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05-24-2016, 10:01 AM   #16
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QuoteOriginally posted by rangercarp Quote
I attended a workshop this past weekend and the instructor told us we should never use 1/3 ISO stops. He described them as "junk" and said image quality is better if you bump up to the next full stop. The argument is that the intermediate ISO's are not true ISO's but the processor simply manipulates the exposure to achieve the intermediate setting.

I have spent over an hour searching old threads and found a few that touched on this issue, but all of them had very few replies and did not come to any real conclusion. For as long as I have been using a DSLR I have used 1/3 ISO stops and never noticed a problem, but then, I never new I should be looking for one.

What is the prevailing opinion out there on 1/3 ISO stops?
I use my K3 at ISO 640 and can see a degradation in quality at ISO800. Should I shoot at ISO800 or 400 now.
Digital images don't cost anything, so try for yourself. At the end you are looking for a decent time, aperture, ISO combination for your shot. Fix either two to define the third setting. Typically time or aperture are more important.

All ISO settings are an amplification of base ISO setting. So to a certain degree you can accomplish an extra 1/3 by adjusting the ISO or photoshop setting.

05-24-2016, 10:12 AM   #17
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I also use 1/3 stops for shutter, aperture, and ISO on my K-5.

Bumping ISO by a full stop when I only need 1/3 does not improve photo quality and requires additional post-processing to tweak exposures. Imagine the shutter, aperture, and ISO are where I want them to be for a properly exposed scene. Then I decide I want a slightly slower shutter to show more motion blur. Aperture has to stay as-is for a specific depth of field and sharpness. If I slow the shutter speed by 1/3 stop the scene will be slightly overexposed, so I should decrease ISO 1/3 stop to compensate.
05-24-2016, 10:34 AM   #18
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QuoteOriginally posted by Sandy Hancock Quote
I'm too lazy to turn the dial three times as far to go from 200 to 400.
Half stops (or even thirds if you really want) are fine for aperture and shutter speed, but sensitivity? Really??
Same here. I used 3rds for a while but got tired of turning the wheel. Now it's full stops for ISO, half stops for aperture and shutter speed. Gets me close enough.

Not that I've noticed any degradation in quality using the in-between steps for ISO.

Oh, and it lets me get away with making fewer import settings in LR
05-24-2016, 11:05 AM   #19
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QuoteOriginally posted by rangercarp Quote
I attended a workshop this past weekend and the instructor told us we should never use 1/3 ISO stops. He described them as "junk" and said image quality is better if you bump up to the next full stop. The argument is that the intermediate ISO's are not true ISO's but the processor simply manipulates the exposure to achieve the intermediate setting.
When using camera automatic exposure, 1/3rd of ev step allow finer adjustments, sensor iso isn't used because internal light meter is used instead, but the best exposure is never achieved without stop down metering or live-view because the lens also produces an error from aperture and light losses through the glass elements, so the result is never as good as 1/3rd ev step accurate. For instance , there is 0.4 Tstops additional exposure from a DFA24-70 versus a Tamron 17-50 at the same equivalent settings. However, when adjusting the exposure manually (using my own evaluation and/or LV, or ambient light meter), find it slower but more relevant to use 0.3ev steps.

05-24-2016, 11:12 AM   #20
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QuoteOriginally posted by rangercarp Quote
I attended a workshop this past weekend and the instructor told us we should never use 1/3 ISO stops. He described them as "junk" and said image quality is better if you bump up to the next full stop. The argument is that the intermediate ISO's are not true ISO's but the processor simply manipulates the exposure to achieve the intermediate setting.

I have spent over an hour searching old threads and found a few that touched on this issue, but all of them had very few replies and did not come to any real conclusion. For as long as I have been using a DSLR I have used 1/3 ISO stops and never noticed a problem, but then, I never new I should be looking for one.

What is the prevailing opinion out there on 1/3 ISO stops?
If we're talking about "true ISO"=native ISO, then there is only one native ISO of the sensor and technically all other ISOs involve processor gains. The native ISO is almost always the lowest numbered ISO such as 80, 100, or in older cameras 200. Non-numbered ISOs which are sometimes referred to as Lo-1, Lo-2, Hi-1, etc. are heavily processed and I'd never go there unless it was my only option.

The EV steps, which I believe is related to what your instructor is referring to has no bearing on the image quality. Most DSLRs default to 1/3 EV steps (which affects ISO, shutter speeds, and f/stop settings). Better cameras allow you to change that in the menu to 1/2 EV steps and with the best cameras whole EV steps.

I have been teaching photography full time since 1996 (both film and digital). It is easier to learn exposure (the relationship between ISO, shutter speed, and aperture) when the camera is set to whole EVs. It is also much faster to change your settings because with 1/2 EVs, you have double the numbers and with 1/3 EVs you have triple. So in my own classes, I recommend students (if possible; not possible on entry level Nikons) to change from the default 1/3 EVs to the 1/2 EV steps. Why? Because they do not yet have the eye to see the difference between that small an increment and to go from, for example 1/60" to 1/500" it would only take them 6 'clicks'; with 1/3 EV steps it would take 9 'clicks'.

