Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-10-2012, 01:29 PM   #16
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
QuoteOriginally posted by zosxavius Quote
Ok...here's what I don't get though. Iso 100 has to be the native iso. If it isn't, how does it possibly use iso 200 and push down?
ISO Settings

QuoteQuote:
If you the work the other way around, down the ISO scale instead of up, and past the optimal base signal level whatever that is, a different scenario occurs. The signal needs reducing, halving with each stop, because with lower ISO's the exposure is longer, it keeps doubling. This raises another problem. Because the pixels are a constant size, whilst reducing the light means a weaker signal, increasing it beyond the pixels maximum collection capacity means over-saturation of the pixels occurs, they can't cope with amount of light, it's just too much information. This ends up leading to reduced image quality via a lower dynamic range because the relationship between different tonal levels is often lost.

A good analogy to use is a liquid container. Pouring in less is not a problem, but pour too much in and the surplus overflows and is lost. The same thing happens when lower ISO's are used than are optimal for the sensitivity of the sensor. Information is lost and when the subsequent signal is reduced, the wrong information results. This scenario, that of reduced DR due to pixel over-saturation can often be spotted in digital camera reviews when DR range ability is quoted, and a better result is produced at say ISO200 than at the base speed of ISO100.

It is for these reasons that camera makers restrict the ISO ranges provided to those they feel give acceptable image quality for the setting used. Some give two alternative ranges, standard and 'extended'. The extended range being offered on the basis that the image quality level outside the standard range might not be all that the user expects, and it is their choice as to whether they use it or not. This is a known problem with Canon's pro DSLR's provided with an ISO50 option. And Sigma's SD14 which has also been given one via a firmware update - along with a warning about reduced DR and image quality. It also seems to exist with the new Sony 12mp CMOS sensors now being used. They appear to have optimum ISO ratings of ISO200 but are being provided with as standard - not part of an extended ISO range - a base ISO100, which has a reduced DR range compared to the ISO200 setting. This is certainly the case with the new Sony A700 DSLR. Nikon's D300, which uses the same sensor, appears to have a standard range of ISO200-1600.
Does this answer it?
Please don't ask me why at ISO80 the K5 preforms the best because it actually shouldn't.
This pure speculation though but maybe the change the response curve of the sensor if they can do that....

06-10-2012, 02:56 PM   #17
Veteran Member




Join Date: Jan 2012
Location: Somewhere, USA
Photos: Gallery
Posts: 453
Original Poster
This is what's really perplexing me. The dr is greatest @ base iso. On the k-7, the dr is greatest @ 100. So 100 should be base right?
06-10-2012, 03:01 PM   #18
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
The sensor is design with ISO200 as base, that it preforms better at ISO100 is probably Pentax faults

Pentax doesn't design the Sensor, in the K20D and K7 it was Samsung for the rest it was mostly Sony.
06-10-2012, 03:05 PM   #19
Veteran Member




Join Date: Jan 2012
Location: Somewhere, USA
Photos: Gallery
Posts: 453
Original Poster
I see nothing indicating that iso200 is base. If it is more sensitive @ 100 in terms of dr, then that should be base. From what I've read if a sensor was designed for a 200 base, dr should be less @ 100.

06-10-2012, 03:07 PM   #20
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
Okay for the thrid time....

Samsung designed the sensor with ISO200 as base.

Pentax "adapt" the sensor somewhat for their camera, which is probably the cause for the better performances.


Since the sensor was designed for ISO200 it means that ISO100 is extended range.


Beside that... why would we actually care about this?
06-10-2012, 03:13 PM   #21
Veteran Member




Join Date: Jan 2012
Location: Somewhere, USA
Photos: Gallery
Posts: 453
Original Poster
Sorry. I'm not trying to argue. All I care about is where dr is greatest. It seems edr is no different than exposing to the left and boosting. Shadows and mids one stop. Its funny. The mode that is supposed to expand dr seemingly weakens it. Maybe I need to do some more testing and use some worst case scenarios to see how much of a real difference it makes.
06-10-2012, 03:33 PM   #22
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
Left? i think you mean right
Yes in a sense it should be ISO200 expose to the right and pulled down but that isn't the case with the K7.
When you look at the response of the sensor you will see that the highlights are the same for ISO100, 200 and 400 but ISO100 reach deeper into the shadows.

I think most of the magic is done with the tone curve but not sure if that's a sensor feature you can alter.
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!
benefit, camera, compensation, dr, dslr, iso, k7, mode, noise, photography, questions
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Macro Caterpillar Enlightened weakhead Photo Critique 3 04-25-2014 05:53 PM
K-x Sony Sensor vs K-7 Samsung Sensor karl79 Video and Pentax HDSLRs 9 09-23-2010 09:35 AM
Travel Enlightened Buddha madhurvyas Post Your Photos! 5 09-21-2010 07:59 AM
Sensor cleaning: Pec-Pads or Sensor Swabs gadgetnu Pentax Camera and Field Accessories 29 09-24-2007 10:52 AM
Sensor cleaning > Sensor Swab > void warranty? Twinky Pentax DSLR Discussion 2 07-28-2007 01:10 AM



All times are GMT -7. The time now is 10:12 AM. | See also: NikonForums.com, CanonForums.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