topic Re: ISO Expansion - ISO 50, Good or Bad? in General Discussion

ISO Expansion - ISO 50, Good or Bad?

Waddizzle — Wed, 18 May 2016 14:09:44 GMT

I am fairly new to DSLRs, with just over 2 years under my belt, but not SLR photography. I am still learning all of the nuances that digital photography brings to the table, compared to my film world from 30 years ago. Let's say I took a sabbatical from the hobby, so I could raise a couple of sons. The drug store disposables were more economical than using an SLR.

Enough of that. I have recently rediscovered that my 6D has ISO expansion at the top end, like most Canon DSLRs. But, it also has an expansion in the low, "L", direction, too. The higher ISOs tend to introduce noise, and freely admit that I have never used them.

However, I recall going through the menus early on, and making a decision not to make ISO 50 available for use. I have run into several occasions where a wide open aperture [f/1.4], ISO 100, and a 1/4000 shutter speed, added up to an overexposure. I found that I either had to stop down the aperture, which upset the bokeh I wanted, or resort to using an ND filter, which frequently introduce their own set of WB and CA problems.

I do not recall the rationale behind my decision to make ISO 50 unavailable for use. Does the ISO 50 setting put extrain strain on the sensor or electronics? At the moment, I cannot think of how it could be harmful. Obviously, there is some drawback associated with it. Otherwise, why would it be made an option, like high ISO expansion, instead of simply making it available at all times?

Re: ISO Expansion - ISO 50, Good or Bad?

RobertTheFat — Wed, 18 May 2016 16:12:17 GMT

I may have read somewhere a while back that sensor performance isn't as good at very low ISO settings, especially when the ambient temperature is unusually low. That's the only reason I can think of for avoiding it. If I were in your shoes, I guess I'd give it a shot and see how it works out. If it were liable to damage the camera, I think the instruction manual would warn you.

Re: ISO Expansion - ISO 50, Good or Bad?

kvbarkley — Wed, 18 May 2016 16:16:21 GMT

Generally, the lowest ISO setting is the one that takes the signal directly from the photosensors. All other higher ISO's have amplifiers to boost the signal.

I would guess that an ISO of 50 actually *attenuates* the signal from the photodiodes, so it won't harm the camera but it won't work any better than ISO 100. Think of it as a neutral density filter.

Re: ISO Expansion - ISO 50, Good or Bad?

diverhank — Wed, 18 May 2016 16:19:57 GMT

Waddizzle, I think you pretty much answered your own questions on this topic 🙂

ISO 50 is an artificial setting taken from ISO 100 and reduced 1 f/stop by the camera. The advantage is, as you stated, it allows you to open the aperture or decrease the speed 1 more stop. The cost of ISO 50 is reduced Dynamic Range. I do not believe that there's a discernible difference in the noise level between 50 and 100 so ISO 50 should be only used when you need to use the extra stop.

Re: ISO Expansion - ISO 50, Good or Bad?

Waddizzle — Wed, 18 May 2016 16:24:02 GMT

@RobertTheFat wrote:
I may have read somewhere a while back that sensor performance isn't as good at very low ISO settings, especially when the ambient temperature is unusually low. That's the only reason I can think of for avoiding it. If I were in your shoes, I guess I'd give it a shot and see how it works out. If it were liable to damage the camera, I think the instruction manual would warn you.

Nah, I'm not worried about damage, no more than using ISO expansion at the top end is a risk. I guess I'm thinking more about image quality, than actual physical harm.

So, far my test shots at ISO 50 don't look any different from ISO 100. But, I'm waiting for a brighter sunny day to test it out, instead of the intermittent rain and cloudiness I've had for the past 10 days.

Re: ISO Expansion - ISO 50, Good or Bad?

Waddizzle — Wed, 18 May 2016 16:28:49 GMT

@diverhank wrote:
Waddizzle, I think you pretty much answered your own questions on this topic 🙂

ISO 50 is an artificial setting taken from ISO 100 and reduced 1 f/stop by the camera. The advantage is, as you stated, it allows you to open the aperture or decrease the speed 1 more stop. The cost of ISO 50 is reduced Dynamic Range. I do not believe that there's a discernible difference in the noise level between 50 and 100 so ISO 50 should be only used when you need to use the extra stop.