If you're shooting in an auto setting, I would leave it at 1/3 EV steps as the camera can fine tune the exposure. But if I'm in TV or AV or Manual, I don't want to spend extra time changing from f/4 to f/11 and in 1/2 EV steps, I can do it more quickly.

FYI: It's possible your instructor knows something I have never heard of before and is correct! But I'd love to see some references or documentation or tests that prove this.
05-24-2016, 11:23 AM   #21
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QuoteOriginally posted by rangercarp Quote
I attended a workshop this past weekend and the instructor told us we should never use 1/3 ISO stops. He described them as "junk" and said image quality is better if you bump up to the next full stop. The argument is that the intermediate ISO's are not true ISO's but the processor simply manipulates the exposure to achieve the intermediate setting.

I have spent over an hour searching old threads and found a few that touched on this issue, but all of them had very few replies and did not come to any real conclusion. For as long as I have been using a DSLR I have used 1/3 ISO stops and never noticed a problem, but then, I never new I should be looking for one.

What is the prevailing opinion out there on 1/3 ISO stops?
ISO in digital is just software based full or 1/3 stops. It's true that you might not see much advantage using say 320 over 400, but there are other reasons to use intermediate stops. For example, you might need a certain shutter speed. As an example, on the K-5IIs, IQ is better at 100 than 80, because 80 is not a native ISO but I often shoot at ISO 80 to increase my shutter speed or open up the aperture in bright light. I guess it's probably not worth it, but for moving water, if I don't have an ND, it might make enough difference.

No matter what, the sensor has an ISO it works at best and all the other ISOs are just junk settings.
05-24-2016, 11:37 AM - 1 Like   #22
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QuoteOriginally posted by Na Horuk Quote
Yeah, but the question is whether shooting ISO 3200 and adding 1/3 EV in Lightroom or Faststone would bring out less noise than selecting ISO 4000 in-camera to begin with (shutter speed and aperture being equal).
In my very unscientific experiments with my K-1, adjusting the ISO in camera produces less noise than compensating exposure later in lightroom (but it is a very close run thing).
05-24-2016, 12:32 PM   #23
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I can't agree with the argument that "the processor simply manipulates the exposure to achieve the intermediate setting." Adjusting ISO doesn't change the exposure all, it's just math performed on recorded pixel values. By definition, exposure is exposing the sensor to light, which is only moderated by aperture and shutter speed. (And perhaps filters, lens design, etc.) I'll admit that theoretically I could see 1/3 stop ISO adjustment having a minuscule impact due to rounding errors, but only on very dark pixels with low values, and not enough to really matter.

If you're interested in the math behind photography, read on! (If not, skip to the TLDR)

Think of it this way, ISO value is the adjustment of the original readout for a pixel on the sensor in terms of percentage, so ISO 100 is 100%, ISO 200 is 200%, etc. Stops are a method of doubling, so the relationship between 'stops' and light is exponential rather than linear. A full stop is simply doubling the value and only uses whole numbers. 1/3 stops are in between and require decimal adjustments, so a pixel with a value of 1 would adjust to 1.26(+1/3), 1.59 (+2/3), and 2 (full stop). Continuing on, the ISO adjustments for a pixel starting with a value of 1 between ISO 100 and ISO 12800 would be:

1, 1.26, 1.59, 2, 2.52, 3.17, 4, 5.04, 6.35, 8, 10.08, 12.70, 16, 20.16, 25.40, 32 40.32, 50.80, 64, 80.63, 101.60, 128, and so on (bold numbers are full stops, 1/3 stop decimals are approximate).

For simplicity, these are usually rounded to be easier to remember off the top of your head when writing them out.*
1, 1.25, 1.60, 2, 2.5, 3.2, 4, 5, 6.2, 8, 10, 12.5, 16, 20, 25, 32 40, 50, 64, 80, 100, 128, and so on

These decimal pixels then have to be rounded to whole numbers when they are recorded, causing a slight error. As the pixel's value increases, the impact of the rounding error becomes significantly less important. (see signal to noise ratio) When you think about how a 12-bit image can have 4096 different values for each raw pixel, and a 14-bit image can have different 16384 values for each raw pixel, this would mean that 1/3 stop ISO adjustments only really affect the very darkest portions of the images. (At least, in any way we could see with our very non-numerical eyes!)

However, this could all be a moot point if ISO adjustment is performed within analog circuitry before being converted to bits and bytes in the analog/digital converter. If it's an analog ISO adjustment I still can't see how full or 1/3 stop adjustments would be better or worse than each other unless there are problems with the analog circuits. An analog ISO adjustment would probably be more accurate than adjusting digital values, though it would still be susceptible to noise and the end results would still be limited to bits and bytes.


TLDR:
Yes, theoretically I can see that 1/3 stop ISO adjustments can cause rounding errors in individual pixels, but would only really affect very dark pixels with low values, and the error introduced will likely be so small that we would never be able to see any negative effects on our images.





