Lumix GX80/85 base ISO

Joris

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Hi, I have a question about base ISO on my Lumix GX80. Panasonic put it at 200, but it can be pushed at 100. On the web one will find that IQ would suffer from pushing it there...

However, both DxO Panasonic Lumix DMC-GX80 : Measurements | DxOMark and Photons to Photos Read Noise in DNs versus ISO Setting,
http://www.photonstophotos.net/Charts/PDR.htm#Panasonic%20Lumix%20DMC-GX80,
indicate that for this camera all readings improve at le lowest available ISO 100.

Why would Panasonic put up a barrier against using the GX80 at its lowest ISO (or is it that I get this all wrong)?
 

WhidbeyLVR

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The usual answer is that highlight recovery is more difficult if you slightly overexpose at ISO 100, because you saturate the sensor (fill the photosites with photons). As long as you don’t saturate the sensor in the highlights, noise should be reduced at ISO 100 vs base ISO.
 

tkbslc

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The usual answer is that highlight recovery is more difficult if you slightly overexpose at ISO 100, because you saturate the sensor (fill the photosites with photons). As long as you don’t saturate the sensor in the highlights, noise should be reduced at ISO 100 vs base ISO.
That is the usual answer, true. But I think the links posted by the OP seem to refute that by showing higher DR at L ISO.
 

Joris

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Thank you for your answer. At 100 ISO the camera would assumedly still expose for the same "average correct" (I usually use Aperture priority at 100 ISO), wouldn't it ? The zebra pattern and the blinkies help adjusting the camera's +/- EV at any ISO setting. At 100 ISO, there seems not to be a reason for the user to be more prone to "slightly overexpose". Please elaborate :) ?
 

WhidbeyLVR

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That is the usual answer, true. But I think the links posted by the OP seem to refute that by showing higher DR at L ISO.
I think that is to be expected, up and until you saturate the sensor. More photons should yield more dynamic range.
 

WhidbeyLVR

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Thank you for your answer. At 100 ISO the camera would assumedly still expose for the same "average correct" (I usually use Aperture priority at 100 ISO), wouldn't it ? The zebra pattern and the blinkies help adjusting the camera's +/- EV at any ISO setting. At 100 ISO, there seems not to be a reason for the user to be more prone to "slightly overexpose". Please elaborate :) ?
If you are careful and use the histogram/blinkies to avoid overexposure, it should be fine. Many folks are just taking point-and-shoot snapshots and trusting the camera to figure it all out.
 

Joris

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That is the usual answer, true. But I think the links posted by the OP seem to refute that by showing higher DR at L ISO.
Y
If you are careful and use the histogram/blinkies to avoid overexposure, it should be fine. Many folks are just taking point-and-shoot snapshots and trusting the camera to figure it all out.
Certainly, that is valid at any ISO setting, but that in no way answers my initial question : "why determine ISO 200 as base ISO instead of ISO 100 ?"
Is there a good reason to favor the 200 base ISO over the lower 100 ?
 
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ToxicTabasco

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I suspect it would depend on the lighting conditions. There is to my eyes no noticeable difference between ISO 100 to 400 in bright lighted well lit conditions. And ISO 100 or 200 look the same in high dynamic range conditions like sunsets. Both seem to have about the same amount of file data in RW2, and any small tiny difference can be adjusted for in editing software. I would suspect that if your pushing the limits of your software's NR and trying to boost massive amounts of data in RW2 files, the difference between ISO 100 and 200 may be helpful.

Nevertheless, it all depends on how the lighting conditions are, and what you expect to adjust in editing. And how you apply ISO in your exposure.

For me, the ISO 100 is extremely helpful to bring down the shutter speed while shooting video in bright light. That little if any difference is impacted more by the video smoothness more than anything. And at ISO 100 with video, it's impossible to see any difference between the noise and sharpness of ISO 200.
 

Joris

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True, I cannot see a diference between ISO 200 and 100 either, but suppose a difference might be visible on large prints. Panasonic seem to imply that the 100 ISO result would show lower, whereas DxO an Photonstophotos, on the contrary, indicate a higher quality.
Will continue to rely on the latter two, whenever I have a choice...
 

BlueBomberTurbo

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I think it's more of the baseline 0 exposure level shifts down by 1 stop. So say you have somewhere around 2.5 stops of highlight recovery and 3.5 stops of shadow recovery at ISO 200. At ISO 100, you'll drop to 1.75 stops of highlight recovery, but go up to 4.5 stops of shadow recovery. So shadow recovery gains quality at the expense of the highlight recovery, which becomes more fragile. You still gain a hair of extra DR based on the charts, though, so it's not all bad. It just requires more careful use vs the other ISOs.
 

