Ev settings

[orion4]

Perhaps this is a dumb question but no one I've asked seems to really know the answer. When doing HDR capture with my Nikon D90, or adjusting an images eV setting to make minor exposure corrections what is actually being changed? I assume depending whether your in Aperture priority, shutter priority, or manual that shutter speed or ISO , Aperture or ISO, and ISO respectively for each priority element must change in order to achieve an ev adjustment. What is actually changing when adjusting ev in each of these 3 modes of capture?

Thanks for enlightening me!

Brian

 

[Steen]

Hi Brian, welcome aboard !

It's been a bit silent here, probably because your question points in several directions and takes quite a lot of answers.

I have the D300, not the D90, but with regards to Exposure Value settings both our cameras should basicly function the same way, so in spite of my camera model I'll give it a try with an answer to your D90 question. Please bear with my english, it is not my native language.

In short (too short) the answer is that:

- ISO is not affected unless you turn ON the "ISO Sensitivity Auto Control".

- you are right that it depends on the mode (Aperture, Shutter, Manual mode), but in general you can think of it like this: if you choose the one parameter e.g. the aperture, the camera will adjusts the other one i.e. the shutter speed - and vice versa.

But it is a little bit more complicated than that. Below I'll try to give you the looong, elaborated and boooring explanation ... :sleep006:

 

[Steen]

1. First a digression
(ISO seems to be the confusion, so lets start with getting that out of the way)​

The true and sober answer to your question is that: "IT DEPENDS".

Because the fact is that your camera actually has an advanced feature called ISO Sensitivity Auto Control which you can turn "ON", and which enables your camera to automatically vary the ISO factor.

Shooting in low light (e.g. an event) you can with this feature instruct your camera about:

- a selected maximum ISO value, and
- a selected minimum Shutter speed

So when you fire away at your chosen Aperture value (and preferred ISO value) you camera will first choose to adjust the Shutter speed.

But if it hits your selected minimum Shutter speed limit, then it starts increasing the ISO value right until it also hits your selected maximum ISO value limit.

At this point the camera has no other choice than crossing the line for your selected minimum Shutter speed and use a slower speed. And that's what it will do.
Some day you can read more about that at p. 166 in your D90 Manual.

It's a brilliant and intelligent feature for certain tasks. But the good thing is that right now you can just forget all about it. For your HDR purpose you don't need it (though you still can use it). Just turn the feature OFF.

 

[Steen]

2. Plain Exposure ​

Ok, now we are back to the basics. And now it gets much easier, because ISO sensitivity will simply remain fixed at the value selected by YOU. Period.
(That is, of course, until you yourself decide to change it for some good reason).

Let's just pretend we want to stay at the base ISO 200. So for now we can just set it there and then forget all about ISO. Your camera will not change or adjust your ISO setting.


Mode A: Aperture Priority

You choose the Aperture to control depth of field (dof), and the camera automatically adjusts the Shutter speed. Bingo. That's it. See p. 82 in your D90 Manual.
Try it out: Put your camera on a tripod and point it at a fixed subject. Rotate the Mode Dial to A: Aperture Priority.
Press the shutter button halfway and watch the aperture and shutter values in either the viewfinder or the exposure display.
Now rotate the sub-command dial (on the front) to another aperture and watch how the shutter speed is automatically adjusted.
You don't need to take any pictures, just watch the values.


Mode S: Shutter Priority

You choose the Shutter in order to either blur or freeze moving subjects, and the camera automatically adjusts the Aperture. That's all. See p. 81 in your Manual.
Try it out: Rotate the Mode Dial to S: Shutter Priority.
Press the shutter button halfway and watch the shutter and aperture values in the viewfinder.
Now rotate the main command dial (on the back) to another shutter speed and watch how the aperture is automatically adjusted.
Don't shoot, just watch the values.


