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Gabriel Devereux

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    Digital Image Technician
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    Australia / United Kingdom

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    gabrieldevereux.com/imaging

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  1. There is a quote (I believe from Toby Tomkins). We live in a world where a computers scaling algorithm impacts colour more than a colourist nuance... Is the colour shift constant throughout scaling from 99% to 1%? If its constant its a software bug - if it shifts sporadically (IE not a constant) then its potentially a signal path / hardware issue that requires software compensation. G
  2. I don’t mean to be obtuse but, that isn’t my question. At what point is a sensors capacitance reached? A photo site well doesn’t exist - A photodiode has a depletion region. A photo site is the area of the photodiode plus circuitry. In terms of managing capacitance with tiny readouts are we talking about actual latitude of the analogue ‘wire’ the photo sites ‘drain’ as in the depletion region itself of a photodiode or the readout time in relation to the shutter. I should also add a photo site doesn’t store photons… it’s a common misconception. Instead electrons absorb the magna of energy from the incoming photons and generate a current.
  3. As always your posts are brilliant and enlightening - May I ask, what do you mean in terms of managing capacitance? Is that in terms of storing charge at the photosite itself? The MOSFET power follower? The impedance prior to the drain causing noise? Or the actual read-outs running to the column amplifiers and then to ADC? Thanks G
  4. I guess the question becomes - as far as I’m aware the easiest thing to scale in a 3T/5T APS Photosite is the photodiode itself. Metal wiring/channels could theoretically get smaller with a smaller voltage but, it’s a constant. Which is why past a threshold a smaller photosite drastically impacts the diode and therefore the total sensitivity of the camera. so…? who knows
  5. It helps that a kino Flo is currently much less expensive than a rival LED of a similar nature in terms of spectral content and arguably build quality. However, LED tech is still, to a certain degree, in its infancy and soon they'll equalise. A more fun answer is... I should emphasise most/all LED fixtures are different. Even a full white light LED doesn't have full consistent 'RGB' spectral content - in the terms of an even coverage over the visible light spectrum in relation to its apparent color temperature. Generally when trying to achieve a certain RGB colour (in most cases mixing multiple frequency bands) the spikiness/unevenness of the spectral content is more pronounced even with RGB... insert more diodes here... WW LED's. An RGB LED has a discontinuous spectrum and RGBWW LED I believe all frequency bands overlap when emitting variations of white (a mixture of warm white and cool white with minor correction to remain on planckian) however, when achieving certain colours is discontinuous. A fluorescents spectral content while spiky is not discontinuous.
  6. Considering a lot of DP's don't even use contrast ratios, no. How you wish a face/scene to be lit in terms of key/fill, mood, chiaroscuro in general is personal taste. Generally, continuity dictates you don't dramatically change the key/fill, lighting in general of a scene without just cause. However, like all aspects of lighting, key/fill ratio's are just a guideline to help you achieve your vision. The only exception I can think of is when second unit is trying to match first. In some cases the cinematographer has to attempt to match these ratios in which its a more exact science.
  7. It's interesting, I'm trying to find the exact law I poorly quoted above. The calculator currently gives an output in LUX. It's written and from my tests, working (in terms of near accurate approximations). Shoot me an email when you're free (have put it above) and I'll send it through as would be great for you to have a play!
  8. Thank you! I've been using a photon counter and using some fun math taking into account certain standards to arrive at photographic values. However, foot lamberts is as perfect! If not more in this scenario. WIth Ev being a constant in this scenario. The variable is R (which as a reference grey card as shown bellow would be a reflectivity of 0.18, I believe muslin should read about a 0.735 which is the figure I'm currently playing with but, unsure!) , is the luminance, in foot-lamberts, is the illuminance, in foot-candles, and is the reflectivity, expressed as a fractional number (for example, a grey card with 18% reflectivity would have ). I've never used a spot meter with foot lamberts (or foot candles). In a sense, according to some law of quantum dynamics (which I've forgot) a photon is destroyed and created on reflection - in a sense you're measuring after destruction and the newly formed photon count is of course theoretically less than and the ratio in a sense between the two is the reflectivity. If one doesn't have a spot meter theoretically you could achieve the same with a light meter (that you wouldn't mind clamping to a controlled point). Thank you again!
  9. I will note, one thing I'm playing with at the moment is massive reflectors like 40' by's. As of course if you're subject is 10' away from a 40' (which is a bit nuts) lamberts cosine law would be required to take into account the outer edges and such. Should be easy enough to compute.
