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01-17-2011, 03:26 PM   #1
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Questions about RAW exif info and EV

I'm shooting RAW images with my kx and then importing them into Aperture 3. Today I took several shots in the snow and I know that I bumped the ev to +2.
When I opened them in Aperture 3, I looked at the exif data and it said "EV 0". So I pulled the camera back out and took another test shot of my computer in RAW and pushed the EV to +2. Once again, I looked at my metadata tab and exif info and it reads exposure bias 0EV and at the top of the tab it also reads 0EV.

Maybe I'm misunderstanding the exif info and procedure.

In manual exposure mode, instead of zeroing my ev I'm bumping it to +2. That should give me the same reading in Aperture, correct?

01-17-2011, 03:33 PM   #2
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QuoteOriginally posted by Deiberson Quote
In manual exposure mode, instead of zeroing my ev I'm bumping it to +2. That should give me the same reading in Aperture, correct?
There is no EV compensation in manual exposure mode, I'm confused. EV is only relavent in the various auto & semi-auto modes.
01-17-2011, 03:55 PM   #3
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What is the +/- two decimal number on the far right of my viewfinder on both my kx and k10? Maybe I'm confusing the issue with incorrect descriptions. I thought that controlled my exposure value. When I'm in manual mode, I can still see it.
01-17-2011, 04:17 PM   #4
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QuoteOriginally posted by Deiberson Quote
What is the +/- two decimal number on the far right of my viewfinder on both my kx and k10? Maybe I'm confusing the issue with incorrect descriptions. I thought that controlled my exposure value. When I'm in manual mode, I can still see it.
+/- in the view finder in manual mode is telling you how over or under your exposure settings are compared to what the camera thinks the correct exposure should be. In manual mode you have complete control over exposure via shutter, iso & aperture. EV compensation therefore make no sense when you control all 3 variables directly.

That +/- indication becomes important though when shooting in manual mode and using a flash in p-TTL mode, as that influences how much power the camera tells the flash to use. But that's a whole 'nother story...

01-17-2011, 04:30 PM   #5
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QuoteOriginally posted by twitch Quote
There is no EV compensation in manual exposure mode, I'm confused. EV is only relavent in the various auto & semi-auto modes.
With some Pentax DSLRs, you can push the Ev compensation button in M mode and it looks similar but not quite the same as Ev comp. in other modes. It's not - Ev comp. in M mode does not alter aperture, shutter or ISO settings. It biases the meter. So the photographer can alter a setting to get the meter back to zero. It's useful but not immediately obvious that the same button works differently in M mode.

Anyway, back to the OP. With my K-7, I can see whatever Ev comp. I've set on the detailed info screen in the camera, and in Photoshop Elements 6, no matter what mode I use. I think Aperture might not interpret the EXIF the same way Pentax does. Try the Pentax software and see what that says.
01-17-2011, 05:36 PM   #6
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QuoteOriginally posted by Just1MoreDave Quote
Anyway, back to the OP. With my K-7, I can see whatever Ev comp. I've set on the detailed info screen in the camera, and in Photoshop Elements 6, no matter what mode I use. I think Aperture might not interpret the EXIF the same way Pentax does. Try the Pentax software and see what that says.
I use Aperture and can confirm it does indeed interprete the EV comp correctly, at least for DNG's which I use.
01-18-2011, 03:33 AM   #7
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Great.....now I have no idea what that function does. Just when I thought I had it figured out.
I'm not even sure how to post this question in the forum so I'll ask you two first.

1. I always assumed that when people spoke about "metering to zero" they were talking about getting that "+/-" light on the right of my viewfinder back to zero. I also assumed that by dialing my aperture or shutter speed (along with whatever iso I had picked) was how I went about getting the meter back to zero.

2. I also assumed that the +/- that I was dialing to get to zero was the EV meter and was the exposure value that people referred to when metering to zero

3. Furthermore, I also assumed that if I was shooting in the snow, for example, and people suggested that I shoot at +2 EV to compensate for the meter being fooled, that's what they were talking about. The +/- in my viewfinder.

