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[OM] MooseRant on Low Light Shoot-Out

Subject: [OM] MooseRant on Low Light Shoot-Out
From: usher99@xxxxxxx
Date: Mon, 27 Jan 2014 19:12:52 -0500 (EST)
LTM writes:

>>I understand our culture's obsession with measurement, rankings and
winners.
>>But when the rankings do not reflect actual
>>performance differences, I can't see how they are of use. What the H
are they
>>measuring? Why?

One has to dig but they do explain the measurments.  Adorama ranked
them  as if the  exact order mattered and did not take into account if 
the differences were
significant from a practical vantage point.

http://www.dxomark.com/en/About/Sensor-scores/Use-Case-Scores

Appears a 25% difference in ISO score is about 1/3 EV and only 
"slightly noticeable".

Curiously the best optics according to DXO perform much better n the 
EM-1 than the Gx-7--perhaps due to the more robust
AA filter.

http://www.dxomark.com/Reviews/Best-lenses-for-the-16-MPix-Panasonic-Lumix-DMC-GX7-Part-1/How-does-sharpness-compare-between-the-Panasonic-Lumix-DMC-GX7-and-the-Olympus-OM-D-E-M1

The difference is most marked for the best performing optic the 75/1.8 
and less of difference with other lenses according to DXO's  
"Perceputal MP"
measure of sharpness,

http://www.dxomark.com/enà¹%20ฟà¸%20à¹%20ฟà¸%20à¹%20ฟà¸%20/Reviews/Looking-for-new-photo-gear-DxOMark-s-Perceptual-Megapixel-can-help-you

Wonder what Moose thinksof this?


 Also Lab testy AG writes:

"This gets back around to one of my original complaints about DXOMark
and the ISO methodology they use. In essence, they redefined what
exposure ISO means and made it completely irrelevant to real-life
usage. When they first launched this method, I, along with a number of
other people, addressed it as flawed, but was out-shouted by the
landscape photographers who were so intent on ETTR as the one and only
method of exposure determination. That exposure method is bogus for
the vast majority of photographic applications, as well as flash
lighting. DXOMark continued on with their screwed up redefinition of
ISO"

Here is their way of doing it again:
http://www.dxomark.com/About/In-depth-measurements/Measurements/ISO-sensitivity

Not sure I like the saturation method either.

ETTR seems more apppropriate for  Canyon cams for some applications.  
(They best get off their sensor duff)


As it was explained to me:


You can simplify the noise additions to the signal in the camera into 
two stages - one is close to the pixel, one is close to the A/D 
conversion. The "real" analog ISO amplifier is closer to the pixel. 
I'll call them "n1" and "n2" here. NB - this is not a real convention.

In low light, you need to amplify the signal to make it brighter - the 
question is just where you do it.

If you do it in post, you're basically applying a multiplication to the 
SUM of n1 and n2.
If you do it in the analog ISO amplifier close to the pixel, you're 
just multiplying n1 - the late stage noise n2 is the same as before, 
and is added as normal without multiplication!

Say we need a 10x brightening (go to ISO1000, if the camera's base ISO 
is 100). To  throw in some arbitrary numbers of n1=5 and n2=20 just to 
see what happens.

Brighten in post:
Total noise = (brightening factor) * (sqrt(n1^2+n2^2))
>>>> 10 * sqrt( 5^2 + 20^2 ) = 206.1

Brighten in analog, with ISO amplifier:
Total noise = sqrt ( (brightening factor * n1)^2 + n2^2)
>>>> sqrt( (10*5)^2 + 20^2) = 53.9

-the noise is much lower when you use the on-sensor ISO amplifiers, 
because of the fact that you don't have to multiply the late stage 
noise too...

In cameras with very low n2 noise (late stage noise) you don't lose as 
much by amplifying in post. Say that we lower n2 to "10" instead - 
that's like getting quieter A/D converters and a cleaner signal path.
Post : 10 * sqrt( 5^2 + 10^2 ) = 111.8
ISO : sqrt( (10*5)^2 + 10^2) = 50.9

Note that the "push in post" noise got a LOT lower - but the "amplify 
with analog ISO" didn't get much better at all. That's because of the 
n1 having to be amplified no matter what, there's no getting around 
that if the image is to get brighter.

That is (fairly simplified) why you can push a Sony sensor quite high 
 from base ISO without the image falling apart, but you can't do it with 
a Canon sensor. The Canon sensor has good high ISO in camera, since it 
has excellent n1 noise. But it's limited at low ISOs by the rather 
strong n2 noise, and that's amplified by pushing in post.
This is also why Canon sensors have lower base ISO DR's, since DR is 
dependent on both n1 and n2. Higher ISOs are almost purely dependent on 
n1.

Pushing the shadows on my OM 5DII quickly gets ugly.  ETTR clearly  
less of an advantage with Sony.

In the final analysis,  it  is really very simple as one need only to 
look for a MSOA designation---"Moose Seal of Approval" and all will be 
well.
Works for me.  :-)

Not quite as  Lab Testy, Mike











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