*You might have noticed this is similar to the progression of shutter speeds, though again they're rounded to make them easier to remember...
1, 1/2, 1/4, 1/5, 1/6, 1/8, 1/10, 1/13, 1/15, 1/20, 1/25, 1/30, 1/40, 1/50, 1/60, 1/80, 1/100, 1/125, 1/160, 1/200, 1/250, 1/320, 1/400, 1/500, 1/640, 1/800, 1/1000
(Remember, 'Stops' are just operations of doubling or halving values!)

---------- Post added 05-24-16 at 03:44 PM ----------

QuoteOriginally posted by robthebloke Quote
In my very unscientific experiments with my K-1, adjusting the ISO in camera produces less noise than compensating exposure later in lightroom (but it is a very close run thing).
Same here on my K-3. This would lead me to believe that in camera ISO adjustment might be done in analog circuitry before being converted to digital.

Analog can be more accurate than digital since it can allow for intermediate values while digital works with whole numbers (in binary).
Here is an example converting four hypothetical pixel values from ISO 100 to ISO 1600, starting in analog and ending in digital.

1, 2.5, 3.2, 4.6 in analog adjusted to ISO 1600 -> 16, 40, 51.2, 73.6 -> then converted to digital: 16, 40, 51, 74
1, 2.5, 3.2, 4.6 in analog converted to digital -> 1, 3, 3, 5 then adjusted to ISO 1600 -> 16, 48, 48, 80

You can see that ISO adjusting in analog can be more precise, but adjusting in digital only give end values in increments of 16, so there is less differentiation between pixels.

05-24-2016, 12:55 PM   #24
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ISO: 1/3 or full stops?

Expert vs. expert. This reference doesn't settle the question, but it does provide another perspective. Michael Freeman has said in an interview:
"The way I normally shoot is aperture priority, with... uhm... quite often a little touch of exposure compensation. And it rather depends on the circumstances, so I'll be rechecking that when we get near to where we are. But quite often I'll have it on minus a third of a stop. And the reason for that is to hold... uhm... highlights. It's just a preference."
Michael Freeman Piccadilly Video Part 1. Begins at 1:57
05-24-2016, 01:10 PM   #25
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QuoteOriginally posted by Apet-Sure Quote
Isn't it true that any sensor has a 'native' ISO? If that's the case, then any other ISO setting is processor controlled, and 'artificial'. To use an audio analogy, the more you turn up an amplifier, the more unwanted background noise you get. Whether you turn it up in small increments or larger increments, it doesn't change the fact that you get more noise. Wouldn't the same be true for the raw output of the image sensor?
Not quite. It is the signal to noise ratio that matters. Pentax have a habit of introducing software noise reduction, even in RAW, past some ISO - 1250 on the K-5/K-5ii, for example. I have no idea whether this is also the case on the K-3 or K-1. On the K-5ii I use 1/3 stop steps but limit the max ISO to 1250 unless I need the extra sensitivity.
05-24-2016, 01:40 PM   #26
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It depends on the camera and how its processing works internally. I think Pentax have a pretty consistent approach and from what I have seen in between steps are as good as major ISO steps.

Interestingly on my copy of the K-x, from my test shots of a scene, I found that it seemed to be happiest at about ISO 140 (lower blue noise than 200 and slightly better dynamic range than 100).

In any case I'm a half stop person. I previously used 1/3 stops but now much prefer half stops for convenience (with still plenty of control). Agree that if you primarily use Tav then 1/3 stops may suit better.
05-24-2016, 02:07 PM   #27
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QuoteOriginally posted by Joseph464 Quote
"The way I normally shoot is aperture priority, with... uhm... quite often a little touch of exposure compensation. And it rather depends on the circumstances, so I'll be rechecking that when we get near to where we are. But quite often I'll have it on minus a third of a stop. And the reason for that is to hold... uhm... highlights. It's just a preference."
That's interesting.
Another thing to mention is the ETTR, exposing to the right. Theory is that overexposing, and then darkening in post, gives overall less noise. Provided you shot raw and did not overexpose, clip any highlights. I like ETTR in certain situations, where you just look at histogram and make sure you don' clip, but go as far right as possible
05-24-2016, 03:04 PM - 1 Like   #28
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There is some weird performance drop for the in between ISOs of some Canon and Nikon cameras. Click
05-24-2016, 03:24 PM   #29
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QuoteOriginally posted by Simen1 Quote
There is some weird performance drop for the in between ISOs of some Canon and Nikon cameras. Click
Wow. This is a "smoking gun". I'd never seen this before, either as data or from anecdotal experience shooting both Pentax and Nikon. Thanks for sharing this....IF I shot Canon, that's a big deal.
05-24-2016, 03:53 PM   #30
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QuoteOriginally posted by Alex645 Quote
Wow. This is a "smoking gun". I'd never seen this before, either as data or from anecdotal experience shooting both Pentax and Nikon. Thanks for sharing this....IF I shot Canon, that's a big deal.
Seems to not be an issue with Sony sensors?

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