Auto ISO in manual = Shutter and Aperture priority.

[robbins.photo]

I think this is a particularly interesting subject and people should be able to discuss it.

Ok, how about a different twist on the concept and consider this:

We could actually start using our digital cameras as if they were digital cameras and stop pretending they're old film cameras. Just stop the silly ISO business entirely since it doesn't really have any effect on the what the sensors in our cameras actually record and otherwise just slows us down and encourages us to be less precise.

I understand the implications of what I'm suggesting -- I'm suggesting kicking the JPEG crutch out from under us entirely and that's a really big crutch. It's complicated by the fact that the cameras are all designed with the "crutch" built in. But there are benefits. I know a lot of the people posting here do in fact save raw files. But most folks who work with raw files still only embrace that discipline partially.

What I'm saying here goes back to a point that Derrel made earlier in the thread about modern camera sensors and how good they really are. The only thing increasing the ISO does in camera is apply an analog amplification to the sensor data which results in less noise on the front end. It does not produce one iota of additional real data. In post processing, my available options for noise filtering are far more sophisticated and I can do a much better job starting from scratch. Furthermore, if you do go ahead an apply that analog amplification up front in the camera then there's no way to back that off and it's burned into your raw file. Any bad results (there can be many) of that amplification become part of your raw file. In other words I'm suggesting there are advantages to saving "really raw" raw files by just giving up the ISO crutch entirely. In terms of the data recorded by your sensor, ISO isn't real so what happens if you stop pretending it is?

I understand what I'm suggesting would not be practical for most and is in fact an extreme position. But when this thread began, the idea that you could put the camera in full manual and just ignore the ISO by letting the camera take care of it got some raised eyebrows. What that method in effect does is allow you to take the photo at the shutter speed and f/stop you require and then hands over to the camera electronics the job of amplifying the sensor signal the appropriate amount. OK, take it a step further and just turn off that camera amplifier as well -- now you have even less to worry about. Since that ISO amplification doesn't in fact give you any real additional data, and it does in fact degrade the image relative to what you can do in post without it's interference, then you have a logical argument for taking this all the way. The concept of variable ISO does not apply to a digital camera sensor. It only applies to electronic image processing -- the JPEG crutch side of the camera.

Joe

I guess the equation here for me would be two-fold, could I actually regularly and consistently produce images of a higher quality than the camera's on-board systems by doing it this way, and if so would the difference in the final output really be so much better than what the camera can accomplish on it's own that it would be worth the additional time it would take to do this in post?

 

[WayneF]

If only ISO 100 were used, the image needing ISO 2400 would be rather dark and hard to judge on the rear LCD preview. I guess that would make it more like the film days, but I'm not going back.

 

[Ysarex]

I understand what I'm suggesting would not be practical for most and is in fact an extreme position. But when this thread began, the idea that you could put the camera in full manual and just ignore the ISO by letting the camera take care of it got some raised eyebrows. What that method in effect does is allow you to take the photo at the shutter speed and f/stop you require and then hands over to the camera electronics the job of amplifying the sensor signal the appropriate amount. OK, take it a step further and just turn off that camera amplifier as well -- now you have even less to worry about. Since that ISO amplification doesn't in fact give you any real additional data, and it does in fact degrade the image relative to what you can do in post without it's interference, then you have a logical argument for taking this all the way. The concept of variable ISO does not apply to a digital camera sensor. It only applies to electronic image processing -- the JPEG crutch side of the camera.

Joe

So you just want everyone to shoot at ISO 100?

Base sensitivity varies from one sensor to another. They're not all ISO 100.

Raising a digital camera's ISO above base either does (1) absolutely nothing to the sensor signal prior to A/D conversion (camera model dependent) or it (2) engages an analog amplifier that amplifies the sensor signal prior to A/D conversion.

