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Hello everyone, As I consider buying my first light meter and delve deeper into the world of cinematography, there are a few questions I can't seem to find (satisfying) answers for, at least online. I'd really appreciate any help in these matters. Question 1 Why is it so important to define a camera's true native ISO. Not the marketed one but the actual real one. I've learned how to do it it but I still don't understand why I'd do it. As an example (hypothetical), let's say I'm using an Alexa and I come to the conclusion that its real ISO is 400 instead of the proclaimed 800. What am I supposed to do with that? Should I question the way the stops are supposedly distributed between shadows and highlights? Supposedly at ISO800 it's -7/+7 stops of range, did that range now move to 400? Like what's happening here? Also, does it differ from camera to camera, even if it's the same model? Or can I trust the results from tests done from people I know I trust; whether online or otherwise, for that specific model? I understand we must test, test and test. As a novice I can assure you this notion is drilled into our minds by almost every self respecting cinematographer, gaffer, DIT etc. And I am thankful for it. However can't we trust these manufacturers at least a little bit? Question 2 I took a cinematography workshop not too long ago, my first, and was introduced to light meters and how useful they are. Now that I'm about to work on my first couple of projects I can't imagine myself not using one. However. During that workshop several people had the same light meter (mostly Sekonic 858) and, surprise, not all readings were the same. From the same position on the same spot, whether reading incident light or spotting, people were getting (slightly to not-so-slightly) different readings. So here's my question, how can I tell if I can trust my light meter? I live in a country where most people don't use light meters and we don't have any kind of support to send them off to calibration. Any suggestions? In case it's essential to make sure that the light meter is reading accurately, does anyone know of someone or of a service center that does this anywhere not in the Americas? Also, has anyone ever dealt with Sekonic's service center, the one in Oman? Many thanks. Don't judge me too harshly on my trust issues :)

Shooting with Sony F5, the idea is to have a final film with a cinemascope look once it'll be projected. I know I can't have the choice but to shoot with the native aspect ration of 17:9 of the F5, I'll so put the letterboxing markers (2.4) that crops the native aspect ratio. My question is: do I lose lots of resolution once I put 2.4 mattes on the 17:9 native to create the cinemascope look? What could be the solutions? If I shoot 4K external could be a better compromise to the loss of resolution? Since I'm recording with an higher resolution then the internal 2K? (When I set the mattes in the camera, do I record already with them? or the markers are just guide lines that help me framing knowing what would be the cinemascope look at the end?) If I shoot with Red Epic (Dragon sensor), what could be the best aspect ratio settings for a final cinemascope look? 6 wide, or do I crop later with the mattes? I can't use any anamorphic so I can't take this possibility into account. Thanks a lot for any help!