I attended, working on one of the camera units. Had a great time, learnt lots, at all sorts of levels. Even how to make good use of the Movie Slate application on my iPhone! Link: http://www.fstopacademy.com/
Archive for the ‘camera technique’ Category
Training: Den Lennie’s “Music Video” Experience
Thursday, October 27th, 2011iPhone 4: LightMeter (app) & Theory
Sunday, October 2nd, 2011iPhone app: “Light Meter”:
- Uses iPhone-4’s cameras (front or rear), displaying image with overlays reporting framerate (can specify fixed e.g. 1/60), f-stop, ISO.
- Usage with my Sony XDCAM EX3 video camera:
- In settings, I set Stops to Halves, as that’s what the camera uses.
- I typically use an EX3 with a Tiffen T1 IR-blocking filter. What’s the ISO for this arrangement?
- I’m unsure in this area, but here’s my stab at it anyway, possibly flawed:
- EX3 ISO varies with mode, but 400 ISO is a reasonable estimate.
- CreativeCow post says: ISO 400 in 1080p modes, ISO 500 in 720p modes, ISO 800 in 1080i modes
- Filter loss is 1/2 stop (http://www.tiffen.com/userimages/T1_IR_Charts_SS.pdf)
- I think that implies corresponding equivalent ISOs of 1080p:320, 720p:400, 1080i:640 (based on data from http://c710720.r20.cf2.rackcdn.com/wp-content/uploads/2011/08/ISO-Shutter-Speeds-Fstops-Copyright-2009-2011-photographyuncapped.gif)
- What do the EX3’s ND filters do to the ISO?
- EX3 has ND1=1/8, ND2=1/64
- (From EX3 user manual, page 50)
- I think ISO is linear, so if Camera is 320 ISO, they imply equivalent ISOs by simple division:
- 1080p: Clear=>320, ND1=>40, ND2=>4.5
- 720p: Clear=>400, ND1=>50, ND2=>6.25
- 1080i: Clear=>640, ND1=>80, ND2=>10
- Alternatively, for ND1 filter you can leave the app’s ISO setting as Clear (no filter) and instead adjust the app’s Correction Factor to -3 EV (though it’s maybe better reserved for simulating lighting variations e.g. due to weather, as in the Exposure Value Table further below).
- I guess from this one off case that EV is logarithmic, since 2^-3=1/8 as per ND1.
- That guess was later confirmed by further web research (further below), stating that EV is an “additive system”, i.e. operates in the logarithmic domain, base 2.
- Caution: being an ISO/EV newbie, I can only hope this is is all correct!
- Nevertheless, when I tried my naive settings they worked just fine – I was successfully able to use the iPhone Light Meter to obtain a sensible camera configuration for good exposure level and (given the ND filters) the kind of shot I want (e.g. degree of DOF). When tested on the camera, they all worked out as expected. Cool!
- EX3 has ND1=1/8, ND2=1/64
- The Light Meter app optionally displays EV400, EV100, Lux, FootCandle. Latter units are explained in great detail at at [johnlind…] link below.
- The app can also “log” readings – in the form of jpg images of the screen and overlays including geographical location – to a DropBox account. For example, when I clicked the [Log] button, a jpf file appeared on my MacBook in the folder [ /Users/davidesp/Dropbox/Photos/Pocket Light Meter].
Exposure Values & Exposure Theory:
- http://johnlind.tripod.com/science/scienceexposure.html
- <<The full name for Exposure Value, or EV, is the Additive Photographic Exposure System. Exposure Value has two equivalent definitions. The first defines how much light will be admitted to the film by the combination of lens aperture and shutter speed. The second defines how much exposure is required by the combination of subject luminance (e.g., how bright it is) and film speed. Setting a combination of aperture and shutter speed on a camera with an EV that equals the EV for the subject luminance and film speed should result in a properly exposed photograph>>
- (The article continues at length. For example the “Additive” element reflects the fact that this system operates in the logarithmic domain. The article also distinguishes luminance from illumination, explains units such as point-source intensity in candelas, flux in lumens, light illuminating a surface in foot-candles, light radiated from an area in foot-Lamberts, luminence in candelas per area (square foot or square metre)
- An EV (Exposure Value) table is presented. I guess (?) this is useful for the iPhone app, where EV can be shifted up/down by a control, to estimate what would be needed should the lighting conditions vary:
- -1 EV: light sand or snow
- 0 EV: bright or strong hazy sun (distinct, sharp shadows)
- +1 EV: weak hazy sun (soft shadows; distinct sun outline in clouds)
- +2 EV: cloudy bright (no shadows; sun creates bright area in clouds)
- +3 EV: heavy overcast, but not “black” (no shadows; sun location cannot be determined)
- +3 EV: open shade (in shadow but 60% sky not obscured)
- +4 EV: deep shade (in shadow with obscured sky; under forest canopy)
- http://en.wikipedia.org/wiki/Exposure_value
- Exposure value is a base-2 logarithmic scale
- (This article has a more comprehensive table of EVs and weather conditions etc. than the above)
f-numbers
Fast Shutter Speeds for Action Scenes
Sunday, December 19th, 2010For action scenes like fast ski-ing, what shutter speed is best?