1. Doing nothing is doing nothing -- if you're saving raw files that you intend to process yourself and nothing has been done to the raw data then are you concerned about nothing? In other words in some cameras raising the ISO from 100 to 400 produces the exact same raw data file with the only difference that the metadata notes the ISO change. In this case the camera's image processor simply uses the information that the ISO was increased and raises brightness when processing the JPEG and likewise raw converters read the ISO value from the stored metadata and boosts the brightness when they default display the demosaiced image. With the raw file being identical either way (ISO 100 or 400) the only thing that raising the ISO accomplished was to provide info for the camera JPEG processor or possibly your raw conversion software -- much ado about nothing or something to do about nothing but either way it's about nothing. It has the negative result of allowing some photographers to believe that something substantive is taking place when in fact it's really nothing. No substantive variation exists in the actual data the sensor records. This is worth understanding.

2. The analog sensor signal is amplified prior to A/D conversion. This really does effect the stored raw file as the amplification is done prior to A/D conversion. It is however critical to note that this process does not in fact alter the sensitivity of the sensor and does not in any way allow the camera to actually record more data. The amount of data the sensor can record is fixed and it's base sensitivity is fixed. You can amplify what you've got but if you've got bupkis then amplifying bupkis just give you bupkis. 1 * 2 = 2 but 0 * 2 = 0.

In this case you have a choice between amplify or don't amplify. That's the substantive thing changing ISO does to the raw capture (then there's all the JPEG related benefits like being able to chimp the LCD). This begs the question, relative to the integrity and usefulness of the raw data, what are the pluses and minuses of signal amplification? Signal amplification is implemented by each specific camera manufacturer and will hopefully reduce noise and keep artifacts at a minimum. If your focus is getting a camera JPEG then how your chosen camera manufacturer implements signal amplification becomes a concern. If your only focus is getting the raw data then you have the additional option of not engaging the signal amplification at all. Is there a difference? Yes. Meaningful? Only in the extreme -- I did originally say extreme. So if you want me to process a raw file for you and squeeze the very last drop of "best possible" from that raw file and you give me a choice between an NEF that was underexposed 3 stops at ISO 100 versus one that was shot at ISO 800 and so signal amplified prior to A/D conversion, I'll take that first option -- I can do better without the prior signal amplification. I have a much more sophisticated capacity to manage noise and artifacts in post.

Then in the spirit of the OP's original post where he's found it very freeing to sort of ignore ISO by putting it on auto, I'm saying I can get "best possible" end results by taking that one step further and just setting ISO to OFF since it isn't making it possible to actually record more data and the signal amplification that it is doing is more of a hindrance than a help. CAVEAT: all the JPEG benefits.

Joe

 

[Ysarex]

If only ISO 100 were used, the image needing ISO 2400 would be rather dark and hard to judge on the rear LCD preview. I guess that would make it more like the film days, but I'm not going back.

Yep, like I said -- JPEG crutch. I know it sounds a little flippant and it's intentional, but you're exactly right. Kick the chimping crutch out from under us and we're all falling down.

For me the more important aspect of this and why I posted this is just understanding. We do all realize that we can't change the ISO of the sensors in our cameras? Right?

Joe

 

[runnah]

I say this about any auto function. It's a tool in your arsenal that you can use to help you get the job done. It's a fool who discards a tool at their disposal.

 

[Ysarex]

I guess the equation here for me would be two-fold, could I actually regularly and consistently produce images of a higher quality than the camera's on-board systems by doing it this way,

yes, absolutely.

and if so would the difference in the final output really be so much better than what the camera can accomplish on it's own that it would be worth the additional time it would take to do this in post?

absolutely not.

Joe

 

[robbins.photo]

I guess the equation here for me would be two-fold, could I actually regularly and consistently produce images of a higher quality than the camera's on-board systems by doing it this way,

yes, absolutely.

and if so would the difference in the final output really be so much better than what the camera can accomplish on it's own that it would be worth the additional time it would take to do this in post?

absolutely not.

