jaygould wrote:
You can set your Auto ISO to begin wherever your camera's dual ISO kicks in. So then you have two choices:
1. 100 ISO
2. Auto ISO (for whenever you need anything more than 100. But it will skip all the ISOs below the dual gain point).
On my Sony, I normally shoot in Aperture Priority mode, in an effort to choose the best aperture for the scene (sharpness, depth of field, etc.) Given the best aperture, if there isn't enough light for a steady shutter speed, I increase the ISO. Any concern over shadow noise, I delegate to DxO Pure Raw or Adobe.
How would I modify my workflow to take advantage of dual gain ? Or does adequate noise reduction in software bypass the issue ?
jaygould wrote:
Since I learned about this (a few weeks ago), I only use ISO 100 and 400 now (where dual gain kicks in on my camera). There is no point in using anything else. It's better to lift the exposure in post. This way you avoid clipping the highlights.
You can set your Auto ISO to begin wherever your camera's dual ISO kicks in. So then you have two choices:
1. 100 ISO
2. Auto ISO (for whenever you need anything more than 100. But it will skip all the ISOs below the dual gain point).
Are you using mirrorless?
Kenneth Lee wrote:
On my Sony, I normally shoot in Aperture Priority mode, in an effort to choose the best aperture for the scene (sharpness, depth of field, etc.) Given the best aperture, if there isn't enough light for a steady shutter speed, I increase the ISO. Any concern over shadow noise, I delegate to DxO Pure Raw or Adobe.
How would I modify my workflow to take advantage of dual gain ? Or does adequate noise reduction in software bypass the issue ?
It would be a pretty simple input from you in my opinion. If you are shooting in a scenario where you know you need to use a faster shutter speed and therefore increase your ISO, shoot at or above the second gain value for your camera. You can find that info on the Photonstophotos website.
Else, if you are shooting in a scenario where you are on a tripod in nice and bright light then use your first base value ISO for your camera.
For example, I am primarily an astrophotographer and landscaper. The two values for my Z6 are 100 and 800. When I am shooting landscapes, I use 100. When I am shooting astro, I use 800. Occasionally I will shoot some Loons handheld in a kayak. I need a faster shutter speed, so I will use 800.
AZHeaven wrote:
Erik Durnall on the A7IV FB page had a video of the dual ISO of the A7IV. After testing he found the dual ISO of the A7IV to be 400 and 1600.
For cinema cameras, at least, there is a distinction between "dual gain" and "dual ISO." Not sure if this distinction applies to stills cameras, though, but I always get confused when I see "dual gain ISO."
In the dual gain sensors used in some cinema cameras, the camera actually captures and averages two images for each frame: one circuit amplifies the higher end of the dynamic range and the other circuit amplifies the lower end; the two images are combined in-camera and dithered down to produce one image with maximum dynamic range.
In dual-ISO (or perhaps more accurately dual-native ISO) sensors, only one image is captured for each frame; the gain is determined by your choice of ISO; typically there are two native ISOs.
"Dual Gain sensors have two paths from the same photo sites. One has a "high" and one has a "low" amplification. Therefore you have two images coming from the sensor, captured at the exact same time from the same photons hitting them. They are entirely discrete from each other. For each frame captured you have two images. Double the bandwidth. Double the memory. Not just at the sensor (which includes its on-sensor circuits and processing) but though the WHOLE camera that has to be able to have a clock speed fast enough to handle dual images. It's like needing the overhead and speed of processing of 48 fps when you're only shooting 24 fps.
Eventually at encoding to a file we can read these images are combined and then then dithered down.
In BMD's dual gain cameras these are dual 11 bit images, that create a combined 22 bit image that is then dithered to a single 16 bit linear image and then converted to log and stored as a 12bit image. None of that happens in the sensor of the circuits of the sensor. The sensor just spits out two frames for every frame you capture.
In a dual ISO camera you have dual amplifications but you only ever use a single one of those "circuits" at a time. You're not processing at 48 FPS, it's only 24 fps. The user chooser which circuit to activate based on their "iso" choice. These are known as dual ISO or dual native cameras. You need half the bandwidth to process the image."
