Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-08-2010, 07:38 AM   #16
Veteran Member
Reportage's Avatar

Join Date: Feb 2009
Photos: Gallery
Posts: 739
QuoteOriginally posted by kittykat46 Quote
Don't tell me some bright engineer in Pentax was given an assignment - go study how dXOMark does its measurement and come back with some recommendations on how to tweak the sensor performance give us that little bit of an edge.

Its not unheard of in the corporate world , if the index is a well publicised and respected one, but I'm just toying around here...
well, has Nvidia or ATI in times past ever optimized their drivers for optimum 3dmark scores rather then actual real world performance?

11-08-2010, 07:40 AM   #17
Pentaxian
falconeye's Avatar

Join Date: Jan 2008
Location: Munich, Alps, Germany
Photos: Gallery
Posts: 6,862
QuoteOriginally posted by kittykat46 Quote
Don't tell me some bright engineer in Pentax was given an assignment - go study how dXOMark does its measurement and come back with some recommendations on how to tweak the sensor performance give us that little bit of an edge.
An engineer (Pentax) on assignment to beat a physicist (DxO)? Poor engineer ...
OTOH, they tried with their raw-level NR and fooled about everybody else
11-08-2010, 08:43 AM   #18
Pentaxian




Join Date: Aug 2007
Location: Madison, Wis., USA
Posts: 1,510
QuoteOriginally posted by falconeye Quote
An engineer (Pentax) on assignment to beat a physicist (DxO)? Poor engineer ...
OTOH, they tried with their raw-level NR and fooled about everybody else
Spoken as a true physicist!
11-08-2010, 09:02 AM   #19
Veteran Member
macTak's Avatar

Join Date: Apr 2010
Photos: Gallery
Posts: 759
I think (considering how idential the results are save for a little greater ISO cheating by Nikon) this shows that it was a really clever move by Pentax to add an ISO 80 option and thus move their camera's ranking ahead of the D7000 and any other cameras going to use that sensor. Just wait, next generation all the compaines (instead of compeating to have the highest ISO as they have been), will be competing to have the lowest ISO

11-08-2010, 09:32 AM   #20
Senior Member
stormcloud's Avatar

Join Date: Oct 2009
Posts: 235
an iso 50 would be nice addition - even if it was just overexposed then brought down in processing - come on pentax firmware update for iso 50
11-08-2010, 09:39 AM   #21
Pentaxian
falconeye's Avatar

Join Date: Jan 2008
Location: Munich, Alps, Germany
Photos: Gallery
Posts: 6,862
QuoteOriginally posted by macTak Quote
add an ISO 80 option and thus move their camera's ranking ahead of the D7000 and any other cameras going to use that sensor. Just wait, next generation all the compaines (instead of compeating to have the highest ISO as they have been), will be competing to have the lowest ISO
Again.

You can't just lower the ISO setting.
The way DxO tests Dynamic Range, it would make no difference at all. The translucent mirror in the SLT-A55 makes no difference either.

The only way to increase DR (for a given read-out noise) is by a higher full well capacity which allows for a true lower iso. Cheating on iso doesn't give you a single extra electron in the well.

I don't fully understand what happened in the ISO 70/83 region to the K-5/D7000 sensors. But it's not about "adding an option". Not at all.
11-08-2010, 09:56 AM   #22
Veteran Member
macTak's Avatar

Join Date: Apr 2010
Photos: Gallery
Posts: 759
QuoteOriginally posted by falconeye Quote
Again.

You can't just lower the ISO setting.
The way DxO tests Dynamic Range, it would make no difference at all. The translucent mirror in the SLT-A55 makes no difference either.

The only way to increase DR (for a given read-out noise) is by a higher full well capacity which allows for a true lower iso. Cheating on iso doesn't give you a single extra electron in the well.

I don't fully understand what happened in the ISO 70/83 region to the K-5/D7000 sensors. But it's not about "adding an option". Not at all.
Falk, I take it that the sensor (for both cameras) had that full well capacty allowing for a true lower ISO, but for whatever reason, Nikon decided not to go that low (unlike Pentax). That's what I meant by adding the option.
11-08-2010, 11:10 AM   #23
Pentaxian
falconeye's Avatar

Join Date: Jan 2008
Location: Munich, Alps, Germany
Photos: Gallery
Posts: 6,862
QuoteOriginally posted by macTak Quote
Falk, I take it that the sensor (for both cameras) had that full well capacty allowing for a true lower ISO, but for whatever reason, Nikon decided not to go that low (unlike Pentax). That's what I meant by adding the option.
I know what you meant. Taken two sensors with the same full well capacity, the same quantum efficiency and the same analog gain setting (e.g., the same sensor actually).

Then both sensors have the same true base iso value, assuming the same microlens fill factor and bayer filter transparencies (which seems to be the case from the other curves).

