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09-10-2010, 07:52 PM   #1
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What does expanded ISO really mean for Pentax?

I've read a few things here on the forums, and also on the broader internet, and I'm wondering if anyone has an answer for us.

Is expanded ISO on the current Pentax bodies done entirely digitally, or as some have suggested, it it simply driving the signal from the sensor harder than falls within the ISO specification? Is it perhaps a combination of both?

Since it sounds as though we're going to have some substantial expanded iso on the K-5, I'd like to know better what will happen when we open that up.

09-10-2010, 07:59 PM   #2
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I beleive it was always intended to say: You can go there if you want, but we wouldn't recommend it for nominal use.

More or less.
Oh and I also think it's a result of eV push, though it doesn't really translate to anything major looking at the performance scale(SNR scaling).
09-10-2010, 09:12 PM   #3
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Since ISO 100 is 'expanded' on both the K7 and Kx, I'm wondering about that myself. 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.

09-10-2010, 11:55 PM   #4
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QuoteOriginally posted by JohnBee Quote
I beleive it was always intended to say: You can go there if you want, but we wouldn't recommend it for nominal use.
Expanding on the above definition (no pun intended), I guess you can say "Expanded ISO is like alcohol consumption, it is there for you if you want it but don't use it regularly".

Sorry I can't help it. My kids say they hate my dad jokes but they still laugh.

09-11-2010, 12:30 AM   #5
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There have been research and tests comparing the natural ISO of the K-x (200) versus the expanded ISO (100) and the result was that ISO 100 was less noisy. So I am eager to wait to see the ISO performance of the K5 from both end of the spectrum.

ISO 50 would help with those extermely sunny days here in California. =]
09-11-2010, 12:46 AM   #6
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QuoteOriginally posted by Clinton Quote
I've read a few things here on the forums, and also on the broader internet, and I'm wondering if anyone has an answer for us.

Is expanded ISO on the current Pentax bodies done entirely digitally, or as some have suggested, it it simply driving the signal from the sensor harder than falls within the ISO specification? Is it perhaps a combination of both?

Since it sounds as though we're going to have some substantial expanded iso on the K-5, I'd like to know better what will happen when we open that up.
Here's what I've found: Does ISO setting affect the RAW file? - Photography - Stack Exchange

QuoteQuote:
On CCDs, the amplifier is effectively in the corner of the sensor, but on CMOS, there is an amplifier built into each photosite, dispersed throughout the sensor. See here.

As mentioned in one thing I recently discovered, most DSLRs have an amplifier before the ADC. They tend to max at 800 or 1600 ISO and are all digital amplifications afterward. The following paragraphs assume a camera that maxes out its analog amplification at 1600:

Unfortunately, the 12 or 14 bit RAW files prevent you from doing what you describe. The digital amplification takes place before the RAW files are stored. There is a maximum value that can be stored, so when you shoot 4-stops overexposed, even though the ADC is not saturated, the RAW file will probably be clipped. However, the technique that overexposes just as much as to not clip highlights is effective at reducing noise, and known as ETTR (Expose To The Right).

Yes, due to the analog amplification, RAW files at higher ISO do contain more detail. However, ISO 1600 and ISO 12800 should contain the same amount of shadow detail (unless there is some additional special processing OR the ADC has effectively more precision than whatever bit depth your RAW files are stored in).

Last edited by Eruditass; 09-11-2010 at 09:51 AM.
09-11-2010, 12:48 AM   #7
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QuoteOriginally posted by Eagle_Friends Quote
ISO 50 would help with those extermely sunny days here in California.
The CPL filters I have drop about 1.5 stops of light. Is there a reason that ISO 50 would be preferable to a CPL?

Thank you
Russell
09-11-2010, 01:04 AM   #8
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QuoteOriginally posted by Russell-Evans Quote
The CPL filters I have drop about 1.5 stops of light. Is there a reason that ISO 50 would be preferable to a CPL?

