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Author Topic: Michael Reichmann, ETTR and Oly OMD EM5  (Read 25471 times)
Vladimirovich
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« Reply #40 on: January 03, 2013, 11:19:06 AM »
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That 5D MII must provide a tremendous amount of headroom.
may be Canon's just meter in such way, despite the fact that their sensors do not do a good job in deep shadows
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« Reply #41 on: January 03, 2013, 11:25:37 AM »
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we shall assume that you tested all raw converters  Cool ?

Well...they say that when you assume you make an ASS of U and ME.  So I'd say better not to assume.  Cool

It seems to be the case with Raw Therapee, Lightroom, and ViewNX.  I'd assume others are the same. (wait...what did I just do?) Wink
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digitaldog
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« Reply #42 on: January 03, 2013, 12:00:02 PM »
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I think you might have left out an ISO value when you said, "The ISO image was shot 'normal'..."  I think you meant, "the ISO 100 image was shot 'normal'..." but don't want to put words in your mouth.  Presuming this is the case...

Do you know of the 5D MIII produces a similar result?

I used an incident meter, set at ISO 100 and used that for the ISO 100 image in terms of shutter and aperture. I then left everything alone expect I upped the ISO to 800.

Don't know about the Mark III. I believe most of not all Canon's exhibit this behavior but not necessarily other camera systems. In the original linked forum posts, I think someone suggested Nikon works differently.
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Andrew Rodney
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« Reply #43 on: January 03, 2013, 12:28:11 PM »
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I used an incident meter, set at ISO 100 and used that for the ISO 100 image in terms of shutter and aperture. I then left everything alone expect I upped the ISO to 800.

Got it.  Thanks...I'll keep that example in mind when discussing these points.
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BJL
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« Reply #44 on: January 03, 2013, 12:32:10 PM »
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See reply #1 in http://www.luminous-landscape.com/forum/index.php?topic=56906.0 (the link was posted in reply #16 to this thread)  The photos were taken with an older Canon, but I believe the E-M5 has the same behavior.
On the contrary, the sensor of the E-M5 behaves far more like the sensors of the Pentax K-5 and Nikon D7000 mentioned in that reply:
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If you use the same shutter speed and f-stop, noise will be more visible the lower the ISO. ...
On some cameras (e.g. Pentax K5, Nikon D7000) the difference will be negligible, in some others (e.g. Canons) will be monstruous.
Putting aside the debate over whether the E-M5 sensor shares a Sony heritage with the K-5 and D7000 sensors, the measurements of dynamic range and SNR at 18% mid-tone level at DxOMark show that for image quality in raw files at equal exposure level (same f-stop and shutter speed), there is no gain beyond about ISO setting of 800: underexposing as low as 800 then pushing in raw conversion will probably give very similar noise characteristics, with the advantage of extra highlight headroom. Then again, E-M5 raw files have rather abundant raw headroom, over one stop, so that might not be a big deal.

By the way, as far as noise levels near midtone level, the graphs of SNR at 18% suggest that there is very little benefit to going above the minimum ISO setting of 200, and no measurable gain in going beyond 400.

On the other hand, underexposing will degrade in-camera JPEG's.  I use JPEG+raw, partly to have the JPEG's as "proofs" with all of the Olympus fixes for distortion and such applied, so when I have time, I prefer to bracket in this situation, starting with a frame at a "correct" combination of exposure level and ISO sensitivity setting.
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Vladimirovich
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« Reply #45 on: January 03, 2013, 12:50:14 PM »
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Putting aside the debate over whether the E-M5 sensor shares a Sony heritage with the K-5 and D7000 sensors
"sony heritage" is multiple ADC on die... Panasonic and Nikon/Aptina (?) designs also have such things... however implementations of Sony sensors in Pentax/Nikon cameras show linear DR graph.... and non Sony implementations show a bit of Canon like non linearity near lowest ISO (see Panasonic GH2, non Sony Nikons) and EM5 DR graph is exactly non Sony like...
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bjanes
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« Reply #46 on: January 03, 2013, 12:58:45 PM »
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camera metering (spot metering or matrix/centerw off a uniform surface) does not care what is your target actual reflectance... it is assuming some (manufacturer defined) reflectance regardless whether you meter off true 18% grey card or white snow and in most cases it is 12.x% (some camera models do differently)... and head room for different channels will be different for different illumination... so you test for a daylight, but you test for tungsten bulb as well and so on.

