How exactly does over/under exposure do?

[lorenzo23]

Hi there,
first post, nice to meet you everyone.

I am familiar with camera concepts, but there is something I don't know: say I set my exposure in manual mode, with a certain ISO, aperture and speed. Then I set the exposure compensation to +1. What happens physically in the camera - a.k.a. on which parameter does the camera act to increase my exposure?
If I have set all three parameters, then I am expecting that they stay the same, but if the exposure needs to be compensated by 1 stop, something has to change

Hope what I ask makes sense

Thanks all,
Lorenzo

[chauncey]

If you're in manual mode and stay in manual mode...I don't think that,
then setting exposure compensation, means anything.

[chauncey]

As an afterthought...on what basis are you choosing those parameters?

My method is to preview the scene in live view>watch the histogram while dialing in my settings,
usually inputting two of the important ones, and using the third one to "push" that histogram to
just shy of the right edge.

[Digital]

Lorenzo, as Chauncey related that if you are in manual mode changing the exposure compensation does nothing. In manual mode you can change the aperture, and/or the shutter speed. Hence you change the exposure compensation YOURSELF.
If you are in aperture priority, changing the exposure compensation either increases or decreases the shutter speed.
In shutter priority mode, changing the exposure compensation changes the aperture by either increasing the exposure, or by decreasing the exposure. You either make the aperture smaller (stopping down) or make it larger (stopping up).
Setting to +1 in either aperture or shutter priority modes increases your exposure either by slowing your shutter speed or stopping up your aperture.
Hope this helps.


Bruce

[Mike Buckley]

Welcome to CiC, Lorenzo.

If you're in manual mode and stay in manual mode...I don't think that,
then setting exposure compensation, means anything.

As Chauncey related that if you are in manual mode changing the exposure compensation does nothing.

That depends on whether Auto ISO is being used, at least on my Nikon D7000. If Auto ISO is enabled, using the exposure compensation button definitely takes over when also using manual mode.

For a recent and relatively thorough discussion of using the exposure compensation button, see this thread.

[Digital]

Mike, I do not use Auto ISO so you maybe right in using exposure compensation in the manual mode.
On your Nikon D7000 how does enabling the Auto ISO allow you to use exposure compensation in the manual mode?
What is the process?


Bruce

[Polar01]

Chauncey I would watch telling newer members one's methods, without some better explanation of the equipment you, yourself are using. If I was using a Nikon, and tried to follow you method I would think that I am doing something wrong, you can not do that with a Nikon camera, however you can do that with a Canon but not all models, there maybe some other makes and models that let you do that.

Cheers:

Allan

[Mike Buckley]

On your Nikon D7000 how does enabling the Auto ISO allow you to use exposure compensation in the manual mode?
What is the process?

I haven't taken the time to determine what happens in various situations. I only know that in one very quick test that I just now conducted, using the exposure compensation button while also using manual mode and Auto ISO changed the shutter, aperture and ISO settings.

I seem to remember (perhaps incorrectly so) that these details were discussed in the thread that I mentioned in my previous post.

[Digital]

Mike, thanks for the information. If you come across anymore information regarding this, please let me know.
After consulting with the experts (instruction manual), on the Nikon D300 using manual mode changing the exposure compensation does absolutely nothing.
That is my story, and I am sticking to it until someone says I am right.


Bruce

[Dave Humphries]

Hi Lorenzo,

Welcome to the CiC forums from me.

As you haven't said which camera model you are using, as you can see; we're all guessing, so here's my contribution

With Nikon cameras, specifically my D7100, even in Manual mode and Fixed iso, setting EC does do something, but it does not alter exposure - it offsets the meter reading*. This enables you to adjust shutter speed, aperture or iso with the appropriate controls while in Manual mode and always aim for the centre 0 of the meter scale - while maintaining an offset to account for the subject vs scene brightness of whatever metering method you use (average/matrix, centre-weighted or spot).

Personally, I usually prefer to leave EC as 0 in Manual and just aim to over or under expose by the amount I'd normally set as EC - this works for up to 2 stops, but in extreme conditions, the scale runs out, so for more offset, I'd have to use it. That said; most of the time, (after the first shot) I ignore the meter and just review the histogram and blinkies and adjust shutter speed, aperture or iso based on what that says, a bit like chauncey does with Live View (which I rarely use for the wildlife subjects I shoot).

Maybe this is how you work too (in Manual mode), which makes the question no less valid, but less relevant to you.

I shoot about 50% of time in Aperture Priority (making extensive use of EC to vary the shutter speed when I need to offset exposure), the remaining 50% in Manual (as above) - it depends on the subject. and the stability of light illuminating it. which mode I use.

* I believe this is true for many recent Nikon models, and from previous discussions here; NOT true of any Canon model.

Cheers,

[chauncey]

better explanation of the equipment you, yourself are using

Point taken...my bad.

[davidedric]

A related angle.

I have the Canon 600D/T3i.

Suppose I set to it to manual and a maximum ISO of, say, 800. Then, if I progressively reduce the aperture to the point where ISO 800 is not sufficient to give a correct exposure, the exposure compensation scale starts to move negative - showing under exposure.

The under exposure is correct, but when I first saw it I was certainly confused because it looked as if I has dialled in negative exposure compensation, which I certainly hadn't.

Dave

[Dave Humphries]

I have the Canon 600D/T3i.

Suppose I set to it to manual and a maximum ISO of, say, 800. Then, if I progressively reduce the aperture to the point where ISO 800 is not sufficient to give a correct exposure, the exposure compensation scale starts to move negative - showing under exposure.