- http://www.dvinfo.net/forum/sony-xdcam-ex-cinealta/472066-ski-race.html
- In general, for action scenes, reduce shutter to 1/125, no faster.
- However some find even 1/125 gives “amateurish” feel, and prefer motion-blur, hence recommend 1/60 (for both 30p and 60p footage).
Shutter Speeds – progressive (24p,25p,50p) and interlaced (50i)
Friday, December 17th, 2010On an EX3, what’s best for indoor shots of lectures etc?
- Normally film runs at 24fps, with a 180° shutter – which is 1/48th second.
- Hence for 25 fps, ideally use 1/50 second, or nearest available match to this.
- Uncertainty: For 50i, each field is at 25fps, so presumably still use 1/50 second ? Depends on how camera works?
- For a shot of someone talking, it would be hard to see the difference between a 1/48th shutter time and a 1/60th shutter time.
- To avoid (conventional) light flicker, frame rate should divide by integer into twice the power frequency.
- EX3 has no 1/50 shutter speed, at least when specified by Time – nearest equivalent is 1/60. This may risk some degree of light-flickering in 50Hz mains countries.
- For 1080i50
- Initially, used “No Shutter”, to maximize exposure with least Gain. But gave noticeable motion-blur.
- For 50p or 25p
- 1/50 or nearest equivalent (on EX3 is 1/60)
- For 50i, opinions vary:
- UseEX3’s nearest equivalent time-based shutter time of 1/60
- Use 180 degrees (assumes this angle relates to frames-per-second, namely 25fps for each frame – but is this valid when interlaced)
- Use No-Shutter (assumes 50i shoots each field alternately, at 50fps, hence no-shutter is inherently 1/50 – but is that assumption true?)
Camera Artistic Techniques
Sunday, July 25th, 2010Camera Artistic Techniques (by Garth of Gold Coast Video Camera Club):
Camera Manual Grip Techniques
Sunday, July 25th, 2010http://digital-photography-school.com/how-to-avoid-camera-shake
- Elbows-in
- Shoot sideways (with respect to to chest), back-elbow against ribcage.
- “Create a Tripod With Your Knee” (bod-pod, as one responder called it)
- Lie face-down (on chest) with hand flat or fisted under lens, to achieve requird tilt.
- “The Machine Gun Hold” – cam-front/lens rests on upper-arm, hand of which grasps upper of other arm. Awkward.
- “Cradle”. A sideways-shooting-mode, with back of camera on shoulder (?) and hands gripping cam from same side, at middle and back.
- It’s best to see the pictures really! At the above link.
Glide-shots: Steady-Shot / Smooth-Deshake-Stabilize / SteadyCam
Sunday, July 25th, 2010Which is best? Depends on the camera, scene and shot dynamics I guess. The same point is queried at the following thread:
Some general advice from a computer-post-savvy author: definitely use the camera’s SteadyShot:
Limitations of post
- Stabilization necessitates motion estimation and image reconstruction, which are extremely CPU-heavy, hence really slow to execute.
- Most stabilization apps (in post) can’t currently cope with motion-blurred edges or parallax effects (though both should be possible in principle, by deconvolution and 3D modelling both informed from multiple frames).
- For rolling-shutter-ed footage (e.g. CMOS sensors as in Sony Exmor as in Sony XDCAM-EX e.g. EX1 & EX3), there exist options to reduce the effect (don’t expect perfection, but may suffice):
- Sony’s ClipBrowser 2.6 can remove this http://www.dvinfo.net/forum/sony-xdcam-ex-cinealta/467511-clipbrowser-takes-out-rolling-shutter.html.