That is true regarding the results obtained with targets of different reflectance. That is why I said one could meter off the white of a computer screen rather than from a gray card. This will give the same results as reading off a gray card. Nikon and most other meters are calibrated for a luminance value that is roughly equivalent to the reflectance of 12% gray. This was pointed out by Thom Hogan way back in 2003.

With tungsten illumination, the head room for the green channel does not change much as shown below. Since green is heavily weighted for the luminance histogram, there won't be much of a change with tungsten as compared to daylight illumination. However, there will be less headroom for red and more headroom for the blue.

Bill
« Last Edit: January 03, 2013, 01:04:22 PM by bjanes » Logged
BJL
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« Reply #47 on: January 03, 2013, 01:17:22 PM »
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You are correct. The histogram and blinkies are from the JPEG preview and not from the raw file itself. Most cameras allow some headroom for highlights by using an ISO sensitivity somewhat higher than the Ssat value measured by DXO, resulting in underexposure.
...
As shown in the table below, the plus 2.33 EV exposure gives no clipping in the camera histogram and blinking highlights, and the plus 2.67 EV exposure does show clipping in the histogram and blinking highlights. Backing off of the plus 2.67 EV exposure to the Plus 2.33 one as suggested would give a raw file 0.67 EV short of full ETTR.
Thanks Bill. The short version is that:
1. From your test, it looks safe to push the D800E exposure level up in, say, half stop increments and then use the the first level that _does_ give highlight blinkies, rather than backing off to avoid them.
2. This should be even safer with the E-M5, which gives raw files with more highlight headroom than most (a bigger gap between the ISO Standard Output Sensitivity calibration of its JPEG output and and the ISO Saturation based measurement of its raw output).


P. S. A camera having an ISO Standard Output Sensitivity [SSOS] higher than its ISO Saturation-based Sensitivity [Ssat] is not "underexposing". The two numbers are simply different measurements of different output formats, with related but different purposes. Imatest calculates both SSOS and Ssat, and has a useful discussion at http://www.imatest.com/docs/sensitivity_ei/
The size of the gap is primarily a measure of raw highlight headroom and the Imatest page above gives this highlight headroom in its equation (8):
HdrSOS(f-stops) = log2( SSOS ⁄ Ssat ) + 0.5      (f-stops or EV or zones)

As I have mentioned in numerous times, Japanese camera makers are more or less required by their industry association CIPA to use ISO Standard Output Sensitivity as the primary method of calibration of the ISO sensitivity settings on their cameras. Insisting that SSOS = SSat would forbid a camera from offering more or less than 1/2 stop of highlight headroom in its raw files, which would be an absurdly rigid restriction on camera design.
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richarddd
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« Reply #48 on: January 03, 2013, 03:11:07 PM »
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If it would be helpful, I'd be happy post a rawdigger analysis of an E-M5 RAW image of a gray card, or any other test I can easily perform.  If so, please be very specific as to what you'd like to see.
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bjanes
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« Reply #49 on: January 03, 2013, 09:28:15 PM »
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P. S. A camera having an ISO Standard Output Sensitivity [SSOS] higher than its ISO Saturation-based Sensitivity [Ssat] is not "underexposing". The two numbers are simply different measurements of different output formats, with related but different purposes. Imatest calculates both SSOS and Ssat, and has a useful discussion at http://www.imatest.com/docs/sensitivity_ei/
The size of the gap is primarily a measure of raw highlight headroom and the Imatest page above gives this highlight headroom in its equation (Cool:
HdrSOS(f-stops) = log2( SSOS ⁄ Ssat ) + 0.5      (f-stops or EV or zones)

