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06-25-2016, 08:30 AM   #1
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Pentax d and z's dynamic range

Do they have 14 or 15 dr stops?

06-25-2016, 09:07 AM   #3
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Ummm Dxo removed Pentax 645Z out of their chart long time ago... That's why I asked this question.
06-25-2016, 09:14 AM   #4
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doesn't mean the measurement was wrong

06-25-2016, 09:42 AM   #5
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QuoteOriginally posted by rlatjsrud Quote
Ummm Dxo removed Pentax 645Z out of their chart long time ago... That's why I asked this question.
You can still access the rating if you know the URL. I'm not sure why it's not listed otherwise (they never said) but I suspect it's because the rating exceeds 100. Perhaps updates are needed to the scale?

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06-25-2016, 10:09 AM   #6
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QuoteOriginally posted by rlatjsrud Quote
Do they have 14 or 15 dr stops?
It is not really possible to have more stops than the bit rate. So in theory a maximum of 14 stops.

However in practice I suspect closer to 12 stops - which my testing with Sekonic meter indicated (see attached), although fewer stops are usable in practice.

Bill Claff's testing indicates 11.7 at base ISO
Photographic Dynamic Range versus ISO Setting
Attached Images
 
06-25-2016, 10:55 AM   #7
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QuoteOriginally posted by Adam Quote
You can still access the rating if you know the URL. I'm not sure why it's not listed otherwise (they never said) but I suspect it's because the rating exceeds 100. Perhaps updates are needed to the scale?
It was there on Dxo site but they really removed the test score.

Pentax 645Z : Tests and Reviews - DxOMark

here's the page where people argued about removing the score.

---------- Post added 06-25-16 at 10:57 AM ----------

QuoteOriginally posted by D1N0 Quote
doesn't mean the measurement was wrong
Then why did they removed even they already tested and scored 101?
06-25-2016, 12:02 PM   #8
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QuoteOriginally posted by rlatjsrud Quote
Then why did they removed even they already tested and scored 101?
because it wasn't supposed test so well?

06-25-2016, 07:22 PM   #9
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QuoteOriginally posted by D1N0 Quote
because it wasn't supposed test so well?
They already did full tests and then posted on their site but they removed everything.
06-25-2016, 08:34 PM   #10
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QuoteOriginally posted by rlatjsrud Quote
Then why did they removed even they already tested and scored 101?
Generally, companies do this because it was considered not in their best interests to leave it up.

Then one naturally wonders as to why it wasn't in their best interest. Should the reason be something rather understandable, such as an error in measurement, then one would expect this to be made known..... it's not that embarrassing and tends to show some transparency which can benefit a brand.

Should the reason be something more compromising....say something in conflict with their closer held comercial imperatives/interests ..... then "stealth" is the normal commercial action....(quietly remove and not acknowledge in this case). If it's a bid deal and likely to be discussed a lot..... then one seeks to control the narrative by getting out on front of it with well crafted "messages and key talking points" etc. These key points will be based around some essence of truth, but most likely nothing to do with the real issue.

Why did it get so far as to be posted? is the next logical enquiry...... simple..... happend to me many times in a past life...... the "every day" part of the organisation goes about doing what it does..... in this case measuring and posting it's stuff (with the normal checks etc)...... then a more "Commercially aware" part of the company gets involved when something is brought to its attention at a later stage ..... normally a complaint in some way..... say an unhappy business partner..... or someone that points out a "unintended consequence". This then normally leads to an additional "approval" or "sign off" stage for all jobs there on in....or at least some addition sign off checks/staff training etc.

Whatever the reason, we are not privy to their current and future business/commercial interest's at any meaningful level..... so it's all just conjecture anyway. What has become clear, with regard to their "DXO One camera", is DXO do consider commercial imperatives when presenting their data!

Last edited by noelpolar; 06-25-2016 at 09:31 PM.
06-25-2016, 09:01 PM   #11
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In July 2015 PF member Class_A and myself discussed dynamic range/ SNR measurement methods being used by some sources including the one mentioned on this thread.
We ( more or less) concluded that a lot of measurements were correct in early days but an error occurred maybe in 2013.
The source company provided correct method in its background web pages, but some camera tests appeared to not follow that method while others did !

The correct Decibel unit of measurement for dynamic range / SNR is based on telephony work in 1930's and has been entrenched by international standards ever since ( eg ANSI and ISO)

ie 20 log (P_ratio) which gives 6dB per f stop or 6db per incremented MSB of the ADC.
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