optimal iso settings

Hi, Just been reading about optimal iso settings for cameras and it seems like lower iso doesn't necesarily produce the best quality image, i've got a gx10, which i believe is the eqiuvalent to a k10 and i'd appreciate what iso's you guys generally use and why?
Many thanx
sarah

I normally have the camera set on Av mode to control the aperture and let the camera take care of shutter speed and ISO.

Thanks, but I kind of want to "set" the settings myself to hopefully achieve a better understanding of how a camera works, but it might be a good idea to use some of the automatic modes.
thanks
sarah

Actually, the lowest ISO setting will generally provide the best image quality.

The trade off is that the lower the ISO the longer the exposure you need to make in order to get your shot - if the light is anything other than bright (think sunny summer days bright) then using the lowest ISO setting will no doubt lead to exposures that are long enough to induce camera shake. Hence to get a better image you need to move to a higher ISO setting.

So the "optimal" ISO setting is the lowest you can get away with without shake ruining your photo. Depending on the prevailing light that could be anywhere on the scale.

Your GX10 will provide perfectly acceptable images up to ISO400 (where I tend to be for brightly lit indoor scenes), reasonable images at ISO800 (dimly lit interiors) but quite noisy images at ISO1600 (which I try and avoid if possible).

Photography is all about trade-offs and a noisy but sharp picture is generally preferred to a clean but blurry one. Experiment a bit and you'll find for yourself what works based on what you find acceptable.

Hope that helps!

As far as i understand it, ISO settings come from film ratings. The higher the ISO the "faster" the film. The higher the ISO the faster the shutter speed/the smaller aperture you can use for a given amount of light. On the other hand low ISO's gave a less grainy effect so better IQ. I digital terms i think it's sometimes refered to as noise. "Too slow at typeing"

Sarah, you're absolutely right that lower ISO doesn't necessarily mean a better image quality but it's a very good start .
I think the key really is to try and get the exposure as close to perfect in every shot, that way you maximise what is achievable at a given ISO setting.
Like Barry I tend to user Aperture priority mode (Av) and also I'm also now using TAv mode mode, this allows you to control both the aperture and shutter whilst the camera sets the ISO (within your defined limits) to maintain the correct exposure. Very useful

Looking forward to seeing some of your shots.

Lower ISO does produce the best image quality - but only when it and the light allows a fast enough shutter speed to prevent motion blur or camera shake. And the longer the lens, the faster shutter speed you need for sharp shots when hand-holding.

Too low an ISO setting results in blurred pictures. High ISO increases the noise (grain) in the pictures.

To generalise (a lot), ISO 100 is good with a short lens on a bright sunny day for a static subject, whereas you may need to use ISO 800 or higher with a telephoto lens on a dull day.

Exposure is all about finding a balance between aperture, shutter speed and sensitivity (ISO).

When in doubt, set the ISO to Auto. It does a reasonably good job of selecting something sensible for you. But consider setting it manually if you think the shutter speed is not high enough otherwise, or, conversely, you want to risk some blur in order to minimise noise.

TAv is a wonderful mode that can allow full creativity while you forget about ISO - but there is only a limited light level range within which your selected aperture and shutter speed can be used.

When outside this range, you're left fiddling about trying to find a useable combination, if you don't switch to another mode.

I think you're talking about base ISO.

The base ISO is the ISO on which the sensor is build around, so they perform the best on that range, dynamic range, noise, etc.
With the K10D/GX10 the base ISO is 100 just like many earlier camera's.
Now they have placed the base ISO at 200 for most sensors.

The K20D has a base ISO of 200 and the K-X and K-7.
The earlier cameras and the K200D and the K-m have a base ISO of 100.

So the optimal ISO for the GX10 is ISO 100.

ps. I believe this is what you wanted to hear right?

I use Av mode with the front wheel controlling the aperture and the rear wheel controlling the ISO. In practice, if a shot requires a shutter speed that is too slow, I have two options, larger aperture or higher ISO. Which I choose depends on how important DOF and how large my aperture already is.

But, for me, I always go with the lowest ISO practical. I see shots taken in good light with ISO and, in my opinion, they're fine but in dodgy light, the higher ISOs don't do well.

I have seen a bit about this too. Up until now I had always shot at ISO 100 as far as possible, assuming that this would give the best quality pictures.

It seems that may not be the case. There seem to be two explanations, both of make some sense.

1/. The analogue part of the sensor will have an optimum signal to noise ratio.

2/. There will be a signal level which requires least processing by the camera, minimising errors and noise introduced by that processing.

People talk about a "native" setting for each sensor and for the K20, as Stefan says, ISO 200 seems to be the figure.

All this is quite simple to prove or disprove - all it takes is to take comparable pictures at ISO 100 and 200. Unfortunately with the grotty weather and the inertia I suffer from at this time of the year, I haven't got round to it.

ISO400 gives the greatest dynamic range on a K10D according to dpreview and Pentax appear to want to give that impression, too. I'll find the quote later.

I've been playing, and I cannot see the grain any more on images taken at ISO 640 IF - and ONLY if - the pic is mildly over-exposed.

Underexposure brings out the spots big time. So set exposure to +0.7 and away you go, you can shoot up to ISO1000 without issues.

I tend to use 100 for the "important" stuff.

Bret

That will blow the highlights in many cases.

All this talk about base ISO being higher than the minimum ISO is irrelevant to Sarah who has a GX10.

Incidentally, one seemingly-knowledgable DPR poster claims the K-7's base ISO is actually lower than ISO 200. Anyway, I haven't noticed ISO 100 images being any worse than 200's.

Hmm it seems base iso of the K7 & K20D is ISO100 indeed.
K-X is around ISO400

K10D makes no different ISO 100 or 200