As I have mentioned in numerous times, Japanese camera makers are more or less required by their industry association CIPA to use ISO Standard Output Sensitivity as the primary method of calibration of the ISO sensitivity settings on their cameras. Insisting that SSOS = SSat would forbid a camera from offering more or less than 1/2 stop of highlight headroom in its raw files, which would be an absurdly rigid restriction on camera design.

The D800e uses REI (recommended exposure index) for its speed rating and I understand that this is also in compliance with the CIPA standards. The REI is arbitrary and the maker could assign whatever value they wish, so that standard is not lilmiting. In my own tests with the D800e exposing the target at ISO 100 according to the light meter reading gives a sensor saturation of 12.2% which is in accordance with the Ssat standard. If I interpret this correctly, Nikon is essentially using Ssat. What I don't understand is that DXO states that the Ssat speed for the D800e is 73 for the manufacturer's ISO of 100.

Regards,

Bill
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« Reply #50 on: January 04, 2013, 09:23:22 AM »
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If it would be helpful, I'd be happy post a rawdigger analysis of an E-M5 RAW image of a gray card, or any other test I can easily perform.  If so, please be very specific as to what you'd like to see.

Do you also have a Nikon or a Canon?  I'd be interested to see if there is a difference in spot meter exposure settings.  So if both cameras are set to ISO 200 and, say, f/8, and mounted with similar lenses, and you spot meter a neutral reference...is there a difference in the shutter speed?

I ask because I suspect that the EM-5 is overexposing by one stop, and that's why it's performance appears to be so good.  When I compare the camera settings of sample images taken at Imaging Resource or DPReview, it always seems like the EM-5 is taking in one stop more light at the same ISO under the same lighting.

In nearly all cases, when DxOMark indicates a lower ISO than the rating, it's because the signal is boosted to the correct level.  This isn't cheating because amplifying the signal adds noise.  It's nothing more than how the manufacturer has decided to process the signal.  However, in the case of Olympus's latest cameras...I think they're cheating.  They're ISO levels measure so low because they're actually changing the exposure from what it's supposed to be.  Basically, I think they're exposing ISO 200 shots as if they are ISO 100.  As far as I'm aware, DxOMark doesn't test for the correct aperture/shutter settings.

Well, that's my suspicion but I don't have an EM-5 to prove it.  And like I said...this is based on sample images (and the fact that DxOMark measure the ISO to be an entire stop off.)  I could just be imagining it all.

Olympus used to indicate how it rates ISO (they used SOS like Pentax) but they don't list the method on the new cameras.  Hmmm....
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« Reply #51 on: January 04, 2013, 09:51:54 AM »
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Hi Folks,
This has all been beaten to death at another photo (review) site's forums.  

YES, the OM-D is about 2/3rds of a stop less sensitive than a Canon.  
YES, the same shutter and aperture will yield a different ISO on an OM-D and many other cameras.

SO, comparing noise between an OM-D and, say for example, a 7D requires the 7D to be set to 1600 ISO while the OM-D is set to 2500 ISO.  

FINALLY, despite this peculiarity the OM-D still has less noise and more detail at these equivalent ISOs than any other MFT and many APS-C cameras.  Of course, it can't touch full frame sensors and some of the latest APS-C sensors are cleaner.  
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« Reply #52 on: January 04, 2013, 10:41:23 AM »
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This has all been beaten to death at another photo (review) site's forums.
Sorry, I did not realize that this was already discussed in other forums.  I do visit other forums, but I never visit the 4/3 areas, so I didn't know (it hasn't really bothered me enough to ask about it until richarddd offered tests.)

