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08-10-2010, 03:32 AM   #1
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K7 EV Compensation - help?

I am trying to understand the EV compensation button and how it works. I thought it would be obvious, but I cant quite make sense of it.

I have a shot lined up with the following parameters

1" @ f16, ISO 100. The EV Bar is indicating five bars to the left, ieminus one and two thirds. This I take this to mean the shot will be underexposed to this degree. I could compensate by changing either the aperture or the shutter speed, but:

Q1 - assuming I want to keep the aperture and shutter as they are am I right to think I can use the EV button in this instance?

If I am then when I press the EV button I now see the EV compensation bar at 0.0, so to compensate I twirl it up to + one and two thirds.

Q2 - why does the EV Bar now say I am underexposing by minus three and two thirds when I just compensated to overexpose?

If I take a photo at that setting - it is underxposed. If I then go back to my EV button setting and twirl the dial so that the EV button display now gives me MINUS one two thirds the subsequent EV bar reading is now at zero, I take the photo, and its exposed exaclty the same as the previous shot - ie underexposed. I am scratching my head here, my assumptions about what EV button does and how it works must be wrong.

I dont understand the manual - page 116
EV compensation for M and X modes
For example, if the EV compensation value is set to +1.5 for M (Hyper-manual) and X (Flash X-sync speed) modes, an underexposure of 1.5 EV is displayed on the EV bar. If you set the exposure value so that the I is displayed at the centre of the EV bar, the image will be captured with the compensated value.

Q3 When it says - "If you set the exposure value..." does it mean setting by using the EV button, or by changing the Aperture/shutter settings?

Anyone help me out here?

08-10-2010, 04:01 AM - 1 Like   #2
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EV Compensation basically effects how your camera meters. If you think your camera's meter is underexposing, you can add positive EV compensation and it will decrease the shutter speed, increase the iso or open the aperture more in order to increase the exposure. I don't use EV compensation in manual mode, but basically it would change how the camera meters a correct exposure and it would be up to you to adjust one of the settings in order to get the exposure correct.
08-10-2010, 05:33 AM - 1 Like   #3
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The answer to Q1 is no: In manual mode, the EV button does not actually affect the exposure. It just "biases" the "0" meter reading (think of it as "moving" the 0-point to the left or right), It does affect the "Green button" operation, because the latter basically zeroes the meter reading.

Following this, the answer to Q2 is relatively obvious: because you've not actually overexposed anything, but in fact moved the "0" point 1 1/3 EV to the right.

For Q3, the exposure value is the combination of aperture, ISO, and shutter speed.
08-10-2010, 06:00 AM - 1 Like   #4
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RBellavance gave you all the correct info, but let me give you a response to Q2 stated another way.

When you use the EV button in Manual mode, you aren't changing the exposure (or it wouldnt' be manual). Instead, you're telling the camera how over- or under-exposed you want the shot to be. Dialing in +1.0 EV using the button tells the camera to bias the meter so that "zero" is now what it considers to be one stop overexposed. You're telling the camera to set up up for an intentional overexposure.

When you adjusted your meter +1 2/3 EV, you set a target exposure that was even farther away from where you already were. So instead of the meter saying you were 1 2/3 stops underexposing, it now said you were 1 2/3 (original metering) + 1 2/3 (added offset fromt he EV button) + 1/3 (a minor fluctuation in the lighting between shots) = 3 2/3 stops underexposed. Changing your shutter speed or aperture to zero the meter from there would have left you 1 2/3 stops overexposed because that's what you asked the camera to do with the EV button.

08-10-2010, 06:48 AM   #5
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QuoteOriginally posted by grayboy Quote

Q1 - assuming I want to keep the aperture and shutter as they are am I right to think I can use the EV button in this instance?
A1: No. It depends what mode you are in. The answer is no, unless you are working in the Sv mode. In that case the ISO value will be altered (if there is still room for it) to under expose the photo.

QuoteOriginally posted by grayboy Quote

Q2 - why does the EV Bar now say I am underexposing by minus three and two thirds when I just compensated to overexpose?
I cannot reproduce this without more information.
You will need to explain much more on your camera settings:
- What mode your camera is in (P, Sv, Tv, Av, M, ...)
- What metering mode it is in (Normal, CW, Spot)
- What (Auto) ISO settings it is in.

- Bert
08-10-2010, 07:28 AM   #6
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Thanks for the response - I have obviously misunderstood how EV compensation works - it seems to be counterintuitive to my thinking - but I'll sit down with a coffee and try to absorb all your answers.

