Why don't digital cameras go below ISO 100?

[keymoo]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

 

[Sugasmune]

D810 has real iso 64 and fake 32

 

[walkaround]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

Because there is no such thing as "ISO 100" in digital cameras. It's just an arbitrary number.

Every camera maker tweeks their sensor and lens combo to get the apparent brightness of a photo to be the same as every other camera using the same "exposure triangle" parameters. So the exposure settings on a tiny pocket cam are the same as a full frame. The total light of course is not the same, due to the tiny lens and sensor on the pocket cam, hence the noise is higher.

Film speed, on the other hand, was per area, so ASA 25 was the same speed regardless of the format used.

 

[The Davinator]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

Because there is no such thing as "ISO 100" in digital cameras. It's just an arbitrary number.

Every camera maker tweeks their sensor and lens combo to get the apparent brightness of a photo to be the same as every other camera using the same "exposure triangle" parameters. So the exposure settings on a tiny pocket cam are the same as a full frame. The total light of course is not the same, due to the tiny lens and sensor on the pocket cam, hence the noise is higher.

Film speed, on the other hand, was per area, so ASA 25 was the same speed regardless of the format used.

Wow....so much misinformation it's almost laughable.

 

[soufiej]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

Not sure why this matters. Sort of like, why is thirty two degrees not zero degrees? Or, why is zero the same as thirty two? The actual numeric value is inconsequential to its practical use. Start anywhere you want and you make the same movement from one up or one down. Today I was in the middle of a staircase and on the fifth step I asked myself, "Why am I in the middle? Yesterday I went up an escalator and I was on the first step but got to the middle."

 

[The Davinator]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

Not sure why this matters. Sort of like, why is thirty two degrees not zero degrees? Or, why is zero the same as thirty two? The actual numeric value is inconsequential to its practical use. Start anywhere you want and you make the same movement from one up or one down. Today I was in the middle of a staircase and on the fifth step I asked myself, "Why am I in the middle? Yesterday I went up an escalator and I was on the first step but got to the middle."

I matters when trying to maintain shutter eeds in bright light.

 

[BertIverson]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

You may get better answers to this question if you post it in the "Photographic Science and Technology Forum". The truly knowledgeable folks seem to frequent the PST forum.

My primitive knowledge on this subject would say that "base ISO" is determined by the "full well capacity" of the sensor. (no more light can be accepted).


Good question though,
Bert

 

[mike703]

http://dpanswers.com/content/tech_iso.php

- scroll down to the bit about 'digital ISO'.

Ultimately there is a tradeoff. All other things being equal, to reduce the base ISO of a sensor from 100 to 50, the photosites have to be able store twice as many electrons before they fill up. At the same tech level that means making them twice as large in terms of surface area, which means halving the resolution of the sensor...

Best wishes

 

[walkaround]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

Because there is no such thing as "ISO 100" in digital cameras. It's just an arbitrary number.

Every camera maker tweeks their sensor and lens combo to get the apparent brightness of a photo to be the same as every other camera using the same "exposure triangle" parameters. So the exposure settings on a tiny pocket cam are the same as a full frame. The total light of course is not the same, due to the tiny lens and sensor on the pocket cam, hence the noise is higher.

Film speed, on the other hand, was per area, so ASA 25 was the same speed regardless of the format used.

Sources:

"In digital camera systems, an arbitrary relationship between exposure and sensor data values can be achieved by setting the signal gain of the sensor. The relationship between the sensor data values and the lightness of the finished image is also arbitrary, depending on the parameters chosen for the interpretation of the sensor data into an image color space such as sRGB.

For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure. The usual design is that the camera's parameters for interpreting the sensor data values into sRGB values are fixed, and a number of different EI choices are accommodated by varying the sensor's signal gain in the analog realm, prior to conversion to digital. Some camera designs provide at least some EI choices by adjusting the sensor's signal gain in the digital realm."

Film speed - Wikipedia

en.wikipedia.org

* * *

Excellent Tony Northrup video on YouTube, skip to 3:36, relevant example slide is at 8:30

* * *

"Most manufacturers specify the ISO of digital cameras – both still and motion picture – based on the settings which tend to create an image of equivalent apparent brightness to a notional photochemical picture..."

http://www.redsharknews.com/technology/item/1966-understanding-iso-in-digital-cameras,-it-s-not-what-you-think-it-is

 

[J A C S]

I believe it is technology related. The full well capacity (FWC) of today's sensors seems to be proportional to the area, roughly speaking. The D810 is a notable exception, and on the other side, there are some ISO 200 sensors with lower FWC per area.

The relationship between base ISO and FWC is a bit loose but up to some degree only. A sensor with a low FWC would clip the highlights if you force it to be exposed as a much lower ISO sensor.

 

[neil holmes]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

My guess is it will come at some point.

