Fs700 raw & iso

S

sissond

Member
Quick question. I'm trying to wrap my head completely around the RAW output of the FS700. Does the FS700 utilize a pre-amp between the sensor and A/D converter that impacts the raw data? Or are ISO adjustments to RAW output simply metadata and ISO setting doesn't really change anything? And can you point me to a definitive source for this answer. I can't find anything official on this.
TIA,
Doug
 
Fairly certain ISO/gain is applied pre-ADC. Sony has a digital ISO function and it's called CineEI and isn't available in the FS700, only FS7/F5/F55. The difference in noise between shooting at high gain vs base gain and pushing in post is quite significant in my experience, and white clip clearly changes. I don't think Sony has ever made a camera that wasn't ADC limited and didn't have adjustable gain amplifiers.
 
Excellent. I thought that was the case, but then I started seeing info on other cameras like RED's and some Blackmagic cameras that do it as metadata.

So, if the gain is applied right after the sensor, and the picture profile doesn't impact the linear gamma output, then does it make sense to use a PP that allows for a lower minimum ISO (than the ISO 2000 of SLOG2)? Or does it not matter because the native ISO for the 700 is already 2000 and you want the RAW signal as far to the right as possible? Just looking at this after typing it, I'm pretty sure that's the case.
Thanks,
Doug
 
ISO is highly depending on PP for internal recording since it is determined by the Sony's specs for each particular gamma curve. ISO2000 is actually the same gain as CINE4 ISO640 for example. The lowest ISO at each PP is actually the same gain with essentially the same white clip and noise performance (besides 709 800%), just a different gamma curve that causes the ISO to be different for each gain level. For RAW output, you pretty much have to use Slog2 anyway.
 
nyvz said:
ISO is highly depending on PP for internal recording since it is determined by the Sony's specs for each particular gamma curve. ISO2000 is actually the same gain as CINE4 ISO640 for example. The lowest ISO at each PP is actually the same gain with essentially the same white clip and noise performance (besides 709 800%), just a different gamma curve that causes the ISO to be different for each gain level. For RAW output, you pretty much have to use Slog2 anyway.
Click to expand...

Okay, I think I get it now. The lowest ISO # changes for each PP, but the gain remains the same. So, changing PP with different ISO # shouldn't affect the RAW. But I might pick a different PP to improve internal for dailies or backup.

Thank you to all,
Doug
 
Picture Profile affects internal recording, not RAW. But it also affects the camera LCD monitor. So if you use that to judge exposure then you are not seeing what the RAW recorder is capturing. This is why Odyssey7Q+ locks you to only certain PP, so that the images match.

Also please note this: The sensor ISO is 2000. You can add gain but the native sensor is still 2000. Picture Profiles may clamp the image, thereby offering a falsely reduced sensitivity, but the sensor itself is not changed.
 
Mitch Gross said:
Also please note this: The sensor ISO is 2000. You can add gain but the native sensor is still 2000. Picture Profiles may clamp the image, thereby offering a falsely reduced sensitivity, but the sensor itself is not changed.
Click to expand...

I think you are going to confuse people by telling them a sensor has an ISO... As far as I understand a sensor can't really have an ISO without a manufacturer specified middle grey which is generally only specified for a particular gamma curve (post-debayer, post-processing). Why would adding gain in an ADC limited system keep the same ISO? You're suggesting that even though white clip changes and noise level change the ISO should stay the same?

Also worth noting is that in my years of using the FS700 I've always found the ISO2000 to not match up with other cameras, and having just tested it directly side by side with an FS5, the image is nearly identical to the FS5's ISO3200. I had a feeling they just adjusted ISO number rather than actually changing the sensitivity of the camera since they use the same sensor. Moral of the story: Be wary of using ISO numbers to do anything but compare to other ISO numbers in the same camera system.
 
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