Need help with exposure question

[Ysarex]

You could lower the EC another stop or so. Maybe it would be better to slow the shutter by one stop or raise the ISO one stop. You could also use the RAW image that would give you more play with the shadow slider. A lot depends on the capability of your camera's DR.

If flash is not an option, you could have added more ambient light, possibly the best solution.

That wasn't possible -- all the interior lights were on. I wasn't comfortable with a slower shutter speed. And in that situation you would have raised the camera ISO. That's your exposure triangle methodology. And in the real world raising the ISO would have reduced DR -- that's what it does. You would have ISO clipped the information out the window with the DR reduction that came from raising the ISO.

So here's a real world example of how applying an understanding of the way the camera works allowed me to take a photo that you would have failed to get if you raised the ISO.

View attachment 165183

Because I didn't raise the ISO I retained the full DR of the sensor and I was able to keep the real world data that you see out the window in my finished photo. And that's a real world example of how you can take a better photo when you understand how the hardware works and can think clearly about it. I got a real world better photo by ignoring the triangle.

Joe

Joe,

This now prompted a thought. I know there is the whole concept of expose to right. As in better to be overexposed by a stop than underexposed.
How does ISO come into play, or does it not?

Tim

Sent from my SM-J737T using Tapatalk

Great question and another can of worms. The term ETTR is unfortunately troll chum so I'm not going to use it. The pertinent term here we want to use is SNR -- the ratio of signal to noise. With digital we get a straight linear response here: more exposure = better SNR. There's absolutely no downside to that except the pragmatic requirements of taking the photos. It's the age old compromise. We're indoors and the light is dim and we don't want to use flash or a tripod and as a result to hand-hold the camera we have to reduce signal. Our hardware is so bleep bleep good now that we can get excellent quality photos with only 1/10 of the signal our sensors are otherwise capable of. Go back and look at that ISO 12K image I posted from my XT-2. Pragmatically I will tell my students that if maintaining a specific shutter speed is the critical factor then set and lock that shutter speed and put the camera on auto ISO. They complain that they were taught to never use auto ISO. Always try to keep the ISO as low as possible is what they were taught. I cuss and tell them to get the bleep photo! Just wanted to say that to maintain perspective.

So SNR is exposure. And here it really matters to say SNR is exposure the way exposure is traditionally defined. SNR is not "proper exposure" the way the ET works. Maximize SNR to the capacity of the sensor and you capture the maximum amount of data and more data is always better than less data. This one is as simple as 2 + 2 = 4.

Some caveats: Digital sensors clip hard. It's a concrete wall and there's no give if you hit it. So if maximum SNR is good, clipping the sensor is bad. In this situation our camera engineers design a hedge into the camera's exposure system. Most people think base ISO refers to the light sensitivity of the sensor -- it doesn't. Base ISO refers to the standard output brightness of the camera JPEG. All of our cameras are to a greater lesser degree designed to deliberately underexpose the sensor. Generally between 1/3 to 1 full stop. If you try to assess that for your camera and work around it you're playing a dangerous game with a concrete wall.

ISO (here I go again) is not an exposure determinant but it certainly changes the data recorded in a raw file if you raise it. Raising ISO boosts, brightens, gains, amplifies, multiplies the data that is being recorded and stored. You read about cameras having a bit depth like 12 bits or 14 bits etc. Most of our cameras now are 14 bits. 2 ^ 14 = 16,384. All our data ends up as numbers. If you record a brightness value and the number the ADC would assign to that brightness value is 300 at base ISO then if you raise the ISO a stop that number is recalculated as 600 and stored. So you see this coming now right -- if you record a highlight value and the number the ADC would assign to that highlight value at base ISO is 6,000 then if you raise the ISO a stop that number becomes 12,000 and if you raise the ISO 2 stops your highlight is clipped because 16,384 is the biggest number you can store. Raising ISO reduces DR.

Go back to the first set of photos I took with the G7 of the fish and jars. My job was to take one photo at ISO 1000 and another at ISO 125 both at the same exposure. To do that I started by calculating the ISO 1000 exposure. Knowing the ISO would be set at 1000 my job was to avoid ISO clipping but get as close as I could to recording maximum data at ISO 1000. That photo had some specular highlights -- look at the front of the jar of dried mushrooms. I allowed those speculars to clip in the ISO 1000 photo. One of the problems I had in making the two photos visually match is that those specular highlights didn't clip in the ISO 125 exposure!

