G6 vs newest sensors: Real difference in high ISO noize

Started Mar 5, 2014 | Questions thread
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texinwien Veteran Member • Posts: 3,320
Re: G6 vs newest sensors: Real difference in high ISO noize

Øyvin Eikeland wrote:

texinwien wrote:

The formula for determining the exact ISO value at any pixel on the x-axis is 50 * 2^(n/60), where 'n' is the number of pixels from x=50 ISO (the far left of the graph). The center of the furthest right E-M5 dot is 473 pixels to the right of x=50 ISO. Plugging that into our formula, we have:

50 * 2^(473/60) = 11,806 ISO

If anything, the graph is unfair to the E-M5 by 42 ISO steps


Øyvin Eikeland


I am not too concerned about the graphical presentation of the data.

Ok, you wrote:

The measured ISO for this setting is only 11848. Therefore the data point is plotted at 11848 along the X-axis. What I do not get is this: How can I find the dynamic range (or SNR) you will get if I set the camera to an ISO of 25600? If the dynamic range in the raw-files are indeed 6.61EV, isn´t it unfair to plot the point just below 12800?

It appeared to me that you were asking about the graphic representation (in addition to asking about finding the DR or SNR 18% at camera ISO 25,600.

I'm not sure what your source of confusion is here, or why you consider the graph to be 'unfair' since DxO clearly labels the x-axis "Measured ISO".

If you hover your mouse over the samples the actual measurements are shown. For example:


Measured ISO: 12663

Manufacturer ISO: 12800

Dynamic range: 5.59Ev

OM-D E-M5:

Measured ISO: 5953

Manufacturer ISO: 12800

Dynamic range: 7.5Ev

I have learned(from this forum) that when both cameras are set at ISO12800 the resulting shutter speed and aperture can be the same for both cameras. The difference in measured iso comes from the fact that olympus deliberately under-exposes the sensor and apply gain digitally in post processing. If I (for some reason) need to shoot at ISO12800 I should compare the two measurement points listed above. It would not be correct to compare them directly I think. That would imply a 2-stop advantage to the OM-D E-M5. How do I calculate the correct dynamic range when both cameras are set at ISO 12800?

Compare the DR at the matching manufacturer ISOs. Since the DxO graphs are plotted using the measured ISOs (and clearly labeled as such), you'll need to determine (by rolling over the graphed points for each camera) which points correspond to the manufacturer ISO for which you wish to compare DR for each camera.

Addendum: and keep in mind that the DR / SNR numbers are calculated based on optimum exposure (to the right), and not based on exposing to the camera's meter. If you expose to the camera's meter with the E-M5, you'll underexpose by about a stop, and the resulting DR will be lower than the maximum possible DR had you exposed optimally to the right.

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