Thank you
Russell
When you want to use both

09-11-2010, 02:07 AM   #9
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QuoteOriginally posted by Eruditass Quote
When you want to use both
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.

Stacking a CPL on top of a ND filter is probably only going to be an issue on wide lenses. Let's hope there is a 10-16mm f2.8 at some point, so that we actually have a fast wide lens: 1/4000, f2.8, and ISO 100, is an EV 15 environment. With just a CPL you are a little above an EV 16 environment.

So for any f1.4 lens, stacking a CPL over a ND grad will work, and for any lens where stacking won't work, there isn't enough aperture to become a limit.

I guess the question then becomes, how much will a ND filter cost, over getting it "free" in the camera? Considering you can get a three stop ND filter for the same price as a one stop ND filter, the "free" one stop solution seems a little less likely to be as viable in the larger scheme of things, so maybe its cost is worth bearing.

If the new camera body has ISO 50, that's great, but if it doesn't, I don't see it as being an issue. The K-r already raised shutter speed to 1/6000, so that camera already is a half stop above the examples above. If the K-5 matches the K-r or raises the shutter speed to 1/8000, you've got your extra stop or close enough to it to take all the f1.4 shots you want in an EV 16 environment. Yeah, I know, you really want to take f1.2 photos. ;-)

Thank you
Russell

Last edited by Russell-Evans; 09-11-2010 at 02:12 AM.
09-11-2010, 08:20 AM   #10
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It's just always nice to have the option. Yeah, it's not a huge deal. But how about panning shots during a high EV situation?
09-11-2010, 09:25 AM   #11
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Even thou it is called digital it all starts as analog. An analog amplifier amplifies the analog charge in the well before it is presented to the A/D converter. The amplifier level that is closest to the ISO gain that gives the lowest noise is said to be the “native” ISO. Form there each step increase in the ISO is a discrete increase in analog gain with an increase in noise and a decrees in DR. Overall this gives the best performances of the system. When you uses extended ISO you are using the highest ISO amp and then taking the data after the A/D and then digitally increasing the under exposed image to brighten it up. This gives more noise and less DR then doing it in the analog amps as the noise is just multiplied. That is why using the analog amps is better but there is a limit on how much you can amplify something before you just start getting noise. When you use a sub full ISO like 300 (200 to 400 is full ISO) you are most likely using a combination of the 2. Over all it maybe better to do the digital in RAW on the PC in PP but if you are using JPG out of the camera you will need to use the in camera extended ISO.

This is for the extended ISO on the up side. I don’t fully understand the extended on the lower side. It should not decrease the noise, in fact in should increase the noise, but it could allow for longer shutter times. How it can do this with out overloading the wells is the part I don’t under stand.

The noise at the native ISO on the sensors being used today is very low and it is only when pushing for max DR and/or gain that the noise start to become visible.

DAZ
09-11-2010, 09:44 AM   #12
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I believe the price you pay is a drop in dynamic range. Dynamic range drops consistently as you raise iso but also a drop when you lower it below the native level.

iso 200 on the k-x has the best possible dynamic range for example.
09-11-2010, 09:49 AM   #13
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QuoteOriginally posted by WerTicus Quote
I believe the price you pay is a drop in dynamic range. Dynamic range drops consistently as you raise iso but also a drop when you lower it below the native level.

iso 200 on the k-x has the best possible dynamic range for example.
True, however the Base ISO of the K-x is estimated to be more like 125 due to the DR measurements people have taken. So I have no idea why they made the lower ISO "expanded"
09-11-2010, 09:54 AM   #14
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QuoteOriginally posted by JeffJS Quote
Since ISO 100 is 'expanded' on both the K7
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 ?
09-11-2010, 10:04 AM   #15
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QuoteOriginally posted by Eagle_Friends Quote
ISO 50 would help with those extremely sunny days here in California. =]
Not such a big issue here in the Highlands of Scotland.
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