Joe

 

[Derrel]

It's a shame that the truth sometimes takes so many words to explain. Joe's two excellent posts above show why the so-called exposure triangle is no longer applicable, now that ISO invariance completely invalidates one of the critical parameters of the so-called exposure triangle.

 

[n614cd]

It's a shame that the truth sometimes takes so many words to explain. Joe's two excellent posts above show why the so-called exposure triangle is no longer applicable, now that ISO invariance completely invalidates one of the critical parameters of the so-called exposure triangle.

Umm.... Based on Joe's vehemence, I think he would state it was never valid. And he really does have a point, and I am glad he decided to tilt at this particular windmill.
Now the question is if my self control can keep my wallet in my pocket or if I am going to be ordering a new camera soon....

Tim

 

[n614cd]

Joe (@Ysarex )

Technique questions. You talked about maximizing the DR range, by finding the clipping point with ISO set to 1000 with fish/jars image. Was the 1000 just a number you picked because of the original posts I made, or was there some other intrinsic value to it? For the garden shot, how did you determine how the settings to maximize the sky exposure looking to recover the garden post process without clipping the sky?

Assuming I follow your lesson accurately, it is nice to see my trial and error actually has some real science behind it. I have found that I get a better image by pushing the exposure to the point where the sky is almost blown, keeping the ISO at 100 and fixing it post process. If the light meter shows more than -2.5, I switch to bracketed shots. Most of the time in LightRoom, if I increase the exposure more than 0.5 I end up with a blown sky. So I am pretty close to the max exposure. So far, I do this all via "guesswork", but I am getting pretty descent at it! Now I wonder if there is repeatable technique I could apply and will serve me better when I switch cameras instead of depending on muscle memory.


Tim

 

[Ysarex]

Joe (@Ysarex )

Technique questions. You talked about maximizing the DR range, by finding the clipping point with ISO set to 1000 with fish/jars image. Was the 1000 just a number you picked because of the original posts I made, or was there some other intrinsic value to it?

Simply your criteria. ISO 100 to 800, on my G7 that's 125 to 1000 -- three stops.

For the garden shot, how did you determine how the settings to maximize the sky exposure looking to recover the garden post process without clipping the sky?

One of the biggest benefits of mirrorless cameras as well as the little LCD compacts is live-view histograms and blinkies for exposure feedback. But before going any further there is no substitute for testing your hardware. So both the G7 and the XT-2 have both of those. If you look at the JPEG of the garden shot you'll see that's terribly green. I had the WB on the camera set to unity so that the live histogram would be an accurate read of the raw file exposure. Here's a link: What is UniWB? | byThom | Thom Hogan Since I don't use my camera JPEGs I'll often leave it set there and just ignore the green JPEGs. (Another example of my behaving far outside the mainstream.) I'm usually able to use those tools to pretty much nail the exposure. The other essential tool for post analysis: RawDigger: Raw Image Analyzer | RawDigger

Assuming I follow your lesson accurately, it is nice to see my trial and error actually has some real science behind it. I have found that I get a better image by pushing the exposure to the point where the sky is almost blown, keeping the ISO at 100 and fixing it post process.

As Yoda would say, "expose or expose not." SNR = exposure. Everything else drops away from that fact.

So back to perspective: Get the shutter speed you require and the f/stop you require and hope that produces maximum SNR for the sensor. If it doesn't do whatever you can to increase the SNR (ISO can't do that) like flash or tripod etc.. Once you've done that take the photo. Given the kind of awesome hardware we have today don't let an inability to reach maximum SNR stop you from taking the photo. I just walked back from the grocery store. I stopped on the way and took a photo and I had to raise the ISO to 400 because it's a gloomy rainy day.

If the light meter shows more than -2.5, I switch to bracketed shots. Most of the time in LightRoom, if I increase the exposure more than 0.5 I end up with a blown sky. So I am pretty close to the max exposure. So far, I do this all via "guesswork", but I am getting pretty descent at it! Now I wonder if there is repeatable technique I could apply and will serve me better when I switch cameras instead of depending on muscle memory.


