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11-14-2014, 12:31 PM   #1
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EV +- in TAv mode?

Until 10 minutes ago I had no idea what EV +- was. I googled and found it explained by a Nikon user. I understood that +ev makes the picture brighter and - ev makes the picture darker. This is done by adjusting the aperture and shutter speeds accordingly. When in aperture-priority, the camera adjusts the shutter speed to get the desired effect (more light for brighter, less light for darker) and in shutter-priority, the camera adjusts the aperture. I'm saying all this just to confirm that I understand EV.

Now my question is, when I'm using TAv mode on my K50, I'm fixing both the aperture and the shutter speed. What does EV do in this case to get the brighter/darker effect? Adjust ISO?

11-14-2014, 12:32 PM   #2
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QuoteOriginally posted by Moropo Quote
Until 10 minutes ago I had no idea what EV +- was. I googled and found it explained by a Nikon user. I understood that +ev makes the picture brighter and - ev makes the picture darker. This is done by adjusting the aperture and shutter speeds accordingly. When in aperture-priority, the camera adjusts the shutter speed to get the desired effect (more light for brighter, less light for darker) and in shutter-priority, the camera adjusts the aperture. I'm saying all this just to confirm that I understand EV.

Now my question is, when I'm using TAv mode on my K50, I'm fixing both the aperture and the shutter speed. What does EV do in this case to get the brighter/darker effect? Adjust ISO?
In TAv mode, the camera adjust the ISO accordingly if you change EV+/-.
11-14-2014, 12:48 PM   #3
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QuoteOriginally posted by Moropo Quote
Now my question is, when I'm using TAv mode on my K50, I'm fixing both the aperture and the shutter speed. What does EV do in this case to get the brighter/darker effect? Adjust ISO?
The best way to find out is to actually give it a try. You should be able to see the ISO change in the rear LCD as you dial in the EV comp (+/-).


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11-14-2014, 12:50 PM   #4
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Thanks.

Now, this adjustment (in whatever mode) is done relative to what? The camera's assumed ideal exposure coming from its reading?

11-14-2014, 01:47 PM   #5
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QuoteOriginally posted by Moropo Quote
.

Now, this adjustment (in whatever mode) is done relative to what? The camera's assumed ideal exposure coming from its reading?
From the meter reading, ideal or not.
11-14-2014, 01:51 PM   #6
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QuoteOriginally posted by Moropo Quote
Thanks.

Now, this adjustment (in whatever mode) is done relative to what? The camera's assumed ideal exposure coming from its reading?
yes the camera is adjusting the exposure based on what it sees... if you are trying to take a picture of something in a shadow (say a bird on a limb), the exposure could be off because the camera might see it brighter than it is (maybe light is streaming through the tree limbs) so you would adjust the ev + to ensure the bird was not too dark...also works the same if you try to take a bird flying in the sky...the camera is metering off the sky so you would push the ev positive
11-14-2014, 02:49 PM   #7
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Thanks very much for the explanation, I now understand!

Is there a formula that the camera follows so you can predict the adjustments? For example, let's say you are in shutter-priority mode and you dial +1 EV. Will that always correspond to a specific aperture adjustment or that changes depending on other variables?
11-14-2014, 03:12 PM   #8
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QuoteOriginally posted by Moropo Quote
Thanks very much for the explanation, I now understand!

Is there a formula that the camera follows so you can predict the adjustments? For example, let's say you are in shutter-priority mode and you dial +1 EV. Will that always correspond to a specific aperture adjustment or that changes depending on other variables?
There is another element in the equation when the camera sets the exposure based on the metering settings "spot, center-weigh or matrix". EV compensation is the likely the last adjustment value being applied after the camera obtains the proper exposure based on your settings.

