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Zak Ray

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  • Occupation
    Cinematographer
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    New York

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  1. PCam appears to use 0.021 for S35 1.78.
  2. Thanks Dom, that's very helpful. The reason I keep pressing for a formula is because I'm working on a DOF calculator and I thought it'd be useful to allow users to plug in their own numbers. But I appreciate the futility of trying to narrow it down to multiple decimal places, fair enough. It's good to know that there's some talk about updating the standard for modern cameras. Does anyone else have an opinion on what that "updated standard" might be?
  3. Thanks David, I agree they should only be used as guidelines, but broadly speaking, I would think the CoC for theatrical projection vs. a home television would be noticeably different; for most people, the movie screen fills up a larger amount of the field of vision, and so the need for precision is greater. Or are you saying even then the difference is negligible? Simon, I agree that human vision has to come into the equation, which is why the "visual acuity" parameter is part of the formula. My (admittedly shaky) understanding of why visual acuity = 1/1000 is derived from here. I could be totally off base here, but thats why I'm asking for the formula 🙂
  4. Thanks Simon. My understanding was that besides lens design, it's also necessary for DOF calculations, and in order to select the right value, one has to consider the size of and distance to the final screen. For example, this post... ...gets at what I'm trying to achieve; specific CoC values for different presentations. I want to know how those values are calculated. I'm not quite sure I understand what you mean by the medium affecting the result.
  5. I get the concept behind CoC, I'm just trying to wrap my head around the formula. I've seen the simple approach ("d/1500") but I want to actually plug in different values for screen size. My understanding of the full formula is this: CoC = (Visual Acuity * Viewing Distance) / (Display Diagonal / Camera Sensor Diagonal) I know the "standard" CoC is 0.001". I assume that's for Super35 1.78, which is a diagonal of 27.54mm. I don't fully understand the visual acuity part, but from what I've read it should be around 1/1000 for normal vision? So with that information, I can reverse engineer the formula to be: (1/1000 * 52') / (57' / 27.54mm) = 0.001" (obviously after converting all the units) 57' seemed like a reasonable diagonal for a theater screen, and 52' was the required viewing distance to get to an answer of 0.001". Is this anywhere near correct?
  6. I'm working on a new app for cine lenses -- if anyone wants to try it I'd love the feedback. Main features will be specs and sensor coverage but general tools like lens matching, FOV, DOF etc will likely be added. If you're interested here's the link: https://mailchi.mp/8fe94682fa6a/lenskitbeta
  7. Thanks Adrian, yes I would love to have some bulbs with high TLCI but it's impossible to find manufacturers that test for it, short of TV/film manufacturers like Quasar. That said, I have noticed that most lights with high TLCI also tend to have a high CRI. So I might take my chances with those bulbs and see what happens.
  8. Here's a few interesting options: 5500K, 93 CRI: https://www.bhphotovideo.com/c/product/1403778-REG/alzo_2000_55_04_di_fs_8w_joyous_spotlight_dimmable.html 5000K, 90 CRI: https://www.bulbs.com/product/LED9A19-81L-950 3000K, 92 CRI: https://www.bulbs.com/product/E12A19DLED930-JA8 2700K, 91 CRI: https://www.bulbs.com/product/F8-5A19DLED927-JA8
  9. Reviving this thread if I may. Anyone made any new discoveries? I was excited about the Quasar A-series, but they took them off the market due to overheating issues.
  10. Thanks guys. So the consensus is I shouldnt be trying any sort of beam angle compensation, meaning in terms of the Aputure light, itd be fair to say that its a 1.5K equivalent. I just have to factor in that its a smaller beam angle. Right?
  11. Thanks Adrian. I hear what you're saying re: measuring the center of the beam, but wouldn't the center naturally dim as the beam angle increases? I might indeed end up renting some lamps to test, but at the moment I'm just comparing a lot of them online to gauge what's in the ballpark of what I'm looking for. And yeah, I know marketing deparments can go a little wild! (I remember the Litepanels Sola 6+ being marketed as a 1600W HMI equiv-- ended up being closer to a 650W tungsten)
  12. Hi all! I'm trying to get all the variables straight in determining light output equivalency. For example, I'd like to compare the Aputure 300D (a claimed tungsten 2K equivalent) to an actual Arri 2K Fresnel. Here's my math: The Arri Photometric calc tells me a T2 fresnel outputs 354 FC at 3m/10ft with the lamp at full flood. The specs on Aputure's website list the 300D at 1800 FC at 1m/3.3ft with the lamp at full flood (using the fresnel attachment). I use an inverse square calculator to convert that to 272 FC at 3m/10ft. So that would lead me to believe the Aputure has about 75% the output of the Arri, meaning it's equivalent to about a 1.5K. However, this doesn't take into account beam angle. The flood beam angle of the Arri is 56º, and the flood of the Aputure is 42º. That's another 25% loss if we account for beam angle. So that theoretically puts the Aputure at 1.1K. I have a hunch that calculating beam angles this way isn't correct. Can anyone weigh in? Thanks!
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