repleo Loc: Boston

I know how to use Exposure Compensation (EV+/-) on my camera and have been using it for years. However, I just realized I don’t really understand how it works. What is the EV+/- dial actually changing – Aperature? Shutter speed? ISO? Is there some extra dimension to exposure that I don’t know about? Does changing the EV have any impact on Depth of Field or noise?

rmalarz Loc: Tempe, Arizona

https://en.wikipedia.org/wiki/Exposure_compensation
http://www.photoxels.com/tutorial-exposure-compensation.html
http://www.digitalcameraworld.com/2012/05/10/what-is-exposure-compensation-free-cheat-sheet/

--Bob

tjphxaz Loc: Phoenix, AZ

I shoot Nikon so that is the terminology I will use. EC works only in P,S,A shooting modes.
If Auto ISO is On, In P, A,S shooting modes adjusting the EV will change ISO to achieve the desired exposure.
If Auto ISO is Off (i.e. you have selected a fixed ISO), then in A and S modes, the EV adjustment will change the factor you are not setting (i.e. in A mode you set desired aperture and adjusting the EV will change shutter speed, in S mode the aperture will change). In P mode, the EV adjustment will change both aperture and shutter speed to yield the desired exposure.

lamiaceae Loc: San Luis Obispo County, CA

Read thru Bob (rmalarz)'s links.

Oh boy, your confusion is what happens to so many people today who never learned photography using film, manual cameras, and hand held meters or taken actual classes and read camera books. Seems everything is that way today.

Hopefully the info in those links will help you. Geeze, how to explain it simply. The light meter in your camera and all photographic light meters are design to expose to a middle gray tone. Ideally if you meter a middle gray in your scene everything will more or less fall in place. But what is the likelihood that a middle gray is in the middle of the spot metering of your camera? Not really likely. Averaging metering can help sort of, but you still may want the tones different then what the camera is telling you. Basically what is happening with Exposure Compensation is you are telling the camera that you do not want the value it measured set at middle gray but at a different value. So in essence you can "lie" to your meter by setting the middle gray to a different value in stops. As you should have read you can set a EV compensation for depending on your camera settings and model 1 stop higher, only 1/2 or 1/3 or 1/4, 2 stops lower, all kinds of values.

Perhaps a way to understand this would be to think in the film sense. Say you've tested or calibrated your film camera and film, say Tri-X (Rated at ISO 400) to actually be 320 for you. So to get the best exposure with your equipment you set your camera to ISO 320. Now since with a digital camera there is no film and the ISO can be any value you want. So imagine you set your camera to ISO 400 and Exposure Compensation to + 1/3 Stop to get an "ISO 320" exposure. Does that help Or make it muddier? Note in the link's example, the mountain with snow, that is where you need to trick the meter into giving you white snow not gray snow. With a digital camera an ISO change would not help alone unless you make a manual exposure or some auto mode with exposure compensation. Even some film cameras had exposure compensation so you could customize one shot but not have to change ISO (then ASA) back and forth.

A footnote: In case you were curious about the EV 1 & 1/2 Stop vs. 1/3 or 1/4 Stops. In the film days the lenses all had actual click stops where the iris "locked" or "set" at f/4, f/5.6, f/8, etc. most camera brands' lenses also had click half way between these, half-stops. Nikon lenses had third-stops, two clicks between whole click stops. Not a big issue since on nearly any camera you already had ISOs and EVs in one-third stops.

lamiaceae Loc: San Luis Obispo County, CA

And for Canon and Pentax Av, Tv, M, etc. But that is not what he actually wanted to know from what I could tell. He knows how to use exposure compensation but want to know or understand why or how it works. A bit different and a different can of worms.

rwilson1942 Loc: Houston, TX

I depends on which mode you are in. If using aperture priority then EV will change the shutter speed, in shutter priority it will change the aperture. I'm not really sure what it would change in manual, I'm a aperture priority guy :)

repleo Loc: Boston

Hi lamiaceae. Thanks for your lesson on Exposure Compensation. All responses are appreciated. And yes, I did learn photography using film, manual cameras, hand held meters and I still take classes, read photography books (and forums like this). In fact for the first ten years taking photos I didn’t even have a light meter and had to go by the little ‘exposure guide’ that came with the roll of film. It was another ten years before I got my first camera (OM-10) with a built-in light meter. In the meantime, I became quite skilled in the dark room trying to compensate for my exposure miscalculations.

