ISO question


TPF Noob!
Apr 22, 2013
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I think I have a pretty good grasp on how shutter speed, aperture value, and ISO value work together. What I'm not totally clear on is this:

I was under the impression that if at all possible you would always want to shoot at ISO 100. I have been taught that the lower the ISO number, the less noise you will have in your shot. I do a lot of re-touching while zoomed in at 100%, sometimes even 200%. So any noise in the picture will affect the outcome.

So am I right in thinking I should always shoot at ISO 100 as long as it's possible based on lighting etc.?

And then as a side question, I read somewhere that some cameras (mine included, Canon t4i) actually produce better results at ISO 200, and that I'll actually get less noise at 200 then I will at 100, assuming good lighting and a good exposure.

The more modern the camera, the farther you can push it. In general, the difference between 100 and 200 should be negligible. Yes you should (usually) shoot at as low an ISO as possible

but no lower

Don't turn your pictures into a mush of camera shake just to keep the ISO low. High ISO noise is (usually) a better picture than a shaky one. It never hurts to keep high ISO noise in the back of your pocket for effect, too. Pictures look different at ISO3200, but not necessarily worse. Depends on what you're going for.
Old inter-webs-formation seems to hang on forever. Years ago, that was probably true, and might still be true for certain older models.

Additionally, it seems that the default ISO setting on most new cameras is still set at 100.

There are a lot of potential "ifs" with your term "as long as it's possible".

Just make the best picture you can in the conditions available.
I also thought this. But as I have been reading Understanding exposure by Bryan Peterson, he uses ISO 200 in broad daylight. I have been trying it lately and getting good results out of it. I haven't zoomed in to 100-200% for editing do see any difference.

I have been happy with the results of these photos so I go back and forth to get the shutter speed and aperture that I am wanting for proper exposure.
You need to shoot at the NATIVE ISO for your camera body for the best image quality, and that varies from camera to camera. It will be the last ISO value that has a number before the readout starts showing "-1", "-2", etc.

That said, you also have to temper that decision with what is necessary for the shot. If there is no way that the shutter speed / aperture combination that you need to use will work then increasing the ISO may be the best option. Sometimes a particular shutter speed is necessary to control camera or subject motion. Sometimes a particular aperture is necessary for depth of field. Sometimes BOTH are necessary. You, as the photographer, have to decide how to best balance all three to get the shot.
SCraig mentioned 'native ISO'.

Many cameras have an expandable ISO range. Nikon calls it Lo and Hi. ISO settings in Lo and Hi are not 'native ISO', because those ISO settings are accomplished with camera software, not electronics on the image sensor.

Next - because of the way digital images work, under exposure makes noise more visible in the darker parts of a digital image, even if native ISO 100 is used.
In fact the concept is known as Expose-To-The-Right or ETTR.
Exposing to the right - Wikipedia, the free encyclopedia
Optimizing Exposure

You might want to note that Jeff Schewe is part of the team that writes the Sharpening/Noise Reduction software that is Adobe Camera Raw's Sharpening panel.
(ACR is use by both Photoshop Camera Raw (Elements and CS 6) and Lightroom's Develop module.)

Sharpening and noise reduction are 2 sides of the same coin. More expert info from Jeff Schewe - Real World Image Sharpening with Adobe Photoshop, Camera Raw, and Lightroom (2nd Edition)

And if you start with Raw image files - The Digital Negative: Raw Image Processing in Lightroom, Camera Raw, and Photoshop
More images have been ruined by zealously adhering to ISO 100 than have been ruined by moving up to ISO 250,320,or 400 in order to achieve the truly NEEDED camera settings.
More images have been ruined by zealously adhering to ISO 100 than have been ruined by not understanding when to increase the ISO in order to achieve the truly NEEDED camera settings.

If I'm outside in daytime, I'm _probably_ shooting at ISO 100.

Here's why: In daytime sun, I want to cut the harshness of shadow by using fill-flash. But that means it's preferable to keep the shutter speed at or below the flash sync speed depending on the subject distance (you can use high-speed sync if the subject isn't too far away.) This means I may be trying to shoot with a shutter speed of 1/200th sec. In bright sun, that's ISO 100, 1/200sec, and f/11.

If your flash doesn't support HSS or isn't strong enough (because the max power it can flash at is cut by the number of pulses of light required during the exposure) then you may have to resort to ND filters to bring the aperture and shutter speed down to a point where you no longer need HSS. Basically if you're getting to the point where you may have to put an ND filter on the lens, then you may as well be cutting the ISO all you can before it gets to that point.
Rule of thumb is the lowest possible. "Possible" is relative to the situation. You have to decide what the minimum is and why. If you want to freeze action, you might need 1/250 and ISO 100 may not give you that, so you have to decide what's the lowest ISO that will give you that speed; it may be 400. When possible, there's no reason to shoot above 100.
More images have been ruined by zealously adhering to ISO 100 than have been ruined by moving up to ISO 250,320,or 400 in order to achieve the truly NEEDED camera settings.

And once more, if you look at the charts produced at dpreview and the like, you will find that some sensors will perform better at ISO 200 than at ISO 100, albeit a bit a hair more noisy. This is true of many Sony sensors, including those used in Nikon cameras.

What people need to understand about digital photography is that you don't actually get the variable ISO that you're thinking you do. The sensor has a fixed sensitivity with it's signal being processed prior to digitization. This analog gain increase is the primary place where noise comes from. With decreased signal as a result of decreased light available at exposure, more noise is visible in the resulting image.

Personally, while I do believe that you should use the lowest ISO possible, this is primarily due to dynamic range than noise and that the whole noisephobia is kind of blown out of proportion.

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