Mode M: Manual Exposure

In Manual mode you are completely in charge. The camera won't save you from underexposing or overexposing by adjusting anything for you. See p. 83.
Try it out: Rotate the Mode Dial to M: Manual mode.
Press the shutter button halfway and watch the shutter and aperture values in the viewfinder.
Rotate the sub-command dial to select an aperture, and the main command dial to select a shutter speed.
At least you can on a scale in the viewfinder see whether you are underexposing or overexposing, but you have to do all necessary adjustments yourself.

In a way you now know what you need to know and understand. Because the rest is similar to this.

 

[Steen]

3. Exposure Compensation (EC)​

When using Exposure Compensation the three modes basicly work the same way as described above, only now you alter the exposure suggested by the camera a bit using EC, in order to deliberately make the picture brighter or darker. See p. 90, and note that it is "most effective when used with center-weighted or spot metering" !

Mode A + EC
You choose an Aperture, the camera automatically adjusts the Shutter - which you then alter (compensate).
Try it: Mode Dial on A, press the shutter button halfway.
Now press the +/- button and rotate the main command dial while watching the changes of the Shutter speed suggested by the camera in the viewfinder.

Mode S + EC
You choose a Shutter, the camera automatically adjusts the Aperture - which you alter with EC.
Try it: Mode Dial on A, press the shutter button halfway.
Now press the +/- button and rotate the main command dial while watching the changes of the Aperture suggested by the camera.

(Mode M + EC ... doesn't make sense)
This combination doesn't make sense, because when you are in Manual mode you are totally in command and the camera cannot compensate anything.
If you want to make the picture brighter or darker you simply adjust either the Shutter or the Aperture, manually. As explained above under "Mode M: Manual Exposure".

Now let me repeat, during all this, ISO stayed where we left it, at 200. No automatic adjustments or implications on ISO whatsoever.
You had completely forgot about ISO ? Good ! No more confusion then

 

[Steen]

4. Exposure Bracketing - e.g. for HDR ​

Also with regards to Exposure Bracketing the basic principles remain exactly the same.
The camera automatically varies exposure by varying either Shutter speed or Aperture in two or three captures. See p. 92 - 94.

Mode A + Bracketing
You choose an Aperture, the camera automatically varies the Shutter, according to your bracketing instructions.

Mode S + Bracketing
You choose a Shutter, the camera automatically varies the Aperture, according to your bracketing instructions.

Mode M + Bracketing
You choose an Aperture and a Shutter. The camera automatically varies the Shutter (!), according to your bracketing instructions, i.e. the camera keeps the aperture (and thereby DOF) unchanged.

Try it out - and this time you actually need to shoot the frame sequence while watching the exposure in the viewfinder:

Choose a mode (A, S, or M).
Press the BKT button and rotate the main command dial to choose the number of shots (e.g. choose 3).
Press the BKT button and rotate the sub-command dial to choose the exposure increment (e.g. choose 1.0).
Shoot the 3 frames - and watch in the viewfinder how the exposure value changes for each shot.
(Remember to put the compensation back to 0 when you are finished using it. It doesn't reset by itself).

(I would rather not confuse you with this, but the truth is that you actually can combine the bracketing with the ISO Sensitivity Auto Control feature mentioned in my initial "1. First a Digression" post.
I suggest you just forget about it for the moment, you can always read about that at a later stage, when all this stuff has become more intuitive. See p. 94).

The most important advise is to try out each mode and setting and watch the changes in the viewfinder. There's nothing like learning by doing.

Good luck, and good light
Steen

 

[Corlan F.]

..

Good luck, and good light

Quite an interesteen summary.

Someday, one should award you some Nikoniae Manuali Emeritus title of some kind, for the numerous posts clarifying the -dreadful- Nikon Manuals...

 

[Steen]

Ha, thanks Corlan
Never mind titles, Nikon can just send me a sample of the new Nikkor AF-S 4/400mm VR ... or hasn't it been released yet