Why would Dynamic Range be reduced? I would not be surprised if would be. Obviously, there is some down side to it. Maybe, the sensor is being operated at such a low power, or amplification, that noise creeps in. Sort of like how driving at a very slow speed dramatically reduces your gas mileage? That's the best GUESS that I can come up with.

Re: ISO Expansion - ISO 50, Good or Bad?

Waddizzle — Wed, 18 May 2016 16:30:28 GMT

@kvbarkley wrote:
Generally, the lowest ISO setting is the one that takes the signal directly from the photosensors. All other higher ISO's have amplifiers to boost the signal.

I would guess that an ISO of 50 actually *attenuates* the signal from the photodiodes, so it won't harm the camera but it won't work any better than ISO 100. Think of it as a neutral density filter.

I was thinking the same thing, except that the amplifiers are still in the signal path at ISO 50, but are operating at such a reduced gain level that extra noise is introduced?

Re: ISO Expansion - ISO 50, Good or Bad?

diverhank — Wed, 18 May 2016 17:17:54 GMT

@Waddizzle wrote:
Why would Dynamic Range be reduced? I would not be surprised if would be. Obviously, there is some down side to it. Maybe, the sensor is being operated at such a low power, or amplification, that noise creeps in. Sort of like how driving at a very slow speed dramatically reduces your gas mileage? That's the best GUESS that I can come up with.

I guess because the image at ISO 100 is darkened to make it ISO 50, you end up losing some highlight end...Dpreview did a review on the 5DMark II and mentioned this... I'm cutting an excerpt from it below:

http://www.dpreview.com/reviews/canoneos5dmarkii/25

Re: ISO Expansion - ISO 50, Good or Bad?

Waddizzle — Wed, 18 May 2016 17:33:26 GMT

Nice info, thanks.

Hmm, that seems a lot like a frequency response thing. Audio amplifiers can suffer from a similar fault. They're designed to amplify a range of audio [light] frequencies equally and uniformly at all gain levels.

However, frequency response of the gain at either the low or high end of the frequency spectrum can drop off, which means the bandwidth becomes narrowed at low gain levels.

In the case of ISO 50, and also at the high ISOs, the drop off in gain must be fairly uniform across most visible light frequencies.

Re: ISO Expansion - ISO 50, Good or Bad?

ebiggs1 — Thu, 19 May 2016 12:29:17 GMT

All sensors can work outside of the ISO settings available in the menus. A sensor dosen't care what ISO setting is used. It works the same at whatever ISO setting. The sensor sends the data to the circuitry and it does the rest. The main reason that more ISOs are not offered is they are too far out of reasonable acceptability by Canon. It does not damage the sensor.

The early Nikons started at ISO 200. ISO 100 was considered low. The settings outside of the ones considered normal are for, you just have to get the shot no matter what situation. But it may not be up to expected quality.

Re: ISO Expansion - ISO 50, Good or Bad?

Peter — Sun, 22 May 2016 09:38:03 GMT

ISO L is ISO 100 overexposed. You will get less noise (due to more photons) and less dynamic range. I have a picture showing the difference in the highlight from a 5D at ISO L and ISO 100.

To get the best out of your sensor, ETTR at ISO 100 is the key. After the exposure you make the raw file darker in your raw converter so it doesn't look too bright.

If you shoot at f/1,4 and 1/4000 and ISO 100 with your 6D you may cut highlights if you ETTR because of the hidden ISO boost at f/1,4. With lenses that the camera can't read the aperture from, for example a M42-adapter, you will never get the hidden ISO boost.
You can do the same just loosing your EF lens a little bit so that the camera and the lens can't communicate.

The attached pictures below show the hidden ISO boost at ISO 100, f/1,4 and 1/50 second from a 7D. This is just the boost, not the light loose due to wide aperture. The ISO boost will get stronger with f/1,2 or f/1. First picture shows the ISO boost, the second picture shows without ISO boost with stoped communication between lens and camera.

This is how to get the most out of the sensor without installing Magic Lantern. With Magic Lantern it is possible to get real ISO 66 or ISO 77 and that will will give more photons (less noise) and higher dynamic range (around 0,38 EV). Still in development mode.

What is true about L and ISO 100 is also true for ISO 320 (ISO 400) and ISO 500 (ISO 400). ISO 320 will get less noise but lower dynamic range. ISO 500 will get more noise and less dynamic range.

