Beginner Exposure calculation from camera

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#1
I've been experiencing something I can't make much sense of recently regarding the automatic exposure calculation with my camera, at least I think it's that.

Most of my shooting as at airshows and car shows, for static displays my settings are usually:

In sunny weather:
ISO 100
Aperture priority (most the time this usually as open as possible for least DOF)

I always keep in mind that when moving into darker locations, one of these could bring a bottlneck (usually ISO/shutter) and I change it accordingly. However what I find is, that in certain outdoor sunny shots even with plenty of light, the camera will think the composition is bright enough (exposure meter at dead center) but you take the picture and it's clearly darker and not ideal. Sometime's this happens vice versa too, but usually it's darker. I have to then use exposure compensation to sort the next one out. This seems to be related to that particular composition/scene. but on a full day of shooting I will probably see this on about 5% of shots maybe.

This has been quite common in my experience for the past few months, pretty consistent.

I was at RIAT recently and started seeing this on a couple of shots also, and after about 200 shots I thought I'd try full AUTO without flash a go. This is automated everything except flash. I found the exposure calculation to be spot on in this mode, for the next 500 shots at least. It always calculated it perfectly. I then thought to myself why not just use this instead of faffing with A mode.

I'm probably going to get questioned that in those bad exposure shots, are you sure something wasn't bottlenecking the exposure, but I have consciously checked the exposure meter in the viewfinder and the camera think's the exposure is correct.

I was using my kit lens for the static shots 18-55

What is it I'm seeing here?
 
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#3
However what I find is, that in certain outdoor sunny shots even with plenty of light, the camera will think the composition is bright enough (exposure meter at dead center) but you take the picture and it's clearly darker and not ideal.
The camera is trying to avoid blow out highlights probably.

No point having a mostly perfectly exposed picture but blobs of blown out white nothing.
 
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Elliott
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#4
you need to look into metering modes and find out what each does and why.

When you are pointing your lens into the sky the camera thinks it's overly bright and tries to compensate for this by reducing the exposure (basically the camera is trying to achieve 18% grey as an average). You need to either override this using exposure compensation or you could switch to spot metering so that the cameras meter ignores the sky and just meters for the aircraft.

The same will happen if you are shooting something with a very dark background. Again the camera will try to compensate by increasing the exposure, thus making it to bright.

Here's a bit of homework ;)

https://www.youtube.com/results?search_query=metering+modes
 
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#5
Sorry for omitting that detail.

I was using center weighted.

Matrix normally gives bad results because of the strong light and spot is too inconsistent.
 
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Steve
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#6
As above, even with centre weighted, the camera is still metering the entire scene (but favouring the centre) so a wide blue sky leads the camera to underexpose the central subject slightly. Ideally, your best bet is to shoot RAW and increase shadow exposure to compensate in post.
 
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#7
As above, even with centre weighted, the camera is still metering the entire scene (but favouring the centre) so a wide blue sky leads the camera to underexpose the central subject slightly. Ideally, your best bet is to shoot RAW and increase shadow exposure to compensate in post.
I found myself doing exactly this, after my session at the airshow, I found myself needing to adjust most pictures.

What I don't understand is why AUTO mode gave better more consistent results.
 
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#8
I found myself doing exactly this, after my session at the airshow, I found myself needing to adjust most pictures.

What I don't understand is why AUTO mode gave better more consistent results.
The simplest way is to compare the EXIF information between those shot in auto mode and those shot in aperture priority. If anything, the camera was likely stopping down the aperture to let less light in (and prevent overexposure).
 
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#9
I found myself doing exactly this, after my session at the airshow, I found myself needing to adjust most pictures.

What I don't understand is why AUTO mode gave better more consistent results.
My guess is that in Auto mode you were getting .jpg images out of the camera, so the camera had already done the processing for you. When shooing raw you get exactly that. A raw image.
 
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#10
I always use spot metering, especially at airshows with and usually expose to the right slightly.

The worst results seem to come from clouds on a sunny day as these tend to be lighter than the blue sky. As mentioned above the camera wants to make an average grey so then the entire composition tends to be alot darker. I also find that autofocus struggles with clouds in the background and points can shift.

Blue sky tends to give perfect results as its nice and clean and gives good contrast to the subject you are photographing. I was at RIAT on sunday and the conditions were just perfect (for once), Duxford the day before had a lower rate of keepers due to the clouds.
 
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#11
I found myself doing exactly this, after my session at the airshow, I found myself needing to adjust most pictures.