4. Finally, is there a difference between exposure value and compensation? I just thought that the you "compensated" for the EV meter not being at zero and that they were essentially talking about the same thing.

Please help me on this. I'll start another thread but at this point I wouldn't even know what to ask. I thought I had that part of the exposure triangle dialed in.

Kevin
01-18-2011, 04:14 AM   #8
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1. "metering to zero" is not a useful concept or technique, forget about it
2. Ev is only relaxant in auto modes, and in those modes the camera decides the ev it is trying to achieve. Ev compensation is about overriding that, so it's the opposite of what you are thinking, ie, only use ev if you want to force the camera away from what it's meter is saying
3. Yes, that is true. It is useful in p, tav, av and tv modes, not manual mode.
4. Yes, ev is the overall light level the camera thinks it should expose to (eg ev10), ev compensation forces the camera to vary from this by a positiv or negative amount.

That's the best I can do, I'm not good at explanations really

01-18-2011, 04:27 AM   #9
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Ok. So why not manual mode? In other words, will manual mode always select the correct exposure?
Here's how I went about a typical shot in M.
1. Point the camera at the subject and let the camera meter the scene.
2. Decide my DOF for the shot and select the aperture and or shutter speed if there is movement.
3. Look at the EV number in the viewfinder and then get the number back to zero based on my ss or aperture that I needed.

But what you guys are saying is that when I move those numbers (aperture and SS) in M, nothing happens? This is the part that I am now completely confused with. I thought manual gave the shooter complete control over the exposure and scene.
Again, thanks for any nuggets with this.
01-18-2011, 04:30 AM   #10
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QuoteOriginally posted by twitch Quote
1. "metering to zero" is not a useful concept or technique, forget about it
2. Ev is only relaxant in auto modes, and in those modes the camera decides the ev it is trying to achieve. Ev compensation is about overriding that, so it's the opposite of what you are thinking, ie, only use ev if you want to force the camera away from what it's meter is saying
3. Yes, that is true. It is useful in p, tav, av and tv modes, not manual mode.
4. Yes, ev is the overall light level the camera thinks it should expose to (eg ev10), ev compensation forces the camera to vary from this by a positiv or negative amount.

That's the best I can do, I'm not good at explanations really
I would have to disagree here

EV comp is extremely useful even in manual mode

Let's imagine you have a lens that always causes the camera to meter with an offset of 1 stop

As opposed to having to remember, and continually compensate when in manual mode why not let the camera do this? The K10d took this function away and has the worst metering of any pentax dslr Just put a TC on a lens to see what I mean

My *istD and K7 allow EV comp in manual and it is very useful for other things as well as a lens exposure offset, you can also use it for shots where you want high key or low key and want a specific point using spot metering as your reference. Many people work this way
01-18-2011, 04:42 AM   #11
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QuoteQuote:
This is the part that I am now completely confused with.
When you close the aperture 1 stop (e.g. 2.8 to 4) and halve the shutterspeed, the total exposure will not change; the amount of light that reaches the sensor will be the same. So nothing changes from an exposure perspective.

Exposure will change if you only adjust one of the two (assuming ISO is fixed)
01-18-2011, 05:10 AM   #12
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QuoteOriginally posted by Deiberson Quote
Ok. So why not manual mode? In other words, will manual mode always select the correct exposure?
that depends on the camera, the K10D specifically does not allow EV compensation in Manual, this is a mistake, I believe, as my *istD and K7D both offer it. EV comp in manual, allows you to set a deliberate bias on the metering, so that when you zero the metering, i.e. match the metered value with aperture and shutter speed, the exposure will be biased by what you select for the EV comp.
QuoteQuote:
Here's how I went about a typical shot in M.
1. Point the camera at the subject and let the camera meter the scene.
2. Decide my DOF for the shot and select the aperture and or shutter speed if there is movement.
3. Look at the EV number in the viewfinder and then get the number back to zero based on my ss or aperture that I needed.
process is OK, and will give you correct exposure for the shot
QuoteQuote:

But what you guys are saying is that when I move those numbers (aperture and SS) in M, nothing happens? This is the part that I am now completely confused with. I thought manual gave the shooter complete control over the exposure and scene.
yes it does. changing aperture and shutter speed will change exposure, but if you change them in proportion, i.e. move from F2.8 to F4 and at the same time cut shutter speed in half, the overall impact on exposure has not changed, all that changed is you have more DOF and a slower shutter, making perhaps the opportunity for blurred image due to camera shake or subject motion. it is only when you change ONE of the two that the exposure actually changes
QuoteQuote:
Again, thanks for any nuggets with this.
Good luck, and I suggest you get a book on basic exposure as it will help re-enforce the points people have made here.
01-18-2011, 06:17 AM   #13
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I have read the books and understand the principals of exposure that you guys are kindly reinforcing. What I don't understand though is this "Lack of EV Comp" in M.

I know that if my aperture is set to f/8 and I decide to open it to f/2.8 that I must also do something with either/both the ISO and shutter speed to compensate for the extra light that I just let in. I get that part. I was always under the impression that was my compensation. In other words, if my EV meter (maybe I'm calling this by the wrong name) in the bottom right of my camera was showing zero @ f/8 and I open up the lens 2 stops to f2/8 that my EV meter in the bottom right would now show "+whatever" because my scene is now over exposed because of too much light. I would then have to adjust (speed up) my shutter speed or iso (lower) to compensate for those extra stops in aperture to bring that meter back to "0".

If that's correct, I'll go back to my OP. For the snow scene I was shooting in yesterday I know I wanted to expose +2 (only because that's what people suggested) so I went to M, metered off my subject to 0 (using the numbers in the bottom right of my viewfinder assuming that is the EV that we're talking abut) and then I slowed my shutter until my number in the bottom right of the viewfinder showed +2. I did it this way to keep my DOF where I wanted it.

When PP, my exif data showed 0EV rather than the +2 my viewfinder showed. This is what I don't understand

So using this technique, what part am I not understanding? I think we're all talking about the same thing but I am using the wrong terms or using the wrong numbers which is causing this pilot error.

I say this because I'm being told this can't be done in M, only in P, AV etc...which is the part I really don't get.

Much obliged.
K

Last edited by Deiberson; 01-18-2011 at 06:23 AM.
01-18-2011, 07:09 AM   #14
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Do the same test in Av and use the +/- button to add 2 stops. Next check the exif.

I think that the EV field in the exif only refers to the setting of the +/- button (ev compensation), not to the difference of the actual exposure to the correct exposure that the camera calculated.
01-18-2011, 08:25 AM   #15
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Ok. The info came up in AV mode. I took 5 shots with my KX
2 manual
iso 1600 f/16 and 1/6th of a second to give me 0 in the viewfinder
iso 1600 f/16 and .6" to give me +2 in the viewfinder

The exif in Aperture 3 both showed 0ev



Next shots were in AV
iso 1600, .3", f/16 and the viewfinder showed +.7 automatically
iso 1600, 1/5, f/16 to bring the viewfinder to 0
iso 1600, 1", f/16 to bring the viewfinder to +2




So now my knowledge of this is beginning to change but not completely understood. Here's what I think is going on and please correct my misconceptions.

EV compensation only deals with the amount of compensation that the CAMERA actually made, not the photographer. For the pictures I took in M, the camera made no adjustments. The adjustments I made where physical decisions on my part so there was no compensation that the camera needed to take. I "manually" overrided them. Is this correct?

When I switched to AV the camera wanted to keep my same settings at f/16 but the best it could do was .3" which in turn made my exposure +.7 as stated in my exif data? (this is the part I'm most confused about) Why did it not meter to "0" and make my exposure faster?

The last 2 shots in AV I manually controlled the +/- to get 0 and +2 and it showed in the exif. So why did it not show in M?
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