11-14-2014, 04:45 PM   #9
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QuoteOriginally posted by Moropo Quote
Is there a formula that the camera follows so you can predict the adjustments? For example, let's say you are in shutter-priority mode and you dial +1 EV. Will that always correspond to a specific aperture adjustment or that changes depending on other variables?
It depends on the mode you choose and whether you have set a fixed ISO or Auto-ISO. There are three settings that control exposure. The camera has a mode for each one to allow you to control it directly. For example, Av mode means you set aperture directly. If you choose a single setting for ISO, the camera doesn't change that either in Av mode, you have to control that too. So the only thing left for the camera to alter is shutter speed. Tv mode is similar with a fixed ISO - the camera changes aperture. In TAv mode, you have control over shutter speed and aperture directly so the camera only has ISO control. ln Sv mode, you control ISO. Shutter speed changes with compensation until the camera hits its minimum or maximum shutter speed. I think aperture is set to the "program line". The K-50 doesn't allow you to set the program line; top-tier cameras allow you to change it for sharpness or depth of field or other stuff. Program mode lets the camera control aperture and shutter speed on its own, also referring to the program line. Exposure compensation can change both those settings. (Aperture seems mostly controlled by the program line on my camera.)

Setting the ISO to Auto ISO appears to make the camera throw all that logic out the window. In Av or Tv modes, exposure compensation raises or lowers ISO first, until the limits you've set on Auto ISO are hit. Then the camera adjusts the remaining parameter it controls. In P mode plus Auto ISO, ISO changes first, then shutter speed and aperture affected by the program line. TAv already has Auto ISO and in Sv it makes no sense.

Green and B mode don't allow exposure compensation.

M mode is a special case because you are supposed to be setting all the stuff yourself directly. You compensate by directly changing the setting you want to change. However, Pentax allows exposure compensation to change the meter reading up or down. No settings are changed directly, but if you are taking shots under conditions where the meter is going to be consistently off, like in the snow, you can bias the meter to overexpose, then use your settings to get a nice zero setting. It's a convenience feature. Auto ISO doesn't work in M mode - Pentax has TAv mode for that.
11-14-2014, 04:55 PM   #10
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QuoteOriginally posted by Moropo Quote
Thanks very much for the explanation, I now understand!

Is there a formula that the camera follows so you can predict the adjustments? For example, let's say you are in shutter-priority mode and you dial +1 EV. Will that always correspond to a specific aperture adjustment or that changes depending on other variables?
There really isn't a formula. The more you use the camera the more you will tune in to what to do but you still will end up taking pictures and looking at the outcome or maybe go to raw but that's another discussion
11-15-2014, 07:13 AM   #11
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QuoteOriginally posted by Moropo Quote
Is there a formula that the camera follows so you can predict the adjustments? For example, let's say you are in shutter-priority mode and you dial +1 EV. Will that always correspond to a specific aperture adjustment or that changes depending on other variables?
I may be interpreting your question a little differently, but yes, it corresponds to a specific adjustment. A change of +1 EV corresponds to opening up the aperture 1 stop to make the picture brighter (or opening the Aperture and raising the ISO a combined amount of 1 stop if you've got Auto-iso turned on).

For example, suppose you're in Shutter Priority and Manual ISO, EV comp set to 0 and your camera reads:

1/250 f/8 ISO 200

If you set EV to +1/2 and change nothing else (including framing, metering mode, etc.) your camera will now be set to:

1/250 f/6.7 ISO 200

If you set EV to +1 and change nothing else (including framing, metering mode, etc.) your camera will now be set to:

1/250 f/5.6 ISO 200

If you set EV to +1 and also turned Auto ISO on (but left framing, metering, etc alone), you'd get one of the following:

1/250 f/5.6 ISO 200
1/250 f/6.7 ISO 280
1/250 f/8 ISO 400

Depending on what the camera thought was the best choice. Trying to predict what the camera will do when it has control over 2 variables can be tricky (as Dave has talked about above), and if where one or both these variables land is important to what you're doing it's best to just take control over them in some way, shoot in TAv mode, or set limits on what Auto-ISO is allowed to pick, and so on.
11-15-2014, 07:23 AM   #12
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yes camera meters a certain EV and chooses settings that give ideal exposure - EV=0. This is why the meter shows a scale from -3 to +3 (or 5 for some models). This can be quite limiting in extreme conditions bur it is easy to work with. It achieves an exposure by choosing aperture, shutter and iso sensitivity. In TAv only iso. In other modes it chooses one thing. And isi if you enable auto iso range. Ev+/- is no secret but it can be a powerful feature to avoid overblowing highlights and such
11-15-2014, 05:49 PM   #13
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