Tim

Test your hardware and get a copy of RawDigger

Joe

 

[zulu42]

This is all very beneficial information for me. I really appreciate the discussion.

What about folks who just work with jpegs? Tria... nope. won't even say it.

 

[zulu42]

I took a photography class from a professional. He drew the triangle on his white board and I think he even wrote "noise" next to ISO. I legitimately deserve my money back.

 

[Ysarex]

This is all very beneficial information for me. I really appreciate the discussion.

What about folks who just work with jpegs? Tria... nope. won't even say it.

Even for folks who only shoot JPEG the triangle remains confusing because it mixes up cause and effect. Consider:

1/250th sec at f/5.6 at ISO 200
1/125th sec at f/8 at ISO 200
1/250th sec at f/8 at ISO 400

Triangle heads are going to tell you that all three of those balance and in fact are equivalent exposures producing images that are subtly different in rendition of DOF, noise and motion stopping. But in fact one of those is exposing the sensor approx. 40% less than the other two and as such is also different in regards to the data captured by the sensor. They are not equivalent exposures. So it can also help JPEG shooters to understand the distinction between the exposure that's responsible for SNR as opposed to the "exposure" that produces normal brightness in their JPEG. The image receiving less exposure has a poorer SNR.

Joe

P.S. Glad you enjoyed the read.

 

[photo1x1.com]

Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice ), despite it seems "a little" off topic by now.

Not being native English, I again feel the wording could be better. ISO invariance implies to me, that it would make no difference whether I push an image 1EV in Lightroom, or 5EV, which would be "100% ISO invariance". Am I wrong in this regard?
When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?

I have done some ISO tests a few months ago, that I repeated last week with a different background to better show the difference.

I also did an ISO invariance test with ISO400 on my Sony A7III. Reading the conversation, I should have done it at ISO100, or ISO 640 (according to this graph Photographic Dynamic Range versus ISO Setting), is that correct?

Oh yes, and one more question, if somebody would be willing to answer: why is the input-referred read noise in this graph: photonstophotos.net/Charts/RN_e.htm#Sony ILCE-7M3_14 higher for lower ISOs?

For those of you interested, I have uploaded the RAW files here: http://www.amriphoto.com/forum/ISOInvarianceTest.zip
In regard to noise, I feel the ISO400 files keep up pretty well up to pushing them +2EV in Lightroom and comparing them to ISO3200. But to be honest, I do see quite a difference starting at +3EV when pixel peeping.
So my conclusion is no real surprise: you have to decide when shooting: is it more important for me to have a higher dynamic range or less noise. In the particular case of my orchid, I would have gone with less noise.

I know this is not a scientific test as it was done with (quality though) LED lights, but it should give a good impression.
Here is a sample - which one do you think is ISO400 +3EV in Lightroom, and which is ISO3200?

 

[n614cd]

Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice ), despite it seems "a little" off topic by now.

Not being native English, I again feel the wording could be better. ISO invariance implies to me, that it would make no difference whether I push an image 1EV in Lightroom, or 5EV, which would be "100% ISO invariance". Am I wrong in this regard?
When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?

I not native English either. I speak American, just ask my French wife (I could not resist)
I have only read the sensor primer a couple of times on the referenced site, so let's see if I get this correct.

• ISO Invariant sensor only deals with the raw data. When you look at the raw data, you will see no changes in the dynamic range when you change ISO. It also shows up in a bunch of other graphs that I do not understand yet; except one that I do not recall the name. This second graph is of the expected gain and shows a flat line where the camera switches from analog gain a hybrid involving digital. For an ISO invariant sensor, that graph would be flat as all gain is accomplished via the digital processing afterwards. ISO in this case is only used in the image processing engine to generate the camera JPEG.
  
• EV in Lightroom is a digital formula to artificially increase the values of the color channels. Similar in concept to the ISO gain you get on a jpeg in an ISO invariant sensor. Since we do not know the formula Adobe has selected, there is no way for us to determine with certainty that a +1 and +3 EV have identical effects on the color channels. Based on my playing around with it previously, I doubt it. As the channel gets brighter, Adobe seems to lose details, soften the image, and which suggests some type of "intelligence" in teh formula that as you push it higher there are differing effects.
  
