac-profiles. Download the zip file, unzip and place the “Sony” folder in the root of an SxS card or SD card in an adapter. Place the card in the camera and go into the “picture profiles” menu and select a picture profile and then “ppdata” and “recall” to load the data into your camera. This will overwrite any PP’s you already have.

Here’s the latest settings I have:

ALL use Detail level -17, Frequency +20, Aperture +25 unless otherwise stated.

AC Warm1: Warm look, less blue/yellow

Cinegamma 1, Black Gamma -25, Black Level -2.

Matrix: Standard, level +8, R-G +14, R-B +12, G-R +4, G-B +8, B-R +4, B-G -18

AC Cool1: Stark cool look, maybe day for night.

Cinegamma 1, Black Gamma -25, Black Level -2.

Matrix: Standard, level +22, R-G -44, R-B -24, G-R -34, G-B =28, B-R -7, B-G -69

AC Elec1:  Electronic, vivid look.

Gamma STD1, Black Gamma -20, black level -3, Detail Level -10, Frequency -40

Matrix Hi-Sat,

NAT1CG-1: Neutral Look, natural colors, less yellow/green.

Cinegamma 1, Black Level -2

Matrix FL-Light, Level +3, R-G +2, R-B +2, G-R +8, G-B +8, B-R -8, B-G -6

Note that for most of these I have used a cinegamma, that is because I would assume that post work will be done on the footage. If your not planning on doing any grading or post work you should consider using a standard gamma which will give a richer looking image or cinegamma 2 which is broadcast safe.

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Genus Hurricane Rig to be sold by Manfrotto.

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Genus Hurricane Rig at BVE

Just an update on the progress of my light weight, modular 3D mirror rig, the Genus Hurricane Rig. In many countries, including the USA and UK the rigs will be available through Manfrotto accredited dealers. To ensure the very highest quality of service and support I am assisting Genus and Manfrotto with a global dealer training programme. In most cases dealers will already have 3D knowledge, but in order to sell the rig they must attend one of our workshops and demonstrate a good understanding of 3D and the Hurricane Rig. The rig was on show on the Canon and Manfrotto booths at the recent BVE show in London where it attracted a large amount of interest. In the UK you will be able to order rigs directly from me via the hurricane-rig.com web site. The advantage of purchasing this way is that I will be able to ensure that the rig will meet your needs and provide after sales support and training if required.

A pair of hurricane rigs at Singapore Poly.

I recently spent a few days in Singapore training the lecturers at Singapore Poly to use the Hurricane Rig. The polytechnic has purchased a rig as a teaching aid for stereoscopic 3D classes. They will be using it with an EX1R and EX3 as well as a convergent design Nano3D. This makes a really good light weight and low cost system. The Nano3D will output an anaglyph output so a conventional 2D monitor can be used on set to align the rig and for monitoring. This can be a big cost saver as 3D monitors are expensive items.

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Genus Matte Box, Rails and Shoulder mount on PMW-F3

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Genus kit fitted to an F3

So here is my current set up. As you may know Genus are making the 3D rig that I designed, so I get to play with the latest Genus bits and pieces. This is my F3 with a pre-production universal riser and base plate. The base plate will fit most camcorders and incorporates mounts for a pair of 15mm rails. Up front I have a Genus Wide 4×4 matte box. I’m really pleased with this light weight matte box with added top flag, it is a good match for the Nikon DSLR lenses that I will be using and is much, much lighter than my old Petroff matte box. It fits lenses up to 105mm  diameter so I will need a bigger matte box for many PL mount lenses (and bigger filters) perhaps I’ll get one of those nice TLS Raven Matte Boxes. For smaller lenses though the Genus 4×4 is really nice. Behind the matte box I have a Genus Superior follow focus. This is a silky smooth FF unit and on this lens it’s driving one of Genus’s clever flexible lens gears. This is a little bit like a hose clip, a thumb screw tightens it up so that it fastens snuggly around the lens. It will fit a much larger range of lenses than a traditional rigid lens gear.  The lens in the pictures is a Tokina ATX-Pro 28-70mm parfocal zoom. This is a great lens, plenty sharp enough for HD video and it doesn’t telescope when you zoom. Breathing is minimal. To match the lens to the camera there is one of Mike Tapas (MTF) excellent Nikon to F3 adapters.

