K-x ISO 100

Hi,

I just got my K-x yesterday, this is my first DSLR, pretty happy with it. Does anyone know what happens to ISO-100? it starts from 200, is it a number game or what? I mean iso-200 equals to iso-100 of other dslr, iso-400 = 200, etc. so it looks high performance at high iso level? how do you know it's actually at ISO-1600?

Thanks.

I believe you have to go into the menu and enable extended ISO range (which should allow you to go to ISO100 as well as ISO12800).

The base ISO for the sensor used in the K-x is ISO 200. This is the actual sensitivity of the sensor. Every ISO above 200 is done through amplification of the signal, so ISO 200 is the real ISO on this sensor. Every sensor has a base ISO. Could be 50, 100, 200 or whatever. ISO 200 as base ISO is very common. The first DSLR from Pentax also used a a Sony sensor (this one was 6Mp CCD) with base ISO 200. All sensors has a limited ISO range and manufacturers tries to make the best ISO range with as less compromises as possible. ISO 200 was choosen by Sony for the sensor used in the K-x. Similar sensor is also used in a few Nikon and Sony entry level DSLR's with same base ISO.

The sensor performs best at the base ISO, that is why performance of ISO 200 is as good as sensors with base ISO 100.

If you want ISO 100 on the K-x, you can activate it by activating the enhanced ISO range. This makes ISO 100 available, but please note that ISO 100 is done through a software trick so it isn't performing as good as ISO 200 (but differencies is very small).

ISO 200 on the K-x is true ISO 200, not fake.
--
Take care
Raphael
http://www.flickr.com/photos/raphaelmabo/

thank you for your thorough explaination, I'm learning now, as I said earlier this is my first dslr, I was a little confused about iso. Now I am all clear. Thanks again!

first moon shot with my new K-x.

While it is clearly true that 200 is the base ISO on the K-x, it is open to debate what the native resolution is - that is the best-performing setting. With the major caveat that I don't own the K-x, it is clear that some folks who have played around with finding the "ideal" ISO have often indicated that 320 (give or take one-third stop) is best for dynamic range while limiting noise. This idea is further confirmed by the fact that tests indicate that dynamic range is slightly better at ISO 400 than 200 which is significantly better than 100. And expanded dynamic range for highlights can only be enabled at 400 or above.

I have the K20D, and it is generally agreed that the sensor has a ISO 200 native resolution - and that is where you find the lowest setting for enabling expanded dynamic range.

The high resolution capabilities of the K-x are undeniable, but it doesn't come without a trade-off. K10D fans are quick to say that none of the Pentax cameras offered since can match its clean low ISO output. That is because it probably has a 100 or 125 native ISO. Of course, it is also a very poor performer above 800.

From a practical standpoint regarding the more recent sensors (from the K20D on), it appears it would be wise to use the lowest possible ISO in low contrast situations in order to limit noise, and a somewhat higher ISO (200 on the K20D and K-7, probably 320 on the K-x) for contrasty conditions where maximum dynamic range is your highest priority.

tulong said:

I just got my K-x yesterday, this is my first DSLR, pretty happy with it. Does anyone know what happens to ISO-100? it starts from 200, is it a number game or what? I mean iso-200 equals to iso-100 of other dslr, iso-400 = 200, etc. so it looks high performance at high iso level? how do you know it's actually at ISO-1600?

Click to expand...

As someone else noted, you need to turn on the ability to set ISO 100 and for Auto ISO to start from ISO 100 as a base.

As to true ISO sensitivity as compared to other cameras, it has been tested, while it is true that ISO 100 is stretching things a bit for this sensor with true base sensitivity at the raw sensor level somewhere between ISO 115 (which can't be set) and ISO 125 (which can) as to improvements in image quality. This means that there is an advantage in image quality using ISO 125 rather than ISO 200 but not much of a further advantage to using ISO 100 other than it automatically will meter for slower shutter speeds, higher aperture values.

Regards, GordonBGood

You may wish to believe the following statements. I don't. Added comments as follows:

JNR said:

While it is clearly true that 200 is the base ISO on the K-x, it is open to debate what the native resolution is - that is the best-performing setting. With the major caveat that I don't own the K-x, it is clear that some folks who have played around with finding the "ideal" ISO have often indicated that 320 (give or take one-third stop) is best for dynamic range while limiting noise. This idea is further confirmed by the fact that tests indicate that dynamic range is slightly better at ISO 400 than 200 which is significantly better than 100. And expanded dynamic range for highlights can only be enabled at 400 or above.

Click to expand...

If you care to believe that "Dynamic Range" is determined by "highlight headroom" without any respect for the lower limit of the "range" , then it is true that ISO 100 has less "highlight headroom" than does any higher ISO. I can detect no difference in "highlight headroom" for identical metering for ISO's of 200 and above on my wife's K-x.