• The advantage of an ISO Invariant sensor when dealing with raw data, is you keep the maximum dynamic range and data. This has two effects; one it "requires" some form post processing the raw data, two if gives the post processing the maximum data to deal with. Note: the post processing can be in Lightroom or other software, or just the jpeg engine in the camera.

Tim

 

[photo1x1.com]

Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice ), despite it seems "a little" off topic by now.

Not being native English, I again feel the wording could be better. ISO invariance implies to me, that it would make no difference whether I push an image 1EV in Lightroom, or 5EV, which would be "100% ISO invariance". Am I wrong in this regard?
When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?

I not native English either. I speak American, just ask my French wife (I could not resist)
I have only read the sensor primer a couple of times on the referenced site, so let's see if I get this correct.

• ISO Invariant sensor only deals with the raw data. When you look at the raw data, you will see no changes in the dynamic range when you change ISO. It also shows up in a bunch of other graphs that I do not understand yet; except one that I do not recall the name. This second graph is of the expected gain and shows a flat line where the camera switches from analog gain a hybrid involving digital. For an ISO invariant sensor, that graph would be flat as all gain is accomplished via the digital processing afterwards. ISO in this case is only used in the image processing engine to generate the camera JPEG.
  
• EV in Lightroom is a digital formula to artificially increase the values of the color channels. Similar in concept to the ISO gain you get on a jpeg in an ISO invariant sensor. Since we do not know the formula Adobe has selected, there is no way for us to determine with certainty that a +1 and +3 EV have identical effects on the color channels. Based on my playing around with it previously, I doubt it. As the channel gets brighter, Adobe seems to lose details, soften the image, and which suggests some type of "intelligence" in teh formula that as you push it higher there are differing effects.
  
• The advantage of an ISO Invariant sensor when dealing with raw data, is you keep the maximum dynamic range and data. This has two effects; one it "requires" some form post processing the raw data, two if gives the post processing the maximum data to deal with. Note: the post processing can be in Lightroom or other software, or just the jpeg engine in the camera.

Tim

@american
Thanks, Tim! I do understand ISO invariance (well, at least I think so ). But ISO invariance would mean, that there is absolutely no noise produced in camera after the analog amplification process. So it wouldn´t matter whether you let the camera do the digital amplification, or the software. But that´s the ideal case which is not the reality in current cameras it seems. Still people talk about ISO invariance. I´d call it relatively invariant, or you´d have to find some kind of index, like LEDs have cri (Color Rendering Index). Because if you call the current sensors ISO invariant, how would you call the ones in 10-20 years "proper invariant" ? So that´s probably the next chance to create misunderstandings. Just like "exposure", "camera exposure", "proper exposure",...

 

[n614cd]

@american
Thanks, Tim! I do understand ISO invariance (well, at least I think so ). But ISO invariance would mean, that there is absolutely no noise produced in camera after the analog amplification process. So it wouldn´t matter whether you let the camera do the digital amplification, or the software. But that´s the ideal case which is not the reality in current cameras it seems. Still people talk about ISO invariance. I´d call it relatively invariant, or you´d have to find some kind of index, like LEDs have cri (Color Rendering Index). Because if you call the current sensors ISO invariant, how would you call the ones in 10-20 years "proper invariant" ? So that´s probably the next chance to create misunderstandings. Just like "exposure", "camera exposure", "proper exposure",...

An ISO Invariant sensor has no analog gain. It does not mean no noise.
And yes, we are currently in a transition. Some companies have switched to hybrid ISO with some analog and some digital. Such as when you read the sensor primer, the specific Nixon is a hybrid. I know my Canon 6D is also.
Per @Ysarex there are a few camera's which are sensor invariant, and others which are relatively close. He named a couple of them, but I need to run into a meeting so I cannot go back and dig them out of the thread.

This transition period is actually the "saving" grace for my wallet right now, and what stopped me from ordering the Canon EOS R so I can keep my same high quality native lenses. Since it looks like I am going to switch systems, I may as well wait....

Tim

 

[Ysarex]

Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice ), despite it seems "a little" off topic by now.

Not being native English, I again feel the wording could be better. ISO invariance implies to me, that it would make no difference whether I push an image 1EV in Lightroom, or 5EV, which would be "100% ISO invariance". Am I wrong in this regard?