Some of my earlier DSLRs had ISO 200 as the low ISO.

My current GX7 also has ISO 200 as the low but has an extended low of 125 ISO.

My Canon 7D has a low of 100 not expandable lower.

My A7/A7s both have ISO 100 as low but expandable 64 and 50 options.

 

[CreeDo]

Sucks your original comment isn't getting much love and the next post down is well-liked... you're right and they're wrong. I guess something about your phrasing is leaving people confused.

For the benefit of those who aren't reading Walkaround's post properly... ISO 100 is simply a "label" hand-picked by the manufacturer to get equivalent brightness between their camera, and all the other cameras out there.

But that setting does NOT factor in the amount of noise in the shot. I think some people have this misunderstanding that ISO 100 = ISO 100 both in brightness and noise level, across any platform.

But in terms of noise, ISO 100 on a Micro Four Thirds is like ISO 400 on a full-frame, it's noisier because the smaller sensor can't gather as much total light (given the same shutter speed and aperture).

And yes, it is somewhat arbitrary in how it's chosen - for example Fuji fudges their ISO numbers a bit so that they are about 3/4ths of a stop darker, but also 3/4ths of a stop less noisy. This tricks the user into, for example, keeping the shutter open longer to get enough brightness... and then when they compare their ISO 400 shots with Fuji to some other camera's ISO 400 shots, they think Fuji has super clean ISO 400 compared to the other guys. They don't, they just lied about the ISO number... the issue is worse at higher ISOs and Fuji's ISO 6400 is actually off by a full stop, it's an ISO 3200 shot.


Loved the Tony Northrup video... shows why it's important, when considering gear, to multiply both focal length AND the f/number by your crop factor. Because we pay out the ass for those low f/numbers, but a MFT f/2.8 is only an f/5.6 full frame equivalent in performance. Nobody's excited or paying extra for f/5.6 but they get misled by the smaller number into thinking they're getting a fast lens with shallow depth of field.

 

[The Davinator]

Nope. The ISO issue here has nothing to do with noise. But do try again.

 

[tjwaggoner]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

Because there is no such thing as "ISO 100" in digital cameras. It's just an arbitrary number.

Every camera maker tweeks their sensor and lens combo to get the apparent brightness of a photo to be the same as every other camera using the same "exposure triangle" parameters. So the exposure settings on a tiny pocket cam are the same as a full frame. The total light of course is not the same, due to the tiny lens and sensor on the pocket cam, hence the noise is higher.

Film speed, on the other hand, was per area, so ASA 25 was the same speed regardless of the format used.

Wow....so much misinformation it's almost laughable.

I'm admittedly no expert but from my reading and understanding of how digital sensors work walk around was correct. Could you share what is incorrect? You have me curious

 

[ully]

When the Asa ratings were changed to Iso the values were copied so that a lens could be used at same settings.

 

[ully]

Simply said there have to be practical limits for everything, even light ,

 

[The Davinator]

Just picked up a Sony A6000 to replace my aging Canon 40D. I've noticed that the lowest ISO setting on both is 100. I fondly remember using Kodachrome 25 on my old Canon EOS 600. I guess it's because IQ can't be improved with lower ISOs on digital tech, but I'm not sure I understand why.

Anyone knowledgeable enough to share why that might be?

Because there is no such thing as "ISO 100" in digital cameras. It's just an arbitrary number.

Every camera maker tweeks their sensor and lens combo to get the apparent brightness of a photo to be the same as every other camera using the same "exposure triangle" parameters. So the exposure settings on a tiny pocket cam are the same as a full frame. The total light of course is not the same, due to the tiny lens and sensor on the pocket cam, hence the noise is higher.

Film speed, on the other hand, was per area, so ASA 25 was the same speed regardless of the format used.

Wow....so much misinformation it's almost laughable.

I'm admittedly no expert but from my reading and understanding of how digital sensors work walk around was correct. Could you share what is incorrect? You have me curious

 

[J A C S]

And yes, it is somewhat arbitrary in how it's chosen [...]

Somewhat is the key word, that is why he is wrong. Try turning your camera into an ISO 10 one by adjusting the brightness.

 

[tjwaggoner]

And yes, it is somewhat arbitrary in how it's chosen [...]

Somewhat is the key word, that is why he is wrong. Try turning your camera into an ISO 10 one by adjusting the brightness.

But don't digital cameras "make up" ISO values sometimes when using auto exposure?

 

[J A C S]

And yes, it is somewhat arbitrary in how it's chosen [...]

Somewhat is the key word, that is why he is wrong. Try turning your camera into an ISO 10 one by adjusting the brightness.

But don't digital cameras "make up" ISO values sometimes when using auto exposure?

Doing it after the shot in this case (low ISO) would be more or less the same.