I use the knowledge above when I shoot landscapes. Then I have plenty of time to make all the settings. For weddings and portraits, I don't really have the time to fix all those settings more than that I never ever shoot at ISO 125, 250, 500, 1000 because of more noise and less dynamic range.

Will your consumers be able to notice any difference? Probably not, but this is how it works and knowledge about your camera equipment is never a bad thing to understand.

Re: ISO Expansion - ISO 50, Good or Bad?

ebiggs1 — Sun, 22 May 2016 13:41:31 GMT

Peter,

The native vs normal ISO was a big thing sometime ago but I thought it was settles that it is a bogus thing. I always knew it was bogus. But others didn't. I know some folks seem to see what you try to describe but is it really there? I think no it isn't.

When the ISO is changed your camera just adjusts the signal gain. You are changing the amount of amplification applied to whatever the sensor saw. Each sensors data can be amplified in this way a certain amount before Canon says it is unusable.

Shooting with one of the extended ISOs, H or L, is the same as editing your photographs in LR then pushing the exposure ahead or back a stop or two.

This is a place where the advertising department has taken control because saying their camera can shoot fro 50 to 1000,000 sounds real impressive. The sensor isn't doing any of it. The circuitry is.

Re: ISO Expansion - ISO 50, Good or Bad?

RobertTheFat — Sun, 22 May 2016 17:36:41 GMT

@ebiggs1 wrote:
Peter,
The native vs normal ISO was a big thing sometime ago but I thought it was settles that it is a bogus thing. I always knew it was bogus. But others didn't. I know some folks seem to see what you try to describe but is it really there? I think no it isn't.
When the ISO is changed your camera just adjusts the signal gain. You are changing the amount of amplification applied to whatever the sensor saw. Each sensors data can be amplified in this way a certain amount before Canon says it is unusable.

Shooting with one of the extended ISOs, H or L, is the same as editing your photographs in LR then pushing the exposure ahead or back a stop or two.
This is a place where the advertising department has taken control because saying their camera can shoot fro 50 to 1000,000 sounds real impressive. The sensor isn't doing any of it. The circuitry is.

I have no opinion about Peter's claims, but I don't think I believe your conclusion. You seem to be conflating analog amplification (in camera) with digital amplification (via editing in LR) without any supporting physics to justify the equivalency. Even if we assume, for the sake of argument, that the in-camera amplification is nominally digital, there's no obvious justification for the assumption that the algorithms applied to accomplish the amplification in camera and in LR would be the same.

Re: ISO Expansion - ISO 50, Good or Bad?

Peter — Sun, 22 May 2016 20:35:46 GMT

@ebiggs1 wrote:
Peter,
The native vs normal ISO was a big thing sometime ago but I thought it was settles that it is a bogus thing. I always knew it was bogus. But others didn't. I know some folks seem to see what you try to describe but is it really there? I think no it isn't.
.
I am not talking about native ISO. I am talking about intermediate ISO and why you shouldn´t use ISO 125, 250, 500 and 1000. Maybe you missunderstood when I wrote "real ISO 66" and Magic Lantern? Real compared to L that what I know is not allowed to be called ISO 50 by the ISO standard. If you define ISO based on the clipping point, your camera's L is actually just ISO 100. This ISO 66 is as true as ISO 100, 200 and 400 are. It allows capturing more photons without clipping, than does ISO 100. Canon L and ISO 100 clip at the same number of photons captured.

I haven´t seen any proofs of the opposite about the intermediate ISO 125, 250, 500 and 1000. I posted a very good link, but it was erased.

@ebiggs1 wrote:

Shooting with one of the extended ISOs, H or L, is the same as editing your photographs in LR then pushing the exposure ahead or back a stop or two.

I wrote that. "ISO L is ISO 100 overexposed". I just didn´t write Lightroom or H.

Re: ISO Expansion - ISO 50, Good or Bad?

ebiggs1 — Mon, 23 May 2016 06:37:27 GMT

Peter and Bob from Boston,

My point is, I know of the theory about the ISO's, but it doesn't exist. It has gone on for years. But my contention is, and I thought it was conceded, to be false. The result is the same. LR or in camera pushing makes no difference.

The primary reason for L and H and H1, H2, or H3 on some cameras is, the product isn't at Canon's standards but is usable if the photographers absolutely wants the shot.