Now, to go below this true base iso value doesn't increase the DR anymore. It just stays constant (with a risk of overexposure). Even if such a thing as negative gain existed, if the well is full it is full. And Dxo measures ISO by observing pixel saturation. At negative gain, the pixel will never saturate and the so-called output dynamic range is damaged. That's not the case here. DxO observes 100% luminosity at K-5 vendor ISO 80.


The point is that your statement implies that Nikon wouldn't use the sensor at base ISO at all. But always with a gain of 91/70=83/70 or +19%.

That's a different statement from just cheating on iso and adding an option. E.g., Pentax could call their extended ISO "50". 50 isn't unheard of for a real value of 70. But it wouldn't change the result.


So, why shouldn't Nikon use the sensor at base gain already at ISO 100, or add an extended ISO 50 step? Not fully exploiting the sensor just doesn't make sense.

The only other idea I could come up with is that the Sony sensor documentation mentions some strange setting lowering the chip's quantum efficiency, e.g., by lowering the photon-electron conversion rate, maybe by applying some reduced voltage somewhere. That would be a strange thing possibly explaining why it is an extended setting for Pentax. But I don't believe this. Just enumerating the possibilities.

Also possible is that the sensor documentation lists gain factors which Pentax choose to underrun after finding out that there is some headroom, i.e., the lowest listed gain isn't the lowest preventing clipping the output DR.


This is a document of Sony's 12MP Exmor chip which may be used in the K-x: http://www.sony.net/Products/SC-HP/cx_news/vol50/pdf/imx021.pdf

It talks about a programmable 24dB gain amplifier. 24dB are 4 stops spanning a region e.g., from ISO 160 to ISO 2500. Any gain above must be done in software, any "gain" below by overexposure. As the gain amplifier must be on chip, Nikon and Pentax have to use the same one. I can't see why Nikon wouldn't use the 0dB setting...

However, I've not found a corresponding document for the sensor in the K-5.


Last edited by falconeye; 11-08-2010 at 11:39 AM.
11-08-2010, 05:45 PM   #24
Senior Member




Join Date: May 2009
Location: Delaware
Posts: 177
D7000 comes close. Close but no bananas. The 7D has suddenly become an expensive doorstop. Heh, heh.

It's good to be the king.
11-08-2010, 05:54 PM   #25
Veteran Member




Join Date: Jul 2009
Location: kobe/japan
Posts: 510
@falconeye , the reason for nikon for not going to lower iso than iso 100 might be related to the way they implement their hardware with sensor. Both nikon and pentax after-tune the base sensor so i take it that it is the hardware than connects sensor that could hamper. If it were a software issue, they might have worked around it.

Just a guess though, most probably i am wrong on this.
11-08-2010, 06:27 PM   #26
Pentaxian
falconeye's Avatar

Join Date: Jan 2008
Location: Munich, Alps, Germany
Photos: Gallery
Posts: 6,862
QuoteOriginally posted by zxaar Quote
@falconeye , the reason for nikon for not going to lower iso than iso 100 might be related to the way they implement their hardware with sensor. Both nikon and pentax after-tune the base sensor so i take it that it is the hardware than connects sensor that could hamper. If it were a software issue, they might have worked around it.

Just a guess though, most probably i am wrong on this.
I would normally agree. But the charm with that sensor is that it is used almost like memory. You read out digital values. Of course, the quality of power supply, cooling and protection from electromagnetic perturbations increases IQ. But by decreasing noise, not by increasing the signal. So, that's no explaination. Maybe, you can force the programmable gain amplifier to a lower gain at 0dB by providing undervoltage to the image sensor. And observe that the ADC did't utilize the entire full well capacity before overrun. But that's an only remote possibility.

OTOH, I know of no other logical explaination except to protect a forthcoming D400.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, d7000, dslr, dxomark, k-5, k-5 ii, k-5 iis, k5, pentax k-5, vs, vs nikon d7000
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Nikon D7000 seems like a better deal than K-5 crossover37 Non-Pentax Cameras: Canon, Nikon, etc. 60 11-07-2010 01:22 AM
Pentax K-5 vs Nikon D7000 image quality seliscan Pentax K-5 5 11-02-2010 01:54 AM
Nikon D7000 First Unboxing videos jogiba Non-Pentax Cameras: Canon, Nikon, etc. 3 10-18-2010 08:23 PM
Nikon D7000 pictured deadwolfbones Non-Pentax Cameras: Canon, Nikon, etc. 4 10-18-2010 04:19 AM
Nikon D7000 officially announced! JohnBee Non-Pentax Cameras: Canon, Nikon, etc. 41 10-04-2010 02:30 PM



All times are GMT -7. The time now is 09:38 AM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top