Kenneth Lee wrote:
On my Sony, I normally shoot in Aperture Priority mode, in an effort to choose the best aperture for the scene (sharpness, depth of field, etc.) Given the best aperture, if there isn't enough light for a steady shutter speed, I increase the ISO. Any concern over shadow noise, I delegate to DxO Pure Raw or Adobe.
How would I modify my workflow to take advantage of dual gain ? Or does adequate noise reduction in software bypass the issue ?
If you shoot in changing light often, or shoot with variable aperture zooms, it's rarely worth the extra effort to hard lock to the two best ISO values. Your most important settings are aperture (for sharpness, vignette, and depth of field) and shutter speed for degree of motion.
Modern tools are so good at mitigating high ISO that it's simply not worth thinking about in faster paced shooting.
Now, if you are tripod shooting a landscape and have more time to set the shot up, then yes, you might as well pick base or the dual gain value.
bjhurley wrote:
For cinema cameras, at least, there is a distinction between "dual gain" and "dual ISO." Not sure if this distinction applies to stills cameras, though, but I always get confused when I see "dual gain ISO."
In the dual gain sensors used in some cinema cameras, the camera actually captures and averages two images for each frame: one circuit amplifies the higher end of the dynamic range and the other circuit amplifies the lower end; the two images are combined in-camera and dithered down to produce one image with maximum dynamic range.
In dual-ISO (or perhaps more accurately dual-native ISO) sensors, only one image is captured for each frame; the gain is determined by your choice of ISO; typically there are two native ISOs.
"Dual Gain sensors have two paths from the same photo sites. One has a "high" and one has a "low" amplification. Therefore you have two images coming from the sensor, captured at the exact same time from the same photons hitting them. They are entirely discrete from each other. For each frame captured you have two images. Double the bandwidth. Double the memory. Not just at the sensor (which includes its on-sensor circuits and processing) but though the WHOLE camera that has to be able to have a clock speed fast enough to handle dual images. It's like needing the overhead and speed of processing of 48 fps when you're only shooting 24 fps.
Eventually at encoding to a file we can read these images are combined and then then dithered down.
In BMD's dual gain cameras these are dual 11 bit images, that create a combined 22 bit image that is then dithered to a single 16 bit linear image and then converted to log and stored as a 12bit image. None of that happens in the sensor of the circuits of the sensor. The sensor just spits out two frames for every frame you capture.
In a dual ISO camera you have dual amplifications but you only ever use a single one of those "circuits" at a time. You're not processing at 48 FPS, it's only 24 fps. The user chooser which circuit to activate based on their "iso" choice. These are known as dual ISO or dual native cameras. You need half the bandwidth to process the image."...Show more →
The terminology is definitely a bit muddied and inconsistent across the industry but here are the terms generally used:
Dual Gain ISO: Camera supports two distinct analog gain/conversion factors, with only used for a given exposure.
Dual Gain Output: Camera supports two distinct gains applied to the same exposure, increasing DR without compromising full-well capacity / saturation.
My video focuses on Dual Gain ISO, but includes a reference to Dual Gain Output in the last chapter, including a simulation of the noise improvement it can produce.
ISO 800 is best for astro only if you view astro through the narrow prism of shooting with star trackers. In all other cases star motion makes ISO 800 mostly useless for night sky photography. I find that particular genre not terribly exciting but fail to see how anything below ISO 3200 at f2.8 is even remotely feasible without a star tracker.
snapsy wrote:
I've published a video explaining what Dual Gain ISO is, why it's important, how to find the dual gain ISO level for your camera (using the Nikon Z6 III as an example), strategies for taking advantage of it, how it affects N-Log, and what the future holds for possible improvements. Although this video uses the Nikon Z6 III as an example, the concept applies to all cameras with dual gain ISO sensors, including other cameras from Nikon, Canon, Sony, etc...
To help make this technical subject easier to understand I use analogies and simplifications to the underlying mechanisms involved in dual gain ISO. If you'd like to dive deeper and gain (ahem) an even greater understanding of how sensors implement dual gain ISO I suggest reading the Aptina Dynamic Response Whitepaper on the subject, which Bill Claff hosts on his PhotonsToPhotos site:
0:00 What is Dual Gain ISO?
