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ISO-less exposure
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May 9, 2018 13:48:13   #
CatMarley Loc: North Carolina
 
I was unaware until recently that the camera exposes everything based on aperture and shutter speed alone. The ISO you dial in is a simple after the fact amplification of the signal, and it happens during the processing, not the exposure itself. So taking a shot with ISO 1600 or 200 makes no difference if you are shooting raw. You can apply the 3EV boost using your ISO dial or pushing the exposure 3EV during conversion of the raw file. Here are 2 jpegs, one was taken at ISO 200 and one at 1600. The 200 jpg straight from the camera was black, and the 1600 jpg was properly exposed. Aperture and shutter were the same both shots. the raw 200 was pushed 3 EV during conversion from raw to jpg. Bet you can't tell the difference!


(Download)


(Download)

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May 9, 2018 14:02:16   #
R.G. Loc: Scotland
 
The usual way of stating what you've recently realised is to say that shutter speed and aperture control how much light reaches the sensor (and therefore determine how strong the sensor's output signal is), whereas ISO determines how much amplification the sensor's signal gets.

There's not much difference between the two shots noise-wise, but the second shot is noticeably softer where contrast and strength of colour are concerned.

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May 9, 2018 14:03:16   #
Soul Dr. Loc: Beautiful Shenandoah Valley
 
The 2nd one has better exposure in the shadow areas. Is that the one that was pushed in raw?

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May 9, 2018 14:03:39   #
BebuLamar
 
There are differences but not by much. The amplification is applied after the exposure but before writing the RAW file. You will see the differences if you test it the other way around. Give the ISO 200 shot correct exposure and over expose the ISO 1600 shot by 3 stops that is you would use the same shutter speed and aperture for both shots (the same exposure). You would have a hard time recover the burned out highlight in the ISO1600 file.

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May 9, 2018 14:11:07   #
AlohaBob Loc: Los Angeles, CA
 
Very interesting. I'm curious as to where/how you found this out.

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May 9, 2018 14:16:30   #
dsmeltz Loc: Philadelphia
 
This is why I usually use auto ISO. Auto ISO gets me in the ballpark

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May 9, 2018 14:21:27   #
CatMarley Loc: North Carolina
 
Soul Dr. wrote:
The 2nd one has better exposure in the shadow areas. Is that the one that was pushed in raw?


Yes. I must have chosen a better tone profile than the camera did. It has a little better DR.

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May 9, 2018 14:24:17   #
CatMarley Loc: North Carolina
 
dsmeltz wrote:
This is why I usually use auto ISO. Auto ISO gets me in the ballpark


The point of this is that you don't have to. You can shoot almost everything at 200 if you shoot raw. The camera doesn't care it shoots everything at its native ISO and only applies the amplification after the fact.

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May 9, 2018 14:25:05   #
CatMarley Loc: North Carolina
 
AlohaBob wrote:
Very interesting. I'm curious as to where/how you found this out.


I finally read the book!

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May 9, 2018 14:27:21   #
CatMarley Loc: North Carolina
 
BebuLamar wrote:
There are differences but not by much. The amplification is applied after the exposure but before writing the RAW file. You will see the differences if you test it the other way around. Give the ISO 200 shot correct exposure and over expose the ISO 1600 shot by 3 stops that is you would use the same shutter speed and aperture for both shots (the same exposure). You would have a hard time recover the burned out highlight in the ISO1600 file.


Yes burned highlights are pretty much gone. But shadows can be mined almost ad lib.

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May 9, 2018 14:37:37   #
SharpShooter Loc: NorCal
 
Sorry Cat but I’m not buying that!
Overexpose ANY area of a scene to the extent of blowout and NO amount of tweaking the +/- EVO will get it back in post, even if shot on DOUBLE RAW!!!
SS

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May 9, 2018 14:39:00   #
CatMarley Loc: North Carolina
 
R.G. wrote:
The usual way of stating what you've recently realised is to say that shutter speed and aperture control how much light reaches the sensor (and therefore determine how strong the sensor's output signal is), whereas ISO determines how much amplification the sensor's signal gets.

There's not much difference between the two shots noise-wise, but the second shot is noticeably softer where contrast and strength of colour are concerned.


Yes. Of course I don't know exactly what profile the camera applied to the raw data. I applied a little lowering of contrast a little sharpening. If I had time to tinker with it, I probably could come up with an identical profile, given enough experimentation with all the variables. The point of this quick experiment was to demonstrate the fact that it is does not matter what ISO you use if you are only interested in the raw file. I usually don't bother with raw because the jpegs I get with the Fuji are usually so good, and my computer is one I built myself in 2004, so raw tinkering is very difficult until I upgrade my hardware. I was just interested in introducing this topic because I had never seen it discussed here. It is something to consider if you are shooting in bad light. The ability to move the exposure by 3 or 4 EV without loss of quality just by shooting raw could come in handy.

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May 9, 2018 14:46:56   #
CatMarley Loc: North Carolina
 
SharpShooter wrote:
Sorry Cat but I’m not buying that!
Overexpose ANY area of a scene to the extent of blowout and NO amount of tweaking the +/- EVO will get it back in post, even if shot on DOUBLE RAW!!!
SS


I just said the same thing. Blown highlights are GONE! But shadows can be brought up out of virtual blackness!
Here is the original jpg at ISO 200 along with the raw 200 to jpg result.


(Download)


(Download)

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May 9, 2018 14:48:17   #
MrBob Loc: lookout Mtn. NE Alabama
 
This is prob. one of the more interesting posts I have read in a long time... brings up all sorts of things to ponder on. I would like to see more comments by other experienced folks with a lot more expertise than myself. A VERY interesting topic Cat... Thanks for posting.

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May 9, 2018 14:58:12   #
E.L.. Shapiro Loc: Ottawa, Ontario Canada
 
Extremely interesting!

For folks like me, who spent a lifetime dealing with film and A.S.A., ISO, din, Weston and personalized exposure indexes, it my be difficult to relate all of that directly to digital/electronic sensitivity ratings. Of course, physically speaking, there is quite a difference between silver halide/chemical technology and the physics of the movement of electrons in a circuit. Film, with its emulsion issues of speed, grain, acutance and the enormous variations of all of theses factors as they are effected by as many variations in processing is a science and sometimes a form of alchemy or witch's brews in itself. Digital photography is more stable, repeatable and predictable- at least to me.

In a practical usage sense, however, it seems to me that are cretin correlations or parallels of the two technologies that hold true regardless of their theoretical differences such as format/sensor size and an increase of nose/grain as the exposure index is increased and how theses phenomena relate to the quality of the final image, especially in critical scenarios or requirements such as where high degrees of enlargement are indicated.

In my own professional/commercial my practice is simply to shoot everything in RAW, oftentimes in manual mode and selection ISO speeds accordingly. Mostly I opt for the lowest speed that is practical but have not experienced any serious quality losses at moderate to higher speeds. I seldom have the need to go as high as 1600 let alone higher. Am I missing something?

Oh!- this is in no way a facetious question. Down here in "commercial land" we get so involved in workaday stuff and production routines that we can miss out on some of the newfangled good stuff and latest discoveries or theories. Please elaborate!

My question is, regardless of where the "amplification" takes place in the digital chain of events, is the any difference in photographic results and does this discovery debunk the common knowledge or conventional wisdom of RAW vs. Jpeg usage, noise issues or anythg in post processing?

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