Bert -Sorry thought I had mentioned what mode I was in - Manual, ISO set to Auto, metering mode Centre weighted
08-10-2010, 07:37 AM   #7
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QuoteOriginally posted by grayboy Quote
Thanks for the response - I have obviously misunderstood how EV compensation works - it seems to be counterintuitive to my thinking - but I'll sit down with a coffee and try to absorb all your answers.
Be aware that what I wrote applies only to the M and X modes. In all other modes, EV compensation works more intuitively, i.e. it will modify the non-fixed settings (eg. shutter speed in Av mode) to achieve the exposure compensation requested.

As an example, I dial f/4.0 in Av mode, with ISO fixed at 100. Let's say the camera sets the shutter at 1/250 with no EV compensation. If I dial in +1EV, the shutter speed will change to 1/125 (assuming the light doesn't change). If I dial in -1EV, the shutter speed will instead go to 1/500.

A similar principle applies in Tv mode, but it is the aperture that will change instead of the shutter speed.

In P, aperture or shutter or both will change depending on the program line you have selected.

And in TAv, the ISO will change.

I admit I'm not sure how Auto-ISO is used with EV compensation in Av, Tv, and P. I have not tried it.
08-10-2010, 07:45 AM - 1 Like   #8
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QuoteOriginally posted by grayboy Quote
Thanks for the response - I have obviously misunderstood how EV compensation works - it seems to be counterintuitive to my thinking - but I'll sit down with a coffee and try to absorb all your answers.

Bert -Sorry thought I had mentioned what mode I was in - Manual, ISO set to Auto, metering mode Centre weighted
Where you set your exposure should depend on What you are taking a photo of (this may have already been discussed). Set your ISO at a Fixed point, I prefer 100. Set your metering mode to Spot for greatest control. You have the Manual mode correct.

Meters, in theory, see only one thing. 18% gray though I've seen some suggest that it is 12% on our modern cameras. So if you spot meter a Black subject and center the meter, the black subject will Be, 18% gray (look at an unmodified b&w version of your photo). If you spot meter a White subject and make no adjustments from center, your subject will be, you guessed it, 18% gray.

To make your Whites white, adjust your exposure a couple stops by slowing the shutter or opening the aperture or adjusting ISO. To go Black, speed up the shutter or close down the aperture. The more you adjust from center, the whiter your whites will be or the blacker your blacks will be. The cost at some point is detail. I never use ISO adjustments in either case. The only time I'll adjust ISO from 100 is if I cannot get a clean shot at ISO 100.

Edit: Once you have your settings for a given scene it shouldn't be necessary to fiddle with the exposure very much unless the lighting is constantly changing.



08-10-2010, 08:49 AM   #9
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QuoteOriginally posted by grayboy Quote

Bert -Sorry thought I had mentioned what mode I was in - Manual, ISO set to Auto, metering mode Centre weighted
As pointed out, there is no EV compensation in manual mode because you have set both the aperture and shutter (and ISO).

EV in manual is a clumsy way of changing the exposure. It changes the zero-point of the meter, which if followed, will +/- compensate the exposure.

In the old days, we just counted aperture or shutter clicks up or down from what the meter said, not change the meter zero point.
08-10-2010, 10:09 AM   #10
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QuoteOriginally posted by JeffJS Quote
Set your metering mode to Spot for greatest control. You have the Manual mode correct.
You lost me here. I have yet to see a pro use anything but matrix metering in the last few years except for extreme contrast (black cat on white stairs). Matrix has gotten extremely good over the years.

EV was derived as a cheat for the user to second guess the light meter. It was a clever way to take advantage of the latitude offered by film and the photographer's experience at resolving a high contrast scene better than the meter, and prioritize what should be exposed properly (e.g. the black cat in the example above).

In M mode the bar graph is your light meter! It's reading a correct exposure, under-exposure, or over-exposure. If you have chosen auto-ISO it will always bump up the ISO to the max you've selected before it will demonstrate an under-exposure.
08-10-2010, 10:30 AM   #11
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QuoteOriginally posted by Aristophanes Quote
You lost me here. I have yet to see a pro use anything but matrix metering in the last few years except for extreme contrast (black cat on white stairs). Matrix has gotten extremely good over the years.
In the 2200+ postings I've made here at PF and the 2800+ over at DPReview, Not in one of them have I ever claimed to be a Pro. I use spot metering because that's what works for me and it's what I've always used. I'll tell anyone who asks, how and why I use it and give advice on how They can use it. I'll offer that advice once, they can then take it, or leave it. No sweat off of my brow either way.

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