"Expanded Dynamic Range" or Highlight Correction in K-x terms always increases the lower limit of ISO sensitivity by a factor of two; thus, with extended ISO sensitivity range turned on it becomes two times ISO 100 = ISO 200. The reason that this "highlight headroom" is higher with Highlight Correction turned on is that it causes the camera to meter for the indicated two times as high ISO sensitivity while actually multiplying the signal by half as much as for the lower ISO, thus giving exactly an additional one stop of additional "highlight headroom".

JNR said:

I have the K20D, and it is generally agreed that the sensor has a ISO 200 native resolution - and that is where you find the lowest setting for enabling expanded dynamic range.

Click to expand...

As above, you clearly don't understand what Expanded Dynamic Range is actually doing, as it works the same for the K20D as Highlight Correction does for the K-x albeit with a different name. The K20D's base sensitivity is the lowest available at ISO 100.

JNR said:

From a practical standpoint regarding the more recent sensors (from the K20D on), it appears it would be wise to use the lowest possible ISO in low contrast situations in order to limit noise,

Click to expand...

Correct.

JNR said:

and a somewhat higher ISO (200 on the K20D and K-7, probably 320 on the K-x) for contrasty conditions where maximum dynamic range is your highest priority.

Click to expand...

Completely incorrect, but believe it if you want.

Regards, GordonBGood

The topic is being somewhat highjacked here. My comments were not primarily related to the EDR issue, of which, I know Gordon has a great deal of interest and understanding. It is only mentioned as a factor in determining what is likely to be the ideal sensor ISO. If we look at it another way, the sensor comparison is ultimately illustrative of what the camera manufacturers' view as a difficult challenge in dealing with maximum EV and clipping. I think it is fair to say that the K-x will clip sooner at 100 ISO than the K20D. And I know from my experience that the K20D has a less-smooth roll-off than the *istD (which does not go below 200).

With the K20D, I am well aware that ISO 200 provides me with the widest DR at some relatively small cost in additional noise - especially in the shadows. It allows me to achieve a gentler roll-off at the high end which is something that was highly valued in the 6 mp sensor design. As Gordon will tell you, a nice soft roll-off can be achieved with or without using the EDR feature. Testing at this site and elsewhere also shows maximum DR is achieved at ISO 200 on the K20D. The review here for the K-x shows a very slightly wider DR at 400 than 200; however, clearly 200 is going to be cleaner. Highlight headroom at 100 has a pretty severe problem, according to the testing. Some folks here have stated a preference for settings somewhere between 200 and 400.

If ISO 125 is considered the ideal setting for the K-x, then it seems odd to me that Nikon and Pentax would view this setting as an exception on this particular sensor, and testing clearly indicates reduced DR performance below 200. I think it is prudent for Pentax (and Sony as the sensor source) to pursue a somewhat higher native resolution if it results in significantly better high ISO performance.

I am sure others have their own thoughts, and perhaps many here will disagree with the engineers who designed this sensor and implemented the standard settings on these cameras.

JNR said:

I have the K20D, and it is generally agreed that the sensor has a ISO 200 native > resolution - and that is where you find the lowest setting for enabling expanded > dynamic range.

Click to expand...

No, the K20D native ISO is 100 not 200. The idea about K20D has native resolution 200 is a misunderstanding.

The enhanced dynamic range is done through a software trick, same as the K-x, as Mr Gordon has explained.

That is why it is ISO 200 on K20D and 400 on the K-x. It uses a double ISO from the native ISO and lifts the shadows in software.

JNR said:

The high resolution capabilities of the K-x are undeniable, but it doesn't come > without a trade-off. K10D fans are quick to say that none of the Pentax cameras > offered since can match its clean low ISO output.

Click to expand...

I have the K10D too and K10D at ISO 100 is similar to K-x at ISO 200.

If they find the K10D to be better at low ISO than K-x, then I say this might be because the JPEG's are tuned differently by in-camera processing and they prefer the tuning of the K10D. I have changed the factory settings for JPEG's on the K-x to suit my own taste, and I get very good low ISO images with K-x. The statement that the good high ISO performance of the K-x means low ISO is "a tradeoff" is not true according to my own experience with both the K10D and K-x.

I do enjoy using my K10D, not because of an idea that it has better image quality at low ISO - rather because it has a larger viewfinder and HyperProgram modes and socket for a cable remote release. And it is weather sealed, while the K-x is not.

I use them for different purposes, but I do enjoy both and the K-x has excellent image pipeline.

--
Take care
Raphael
http://www.flickr.com/photos/raphaelmabo/

Why not get yourself a K-x and make your own testing and write from your own experience with the K-x instead of writing about the K-x from your own experience with the K20D? They are not using the same sensors!