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YES, the OM-D is about 2/3rds of a stop less sensitive than a Canon.
That's what DxOMark shows as well, which is in line with the difference in area.

Quote
FINALLY, despite this peculiarity the OM-D still has less noise and more detail at these equivalent ISOs than any other MFT and many APS-C cameras.
There, I beg to differ.  That's only at ISO 200 and because Olympus is exposing ISO 200 as if it's ISO 100.  Most APS-C cameras have a real ISO 100, and that's where they leave the OM-D and new Pens behind.

The comparison at equivalent aperture/shutter values is important because when you start shooting in low light, those are your limits.  People will buy an OM-D thinking they're going to get great performance in low light...but they're not because their ISO will be higher than a Canon or Nikon (for any given aperture/shutter combo.)  In the end, they're going to get 2/3rds stop more noise...not the APS-C noise level that they were led to believe the camera can deliver.  The deception of the buyers is what bothers me most about this...they're not getting what they think they're getting.
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« Reply #53 on: January 04, 2013, 11:03:58 AM »
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...
...not the APS-C noise level that they were led to believe the camera can deliver.  The deception of the buyers is what bothers me most about this...they're not getting what they think they're getting.


I agree that their ISO ratings look deceptive. I will not comment about whether this was deliberate deception by Olympus or not.  BUT, despite that 2/3rds stop difference, the OM-D is better than my 7D in resolution and noise performance.  This is born out by DXO and many testers.  I believe that I said "MANY" other APS-C cameras.  The diversity of options in that space is pretty wide and I think it is enough to say that the OM-D MFT sensor is in the same quality range with the APS-C sensors even when you factor in an equivalent exposure that requires "different" ISO settings. Some APS-C are better some are worse. I don't really care about debating the last 3% of quality and I would estimate they all fall in that area.
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Fike, Trailpixie, or Marc Shaffer
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« Reply #54 on: January 04, 2013, 11:21:02 AM »
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BUT, despite that 2/3rds stop difference, the OM-D is better than my 7D in resolution and noise performance.  This is born out by DXO and many testers.

That's true, but the 7D is over three years old now.  When comparing the OM-D to APS-C cameras with Sony sensors released around the same time, it rates over 2 dB less (a smidge over 2/3 EV more noise.)  This makes sense to me, as all the sensors are made by Sony and of similar tech, so you'd expect the difference to be based on size.  The bottom line is that there's nothing special about the OM-D sensor.  What's different is the exposure.  Canon can issue a firmware update for all their cameras changing the ISO 100 label to ISO 800...and now the OM-D performance will be abysmal in comparison!

That's definitely not what the CIPA had in mind when they issued the latest digital ISO standard.
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richarddd
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« Reply #55 on: January 04, 2013, 04:38:47 PM »
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Do you also have a Nikon or a Canon?  I'd be interested to see if there is a difference in spot meter exposure settings.  So if both cameras are set to ISO 200 and, say, f/8, and mounted with similar lenses, and you spot meter a neutral reference...is there a difference in the shutter speed?

I ask because I suspect that the EM-5 is overexposing by one stop, and that's why it's performance appears to be so good.  When I compare the camera settings of sample images taken at Imaging Resource or DPReview, it always seems like the EM-5 is taking in one stop more light at the same ISO under the same lighting.

In nearly all cases, when DxOMark indicates a lower ISO than the rating, it's because the signal is boosted to the correct level.  This isn't cheating because amplifying the signal adds noise.  It's nothing more than how the manufacturer has decided to process the signal.  However, in the case of Olympus's latest cameras...I think they're cheating.  They're ISO levels measure so low because they're actually changing the exposure from what it's supposed to be.  Basically, I think they're exposing ISO 200 shots as if they are ISO 100.  As far as I'm aware, DxOMark doesn't test for the correct aperture/shutter settings.

Well, that's my suspicion but I don't have an EM-5 to prove it.  And like I said...this is based on sample images (and the fact that DxOMark measure the ISO to be an entire stop off.)  I could just be imagining it all.