Stanga

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I did some tests, just for fun, in RAW and JPG mode from 100 to 800 ISO. In JPG mode it was possible to see a worthwhile difference between 100 ISO and 200 ISO. I remember saving the files one of my many external drives. I'll see if I can find them.
 

Joris

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I did some tests, just for fun, in RAW and JPG mode from 100 to 800 ISO. In JPG mode it was possible to see a worthwhile difference between 100 ISO and 200 ISO. I remember saving the files one of my many external drives. I'll see if I can find them.
Ever find those images ? You do not make clear if your impression of IQ at 100 ISO is better than at 200, corroborating or Photonstophotos and DxO on the one hand or Panasonic on the other.
 
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archaeopteryx

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Not Stanga, but I use my G7 (which seems to have the same or nearly the same sensor as the GX80) at ISO 100 and 200 my experience of modest improvement seems consistent with DxO's and Bill Claff's measurements.

Why would Panasonic put up a barrier against using the GX80 at its lowest ISO (or is it that I get this all wrong)?
Old question, but my personal suspicion's just that nobody's felt like changing the firmware to make ISO 100 a regularly accessible ISO rather than requiring [Extended ISO] be set. That might be ideologically based on ISO 100 being obtained by a one stop ISO 200 ETTR and a pull in post but, as Panasonic publishes only a stub datasheet for sensors like the MN34230, special access to what's essentially Panasonic internal information seems needed. In particular, I would suspect some interaction with i.Dynamic.
 

Joris

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http://www.photonstophotos.net/Charts/RN_ADU.htm#Panasonic Lumix DMC-GX80_12,Panasonic Lumix DMC-GX85_12

Some time ago I asked Photostophoton's Bill Claff the question why Panasonic would designate 200 as the base ISO instead of 100 : He gave me an answer that I do not really fathom :

<<Native ISO is ISO 100 but below ISO 160 is affected by 12-bit ADC instead of 14-bit ADC so they list ISO 200 as native.>>

Can anyone shine me their light on what 12-bit ADC (analog-to-digital converter) vs 14-bit ADC means and what the impact is on the GX 80/85's IQ at 100 ISO vs 200 ISO .
 

ScottinPollock

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I thought all Panasonic m43 cameras were 12bit, with some being 10bit with electronic shutter.
 
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http://www.photonstophotos.net/Charts/RN_ADU.htm#Panasonic Lumix DMC-GX80_12,Panasonic Lumix DMC-GX85_12

Some time ago I asked Photostophoton's Bill Claff the question why Panasonic would designate 200 as the base ISO instead of 100 : He gave me an answer that I do not really fathom :

<<Native ISO is ISO 100 but below ISO 160 is affected by 12-bit ADC instead of 14-bit ADC so they list ISO 200 as native.>>

Can anyone shine me their light on what 12-bit ADC (analog-to-digital converter) vs 14-bit ADC means and what the impact is on the GX 80/85's IQ at 100 ISO vs 200 ISO .
Hmm, does this suggest that gradients would be more rough at ISO100?
 

Wasabi Bob

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"Base ISO" is where the sensor is essentially running at unity gain, its native sensitivity. In this case, if the camera offers ISO 100, its usually via extended ISO. It's usually achieved by a gain reduction of ~ -3db. I've measured the noise difference between ISO 200 & 100 using Imatest. Measurable - yes : Visible - no. The downside is that at ISO 100 a very small drop in DR will result. For the uber pixel-peepers ISO 200 will provide the best overall performance.
 

Joris

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The downside is that at ISO 100 a very small drop in DR will result. For the uber pixel-peepers ISO 200 will provide the best overall performance.
Well, according to both DxO-Mark and Photonstophotos (<<DxOMark doesn't test intermediate ISO settings like ISO 125 and ISO 160 and they do not use the same procedures as PhotonsToPhotos. But their measurements are consistent with mine. Cheers, Bill Claff>>) all the GX80 (and GX85)'s readings, contrary to many other cameras, dynamic range and color sensitivity included, improve at 100 ISO :

https://www.dxomark.com/Cameras/Panasonic/Lumix-DMC-GX80---Measurements (click on the tabs)
  • ISO Sensitivity
  • SNR 18%
  • Dynamic Range
  • Tonal Range
  • Color Sensitivity
  • Full SNR
  • Full CS

http://www.photonstophotos.net/index.htm
 

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