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09-11-2010, 10:24 AM   #16
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QuoteOriginally posted by RBellavance Quote
As far as I know, ISO 100 is *not* expanded on the K-7, it is the "native" ISO of the sensor. Do you have a source that shows otherwise ?
Error on my part. For some reason I had highlight correction turned on and that limits the lower end to 200. I couldn't tell you why I turned on highlight correction but after doing so I couldn't get back to 100 (which is normally where I shoot).. Brain fart ... Apologies for the misinformation..



09-11-2010, 11:48 AM   #17
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I'm still figuring out this stuff myself, but I believe that you could get an "ISO 50" ish effect by overexposing (ETTR) an ISO 100 image, and then pulling exposure down a stop in post.

The more you expose to to the right, the more bits are stored per pixel (assuming you do not blow the pixel). Since you have more bits there, you have more dynamic range to work with. If the camera automates this, you would have an artificial ISO 50.

By extension, we can also see why increased ISO's decreases the dynamic range: if you multiply every pixel by a constant, then you effectively lose latitude before you begin to blow the highlights.

A smart DR expander algorithm would only apply an increased ISO to darker areas of the image, but that can easily be done in post anyways.
09-11-2010, 01:23 PM   #18
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Hi

QuoteOriginally posted by Russell-Evans Quote
1/4000, ISO 100, and F1.4 is an EV 13 environment. EV 14 for the same at IS0 50. Add the CPL at ISO 50 an you are close to EV 16. Hard to imagine needing f1.4 in an EV 16 environment much, but OK.
Things change when you are using fill in flash, because of the max sync speed. There the iso 50 can be very useful.

Cheers - Klaus
09-11-2010, 07:49 PM   #19
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QuoteOriginally posted by JeffJS Quote
More importantly (to me) what will ISO 50 look like on the K5 since it too, is expanded. I still couldn't care less about ISO 25000. They can't drive it low enough for me.

If we could get it down to 25, maybe it would be like digital Kodachrome :-)

09-11-2010, 07:51 PM   #20
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QuoteOriginally posted by SpecialK Quote
If we could get it down to 25, maybe it would be like digital Kodachrome :-)
I'm thinking the same thing but not holding any hope for it. People can't live and take photos without 250000 so that's the more likely trend.

09-14-2010, 02:22 PM   #21
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This still brings us to the question of how does it work on our Pentax bodies. Does it underexpose and push the image digitally, or does it turn up the line amplification beyond recommended limits?
09-14-2010, 02:52 PM   #22
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QuoteOriginally posted by Clinton Quote
This still brings us to the question of how does it work on our Pentax bodies. Does it underexpose and push the image digitally, or does it turn up the line amplification beyond recommended limits?
Does my post not answer your question?

https://www.pentaxforums.com/forums/pentax-dslr-discussion/114039-what-does-e...ml#post1175528
09-15-2010, 02:39 AM   #23
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From what I read on the Internet, ISO 200 is the "natural" ISO for most sensors. Expanded ISO works by "overloading" the sensor with light, in other words reducing any headroom available for highlights (but raising the shadow details away from the noise floor). Thus, the dynamic range is markedly reduced, along with the noise.

So, unless your scene is low in contrast and has interesting lowlight details, I would say that anything less than ISO 200 is probably best avoided.

09-16-2010, 07:29 AM   #24
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QuoteOriginally posted by Eruditass Quote
Does my post not answer your question?
Your answer states that we may get more shadow resolution from expanded iso on cmos sensors due to the 16 bit to 14 bit conversion that occurs before raw files are stored; which was an interesting idea I hadn't considered; however my question of is this how Pentax expanded iso works?

Is the expanded ISO on our Pentax bodies entirely digital or is it being driven beyond normal limits in analog, or a combination of the two?
09-16-2010, 03:03 PM   #25
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QuoteOriginally posted by Clinton Quote
Your answer states that we may get more shadow resolution from expanded iso on cmos sensors due to the 16 bit to 14 bit conversion that occurs before raw files are stored; which was an interesting idea I hadn't considered; however my question of is this how Pentax expanded iso works?

Is the expanded ISO on our Pentax bodies entirely digital or is it being driven beyond normal limits in analog, or a combination of the two?
If you go to the link and look at the rest of the answer and the comments, I mention that it is analog up to 1600, then it is digital.

Expanded appears to be nothing more than a marketing term.
09-17-2010, 12:27 AM   #26
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Also looking forward to the ISO 50 setting which is good to lengthen the exposure times so I don't need as much ND Filters. At least it's one stop longer than ISO 100 so comes in very handy for me who mostly shoots long exposures anyway.
09-17-2010, 05:38 AM   #27
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aside from how it is done, the best "reason" I can see for it is as others have already pointed out. There will always be needs for lower ISO to match especially the ISO25 and 50 film shooting. This can be especially true when wanting open apertures to limit DOF. There is some discussion (although I have not gone through the math myself ) that the ASP-C format increases DOF, so if you want a wide open shot, then you are stuck if ISO 200 is the bottom limit in bright conditions.

In addition, many shooters with studio lighting setups had worked all the settings for ISO25 or 50 films, and would benefit, although by now, 7 years after the introduction of th e*istD with an ISO200 lower limit, I am sure they have redone the lighting.
09-18-2010, 05:03 AM   #28
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My understanding is that the normal range on each camera is what the camera is capable of with amplification of the sensor signal, while the expanded range uses software to underexpose the image and push it a stop. My feeling has generally been that if the camera's software can do this, you probably can do it on your own without too much problem.

As to the lower end iso range, as others have mentioned, it gets you the ability to shoot in brighter situations, wide open, but at a little bit less dynamic range. I personally wouldn't use that too much.
09-20-2010, 12:42 AM   #29
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QuoteOriginally posted by Rondec Quote
My understanding is that the normal range on each camera is what the camera is capable of with amplification of the sensor signal, while the expanded range uses software to underexpose the image and push it a stop. My feeling has generally been that if the camera's software can do this, you probably can do it on your own without too much problem.

As to the lower end iso range, as others have mentioned, it gets you the ability to shoot in brighter situations, wide open, but at a little bit less dynamic range. I personally wouldn't use that too much.
Yes, and just as you can emulate the high-ISO end by under-exposing and pushing in PP, you could emulate the below-ISO200 end by over-exposing and pulling in PP. So, you don't really need the in-camera "expanded-ISO".

(This assumes the sensor sensitivity is at ISO200 - which, as I say, is something I read on the Internet.)
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