  10. Yes! The angle does however, I find in most lighting scenarios DoP's try... (or potentially should) try and keep the normal of a bounce perpendicular to the subject. If they don't generally the light is sharper and the projected light is uneven (unless of course this is a desired effect... which does somewhat elude me) note the infamous Roger Deakin's cove does make a lot more sense! Funnily enough though, lamberts cosine law is pretty simple to calculate. In fact in terms of what we do a simple rule is if you're subject is more than 60 degrees from your reflectors normal (a hypothetical direct line being projected perpendicularly from the reflector) you loose a stop and at that point it does increase exponentially. In terms of specularity, I believe you're correct! I remember reading a post you wrote a while back. I'm not too ofay with the exact point a surface becomes 'near' lambertian to which this calculator is <85% accurate, but I've noted most non-specular materials such as Ultra bounce are near enough however, materials such as silver stipple is another question. The issue is well is as soon as you need to start inputting the normal of your incoming source in relation to the normal of your reflector the inputs become more complex. It's fine for people that know, but the goal of this preliminary one is for it to be a (while slightly inaccurate in terms of a quarter of a stop which I believe should be negligible) a fool proof calculator with the only information required is available from a fixtures photometric chart. Would be great to talk more! As always talking makes one think which of course helps. My email is gabjol@me.com
  11. I should note, currently it also only works for non-specular light reflectors. Working on a calculator that can. Also working on one for a diffuser.
  12. Hi, I'm currently finishing off a soft-light large reflector fall-off calculator. The calculator, in premise, works by modelling the reflecting soft surface as being composed of many point sources, say m*x, whose total light output is the same as total luminous flux of the original light sources (minus losses). If the total luminous flux of the sheet is L, then the luminous flux of a single point source is L / m*n Of course above is heavily simplified, the goal was to take into account the majority of the variables one can compute while not making user input absurd. The only factor not taken into account is lamberts cosine law in terms of an assumption the point sources emit light isotropically in a solid angle of 2(pi) steradians (only in front of the surface). The calculator calculates light-output along the normal of the reflector - with that if the calculated point is 'off' normal one would need to take into account the appropriate light loss. In terms of reflector material, that's where I'm stuck as I don't have a large inventory of industry standard rags (doing this while on holiday in a very remote region). A simplified way of calculating light loss from each reflector material (ultra bounce, muslin, grey card) is to just compute from it's LRV (Light reflectance value - such as a standard grey card being 18%). I'm currently calculating from muslin and assuming a LRV of 73.5% as that's the reflectance value of cotton fibre. However, if anyone had at there disposal industry standard Muslin rags (with fireproofing etc), Ultrabounce and so on and would be willing to do a few tests for me, that'd be incredibly useful! There are 'proper' ways of doing it, but, from my tests with non-standard material if one has a spot meter (preferably one that gives an FC output), lights and a grey card it can be easily found. My set-up works by setting up a grey card and lighting appropriately so that the projected light is, within reason, even. I then try to have my card read at 50fc, approx T4, 400ASA, 180 degrees. I then set up the tested rag directly adjacent or directly behind the grey card and take another reading. Typically (when the grey card is set-up in front of the material) I'll take a reading, remove the card and then take a reading in the exact same place on the material. https://en.wikipedia.org/wiki/Light_reflectance_value If anyone has any spare time and fancies contributing some information to this project it would be fantastic and greatly appreciated! G
  13. In terms of designing a permanent set, with the goal of it lasting years to come and it being capable to adapt to multiple camera packages store bought commercial LED's are probably not going to be your friend. Flicker, a more quantifiable issue is more easily overcome in terms of just finding an LED fixture with a fast, consistent frequency that aligns with your frame-rates. However, colour shifts and spectral content is a variable dependent on another variable, your camera package. From my understanding only quite expensive fixtures designed for superior spectral content (in terms of RGB LED's) or again white light fixtures designed with spectral content in mind would be suitable for this kind of set-up. I know aperture made a bunch of discontinued 3200k 'white light' LED's. I've never used or tested them but that may be an interesting avenue to explore! I imagine they wouldn't be too expensive now. (The only reason I recommend them as logic would dictate they've taken a higher frequency band LED and used a strong fluorescent phosphor to emit a wide even frequency band, as a single phosphor LED typically has more spectral content).
  14. Hi All, For an upcoming shoot I'm utilising multiple FX3's and need to record ProRes RAW for a final deliverable of ProRes 4444 (transcode). I need to record from multiple FX3's for a number of hour long increments and was hoping to record externally to a Shogun or such with 8TB SATA SSD's. I'm thinking of taking the UHD 16-bit Linear RAW out (from HDMI which is odd) > Cat3 HDMI > BMD 12G HDMI to SDI Adapter > 12G BNC to Shogun. I'm going off the fact you can take a similar output utilising a 12G out from the FX6. Has anyone ever tried this? Also has anyone tried the Samsung/Sony 8TB SATA SSD's with 500 MB/s write speed + on the Atomos external recorders? Thanks Gabriel
  15. Potentially metamerism - the lack of spectral content from a few modern LED fixtures leads to a smaller gamut of colours being resolved (less energy/information = less colours). Note, this isn't just with LED fixtures but most spiky spectrums. LED's are just potentially spiky and discontinuous which does emphasise this effect. The camera package and more importantly the spectral curves of the camera lining up with the spectral distribution of the fixture also has impact. As then you have less information being emitted and then the camera not even capturing that information.
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