You make assumptions about the K-x from your experience with the K20D and in my view this only causes confusing for the OP here.
K-x and K20D has different imaging pipelines.

--
Take care
Raphael
http://www.flickr.com/photos/raphaelmabo/

No doubt that would be best. That's why it makes sense for others to weigh in, as stated. On the other hand, a lot empirical evidence has been offered by design engineering decisions and testing, so I thought they were worth mentioning.

Before reading this thread, I had not really thought much about using ISO 100 on my K-x. I just always default to 200 unless I need the extra light. But just yesterday I found a good reason to use 100. I knew I wanted a 5-second exposure and I didn't really want to stop down any further (for DoF reasons). Nor did I want to use the ND filter. So I gave ISO 100 a try and was very happy with the results. I'm not sure my eye is good enough to start comparing the subtle differences in IQ between ISO 100 and 200. I'm just glad the camera had 100 as an option for this shot.





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-- Joe S.
'The laws of nature are but the mathematical thoughts of God.' ~ Euclid

No doubt about it, that is a very good, specialized reason to utilize ISO 100. Under controlled circumstances, no doubt 100 can be a very useful "pull".

Did you feel like you got shallow enough DOF, or do you feel like nothing short of FF is what you're missing? (A rhetorical point.)

Fine shot.

JNR

JNR said:

Did you feel like you got shallow enough DOF, or do you feel like nothing short of FF is what you're missing? (A rhetorical point.)

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I would definitely have liked a little shallower DoF. Probably 5.6 would have been ideal for what I was aiming for, rather than 7.1. So FF would have gotten me that at 7.1 or even 8. But the size of APSC cameras is more to my liking. It's a trade-off either way, and overall I'm happy with what I've got.

JNR said:

Fine shot.

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Thank you. This is actually one of my personal favorites, so I'm glad someone else enjoyed it as well.

--
-- Joe S.
'The laws of nature are but the mathematical thoughts of God.' ~ Euclid

It isn't the kind of shot people generally think of taking, so you have good reason to be proud of it. I think the DoF is just right as it seems virtually in sync with the motion. Not something we generally think about - but very effective here.

Of course, in the natural environment where you tend to encounter greater inherent dynamic range, ISO 100 would be a slight disadvantage. This is why the sensor designers decided to exclude it from the standard ISO range. Personally, I would always have it activated because more often than not the full dynamic range is not needed.

JNR said:

Of course, in the natural environment where you tend to encounter greater inherent dynamic range, ISO 100 would be a slight disadvantage. This is why the sensor designers decided to exclude it from the standard ISO range. Personally, I would always have it activated because more often than not the full dynamic range is not needed.

Click to expand...

That brings up a question in my mind -- does having the expanded sensitivity turned on have any negative effects (such as on DR) when using ISOs in the non-expanded range? In other words, if I keep that menu option always on, will it affect images shot at ISO 200-6400? If so, I would only want to activate it when I need it. If not, then it would make sense to always keep it on as you suggested.

--
-- Joe S.
'The laws of nature are but the mathematical thoughts of God.' ~ Euclid

GordonBGood said:

JNR said:

From a practical standpoint regarding the more recent sensors (from the K20D on), it appears it would be wise to use the lowest possible ISO in low contrast situations in order to limit noise,

Click to expand...

Correct.

Click to expand...

By lowest possible ISO, do you mean the lowest normal ISO (camera's base) or the lowest expanded ISO?

Generally speaking the benefit of lower ISO is less noise. But does that still hold true when going below the native ISO of a sensor? Or is this simply a convenient substitute for an ND filter which allows a longer exposure or wider aperture, but has no effect on noise?

--
-- Joe S.
'The laws of nature are but the mathematical thoughts of God.' ~ Euclid

It has absolutely no impact on the other (regular) ISO ranges. I have the K20D, but not the K-X, and so my only extended ISO is on the high end. You can be quite sure that the K-X users here generally agree that the low-end restriction is unwarranted.

Even the loss of high sky clipping in sunlight at 100 is pretty minor (but real at one-third stop), based on the tests I've seen. As for 200, it should work the exact same way in either setting.

JNR

JNR said:

It has absolutely no impact on the other (regular) ISO ranges. I have the K20D, but not the K-X, and so my only extended ISO is on the high end. You can be quite sure that the K-X users here generally agree that the low-end restriction is unwarranted.

Even the loss of high sky clipping in sunlight at 100 is pretty minor (but real at one-third stop), based on the tests I've seen. As for 200, it should work the exact same way in either setting.

Click to expand...

Good to know. I guess I'll just keep the option turned on in the menu, but only go down to 100 when needed. Thanks.

--
-- Joe S.
'The laws of nature are but the mathematical thoughts of God.' ~ Euclid