The Base ISO of Gemini

[Christoffer Glans]

It's always been a discussion around Red about what ISO is actually the base ISO. Some influencers always point out that ISO is irrelevant when working with the sensor, but it's not. ISO is just a mathematical calculation (Gain) of how the base image is handled. Basically, most cameras have been set around ISO800, Alexa, Red, Sony, most of them handle the best balance of DR at 800 and should be exposed at that ISO for the best possible image. After a few years of use, I would say Dragon is around ISO640 for optimal DR, but it can also be different between cameras of the same sensor type and model.

But this becomes more interesting when speaking of Gemini. Where is Gemini rated? It cannot be both standard and low light, because one of the modes is just a different voltage. Is it ISO800 or closer to ISO2500 that is the base ISO? I think it would be of tremendous help if we could clarify what the sensor is most optimal for and not just speculated.

 

[Misha Engel]

 

[Christoffer Glans]

So, how does this work with Gemini? If the camera body is the same between Helium, Monstro and Gemini, is the Gemini the only one having two circuits? Wouldn't both Helium and Monstro be able to have two modes as well? Or is the Gemini sensor the only one which can handle two voltages?

Because the noise at 800 is less than higher ones, even comparing low light to normal. So it wouldn't work as the graph shows.

 

[Phil Holland]

Hi Christoffer,

The general base advice for Gemini as it is a dual sensitivity sensor:

- Standard = ISO 800
- Low Light Mode = ISO 3200

Remember when you do your Sensor Calibration (Black Shading) you want to do it for whatever mode you are filming in.

 

[Misha Engel]

So, how does this work with Gemini? If the camera body is the same between Helium, Monstro and Gemini, is the Gemini the only one having two circuits? Wouldn't both Helium and Monstro be able to have two modes as well? Or is the Gemini sensor the only one which can handle two voltages?

Because the noise at 800 is less than higher ones, even comparing low light to normal. So it wouldn't work as the graph shows.

AFAIK and can explain at the moment.

Every sensor has a noise level (mainly due to temperature).
The circuit after the pixel is a capacitor(still in/on the sensor) to store the amount of electrons created by the photons(light) on the semiconductor pixel.
A dual ISO sensor has not one but two capacitors for each pixel.
Lets assume ISO 800 has a noise of 1 (small capacitor) and ISO 5000 has a noise level of 4(big capacitor).
When you shoot ISO 6400 at the first native ISO-level(800) you will have a noise of 8 x 1noise = 8 noise (8x digital gain).
When you shoot ISO 6400 at the second native ISO-lavel(5000) you will have a noise of (6400/5000) x 4 noise = 5.12 noise (64/50x = 1.28x digital gain).

 

[andrewhake]

Red made it clear in their documentation and tech videos that the Low-Light mode on Gemini will not have as much dynamic range as the standard mode, which makes sense. As Phil mentioned though, ISO 800 in standard mode should give you the best dynamic range the sensor is capable of. Low Light mode is really there for shots that just aren't possible in the standard mode. All that said it's not like the dynamic range massively suffers if you make slight ISO adjustments.

I don't think it's really as cut and dry as a "base ISO" unless you are shooting test images in a very controlled environment.

 

[Don Walker]

This is interesting. The cameras base ISO of 800 vs REDTECHs IPP2 Overview video which states that they have re-rated the ISO by one stop to better match light meters. So when using ISO 400 in IPP2 it is the same as 800 in legacy cameras and processes. Does this mean that 400 in IPP2 is actually 800? Probably. Which then means when you are in 800 in IPP2 then it's actually 1200. Reading the great info in this and then comparing it to how I actually use ISO for production and then what RED recommends in their tech videos makes me believe that there is too much emphasis placed on this one setting in the camera for 98% of digital acquisition. This sensor is great and looks good from 400 to 1200 in standard mode when using IPP2. Which is how I work. Usually I start with a base of 400 in IPP2 and go from there. I use it as part of the exposure equation between shutter angle, frame rate and ISO. ISO was important when it was a film camera and you had to base your exposures based on the ISO of the film in the camera. In digital it's a setting and allows you more flexibility then a single ISO film camera. That's not to say being mindful of your setting isn't important and that there aren't ramifications for your decisions on set. You need to shoot with the camera and learn it, that way you are able to maximize its capabilities. If I told you the base ISO is 800 it really means nothing to you in the grand scheme of things. My bet is that you will find yourself in all kinds of lighting situations and will be moving the ISO setting all the time which is how it's supposed to be.

 

[Nick Morrison]

This is interesting. The cameras base ISO of 800 vs REDTECHs IPP2 Overview video which states that they have re-rated the ISO by one stop to better match light meters. So when using ISO 400 in IPP2 it is the same as 800 in legacy cameras and processes. Does this mean that 400 in IPP2 is actually 800? Probably.

No. In IPP2, ISO levels now match Meters.

So 400 is 400
And 800 is 800.

In legacy mode, the ISO was off by one stop - so Dragon 800 ISO would match 400 on your Meter.

The base ISO of Gemini is up for debate. I generally consider the "base" ISO the highest one w/out NOISE.

So far 400 Gemeni has ZERO noise, and 640 has a smidge (but cleans up easily).

800 probably gives you the most lattitude (like on Alexa), but just like on Alexa if you want super clean then best to ISO down.

We still need to do more tests on our end, but overall we're blown away by Gemini.

The LL is for real.