Personally what I have seen seems to prove it to me. Of course this is an area where I love to delve in to. Love the discussion guys.

Perhaps a Moderator that knows Canon can shed 'light' on this?

Re: ISO Expansion - ISO 50, Good or Bad?

Peter — Mon, 23 May 2016 12:44:58 GMT

Well, rawdigger shows the opposite. The exposure at ISO 160 is in fact the result of exposure at ISO 200, but shifted to the left by 1/3 EV. This suggests that though the noise at ISO 160 seems to be lower than noise at ISO 200, the signal-to-noise ratio is the same and there is no benefit of using ISO 160, at least if you shoot raw. On the other hand if you shoot video or jpg it may be handy to use 160, 320, 640.

Forum threads at magic lantern and the creator of rawdigger showed 2013-2014 that this is true. What has happend since 2014 that shows something else?

Re: ISO Expansion - ISO 50, Good or Bad?

Waddizzle — Mon, 23 May 2016 13:12:03 GMT

"Shooting with one of the extended ISOs, H or L, is the same as editing your photographs in LR then pushing the exposure ahead or back a stop or two. .... The sensor isn't doing any of it. The circuitry is. "

Sorry, but I simply do not see how that assertion could hardly be true. Note, this does not mean I disagree. It means your explanation to support it is pretty thin.

As I stated in my original post, I've run up against a wall where my settings are f/1.4, 1/4000, and ISO 100 add up to an overexposure. What you're saying is that if I capture the overexposed image at ISO 100 and post process, then that would be the same as shooting the originial shot at ISO 50?

I never knew that LR contained any circuitry.

Re: ISO Expansion - ISO 50, Good or Bad?

ebiggs1 — Mon, 23 May 2016 14:27:24 GMT

Peter I am not trying to say there isn't a difference, I am trying to say, possibly not clearly, the difference is in the processing. It doesn't come from the sensor. It doesn't really matter whether it is done in camera or in post. The results are or can be the same.

After all the resulting product is what is important not how it got there. As you change the ISO, you are simply adjusting the signal gain. This amount of analog gain or amplification applied to what the sensor saw. Absolutely this is analog vs digital, as Robert pointed out, gain but in the end it results in the same product.

True I am talking the H side of the ISO range so what happens at the L side? The camera effectively cuts the shutter speed from ISO100 in half. In other words the digital gain is .5 instead of 1. It then adjusts the tone curve and BAM, you have ISO 50. Obviously twice as much light results in less noise. But other areas suffer, like highlights as they will clip much faster. This same thing can be applied in post and shot at ISO 100.

This is easy to test. I don't need to tell you or Bob from Boston how but you might want to do it. I guess what I am trying to say is all ISO numbers are just that numbers. They are values of amplification in the circuitry.

Re: ISO Expansion - ISO 50, Good or Bad?

Peter — Mon, 23 May 2016 14:27:41 GMT

Ebiggs1 is right about L, H and H1, H2.

L is in the 6D just ISO 100 overexposed and digitally pulled down. You can do the same in Lightroom or whatever you want to use. In 5D classic, H is ISO 1600 underexposed and digitally pushed one step. You can do the same in Lightroom.

If you want more reading to geek you down in the thingy, just google iso 160 and magic lantern.

Re: ISO Expansion - ISO 50, Good or Bad?

Peter — Mon, 23 May 2016 14:49:18 GMT

Seems maybe we missunderstand each other, Ebiggs1, and probably because of my English.

This is how I have got it:
L is ISO 100 overexposed 1 step. Same thing if you shoot ISO 100 overexposed and pull it back 1 step in LR.
ISO 100, 200, 400, 800, 1600 etc are analog signals.

ISO 160 is ISO 200 digitally pulled. ISO 250 is ISO 200 pushed. Same thing can be done in LR.

ISO H is highest analog signal digitally pushed 1 step. Same thing can be done in LR.

To shoot ISO 100 and digitally push it in LR 3 steps is worse than to shoot ISO 800 in camera. It works on newer Sony sensors but not with Canon sensors. It is calles ISOless. There have been examples comparing Canon sensors and Sony sensors by shooting ISO 100 and digitally push it 5 steps to show how much greater Sony is. But that is not how to use a Canon. A Canon gives much better results if you use the analog signals before pushing the signal digitally.