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11-19-2010, 11:40 PM   #1
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ISO 100 - 0r 3200 when and why?

When an why? i know what 100 gives you more detail but with good lite why still people used 200 or 400 iso? and what about 1600? at nite low lite? anybody have sample fotos ?

11-20-2010, 06:12 AM   #2
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Lowest iso on any camera is the best iso for two reasons: you have less noise at low iso and you have more dynamic range. For instance, the K7 has about 11 and 1/2 stops of dynamic range at iso 100, but by iso 800 it is only at about 7. This means that colors will tend to be more washed out and just won't look good. The detail may still be pretty good, but if there is much noise, noise reduction software tends to soften photos.

Unfortunately, we can't shoot at iso 100 all of the time. The issue is one of shutter speed. You would prefer to shoot with a shutter speed of 1/focal length * 1.5 to eliminate camera shake and to do this, you often have to push your iso up more than a little bit. If you are shooting action, you often have to have even faster shutter speeds (1/250 second) to freeze it and so will push iso as high as you can comfortably go to freeze it.

Last edited by Rondec; 11-20-2010 at 06:18 AM.
11-20-2010, 06:22 AM   #3
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Just a couple of photos. The first was shot at iso 3200 on the K7. It was a dark restaurant and my daughter just doesn't hold still for photos, in general. Not a great photo, but it demonstrates how photos get soft at high iso. Second photo shot at iso 200 on the K20. I exposed for the sky and still was able to add quite a bit of fill light to bring up my kids faces.



11-20-2010, 12:48 PM   #4
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You might want a specific shutter speed/aperture combination that requires a higher ISO.
As far a samples, just look around the galleries. Some are actually entitled "High ISO...".

11-20-2010, 02:53 PM   #5
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Ok ,cool Thanks guys , its good to know i will do my home work, do lots of shoots, try it all ... thanks for your time
11-20-2010, 03:04 PM   #6
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1) The main thing is, if you're shooting scenics or non-moving stuff outside in really nice sun and you can do 100ISO at F8, with a shutter speed of around 1/60, you're golden.

2) If you have those same light conditions, but you're shooting people skiiing or running...and you want to keep that same optimum F8 aperture aperture...you have to up the ISO to 400 to give you a faster shutter speed of 250. (That may or may not be enough though, but I'm using this as an example.)

So, I always suggest to people to ALWAYS use manual ISO. It's the best and easiest way to bring you to the best final combination of ISO, F stop and shutter speed.

You only go to the super high ISOs when you really need them--indoors, dark, no flash, and to maintain a sharper aperture/more depth of field than the widest F stop on your lens will allow you.
11-21-2010, 09:25 AM   #7
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Generally you want the lowest basic ISO available. In that respect, ISO is different to shutter speed and aperture, because there are artistic reasons for wanting both fast or slow shutter speed and both wide or narrow aperture. The only reason for high ISO is when there isn't enough light for the combination of shutter speed and aperture that you want without it. (And even then you should consider using a tripod or flash instead.)

With some cameras (eg K-x) the lowest basic ISO is 200. For those cameras, 100 is only available as "extended range", which involves fancy digital manipulation which is best avoided. So that's usually why people use 200.

Cameras have an auto-ISO setting where you can give it a range of ISO to use. With a K-x I often set it to 200-400 because I can't really tell the difference between them, and it gives the camera a bit of freedom to adjust other settings to the conditions. That may be why you sometimes see pictures with ISO 400. Or I might set 400 manually if the camera can't figure it out for itself. ISO 400 allows double the shutter speed than ISO 200 for virtually no loss in quality, so I use it when the shutter speed would otherwise be below 1/40s and I can't use a tripod. (Above 1/40s the camera's anti-shake is usually good enough.)

More modern cameras perform better than the K-x at high ISO so higher settings may become more common.
12-05-2010, 01:04 PM   #8
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The human visual system evolved such that we we look differently at personas and at things. With things such as 'scapes, buildings, structures, we generally want to see great detail. With personas such as human and animal features and parts, we can deal with and recognize much less detail. A classic example is the 8x8 pixel image that, when you squint, is unmistakably a portrait of Abe Lincoln.

This doesn't mean all portraits should be soft and all 'scapes should be hard. A soft, fuzzy, noisy, impressionistic shot of a thing may turn it into a persona, and vice-versa -- a sharp, hard ID shot can turn a human or animal into an object. This *does* mean that you have great leeway in approaching subjects. My basic rules of sensitiviity (ISO/ASA) are:

* Use the lowest sensitivity possible -- you can always add noise/softness later in PP.
* Dynamic subjects and low light often demand higher ISO -- and noise can be PP'd away.
* Don't be afraid to increase ISO -- any shot you get is better than a shot you don't get.

Sensitivity is a vast area to be explored, intertwined with shutter speed and aperture to make motion freeze or flow, to make DOF thin or thick, etc. Shooting is free with digital cams. Shoot away, trying many different combinations. See what your comfort zones are re: noise when shooting different subjects. And remember that an image seen on your computer screen may look VERY DIFFERENT when printed, matted, framed, and hung. Especially portraits, where high-ISO noise may become irrelevant.

12-05-2010, 05:09 PM   #9
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QuoteOriginally posted by Brangdon Quote
With some cameras (eg K-x) the lowest basic ISO is 200. For those cameras, 100 is only available as "extended range", which involves fancy digital manipulation which is best avoided. So that's usually why people use 200..
I've turned 'on' the expanded range and shoot at iso 100 in good light on K-x... Been set like this for a couple months now...