Genus hand grips and Follow Focus

Underneath the lens I have a pair of hand grips from the Genus shoulder mount kit. The shoulder pad is right at the back behind the camera. For a little bit of extra convenience I have a Genus GAP adapter plate that allows me to use a quick release VCT-14 tripod plate.

The only thing left to sort is a loupe for the LCD screen. I’ve experimented with a Hoodman DSLR loupe that I have and this almost works. It doesn’t cover the full width of the LCD, but does allow me to use the LCD as a viewfinder when using this shoulder rig. I guess I need to get the Hoodman Hood Riser and Hood Strap to make the loupe fit the LCD correctly. I’ve read elsewhere that it does not fit the F3, but my experiments with the loupe alone suggests it will fit. Anyone else tried it yet? I’d rather go this route than getting a Cineroid viewfinder.

The tripod is a Manfrotto 509. This one of their new silky smooth “bridge” style heads. The 509 is a mid weight head with a pretty high payload capability, true fluid action and variable counter balance. I’m going do a separate write up on the tripod, it’s really rather good, especially considering the price!

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PMW-F3 Aliasing Update: Not the issue I feared it might be!

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A further update. Sony have requested the original clips with the moire, and I have provided them with these. I have not been able to reproduce the effect with any other brickwork, roof tiles or other repeating patterns other than charts. There seems to be something about the particularly dark shade of bricks with very bright mortar (cement) that the F3 doesn’t like. In addition I have not heard from anyone else using an F3 out in the wild that is having any issues. At least now I know what to watch out for. The moire was only slight and my wife didn’t spot it until I pointed it out to her.

I am very pleased with the images I’m getting from my F3 having just finished my first paying job with it. It was nothing exciting, just a corporate shoot, but the shallow DoF and reduced amount of lighting required has resulted in some really nice footage of an otherwise dull subject. I can’t show you the clips due to client confidentiality, but the client likes the look a lot and it was easier to achieve than it would have been with a DSLR thanks to the proper video camera ergonomics.

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PMW-F3 Aliasing Update: Not the issue I feared it might be!

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A further update. Sony have requested the original clips with the moire, and I have provided them with these. I have not been able to reproduce the effect with any other brickwork, roof tiles or other repeating patterns other than charts. There seems to be something about the particularly dark shade of bricks with very bright mortar (cement) that the F3 doesn’t like. In addition I have not heard from anyone else using an F3 out in the wild that is having any issues. At least now I know what to watch out for. The moire was only slight and my wife didn’t spot it until I pointed it out to her.

I am very pleased with the images I’m getting from my F3 having just finished my first paying job with it. It was nothing exciting, just a corporate shoot, but the shallow DoF and reduced amount of lighting required has resulted in some really nice footage of an otherwise dull subject. I can’t show you the clips due to client confidentiality, but the client likes the look a lot and it was easier to achieve than it would have been with a DSLR thanks to the proper video camera ergonomics.

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PMW-F3 and EX1R aliasing comparison.

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PMW-F3(top) and PMW-EX1R(bottom)

Here is a roughly done (sorry) comparison of the aliasing from an EX1R at the bottom and my F3 at the top. The F3 had a Nikon 18-135mm zoom, both cameras were set to default settings, 25P. The F3 clearly shows a lot more chroma aliasing appearing as coloured moire rings in both the horizontal, vertical and diagonal axis. The EX1R is not alias free. The chroma aliasing from the F3 is not entirely unexpected as it has a bayer sensor and there is always a trade off between luma resolution and chroma resolution and the point where you set the optical low pass filter. Frankly I find this performance a little disappointing. More real world test are needed to see how much of a problem this is (or is not). To put it in to some perspective the F35 aliases pretty badly too, but that camera is well known for producing beautiful images. I hope I’m being over critical of this particular aspect of the F3’s performance, because in every other respect I think the camera is fantastic.