Right. ISO invariance basically means the read noise in the system no longer matters. You get the same result from digitally scaling the data in post as you would get from applying analog gain to the sensor signal prior to ADC.

When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?

That's why I like Bill Claff's website and test data as opposed to other sites like DXO. Do we set that standard based on what a machine can measure or on what we can practically see? Bill for example rates your camera's DR capacity at 11.6 stops. DXO rates it at 14.7 -- I believe Bill. In referring earlier to my XT-2 I said it was for all practical purposes ISO invariant. I'm sure there's a machine out there that says it's not ISO invariant. In the end all that matters to me is can I take the photo.

I have done some ISO tests a few months ago, that I repeated last week with a different background to better show the difference.
View attachment 165219

I also did an ISO invariance test with ISO400 on my Sony A7III. Reading the conversation, I should have done it at ISO100, or ISO 640 (according to this graph Photographic Dynamic Range versus ISO Setting), is that correct?

Correct. Your camera is most certainly not ISO invariant and very ISO invariant both at the same time -- just like my Fuji. Your Sony is fitted with a dual impedance sensor. The sensor has two read channels. You've got ISO invariance in each read channel separately but not across them. Your test here compares the two channels one to the other -- NOT ISO invariant.

Oh yes, and one more question, if somebody would be willing to answer: why is the input-referred read noise in this graph: photonstophotos.net/Charts/RN_e.htm#Sony ILCE-7M3_14 higher for lower ISOs?

Dual impedance sensor -- it's really like having two sensors in the camera, one for low ISOs and another one for high ISOs.

For those of you interested, I have uploaded the RAW files here: http://www.amriphoto.com/forum/ISOInvarianceTest.zip
In regard to noise, I feel the ISO400 files keep up pretty well up to pushing them +2EV in Lightroom and comparing them to ISO3200. But to be honest, I do see quite a difference starting at +3EV when pixel peeping.
So my conclusion is no real surprise: you have to decide when shooting: is it more important for me to have a higher dynamic range or less noise. In the particular case of my orchid, I would have gone with less noise.

I know this is not a scientific test as it was done with (quality though) LED lights, but it should give a good impression.
Here is a sample - which one do you think is ISO400 +3EV in Lightroom, and which is ISO3200?

Sorry to do this to you but you need to re-do the test and stay in one or the other of the two impedance channels on the sensor.

Two more concerns with your test data: 1. If you look at all the EV 0 exposures in RawDigger you're nearly a full stop underexposed (defined in this case as reaching sensor saturation). 2. Sony is notorious for cooking their raw files and slipping in some lossy compression. I don't know specifically about your camera but that may be a factor.

There's another complication to this topic that needs to be considered and that's the external processing software. All raw converters don't take the same approach to what they're doing and it can matter a lot in this regard. How to assign value to this difference is personal so I think both choices are entirely valid. If you've ever spent time programming a computer you know that there can be a huge difference in performance based on math precision. If you really want to keep computer software moving fast make sure all the math stays integer based. Nothing slows down a computer processor like math with floating point numbers.

The above said processing speed is a critical issue for raw conversion software and I believe LR has its thumb on the scale tipping toward speed over precision. You may be quite surprised to compare the same test processed in LR and then again in say C1 or SilkyPix.

Joe

 

[AlanKlein]

It's a shame that the truth sometimes takes so many words to explain. Joe's two excellent posts above show why the so-called exposure triangle is no longer applicable, now that ISO invariance completely invalidates one of the critical parameters of the so-called exposure triangle.

Isn't this expose for the highlights just like in chrome films? YOu then adjust the sahdow using the shadow slider just as before. The only difference is the better sensors today allow better results. If you expose for the shadows, the highlights clip. Same with digital same with chromes. Raising or lowering the ISO has no effect on the large difference in stops between shadows and highlights. That's why we use graduated ND filters or DHR. If the sensor allows a greater range because of it's DR, that's just another advantage of a better sensor. But settings still have to be adjusted based on a triangle of settings. I don't see what's changed. Maybe I'm missing something.

 

[AlanKlein]

If an a variance sensor allows you to keep the iso at 100, let's say, you still work with triangle. It's like always using 100 ASA (ISO) film. You still have to set the light meter's ASA(ISO) to 100 to get the other two settings of speed and aperture.