Anyone explain what kind of 'fancy digital manipulation' is employed and why it should be avoided please?
12-05-2010, 05:31 PM   #10
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QuoteOriginally posted by DaveHolmes Quote
I've turned 'on' the expanded range and shoot at iso 100 in good light on K-x... Been set like this for a couple months now...

Anyone explain what kind of 'fancy digital manipulation' is employed and why it should be avoided please?
I never agreed with that opinion, and shoot at 100 99% of the time.

Especially in sunny South Florida.

How can a sensor working at 100 be more manipulated than 200? And my guess is, the only reason 100 and the higher range are associated with the Pentax's expanded sensitivity setting is for people who are new to photography--where 100 isn't going to cut it and the shots aren't going to come out great, and the mega-high ISOs aren't going to cut it for noise and the shots aren't going to come out great either.

In other words, Pentax is steering you away from these settings for beginner shooter reasons.

Ironically, you have to DISABLE highlight correction for expanded sensitivity, so how the hell is shooting at 100 WITHOUT that digital manipulation considered fancy digital manipulation?

ISO 100 in good light ROCKS.
12-10-2010, 02:46 PM   #11
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QuoteOriginally posted by DaveHolmes Quote
Anyone explain what kind of 'fancy digital manipulation' is employed and why it should be avoided please?
As I understand it, the camera gets ISO 100 by over-exposing the image (so you get the slower shutter speed), and then making it darker again digitally with firmware. The result has less dynamic range than shooting at ISO 200. Over-exposing means you aren't getting the optimum performance out of the sensor.

You can get a similar result by over-exposing manually and darkening it by hand during post-processing on a PC. Doing it on a PC gives you more control over doing it in-camera. I've seen it claimed that the natural sensitivity of the sensor is around ISO 125, so it may be that using ISO 100 in-camera does have an advantage over the manual post-processing method, but that would mainly apply to shooting in JPEG. If you shoot in RAW, post-process in RAW and then reduce to JPEG you can probably do a better job manually than the camera can.

QuoteOriginally posted by Ira Quote
How can a sensor working at 100 be more manipulated than 200?
Because its natural, optimum sensitivity is higher than 100. The meanings of the ISO values were defined long ago, in terms of an abstract exposure model; ISO 100 does not mean "the sensor's optimum sensitivity". There's no reason it has to be a good fit for a particular camera's hardware.

I don't think Pentax avoid ISO 100 by default because they are concerned about beginners getting too-slow shutter speeds. They could instead avoid it in auto/beginner modes and allow it in full PASM modes. Any mode which allows manual exposure compensation will let you take a bad picture due to over-exposing.

It's just that shooting at below the sensor's optimum sensitivity is a slightly strange thing to do. It's available for people who want to sacrifice some dynamic range for slower shutter speeds and want the convenience of doing it in-camera, but it's not the default because it's not obvious that's what will happen.
12-10-2010, 04:20 PM   #12
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QuoteOriginally posted by Brangdon Quote
As I understand it, the camera gets ISO 100 by over-exposing the image (so you get the slower shutter speed), and then making it darker again digitally with firmware. The result has less dynamic range than shooting at ISO 200. Over-exposing means you aren't getting the optimum performance out of the sensor.

You can get a similar result by over-exposing manually and darkening it by hand during post-processing on a PC. Doing it on a PC gives you more control over doing it in-camera. I've seen it claimed that the natural sensitivity of the sensor is around ISO 125, so it may be that using ISO 100 in-camera does have an advantage over the manual post-processing method, but that would mainly apply to shooting in JPEG. If you shoot in RAW, post-process in RAW and then reduce to JPEG you can probably do a better job manually than the camera can.

Because its natural, optimum sensitivity is higher than 100. The meanings of the ISO values were defined long ago, in terms of an abstract exposure model; ISO 100 does not mean "the sensor's optimum sensitivity". There's no reason it has to be a good fit for a particular camera's hardware.

I don't think Pentax avoid ISO 100 by default because they are concerned about beginners getting too-slow shutter speeds. They could instead avoid it in auto/beginner modes and allow it in full PASM modes. Any mode which allows manual exposure compensation will let you take a bad picture due to over-exposing.

It's just that shooting at below the sensor's optimum sensitivity is a slightly strange thing to do. It's available for people who want to sacrifice some dynamic range for slower shutter speeds and want the convenience of doing it in-camera, but it's not the default because it's not obvious that's what will happen.
Dxo seems to indicate that Dynamic Range is roughly equivalent for the kx at iso 100 and 200, but as you say, it is added to allow people to shoot with slower shutter speeds in bright sunlight. Nothing lost and maybe something gained...
12-10-2010, 04:55 PM   #13
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QuoteOriginally posted by Brangdon Quote
Because its natural, optimum sensitivity is higher than 100.
Natural sensitivity?

We're talking about a digital machine here, and even with film, people played with film's native ASA ratings to accomplish wonderful things.
12-12-2010, 09:46 AM   #14
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QuoteOriginally posted by Ira Quote
We're talking about a digital machine here,
The early stages of a sensor are analogue. Normally changing ISO means changing the analogue amplification; it's not a digital thing. If it were digital it could indeed be lossless.

If there was no lower limit on ISO, and no compromises involved in going lower, why do you think cameras don't provide ISO 50 or ISO 25? They'd both be useful for taking slow shots eg to blur water motion. Instead we have to use NG filters.

QuoteQuote:
and even with film, people played with film's native ASA ratings to accomplish wonderful things.
Not sure what film has to do with it. If you want to do weird and wonderful things, go ahead; that's why extended ISO is available.
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