UPDATE: I’ve taken a look at the MTF curves for the F3 and they are quite revealing showing that an OLPF is in use which is giving an MTF50 of around 800 LW/PH V and 950 LW/PH H. This is not quite as high as an EX1 and are quite reasonable figures for a 1920×1080 camcorder.  This suggests that the aliasing is largely limited to the chroma sampling of the sensor. As this is a bayer (or similar) type sensor the chroma is sampled at a reduced rate compare to luma, which is why coloured moire is not entirely unusual.

Tests performed with a Tokina ATX-Pro 28-70mm lens at 25P

Feeling a bit better about my F3 now 🙂

PMW-F3 Horizontal MTF
PMW-F3 Vertical MTF
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PMW-F3 Aliasing and Moire.

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I’ve been testing and playing with my F3 and first off let me say this… I love this camera, it produces amazing images and I can play with lots of lenses!

But, it’s not all roses. The F3 suffers from aliasing. A zone plate shows extensive aliasing. Until today this had not caused any concerns as I had seen little evidence of it in actual footage, but when shooting some brick houses this afternoon I came across some coloured moire patterns appearing as faint coloured stripes across the brickwork in the footage. It’s not anywhere near as bad as a DSLR, my wife looked at the footage and didn’t notice it until I pointed it out to her, but it’s certainly there. This is disappointing on a camera at this price level, my EX1 doesn’t do this. Now the zone plate shows this to be an issue with the cut off of the optical low pass filter, so I doubt that there is much that can be done in the firmware, but then Sony have done some clever stuff in the past with firmware updates. When working on my picture profile settings I did find that increasing detail above -15 would increase the visibility of the aliases on the zone plate, however when I tested various detail settings with the brickwork there was little difference. I think Nigel Cooper has also seen this, but I’ve not seen it mentioned anywhere else. Has anyone else observed this?

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PMW-F3 Picture Profiles. First Batch.

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OK here we go. Here are some notes from testing my PMW-F3. First thing is… aliasing… a zone plate looks pretty bad with a fair amount of aliasing. I had heard rumours of this from others with pre-production units, but in the field I had not seen anything that would worry me. While the zone plate is not pretty, real world aliasing looks acceptable. I usually use brickwork and roof tiles to test for moire and these look clean on my F3. I think a fine patterned shirt could cause concern and I need to look into this further. I am surprised that there is not more about this on the web!

Excessive detail correction does increase the aliasing, however turning detail and aperture off does not reduce the aliasing significantly. Keep the detail level below -15 to avoid increasing the strength of the aliases. Above -15 the aliasing artefacts are more noticeable. Detail “Off” appears to be the same as Detail -25. Below -25 the image softens, below -45 very noticeably and there are some strange increases in aliasing below -50. For the moment I will be using detail at -17 or off.

The aperture setting can be used to add a little sharpness to the image to compensate for not using detail or a low detail setting. Aperture does not increase the appearance of the aliasing artefacts as strongly as the detail correction. I like the added crispness I can get with Aperture set to +30 combined with detail at -17. I would strongly recommend against using a raised aperture setting if you have detail higher than -15 as this will add sharpness to any detail corrected aliases and lead to twittering edges on horizontal and vertical lines.

Colours have that usual Sony look. Not bad and pretty natural looking, but for me a little on the green side. For a more natural 1:1 look I quite like these Matrix settings:
R-G +10, R-B +4, G-R 0, G-B +14, B-R +3, B-G -3, Std Matrix.

For a more Canon like look with Rec-709 Matrix I came up with these:
R-G -2, R-B +9, G-R -11, G-B +2, B-R -16, B-G -10, Std Matrix, level +14, Blk Gamma -20

For use with Cinegamma 1 I use the above with Matrix Level +25, Blk Gamma -36. Highlights are a little washy, but as with any Cinegamma the best results are obtained by grading in post production.

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Download and print your own test charts.

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Clearly these will never be as good as, or as accurate as properly produced charts. Most home printers just don’t have the ability to produce true blacks with razor sharp edges and the paper you use is unlikely to be optimum. But, the link below takes you to a nice collection of zone plates and resolution charts that are useful for A/B comparisons. I split them up into quarters and then print each quarter on a sheet of A4 paper, joining them all back together to produce a nice large chart.
http://www.bealecorner.org/red/test-patterns/