I just wanted to know the mechanism of how it worked on a digital camera. I seem to recall that on my old OM-10, exposure compensation was really just a way of tricking the light meter into thinking you had changed the ISO (or ASA) as it was back then. I usually found it easier to adjust exposure with the aperture or shutter speed than fiddle with the little ring and risk forgetting to change it back. In particular I was trying to understand what my A6000 was doing when I use EV +/- with a manual lens. (I still have my 30 year old lenses from my OM-10 days).

I did find what I think is the answer to my question in two of the links provided by rmalarz above (thanks rmalarz) although the articles barely touched on the ‘how’. I read several articles on the subject with no answer before turning to UHH. For anybody else who might have the same question, or who never even thought about it, the answer is – it depends. It depends on your camera and on whatever priority mode you are in. If you have set one of the exposure parameters, the camera will adjust one or other or both of the other two parameters. If you set two, it will adjust the third. Presumably if it changes aperture it will also change DoF and if it changes ISO it could affect noise. Since you can adjust exposure compensation up to two stops (or more) that it not something to overlook.

Apaflo Loc: Anchorage, Alaska

Exposure Compensation does the same thing on all cameras, and it is the same no matter which exposure mode is used. EC changes what the light meter reads!

All that Exposure Compensation directly does is bias the light value indicated by the light meter. The indicated level added to the EC setting gives what the meter is actually reading. Hence if you set EC to 0 EV and read a scene that has a lot of light the light meter might say the Light Value is 15.6 EV. If EC is changed to -1 EV the light meter will say the Light Value is 16.6 EV. If EC is set to +1 EV the light meter will say the Light Value is 14.6 EV.

It is a way to calibrate the light meter to whatever bias you want it to have. If you think the scene reflects more than 18%, you'll want a slightly positive EC value to cause the meter to indicate higher in order to more accurately measure the light.

Exposure Compensation is only about accurate light metering. It does not by itself know what to do about more or less light. The photographer is in charge of deciding what happens as a result! Set the camera to Aperture Priority and you are assured the aperture (and thus DOF) will not be changed. Turn off AutoISO and you are assured the ISO will not be changed... and so on for similar effects in other modes.

The single constant is always, and only, that changing EC will change the value indicated by the light meter.

steveg48

The way I use it is to set the camera to aperature priority and auto iso to off. Then the camera will set the speed based on the compensation value. That way I maintain my desired depth of field.

I would not use exposure compensation in shutter priority because I don't want the camera to control the aperture. If I want a specific speed I would shoot in manual, set the desired aperature and if the exposure were not to my looking I would boost the iso.

My cameras (Nikon D810 and Sony A7Rii) are pretty good at higher isos and both have live histograms-both of which are helpful.

Tracy B. Loc: Indiana

What if you were already using the largest aperture in aperture priority mode and wanted to up the EC? What would happen then?

lamiaceae Loc: San Luis Obispo County, CA

Well, there you have it, everyone saying the same thing in different words. All seemingly relatively correctly. I guess my problem with not just ignoring the entire business or not thinking you have had experience with older equipment is that I am a science guy. Here involved with photography, an art, but formal training as a biologist. Think is I always want to know how and why, an affliction I've had since childhood. I guess since I already know how it works on all light meters, film camera, hand held, and digital, I would never need to ask later. I usually want to know how and why something works before I use it. So if I had the experience of using something for some time, I would never ask later how it works. But I probably should not feel everyone else is the same. That seems not to be the case. Seems many if not most people just use tools without know how they work. A bit foreign to me. You seem to already know too, yes, you are just tricking the meter.

Jrhoffman75 Loc: Conway, New Hampshire

To Tracy B. - EC changes what you are not setting. In Aperture Priority mode EC shifts shutter speed; doesn't matter what aperture you have set.

lamiaceae Loc: San Luis Obispo County, CA

Interesting hypothetical question. What happens when you "ask" for a larger stop than available. I have not tried that. May depend on mode -- camera might then adjust shutter. Likely that is a lot of stops!

That kind of happens when I use older film Pentax lenses of the K and M series. Since they have no electronic contacts if I try shooting in Shutter Priority mode, the camera automatically makes Aperture Priority setting adjustments anyway, i.e. the shutter speed varies. The A series and newer have contacts for both AE in Av & Tv modes.

lamiaceae Loc: San Luis Obispo County, CA

Original question was not "how to use" but "how does it work" or "why does it".

Tracy B. Loc: Indiana

Thanks, interesting.