Olympus used to indicate how it rates ISO (they used SOS like Pentax) but they don't list the method on the new cameras.  Hmmm....
I don't currently have a Nikon or Canon to compare.

The issue of the accuracy of Olympus's ISO rating has been debated extensively on another site.  For that matter, the meaning of ISO for RAW has been debated extensively.
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allegretto
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« Reply #56 on: January 04, 2013, 10:04:11 PM »
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Just a subjective observation here, but a careful one if not quantitative.

Have used several systems this year (Nikon, Fuji, Sony and Leica) and just used an OM-D. Found, relatively that it tends to overexpose many scenes. Immediately de-comped  a third and probably needs one more click.

Which in a way I guess is saying that you can't cheat physics.
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BJL
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« Reply #57 on: January 05, 2013, 06:59:02 PM »
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Just a subjective observation here, but a careful one if not quantitative.

Have used several systems this year (Nikon, Fuji, Sony and Leica) and just used an OM-D. Found, relatively that it tends to overexpose many scenes. Immediately de-comped  a third and probably needs one more click.
Do you mean in standard JPEG output? Because in raw files, the observation from DxO etc. is that it goes in the opposite direction, placing raw output at lower levels than other cameras.

Are there any measurements on the EM5 about:
(a) how the shutter speeds chosen by the in-camera metering with aperture priorty mode compare to other cameras? (In particular, does it choose slower shutter speeds than "advertised" by the ISO setting, which would require choosing a higher "ISO" setting to get comparable shutter speeds to other cameras in the same lighting conditions?)
(b) how the tonal level placement in default JPEG output looks when one chooses exposure setting based on external metering? (That is, does it give overexposed or underexposed JPEG output when used with an external meter?)

I ask because the DxO measurements of Ssat on raw files say nothing about the answers to these questions, and this discussion seems to confuse no less than three different issues by the persistent use of "ISO" as if it has a unique well defined meaning.
« Last Edit: January 05, 2013, 07:48:27 PM by BJL » Logged
BJL
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« Reply #58 on: January 05, 2013, 07:20:16 PM »
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When comparing the OM-D to APS-C cameras with Sony sensors released around the same time, it rates over 2 dB less (a smidge over 2/3 EV more noise.)  This makes sense to me, as all the sensors are made by Sony and of similar tech, so you'd expect the difference to be based on size. ...
 
Canon can issue a firmware update for all their cameras changing the ISO 100 label to ISO 800...and now the OM-D performance will be abysmal in comparison!

That's definitely not what the CIPA had in mind when they issued the latest digital ISO standard.
I agree; that is why I am curious about comparisons at equal exposure level, such as same light source, same aperture ratio, shutter speeds of 100, 200, 400, etc. DxO does not do this, since its Ssat measure has nothing to do with how much exposure the sensor gets, but just about how much the photosite signals are subsequently amplified to produce raw output.

In this context, it is interesting to compare the DxO results for the three 2012 Olympus models, all using the same sensor AFAIK. The two newer "consumer" models, EPL5 and EPM2, score a bit better than the EM5 in the "sports" score, apparently because they have slightly "higher" curves for DR and SNR at 18%. But the dots on those curves for equal ISO settings are mostly the same or slightly lower for the new models, but also slightly to the right which moves the curves up. So the curves are only higher because the consumer models have slightly higher DxO Ssat scores, due to those two consumer models placing their raw output at slightly higher levels. This is purely a matter of how much analog (and/or digital) amplification is applied, and the slightly greater amplification used with the consumer models does not improve noise levels at all.
« Last Edit: January 05, 2013, 07:46:15 PM by BJL » Logged
allegretto
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« Reply #59 on: January 07, 2013, 02:15:19 PM »
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thanks, no I mean RAW

will post examples when I figure out how you guys do the posting of such large files to this site...
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