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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 16 May 2009 (Saturday) 06:20
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Half-stop ISOs (1250, 2000 etc.) what are these?

 
EOSNewbie
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May 17, 2009 07:41 as a reply to  @ post 7936731 |  #31

It's my understanding that the ISO on a digital sensor is determined by how much electricity the sensor is charged with. Where is the information coming from that says the intermediate stops are 'pushed' or 'pulled' with software? It wouldn't make a whole lot of sense to design a processor to manipulate an image when the same processor can simply increase a voltage parameter to the circuitry feeding the sensor, thus increasing or decreasing the ISO.

It may be software that calculates the voltage required for each ISO selected, but overall there should be no difference in how the sensor receives it's voltage. Basically what I'm reading here is that for Native ISO's, the camera has circuitry to send a certain voltage directly to the sensor, while the intermediate ISO's process the image differently. I can't get my head around the possibility that Canon doesn't simply line up a few more tiny resistors, or capacitors to achieve the ISO, but instead uses software and processing power at the processor to achieve the same thing.

 ???


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tzalman
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May 17, 2009 08:57 |  #32

EOSNewbie wrote in post #7936822 (external link)
It's my understanding that the ISO on a digital sensor is determined by how much electricity the sensor is charged with. Where is the information coming from that says the intermediate stops are 'pushed' or 'pulled' with software? It wouldn't make a whole lot of sense to design a processor to manipulate an image when the same processor can simply increase a voltage parameter to the circuitry feeding the sensor, thus increasing or decreasing the ISO.

It may be software that calculates the voltage required for each ISO selected, but overall there should be no difference in how the sensor receives it's voltage. Basically what I'm reading here is that for Native ISO's, the camera has circuitry to send a certain voltage directly to the sensor, while the intermediate ISO's process the image differently. I can't get my head around the possibility that Canon doesn't simply line up a few more tiny resistors, or capacitors to achieve the ISO, but instead uses software and processing power at the processor to achieve the same thing.

???

This information has been stated and restated so frequently that I thought it had reached the status of "things that are just generally known." However, if you want an authoritative source maybe this will do:
https://photography-on-the.net …hp?p=7465918&po​stcount=13

However, I think your understanding of how the CMOS sensor works is a bit off. The photon absorbing and voltage outputting top layer of the chip has just one never-changing sensitivity. Its output is amplified 2x, 4x, 8x, etc. to acheive higher levels of "effective" sensitivity. In expensive cameras a second stage of amplification provides the intermediate steps and in cheaper cameras it is done later, after the analog/digital conversion. The reason is is simple business economics; it cost nothing to do one more digital manipulation of the data, but more complex chips are more expensive.


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Panopeeper
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May 17, 2009 10:59 |  #33

Pandya wrote in post #7936578 (external link)
Native ISOs are the sensitivies the imaging sensor in the camera actually provides, natively

LOL, this is a great discovery. However, there is only one native sensitivity of a sensor.

More accurately, there is no such thing as sensor sensitivity, that is a creature of the processing. The related characteristic of the sensor is the quantum efficiency.


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cdifoto
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May 17, 2009 11:13 |  #34

I tend to avoid over thinking things and simply set what seems to be right given a certain situation. I have more important things to think about than signal to noise ratio most of the time.


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PIXmantra
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May 17, 2009 12:13 |  #35

In the purest sense, YES...

Panopeeper wrote in post #7937450 (external link)
LOL, this is a great discovery. However, there is only one native sensitivity of a sensor.

More accurately, there is no such thing as sensor sensitivity, that is a creature of the processing. The related characteristic of the sensor is the quantum efficiency.

...If you call analog-gain levels a part of that "processing" too, well, I would have to fully agree.

Moreover, I am not sure if ISO per-se should actually exist in Digital Photography. A sensor, as whole, is free from the dreadful limitations of film (in most respects), and therefore has the potential to simplify the exposure process to only Shutter Speed and Aperture, in principle.

Nevertheless, I just wanted to THANK YOU for your non-nonsense approach and your overall analysis which are definitely the most appropriate and sound for evaluating advantages between implementations. In any case, keep in mind that our final results are delivered in the RGB domain and, at the end of the day, we are interested in those advantages and benefits that effectively survive, once they emerge and show-up in the RGB arena.

BTW, gotta love that RGB Analyzer...