2:44 How to find Dual Gain ISO level
5:46 ISO doesn't cause noise
6:40 Dual ISO shooting strategy
7:48 N-Log and Dual Gain ISO
8:22 Future: Dual ISO readout
RoamingScott wrote:
If you shoot in changing light often, or shoot with variable aperture zooms, it's rarely worth the extra effort to hard lock to the two best ISO values. Your most important settings are aperture (for sharpness, vignette, and depth of field) and shutter speed for degree of motion.
Modern tools are so good at mitigating high ISO that it's simply not worth thinking about in faster paced shooting.
Now, if you are tripod shooting a landscape and have more time to set the shot up, then yes, you might as well pick base or the dual gain value.
snapsy wrote:
My video focuses on Dual Gain ISO, but includes a reference to Dual Gain Output in the last chapter, including a simulation of the noise improvement it can produce.
Ah yes, I saw that piece at the end; I hadn't watched it all the way through.
The older Blackmagic Design cinema cameras that I use have this dual gain output, which is nice, although their sensors are tiny (smaller than Micro Four Thirds) and need a lot of light. I was taught originally to shoot everything on these cameras at the "native" ISO of 800 and use ND filters to bring down exposure to avoid clipping in brighter conditions, while generally exposing to the right to maximize the amount of light hitting the sensor. But I've recently been won over by another faction of users who advocate for using lower ISOs, like ISO 400, in low-light conditions: it essentially fools you into exposing to the right, but in a more controlled way, because the image will look underexposed on your monitor otherwise. This approach reduces shadow noise at the expense of higher risk of clipping the highlights.
For daylight conditions, they advocate shooting at ISO 800 to capture detail in the highlights (again, using ND filters if necessary); you don't have to worry about shadow noise in those conditions. None of this ISO adjustment affects the amount of light hitting the sensor, it just helps guide you into making exposure choices that will maximize the amount of light received by the sensor to minimize noise and preserve highlights.
It's totally counterintuitive, but it works as long as you can actually see anything on your monitor in dark environments with your aperture wide open; when it's just too dark I have to bump up ISO or increase shutter angle (equivalent to reducing shutter speed, which increase motion blur). Or maybe I'll get a Z6iii for those conditions.
GroovyGeek wrote:
ISO 800 is best for astro only if you view astro through the narrow prism of shooting with star trackers. In all other cases star motion makes ISO 800 mostly useless for night sky photography. I find that particular genre not terribly exciting but fail to see how anything below ISO 3200 at f2.8 is even remotely feasible without a star tracker.
How does a different ISO change the apparent motion of stars?
RT-- wrote:
How does a different ISO change the apparent motion of stars?
Static or landscape images you can pull up in post, but with stars we are moving - so on a tracker you can shoot low ISO and longer exposure - but for static images (stacked or not) you need to balance shutter speed with star movement, so generally faster shutter to minimize trailing with high ISO and then potentially stacking to bring out more signal over the noise.
RoamingScott wrote:
If you shoot in changing light often, or shoot with variable aperture zooms, it's rarely worth the extra effort to hard lock to the two best ISO values. Your most important settings are aperture (for sharpness, vignette, and depth of field) and shutter speed for degree of motion.
Modern tools are so good at mitigating high ISO that it's simply not worth thinking about in faster paced shooting.
Now, if you are tripod shooting a landscape and have more time to set the shot up, then yes, you might as well pick base or the dual gain value.
I typically shoot auto iso and set both the aperture and shutter and let the camera figure out what iso I need. The only time I can see setting iso for best quality is shooting landscapes, and even then there can be reasons why I need to set the iso away from their optimal settings.
RT-- wrote:
How does a different ISO change the apparent motion of stars?
It does not, I think the other user was referring to that ISO 800 is useless if you are not using a star tracker. Although it needs to be said ISO 800 and 3200 don't actually increase any signal, just that 3200 will make the back of camera preview brighter.
For years I use the following ISO strategy with my A7III:
Normally ISO 100.
Only if shutter speed is a little bit slow for handheld shooting, I quicken it by going to ISO 200.
If I have little light or need fast shutter speed (moving subjects...), I go to ISO 640 (the dual gain point in this camera).
Only if ISO 640 absolutely doesn't suffice, I go higher (just as much as I need).
The range from ISO 250 to ISO 500 I avoid like the plague 😎
