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Author Topic: Mark Dubovoy's essay  (Read 53539 times)

Herb19

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Re: Mark Dubovoy's essay
« Reply #140 on: December 22, 2010, 09:28:29 AM »

I did a few tests

http://www.datarescue.com/photorescue/freefiles/compare40d5dmkII.jpg

http://www.datarescue.com/photorescue/freefiles/5dmk2.jpg

http://www.datarescue.com/photorescue/freefiles/40d.jpg

40D / 5DMK2 - tripod - remote trigger - 1 meter from target - auto exposure - lighting poor on purpose to better see the noise. Shot in RAW, converted to jpeg at max quality with no adjustment whatsoever, ISO 800

AFAIC

- the gain boost is quite visible, maybe a bit less on the 40D, but the auto-exposure chose different parameters.
- the practical impact, at least at pixel peeping level, of the gain boost is more significant than the raw noise number indicate, probably because noisy pixels have a bigger than expected impact on the RAW conversion.
- the DOF decreases as expected (it is very visible on near tangent images of printed text, as posted earlier) at least on the 5D
- the 40D doesn't seem to exploit that DOF increase fully, but that's just a gut feeling, and DOF is bigger anyway.



Pierre,

Interesting data, nicely done. Seems indeed that gain (noise) increases at wider apertures. The change of DOF is clearly visible.
Expected to see slightly more gain (noise) increase of the 40D compared to the 5D as per DxO labs figures / smaller 40D photo sites.
Probably the difference of 0.1EV is neglectable / not visible in this test.

Please note that the DOF of the 40D is smaller because you are shooting both camera's from the same distance.

Calculated DOF for a 85mm lens on both camera's focussed on 1 meter distance is as follows:

             5Dmk2          40D

f/2.0       1.6cm          1.0cm
f/1.8       1.5cm          0.9cm
f/1.4       1.1cm          0.7cm
f/1.2       1.0cm          0.6cm

Of course these figures are approximate for standard eyesight on printed matter. However close enough for validation of this test I think.
Used the DOF calculator on the Cambridge in Colour site.
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

These distances are very close according your test shots.

So it looks that gain (and noise) is increasing towards wider apertures and still the influence of aperture on DOF remains visible towards f/1.2.

Herb
« Last Edit: December 22, 2010, 09:51:01 AM by Herb19 »
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NikoJorj

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Re: Mark Dubovoy's essay
« Reply #141 on: December 22, 2010, 09:55:48 AM »

- the DOF decreases as expected (it is very visible on near tangent images of printed text, as posted earlier) at least on the 5D
- the 40D doesn't seem to exploit that DOF increase fully, but that's just a gut feeling, and DOF is bigger anyway.
Thanks for the test!
The width of DoF doesn't seem that impacted, but I fell that the bokeh changes with the max aperture, see the blue line at left side of the ruler...
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Nicolas from Grenoble
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pegelli

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Re: Mark Dubovoy's essay
« Reply #142 on: May 28, 2017, 06:42:57 AM »

Let me also respond directly to the comment that the data cannot be found on the DxO site.  There is a new release of the DxO site coming in a few weeks.  It will contain a lot of new data, including the data that support this open letter.

While there has been some discussion on the depth of field issue, l would like to repeat what I said in the open letter, which is that DxO is in the process of performing thorough focus measurements. Once the final focus measurement data is available, we will be able to put this issue to rest.
Sorry to reopen a very old discussion, but I was reminded of this thread due to a question in another forum.

Has anybody seen the promised further data from DxO, either on the "hidden" iso gain as well as on the "reduced DOF" claim? I haven't, but would be interested to read more on this in case it has been published and I missed it.
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pieter, aka pegelli

scyth

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Re: Mark Dubovoy's essay
« Reply #143 on: May 28, 2017, 08:41:11 AM »

Has anybody seen the promised further data from DxO, either on the "hidden" iso gain

photonstophotos.net

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