PIX


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Panopeeper
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May 17, 2009 13:50 |  #36

PIXmantra wrote in post #7937802 (external link)
...If you call analog-gain levels a part of that "processing" too, well, I would have to fully agree

Of course that's what I meant. However, it is not useful to include more details, for that process is hardware specific (and I am not a HW guy anyway).

I am not sure if ISO per-se should actually exist in Digital Photography

There is a need for a component to "relativate" the exposure. Nevertheless, the concept is thoroughly messed up. Orginally it refers to a certain grey level appearing with a certain intensity in the output. Yeah, what is the output? Raw? In camera JPEG?

But that's the smaller problem. Even when talking about raw only, how does one define the output level? The fake ISOs increase the output level - but they are not really different than increasing the intensity in raw processing. Now, should the result of the fake (numerically derivated) ISO be accepted? Then "pushing" in raw processing has to be accepted as well.

The MFDBs do not fake the ISO like DSLRs, they do not multiply the pixel values; instead, they simply record, that the "ISO expectation" is let's say 800. It is the task of the raw processor to automatically adjust the intensity. Is this equivalent to the "real ISO"? The raw image data is absolutely identical with ISO100, 200, 400, 800 - so how can we talk about different ISOs?


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May 17, 2009 17:17 |  #37

cdifoto wrote in post #7937514 (external link)
I tend to avoid over thinking things and simply set what seems to be right given a certain situation.

+1.



  
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versedmb
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May 17, 2009 18:39 |  #38

cdifoto wrote in post #7937514 (external link)
I tend to avoid over thinking things and simply set what seems to be right given a certain situation. I have more important things to think about than signal to noise ratio most of the time.

True, but to me its useful to know that, for example, ISO 500 will be be more noisy than ISO 640.


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versedmb
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May 17, 2009 18:39 |  #39

tzalman wrote in post #7936359 (external link)
The chart below illustrates it. (Prepared for the 40D by John Sheehy.) The amount of noise caused by increased electronic amplification of the ISO does not increase linearly. The difference between 100 and 200 is only 112% while the difference between 800 and 1600 is 170%. At the same time, the pushed ISOs (125, 250, 500, 1000) will always be noisier than the amplified ISOs from which they are derived (100, 200, etc.) and the pulled ISOs (160, 320, 640, 1250) will always be cleaner then their sources (200, 400, etc.) In fact, pushing 100 to 125 does more damage than amplifying it to 200 and pulling 200 to 160 more than overcomes the increased noise caused by the amplification. However, because of the big jump in noise from 800 to 1600, 800 pushed to 1000 is about the same as 1600 pulled down to 1250. 1000 gives you almost half a stop more dynamic range but 1250 allows a slightly faster shutter.

This should be a sticky somewhere. Thanks. I knew I had seen that somewhere - now I remember coming across John's posts on dpreview.


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May 18, 2009 06:49 |  #40

I don't know the technical answer to your question. I dont worry about noise at any ISO. I use whatever gets the shot then use Noiseware. Works great and there is a free version.



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Karl ­ C
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May 18, 2009 07:03 as a reply to  @ HoosierJoe's post |  #41

cdifoto wrote in post #7937514 (external link)
I tend to avoid over thinking things and simply set what seems to be right given a certain situation. I have more important things to think about than signal to noise ratio most of the time.

Exactly.

versedmb wrote in post #7939369 (external link)
True, but to me its useful to know that, for example, ISO 500 will be be more noisy than ISO 640.

Have you ever shot with film?


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May 18, 2009 10:03 |  #42

versedmb wrote in post #7939369 (external link)
True, but to me its useful to know that, for example, ISO 500 will be be more noisy than ISO 640.

Karl C wrote in post #7942207 (external link)
Have you ever shot with film?

I fail to understand the point.



  
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Panopeeper
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May 18, 2009 10:19 |  #43

jr_senator wrote in post #7943059 (external link)
I fail to understand the point.

I wonder why Karl is shooting with a 5D instead of for example with a Powershot A640, or at most with a 10D.


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May 18, 2009 10:27 |  #44

Panopeeper wrote in post #7943168 (external link)
I wonder why Karl is shooting with a 5D instead of for example with a Powershot A640, or at most with a 10D.

Damn, another point I fail to understand.



  
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versedmb
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May 18, 2009 12:20 |  #45

jr_senator wrote in post #7943202 (external link)
Damn, another point I fail to understand.

Ditto. ;)


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Half-stop ISOs (1250, 2000 etc.) what are these?
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