Joe

Well that saved me a ton of time testing that theorem.. auto ISO it is! Lol

 

[Braineack]

So if you want me to process a raw file for you and squeeze the very last drop of "best possible" from that raw file and you give me a choice between an NEF that was underexposed 3 stops at ISO 100 versus one that was shot at ISO 800 and so signal amplified prior to A/D conversion, I'll take that first option -- I can do better without the prior signal amplification. I have a much more sophisticated capacity to manage noise and artifacts in post.

I feel like I misunderstand how the A/D conversion and amplification works.

I just did this and cant see any difference.

1/25, f/5.6 ISO 200 EV+3.0 and ISO 1600 EV 0

 

[Vince.1551]

He meant off camera processing of raw file ..of an under exposed image

 

[Braineack]

He meant off camera processing of raw file ..of an under exposed image

i did that.

both were taken at 1/25 and 5.6.

I added +3.0 in LR to the ISO 100 image.


only thing is, that's not practical when you need shutter speeds in any usable range.

 

[Vince.1551]

i did that. both were taken at 1/25 and 5.6. I added +3.0 in LR to the ISO 100 image. only thing is, that's not practical when you need shutter speeds in any usable range.

Oh ok. I see what you mean. I feel as long as high ISO is visibly acceptable, why take the trouble or extra step to process the exposure in LR or PS. Auto ISO still works pretty well in practice.

 

[Overread]

I guess the equation here for me would be two-fold, could I actually regularly and consistently produce images of a higher quality than the camera's on-board systems by doing it this way,

yes, absolutely.

and if so would the difference in the final output really be so much better than what the camera can accomplish on it's own that it would be worth the additional time it would take to do this in post?

absolutely not.

Joe

Well that saved me a ton of time testing that theorem.. auto ISO it is! Lol

Exactly - if the amount of work in editing is increased significantly and if the gain is nothing to negligible I don't see any virtue in changing how everyone uses ISO currently.

Plus added to that everything I've read has always stated very clearly that a higher ISO gives less noise than underexposing using a lower ISO. In fact this theory goes against the tried and tested "expose to the right" theory.

Considering that it makes photo review harder - editing longer and more complex - and offers little to no gain (and might even have a negative impact) I just don't see any reason other than a hatred of ISO

 

[photoguy99]

Analog amplification prior to A/D doesn't create more info, but it does let you measure more of the info that's there. If you have a known analog signal in hand, you can always do better by adjusting levels in the analog domain to match your A/D.

I guess I have no idea what the heck Ysarex is on about.

 

[Ysarex]

So if you want me to process a raw file for you and squeeze the very last drop of "best possible" from that raw file and you give me a choice between an NEF that was underexposed 3 stops at ISO 100 versus one that was shot at ISO 800 and so signal amplified prior to A/D conversion, I'll take that first option -- I can do better without the prior signal amplification. I have a much more sophisticated capacity to manage noise and artifacts in post.

I feel like I misunderstand how the A/D conversion and amplification works.

I just did this and cant see any difference.

1/25, f/5.6 ISO 200 EV+3.0 and ISO 1600 EV 0

Yep, and if in fact you can't see any difference at all, that means your camera's electronics are doing a great job with the analog amplification. But in terms of the final image, if in fact you do want only the raw file, then the ISO 1600 gave you nothing substantive (there's all the JPEG advantages of course). Again in the spirit of the OP's original post here, that means if the ISO gives no benefit then you lose nothing substantive to ignore it.

Again I wanted to add this here to also make the point that raising the ISO on a digital camera doesn't get you more recorded data.

In my experience the analog amplifiers out there aren't all as good as the one you're using. I've got to run right now but I'll post an example a little later.

Joe

 

[photoguy99]

Bumping the ISO will always reduce quantization noise as compared with adding back exposure in post. Unless the analog amplification is introducing enormous amounts of noise, bumping the ISO at the sensor will give you better results than digitally amplifying the signal in post. I can't imagine why anyone would bother building an analog amp that bad, but I suppose it's possible.

Assuming that you're not clipping anything that matters to you, bump the ISO.

Incidentally, quantization noise will basically vanish when you resize a photo. So use caution if you choose to dispute my remarks.