ISO setting with RAW

On a recent divetrip I frequently used the maximum aperture + maximum time acceptable without getting to much blur. I used a combination of F2.5 and 1/50 with RAW.

I experimented with different ISO settings, ISO 80 and 200. Now, is it correct to say that the ISO setting does not matter for the raw capture. Only how bright the picture appear on screen, and the parallel JPEG image.

With RAW I have exposure latitude to press the result afterwards (i.e. raise ISO)

Is this correct, and if not how does ISO affect RAW capture?

Cheers

O

ISO most definitely does affect RAW capture.

ISO is the sensitivity of the sensor itself when it's capturing the image. Maybe with cameras of the future you can change the ISO on RAW files; but as I'm aware of, there are none with which you can change the ISO after the photo has been taken.

I'm not sure you quite understand what ISO is. It's essentially the same thing as film speed and affects how sensitive the sensor is to light. Higher ISO means higher sensitivity, thus faster shutter speeds are achievable; but the increased sensitivity will also generate more noise. The opposite for low ISO. Generally it's best to keep the ISO as low as possible unless you can't get a fast enough shutter speed with the available light or want to introduce noise for artistic reasons.

A RAW file can be called a digital negative.

It provides greater bit depth and doesn't permanently apply any post processing elements onto the picture which are made when a JPEG is created. These include contrast, sharpness, saturation and perhaps most importantly white balance.

ISO is applied at the point the image is taken, so you can't change it later in post. Much like you can't change the aperture or shutter speed.

Further reading:

http://en.wikipedia.org/wiki/Raw_image

I'm not sure you quite understand what ISO is.

Actually I do for film. The problem is it is a film-concept from start just transfered to digital. Film has has a certain sensitivity, BUT film can be "pressed" in the development process to change the sensitivity after the exposure has been made.

For digital, the question is if ISO affects the gain in the A/D circuit before digization of the pixel, or if it is a fixed 12-14bit setpoint, and the ISO is affected by adjusting the wihitepoint. I think from our discussion that it must be the former. If it is the former, the gain of the signal + noise setting cannot be changes afterwards.

The gain you get from adjusting ISO is "baked" in the raw file. However if you underexpose a bit, this can be fixed in post - this can be noisy. If on the other hand you overexpose so the histogram is piled up on the right side, you cannot recover highlight details. You cannot shoot at ISO 1600 and go back to 200 in post of you want a "normal" looking photograph. White balance is an interpretation of the raw file so is as flexible in post as it is in the camera setting. Hope this helps.

For digital, the question is if ISO affects the gain in the A/D circuit before digization of the pixel, or if it is a fixed 12-14bit setpoint, and the ISO is affected by adjusting the wihitepoint. I think from our discussion that it must be the former. If it is the former, the gain of the signal + noise setting cannot be changes afterwards.

I believe that ISO setting on a digital sensor is the gain in the A/D converter.

oskar: Sorry for assuming hehe!