Isn't that just the meter working Dave?

Well that's how I'd think it would be, because you're in Manual, that scale isn't showing EC any more, it is just the exposure meter scale.

[rpcrowe]

If I am shooting in manual exposure mode and need a less or more exposure, I simply choose a smaller or larger f/stop or a faster or slower shutter speed. The exposure at which I am shooting is visible in my 7D viewfinder and I can adjust the shutter speed and f/stop independently using the two control dials.

The only time I would use exposure compensation is when I am shooting in Programmed; Aperture Priority or Shutter Speed Priority. I have never shot in Auto but this would be true for that mode also. I can still adjust the shutter speed or aperture using the two control dials but, in the above situations, the total exposure is locked in. Using a faster shutter speed will cause the camera to select a larger aperture or using a slower shutter speed will result in the camera using a smaller aperture. The only way to adjust the total exposure to get more of less exposure is by exposure compensation...

[Mike Buckley]

because you're in Manual, that scale isn't showing EC any more, it is just the exposure meter scale.

In your and my Nikon cameras, there are two displays -- the exposure meter and the exposure compensation -- and they need to be used concurrently. The exposure meter never displays exposure compensation; it always displays the exposure regardless of what method is being used to achieve it. The purpose of each display never changes.

As an example, the exposure meter may be showing one stop over exposed and the exposure compensation display may display zero compensation. If you then use the exposure compensation to reduce exposure by one stop, its display will indicate that you have done that. The exposure meter will then indicate that the exposure is neither under nor over exposed.

My point is that the exposure meter displays the exposure and the exposure compensation displays whether in fact exposure compensation is being used to achieve the exposure.

[Digital]

Lorenzo, it would definitely assist us if we knew the make, and model of your camera.
Dave, alluded to this in an earlier post.
That way we could get address your issue more accurately.

Bruce

[drjuice]

Hi, Lorenzo -

Just a suggestion from somebody who's watched her students go nuts until she points them towards the manual:

The absolute best way, as far as I'm concerned is to work your way through the manual, keeping a notebook handy (I like a school composition notebook with graph paper ruling in it) to write down what happens when you change one setting (which ever one matches with the section of the manual you're reading) and leave ALL THE OTHERS ALONE. How is the picture you get of a particular subject without changing anything (if your particular camera will automagically change settings to always put the EC on 0, change everything you can to manual and start over) except EC to -3, -2, -1, 0, +1, +2, +3 such that you get 7 different images? I strongly suggest that you get in the habit of listing out your settings and leave space to the right for writing down what you observe when you look at each of those 7 images on your computer screen. The one at zero will be a "correct" setting in many camera systems when you use automatic exposure. If you like, I can scan in the page from my notebook when I was learning exactly how to manage my camera. BTW - It also has a Xeroxed copy of the page with the instructions on it on the facing page, just in case I mess up. FYI - I have a Sony alpha700 and it's possible to download a .pdf file of the manual from their website. JEEZ, I WISH THEY'D LET ME ADD MY OWN .pdf NOTES IN THE .pdf FILE NEXT TO THE INSTRUCTIONS!

By the way, in my view why students (and others) go nuts is because reading the very fine manual (RTVFM) is the last thing any techie/geek/nerd does when getting a new piece of hardware. They want to get out and "do stuff". A person closer to me in age (I'm older than dirt) than to the students recently got a new Canon three days before going to Germany. I recently watched all of his slides and it clearly took him the better part of the first week of his trip to learn to control what was happening in the camera, so I have not a very good idea of the ride he and his wife had up the Rhine River since that was the first thing they did after sleeping off their jet lag!

Hope this helps.

virginia

[Brownbear]

I have a Nikon camera and I have been experimenting, off and on with auto iso with birds in flight for a few weeks now.

http://www.robertotoole.com/2011/12/...ird-auto-mode/

When I see clipping in my histograms, using the exposure compensation button definitely effects the exposure bringing it back towards the middle... I suspect that most of the time it does this by changing the iso, unless exposure is too low, in which case it will drop the shutter speed to get the right exposure.

So while I don't quite understand how exposure compensation works with auto iso in Manual mode, it does work.

[William W]

I have the Canon 600D/T3i.

Suppose I set to it to manual and a maximum ISO of, say, 800. Then, if I progressively reduce the aperture to the point where ISO 800 is not sufficient to give a correct exposure, the exposure compensation scale starts to move negative - showing under exposure.

The under exposure is correct, but when I first saw it I was certainly confused because it looked as if I has dialled in negative exposure compensation, which I certainly hadn't.

Dave

That means you were using a Canon DSLR in Manual Mode, with AUTO ISO engaged.

The display was working correctly, as Dave has mentioned.

Notwithstanding this fact - you certainly didn't dial in any Exposure Compensation: because you cannot. It is impossible so to do with a Canon DSLR.

There are other differences as to how EC works with different manufacture's cameras.

The 'Safety Shift Av/Tv' Function is one to be aware of, with Canon DSLR Cameras - I believe I mention that function, in the Link that Mike made in his post above.

WW

[jcuknz]

[EDIT 3 ... if you know how to read the EXIF information you should be able to answer the question for yourself. EXIF is like in the old days a photographer would make a note of the pertinent details of each shot they took except the camera does it for us with the exact second the photo was taken [ if we have set the camera up properly when we bought it ]

If you make a note of what you set the EXIF will tell you what the camera did.