jose_aguirre

<p>Excellent. The analogy could not be better.<br> As I said earlier I have no trouble reading English but convey an accurate idea costs too much and I use google translator.<br />As we know, textual translation is not always appropriate to express some subtleties of language that are necessary for proper context so I thought the following to not be clear if I upload a post in Spanish.<br> I will try to express myself in short sentences, in such a way that the automatic translator requires less range "interpretation" and also upload it in English, I will include the original text in Spanish language in which I can express myself more clearly.<br> Understood that the difference between the specular rebound and diffusion of the light beam on an object produces the need for the introduction of a correction factor, in this PI case, to convert the effect of light energy carried in a light beam when it becomes a spherical distribution, the following question arises me why consideration is made on a sphere or rather on a spherical cap and not on a circle every time when the light beam "hits" on the plane (jet water against the wall), actually what occurs is a flat figure and not a volume.<br> I guess the general expression comes from that source model must be formed by a cone of light expressed in SR which in turn affects the inside of a spherical cap space and relationships arise from combining spherical aggregates with quadratic areas and lengths which they are obviously linear.<br> Turning to the luminance, be noted that the measurement is performed against a reference luminance value "lit my doubt." All a flash!<br> This is absolutely essential and yet, despite having quite sought in this regard, it is never explicitly stated.<br> Now I add a question: there is a "standard" reference luminance or is chosen for convenience?<br />Perhaps because I am familiar with the issues RF, I tend to assume that it is something like dBm, which as you surely know perfectly, it is potentiometric reference that simplifies the end all calculations in the world of Radio communications and sound.<br> If such were the case, there is no problem of understanding the concept of a "negative luminance value."<br> Again, the concept of measurement with respect to a reference value of luminance is the "golden key" to the question.<br> Having mastered these fundamental concepts convey what the source of discussion and exchange of ideas among a group of electronics hobbyists and technology and why friends environment is linked to photography.<br> Thank you very much for your time and congratulations for the strength and clarity of explanations.<br> Down, in spanish</p> <p>Excelente. La analogía no podría ser mejor.<br> Como expresé anteriormente no tengo problemas para leer en inglés pero transmitir una idea exacta me cuesta demasiado y uso el traductor de google. <br />Como sabemos, la traducción textual no siempre es adecuada para expresar algunas sutilezas del idioma que son necesarias para lograr un contexto correcto así que pensé en lo siguiente al no tener claro si puedo subir un post en español.<br> Trataré de expresarme en frases cortas, de tal suerte que el traductor automático requiera menos rango "de interpretación" y además de subirlo en inglés, incluiré el texto original en español idioma en el cual podré expresarme con mayor claridad.<br> Comprendido que la diferencia entre el rebote especular y la difusión del haz de luz sobre un objeto produce la necesidad de la introducción de un factor de corrección, en este caso PI, para convertir el efecto de la energía luminosa transportada en un rayo de luz cuando se convierte en una distribución esférica, me surge la siguiente duda: por qué la consideración se realiza sobre una esfera o mejor dicho sobre un casquete esférico y no sobre un círculo toda vez que cuando el haz de luz "impacta" sobre el plano (chorro de agua contra la pared), en realidad lo que produce es una figura plana y no un volumen.<br> Supongo que la expresión general deviene de que el modelo de origen debe estar formado por un cono de luz expresado en SR que a su vez incide sobre el interior de un casquete esférico hueco y las relaciones surgen de combinar magnitudes esféricas con áreas cuadráticas y con longitudes que obviamente son lineales.<br> Volviendo al tema de la luminancia, hacerme notar que la medición se realiza contra un valor de luminancia de referencia "iluminó mi duda". Todo un flash !<br> Ese hecho es ABSOLUTAMENTE FUNDAMENTAL y sin embargo, a pesar de haber buscado bastante al respecto, jamás está explicitado.<br> Ahora agrego una duda: hay una referencia "standard" de luminancia o se elige por conveniencia ?<br> Quizás debido a que estoy familiarizado con las cuestiones de RF, tiendo a suponer que es algo así como el dBm, que como seguramente usted conocerá a la perfección, se trata de una referencia potenciométrica que simplifica al extremo todos los cálculos en el mundo de las radiocomunicaciones y del sonido.<br> Si tal fuese el caso, no hay ningún problema de entender el concepto de una "luminancia de valor negativo".<br> Nuevamente, el concepto de medición con respecto a un valor de referencia de luminancia, es la "llave de oro" para la cuestión.<br> Una vez asimilado estos conceptos fundamentales transmitiré cuál es el origen de la discusión e intercambio de ideas entre un grupo de amigos aficionados a la electrónica y la tecnología y por qué está ligado al ambiente de la fotografía.<br> Muchas gracias por su tiempo y las felicitaciones por la contundencia y claridad de las explicaciones.</p>

<p>First of all, thanks for the quick response. Fast and very accurate.<br> I carefully follow your articles in Spanish (my native language) in your photography blog and many others written by you at different sites or as courses that can be read or downloaded from the Internet.<br> I have some rather subtle doubts. I read in English without problem but write them, that's something different if I really want to convey the exact idea. (much more if it has included a dubt more than a idea !)<br> I do not know if this site is permitted up a comment in a language other than English.(¿?)<br> I study a little about your answer because not sure why intervenes PI number.<br> My interest is more linked to the electronic portion of photometry, but I admire photography as an artistic discipline and its documentary value.<br> <br />And that is why I value your articles because I learn a little (as a novice ) of photography and when is necessary the mathematical physicist rigor, you perfectly explicit about these.<br> That's not easy to find on the Internet and helps a lot in learning, especially when that they want to learn has some knowledge of physics and mathematics which it is the place where all languages happily converge.<br> Those blogs o artistic notes that are too oriented to photography itself ignored those concepts or not to give it true importance.<br> <br />I will now review the concepts that told me and surely return with some more specific question .<br />Again, thank you very much.</p>

<p>According to the indication of Paco Rosso I understand that the relationship between the illuminance of a scene and its corresponding luminance is always equal to the ratio of 270 to 15.41 ?<br />That would be a fixed reflection factor for the scene.<br />I guess it can be really valid if one uses an 18% gray card or anything like that but not in the case of a real scene .<br />I try to learn about it and really the Paco's answer is the most precise and specific that I found on the subject. Thank you very much for sharing.</p>