- Gunnar Thalin’s Deshaker plugin for VirtualDub can compensate for this.
My experiences:
- Stabilizing Tools:
- Gunnar Thalin’s Deshaker works really well. And it is multi-threaded, really speeds up the process. The author says it is more intended for handheld pans etc. than fast-shaking shots from vehicles etc. (but has nevertheless seen good results in such situations).
- The author says [http://forum.doom9.org/showthread.php?p=1418923] to try “to stabilize only on the most distant parts in the frames, since the moving inwards-effect is less there”. And “you should probably increase the value for [discard motion of blocks that move > X pixels in wrong direction]. That’s to allow the blocks to move “freely” a little, since Deshaker can’t handle the “moving inwards”-effect.
- Possibly equally applicable to other smooth/stabilize/deshake tools ?
- Boris’s Optical/Motion Stabilizer (in Boris Red 4.3.3 on XP) is only single-threaded and I find it slower, clunkier and less intuitive than Deshaker. Has a Smooth mode, which is like the others here, as well as a Stabilize mode (try to keep frame static, no good for motion then). The other tools can be configured to do the same thing.
- Mercalli in Sony Vegas has no mode for 720p50 but otherwise is pretty good and very intuitive and configurable.
- FCP’s SmoothCam Effect worked best for a challenging clip for wobbly-hand-held camera tracking close past an object (a Formula-1 car) hence huge degree of moving-inwards effect. The default settings worked straight away. The result quality was way above that of the other tools. On the other hand sometimes it’s not the best (sorry, forgot the exact situation).
- Gunnar Thalin’s Deshaker works really well. And it is multi-threaded, really speeds up the process. The author says it is more intended for handheld pans etc. than fast-shaking shots from vehicles etc. (but has nevertheless seen good results in such situations).
- Cameras & Shots:
- Historically, using a TRV33 DV HandyCam indoors (hence low-light hence long shutter time):
- Way back in the past, using a (now ancient) TRV33 DV handy-cam (which has huge sensor margin i.e. spare pixels), when I shot big zooms to lecture audience individuals (e.g. question-time) I had the camera’s steady-shot (digital, not mirror) enabled and used Gunnar Thalin’s Deshaker (VirtualDub plugin) also. The result was astoundingly steady.
- The same arrangement worked OK with hand or shoulder mounted cam for walk-throughs past nearby objects (e.g. walls, people, furniture).
- An attempt to do the same thing without steady-shot enabled on the camera resulted in seriously motion-blurred edges.
- Now, using a Sony EX3:
- With camera Steady-Shot set to Medium, hand-held pans and motion past nearby objects seem to acquire a positional instability, as if the camera feedback mechanism needs greater damping. Maybe the camera’s internal mirror “suspension” has to be tighter (than the TRV33 digital equivalent) because it lacks the generous pixels margin of the TRV33? or maybe something to do with the mirror’s inertia? Or (real-time-constrained) processing-power?
- Experimentation is needed with the camera’s other SteadyShot modes (High, Low).
- In the absence of more generous sensor pixel margins, I wish it could be loosened-up e.g. to allow black borders (to crop in post) so as to permit smoother rides overall.
- With camera Steady-Shot set to Medium, hand-held pans and motion past nearby objects seem to acquire a positional instability, as if the camera feedback mechanism needs greater damping. Maybe the camera’s internal mirror “suspension” has to be tighter (than the TRV33 digital equivalent) because it lacks the generous pixels margin of the TRV33? or maybe something to do with the mirror’s inertia? Or (real-time-constrained) processing-power?
- Historically, using a TRV33 DV HandyCam indoors (hence low-light hence long shutter time):
Shutter speed effect on snowfall
Monday, February 8th, 2010Great sequence of images tally with my general experience:
Basically:
- 1/100 looks slushy, grey and indistinct “cords” (not flakes/lumps)
- 1/500 looks crisp – can see individual snow flakes/lumps falling
Also, from my own experience, is best to focus on 2 metres or so away. Focus matters since DOF small when aperture maxed as one may do to allow max shutter speed (depending on lighting conditions, most likely overcast)