iso settings in raw

[arjenvdm]

I use a Fuji S2 and PS CS raw file converter. I shot at 1/180s f 5.6 in raw. Once at iso100, once at iso400. Then I converted the iso100 at exposure +2.0. I converted the iso400 at exposure +0.0
I thought this should give me exactly the same image. The iso 100 file showed a lot more image noise in the shadows. I thought this should not happen. Where do I go wrong?

[arjenvdm]

NOw I did the opposite: I exposed for iso 100, and shot in raw at iso100 and at iso400. The result: at iso400 I got burnt out highlights, I could not recover them with exposure at minus 2.0
Where do I go wrong?

[JohnMalloy]

You are assuming too much...exposure latitude is for midtones, you should base your exposure there and allow the latitude to enable you to recover lost shadow or highlight data with the extra range...

As you just proved, quality begins with a correct exposure....

[arjenvdm]

My problem is this: I assumed that a raw file has the same information, regardless of the iso setting. The shutter speed and aperture were the same, only the iso setting was different. The images came out radically different. Is there something happening in the camera (Fuji S2) , or in the raw file converter (in PS CS)?

[skirkpatrick]

Unlike the camera settings, like sharpness or color balance, which only affect in-camera JPEG encoding, changing the ISO setting amplifies the values coming off the sensor as they are first digitized. So tones in the shadows of an ISO 100 shot that might fall between 1 and 64 will now be rendered from 4 to 256 at ISO 400, improving signal to noise. (oversimplified example).

[arjenvdm]

OK, that's clear. It confirms my findings. Just for my curiosity: is the sensor working in a different way, depending on the iso setting, or is the information from the sensor processed diffently for different iso settings before it is saved in raw?

[MichaelT]

The RAW file is different for an ISO 100 and 400 shot. As mentioned the values are already "amplified" in the RAW file when you shoot at ISO 400 and less light has hit the sensor based on the proper exposure. So much has changed. Differant amount of light hitting the sensor and sensor "gain" being different in the camera electronics.

Always set ISO for best exposure at the time of capture, based on light, depth of dield needed, and motion needed or stopped.

[arjenvdm]

I get that. Now I have a situation where I need a very big contrast range. (Recently I did a portrait of a pinball champion, with the machine, and the guy was lit by the lights of the machine). I shoot in raw, exposing for the highlights, and brighten shadows in the computer. Would I gain image quality when I convert the file twice at different "exposure" settings, or can I convert once, and brighten the shadows at 16bit tiff in ps?

[skirkpatrick]

(especially if the picture has things that move) but you can develop the raw file in more than one way, into a 16 bit TIFF, and then use various methods to combine the regions that each develop gets bets. Or you can (in COne) adjust exposure to get the highlights all in proper range, then set the "film type" to be "extra shadow range" and you will have gained a stop or 1 1/2 stops in expressed range. Then you use the curve tool to put the contrast where you need it. If you need dodging and burning, that is still for Photoshop, so save the result in 16 bit format.

Michael, can RSE easily give you extended dynamic range? Or will it soon?

[MichaelT]

RSE has a range of adjustments available including a very unique fill light. And more features will definately appear in RS$.

So yes, RSE can enahnce the dynamic range of image files.

In the case of the pinball machine. I would have (if i thought of it at the time) shot with a tripod, and taken a few shots with the person. Then i would have taken various exposures (and potentiall different ISOs0 wothout the person, and then I would have all that i needed as long as I had proper exposure of the person shots.

[arjenvdm]

I considered the tripod. But the situation was hectic, with many people congratulating him. I did not want to have to get the tripod from my car. And I had a deadline to meet. But that would be the best solution. What I did not do was make some handheld extra shots and use something like photomerge. Anyone tried something like that? Probably not gonna work, but I am going to give it a try.
I downloaded the trial version of RSE. I cannot open my raw files. Does it support Fuji S2?

[MichaelT]

Fuji is not yet supported but it will be.

[robertsj]

I considered the tripod. But the situation was hectic, with many people congratulating him. I did not want to have to get the tripod from my car. And I had a deadline to meet. But that would be the best solution. What I did not do was make some handheld extra shots and use something like photomerge. Anyone tried something like that? Probably not gonna work, but I am going to give it a try.
I downloaded the trial version of RSE. I cannot open my raw files. Does it support Fuji S2?

In addition to making multiple develops (or using a tripod and manually putting together multiple exposures), you might also be able to use the high dynamic range setting in PS CS2. Don't know if your camera supports it, but with the Canons I can bracket by an equal amout--say -2 0 +2 in this case--over 3 (quick) frames. HDR processing then takes care of the composite more easily than a fully manual process.

[MichaelT]

Yes, with tripod required for best results..