Priority mode and auto ISO

[wfooshee]

I get everything you're saying, but until I have gear that's useful over 800, then it is what it is here.

As for black frames, it's not a constant thing or a regular process. I will have some underexposed JPG previews, but not really black except for once in a blue moon.

 

[JBPhotog]

When using shutter or aperture priority is it better to use auto ISO or select ISO?

Depending on your camera brand, there may be a menu setting where you set the maximum ISO and minimum shutter speed, check this. So if you wish to use Aperture priority and Auto ISO the shutter will fluctuate to compensate for exposure first while maintaining your preferred ISO. When the light level diminishes lower than the minimum shutter speed you set in your menu setting, then Auto ISO kicks in and adjusts to a higher sensitivity to balance the exposure triangle. It is essentially the same in Shutter priority, the aperture will fluctuate until it reaches its minimum then Auto ISO kicks in. Many cameras also allow for a maximum ISO to be used in the Auto ISO mode.

In either scenario, you decide if DOF or shutter speed is your critical setting.

Generally in a fixed lighting situation Auto ISO is of no benefit, however if you have light and shade such as in a sport or active subject such as wildlife then Auto ISO can be a benefit.

 

[freixas]

My own experience is that I sometimes [usually] get better results boosting in post than letting my D7200 shoot with high ISO. I've gotten usable images several times from frames that were black when loaded into the RAW processor in Photoshop.

This sounds strange. Are you basing this on a subjective impression based on taking totally different images, or have you done a controlled experiment?

The way the circuitry works, for the same shutter speed and aperture, a higher ISO setting should never produce more noise. For ISO invariant cameras, the noise will be the same at any ISO; for most cameras, it will be less.

 

[JBPhotog]

This sounds strange. Are you basing this on a subjective impression based on taking totally different images, or have you done a controlled experiment?

The way the circuitry works, for the same shutter speed and aperture, a higher ISO setting should never produce more noise. For ISO invariant cameras, the noise will be the same at any ISO; for most cameras, it will be less.

Without lots of testing, claiming the D7200 a crop sensor camera, is ISO invariant is a stretch. Very few modern cameras are in this category and it doesn't apply in every circumstance.

 

[petrochemist]

If the conditions are such that the camera will probably be able to meter OK I'd probably got auto ISO. There have been times in shutter priority that I've selected a speed outside of the range that give apertures my lens can reach. On manual ISO that throws the 'exposure'. (Yes I know ISO is not a factor in the proper definition of exposure, but those who hark on about this never offer a suitable alternative that includes it. AFAIK none of my cameras are iso-invarient so it is a significant factor for my use).

I don't normally use Sv, but find it great for things like panning where movement blur is wanted, and which I sometimes want to use a wide range of shutter speeds for - pushing the limits once a moderate shot has been bagged. For most shots DOF is more important or as fast as practical is the right speed for me (ie fairly wide aperture)

Most cameras have some options on how auto ISO works. Either simply limiting the maximum ISO you'll permit it to use, or in some cases adjusting how readily it increases the ISO.

If the conditions are tricky to meter for I'd probably be fully manual, and spend a bit more time reviewing shots.

 

[Derrel]

Nikon D7200 Review


page 13: "The ISO 100 shot pushed by 5EV is essentially indistinguishable from the native ISO 3200 shot, even down to the darkest tones in the image. This is very impressive performance: the D7200 is probably the closest to being a truly ISO Invariant camera that we've seen. This means that you could reduce ISO (and the hardware amplification that goes with it) by 5EV in order to retain 5EV of highlight detail, then adjust the brightness afterwards with no additional noise cost."

 

[freixas]

This sounds strange. Are you basing this on a subjective impression based on taking totally different images, or have you done a controlled experiment?

The way the circuitry works, for the same shutter speed and aperture, a higher ISO setting should never produce more noise. For ISO invariant cameras, the noise will be the same at any ISO; for most cameras, it will be less.

Without lots of testing, claiming the D7200 a crop sensor camera, is ISO invariant is a stretch. Very few modern cameras are in this category and it doesn't apply in every circumstance.

If you can find anywhere that I claimed that the D7200 was ISO invariant, I'll eat my hat.

What I said was that there are no cameras where a higher ISO will result in more noise, given the same scene and the same shutter speed and aperture for comparison shots. wfooshee claimed the opposite and my question was whether he had ever done a proper comparison.

If, as Derrel's link implies, the D7200 is close to ISO invariant, then it might be easy to get convinced that lower ISO shots were better, if the shots being compared were of different scenes taken with different shutter speed and aperture settings.

I don't know why having a crop sensor would prevent a camera from being ISO invariant. ISO invariance has nothing to do with sensor noise; it has everything to do with noise added downstream from the sensor. If the downstream noise is exactly zero, then the camera is absolutely ISO invariant, even if the sensor is the size of a pinhead and produces noisy images. The crappy images would be equally crappy at any ISO setting.

 

[Derrel]

My experience---excessive noise is best countered by exposing MORE, with a slower shutter, more flash/light, or a wider aperture, or some combination. If the D7200 noise is "bad" at 800 ISO, maybe elevate the ISO to 1,250, and dial in exposure compensation of + 0.7 EV or maybe go even higher in ISO and add-in + 1.) EV