bnk1953
Junior Forum Member
Posts: 184 
Open to constructive criticism of photos: Yes
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Post by bnk1953 on Mar 5, 2020 18:45:30 GMT
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Post by Peterj on Mar 5, 2020 19:37:02 GMT
Absolutely! Exposure definition (only aperture + shutter speed control light amount) is rather a hard sell to many folks, and it's exacerbated by using camera sensitivity to light.
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Post by kdcintx on Mar 6, 2020 16:51:55 GMT
Very good explanation and demonstration that ISO is not part of the actual exposure of the sensor to light. Thanks for sharing.
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Post by pontiac1940 on Mar 6, 2020 17:40:18 GMT
bnk1953 Wow that was excellent. (How good was it? I watched all 12 minutes 50 seconds of it!) Good information that was well presented. The guy is good. Thanks for posting this. Clive PS: I do not mean to distract from this excellent post, but this is closely related. Below is a handout I wrote many years ago in the days of film. It was updated about 7 years ago. The basics are the same. It goes into speed and apertures in some detail ... and mentions ISO (thankfully in the correct context  ) Anyone is free to download the PDF ... clivesphotos.weebly.com/uploads/5/1/0/9/51095487/photography_basics____updated_2014__cas.pdf
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Fauxtoto
Established Forum Member
Quebec, Canada
Posts: 426
Open to constructive criticism of photos: Yes
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Post by Fauxtoto on Mar 13, 2020 19:18:32 GMT
Thank you for sharing this fun and informative video concerning what is ISO and how it relates to exposure. After viewing it, I fell on this short related article. Paraphrasing both sources, I prepared a written summary to highlight key points: 1. Only shutter speed and aperture affect how much light is hitting the sensor. ISO does not. Increasing ISO has nothing to do with with increasing how much light hits your sensor. 2. The sensor is composed of a number of photosites, one photosite for each pixel. 3. During the exposition, light photons are collected in the sensor’s photosites, producing an electrical charge. The brighter the light, the more photons are collected, and a higher electrical charge is generated. Different pixel photosites register different electrical charges. 4. Once the exposure is complete, each individual pixel photosite’s electrical charge must be measured and then turned into a digital value by an analogue-to-digital converter. 5. Increasing ISO consists of amplifying the electrical charge in the sensor’s photosites. 6. The higher the ISO, the more the camera amplifies the electrical charge. The more the electrical charge is amplified, the brighter the image is. 7. The amplification of the electrical charge occurs after the sensor is finished being exposed to light, but before each individual photosite’s electrical charge is sent, from the sensor, to the camera’s analogue-to-digital converter. 8. At its lowest native ISO (for example ISO 160 for the Fujifilm X-T3 camera), a camera does not need to amplify the voltage at the sensor before the electrical charges are sent to the camera’s analogue-to-digital converter. 9. ISO does not create noise. ISO is amplifying the noise that is already there to begin with. 10. The more the electrical charge is amplified with ISO, the more the noise is amplified. Still, as stated in the video, having ISO in the “Exposure Triangle” [with shutter speed and aperture] is helpful to conceptualize how the various controls of the camera work together to create the image. |
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Post by tonyw on Mar 13, 2020 20:59:06 GMT
Good summary. I was particularly interested as I have that camera although the principle applies to all digital cameras. I continue to be impressed by how much better sensors are these days compared to my first digital camera - back some 23 years ago. The sensor in that Fuji, like many others these days, is ISO invariant which basically means that, if you shoot RAW, whether you use ISO in camera to amplify or use "Exposure" in post-processing makes no difference to the result. So shoot at low ISO in low light and what appears all black can be recovered in post processing just as if you had shot it with a high ISO camera setting to start with. Must admit I don't really see the point of doing that as with mirrorless cameras what you see is what you get so I don't really want to see nothing in the viewfinder when taking a shot! I do however use the principle with landscapes with a big difference in brightness between the sky and the shadows - so I usually expose for the sky knowing that I can always boost the shadows selectively later in post processing.
Tony
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Post by hmca on Mar 14, 2020 14:28:15 GMT
I have found this thread to be very informative. Thanks to all who contributed here.
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) Anyone is free to download the PDF ... 