What I don't understand is why AUTO mode gave better more consistent results.
Auto modes normally default back to Multi/Matrix metering. This is a more advanced mode than Centre Weighted, and from what I have read in the past, compares what it 'sees' to scenes in its memory, sunsets for example amongst many more, to try and get more accurate exposure more often. An Auto Mode will also most often be Jpegs, may default to a specific Scene Mode it 'thinks' is appropriate if it is an 'Intelligent Auto', and that will also have a Picture Control/Picture Style applied depending on what type of scene it thinks it is which will affect colours, contrast and sharpness. Auto Modes do a lot more than just set Shutter, Aperture and ISO. Obviously the downside it is making all the decisions and may not really know what it is 'looking' at. ;) If it works in a certain situation though, use it. ;)
 
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#12
EXPOSURE: Simplified & non-technical explanation.



The first thing to realise is that the light falling on a scene determines what the exposure should be, the light reflected from a scene varies according to what is doing the reflecting. As camera meters measure reflected light this can cause problems. If you were to measure the light falling on the scene, using an incident light reading, you would not have to worry about adjusting exposure for different scenes which reflect different amounts.



Your camera is taught that all scenes reflect 18% of the light falling on them (Digital cameras may be taught that it is 14% or 12% depending on the camera but I will continue with 18%)



First consider taking a picture of a landscape which, on average, is reflecting 18% of the light falling on it.

When your camera is pointed at the landscape it thinks ' That scene must be reflecting 18% of the light falling on it so I need to set an exposure to suit that light. '

If the light gets brighter the camera thinks ' That scene is still reflecting 18% but it is brighter now so the sun must have come out so I need to reduce the exposure to suit the new brighter light '

If the light gets dimmer the camera thinks ' That scene is still reflecting 18% but it is darker now so the sun must be behind a cloud so I need to increase the exposure to suit the new dimmer light'



So far so good but what about scenes which reflect more than 18% such as snow.

When your camera is pointed at the snow scene it thinks ' That scene must be reflecting 18% of the light falling on it but it is very bright so it must be very sunny so I need to reduce the exposure to suit the very bright light '

This means that, although the camera meter shows the exposure as correct, it has actually reduced the exposure and will cause the white snow to be grey.



A similar thing occurs when you photograph a very dark scene, a black horse for example.

Your camera thinks ' That scene must be reflecting 18% of the light falling on it but it is very dark so it must be very overcast so I need to increase the exposure to suit the very dim light'

This means that, although the camera meter shows the exposure as correct, it has actually increased the exposure and will cause the black horse to be grey.



Having read and hopefully understood all that many digital cameras have an in-built library of shots which your shot is compared with, the camera can then think 'OK that shot is very like the snow shot that I have in my library so I will overexpose it a bit' I am only familiar with my Nikon and that compares shots with its library when it is in Matrix metering mode and not in the other modes.



The best solution to all the above is to use the histogram, this will show you what you have recorded and you can can use exposure compensation to get the correct exposure for that particular shot – making whites white or blacks black.
 
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#13
Thanks for all your input, but I'm not sure we are along the right lines here. I now have some sample shots, I'll explain exactly what I see.

https://photos.app.goo.gl/9c6cesxoUTiMLyw1A

DSC_7401 - auto no flash
DSC_7402 - aperture priority, ISO 200, f-stop at lowest possible setting.

The exposure is worse on 7402. Same composition. Same metering mode as 7401. 7401 was taken at 1/200 ISO400. 7402 was taken at 1/400 and ISO200. The 7402 shot had plenty of space on it's shutter speed to get a higher exposure. Why did it not do it? And why does it do it better on 7401's auto mode? Is there some other setting coming into play? Focus mode maybe? Exposure compensation is the set for both at 0. I don't understand. If I do exposure compensation on aperture priority then it would work, but something wrong is happening with it calculating exposure on the semi manual mode. I also experimented by changing metering modes using this same composition, for the semi auto mode it would make hardly any difference. But the auto shot worked fine.

DSC_7403 - aperture priority, ISO200, 1/320. f-stop at lowest possible setting.
DSC_7404 - Auto no flash. Took it at 1/200, ISO400, 7.1 f stop.

Again, plenty of shutter speed to play with on 7403 but it pushed it to 1/320. It could have just set the shutter speed slower to get a better exposure. Why did it do a better job on Auto mode? I did not leave aperture priority mode with any bottleneck settings. All same metering modes.
 
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#14
The exposure is worse on 7402. Same composition. Same metering mode as 7401.
According to the EXIF data, the metering modes aren't the same in 7401 (matrix) and 7402 (centre weighted). You are using the 'Auto (Flash Off)' Scene mode. I assume this has switched your metering mode. If you use 'P' mode instead, this should leave the metering mode alone (and won't change ISO unless you also turn Auto ISO on). But you may be better off with matrix metering, which seems to have done a better job in this case.
 
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#15
According to the EXIF data, the metering modes aren't the same in 7401 (matrix) and 7402 (centre weighted). You are using the 'Auto (Flash Off)' Scene mode. I assume this has switched your metering mode. If you use 'P' mode instead, this should leave the metering mode alone (and won't change ISO unless you also turn Auto ISO on). But you may be better off with matrix metering, which seems to have done a better job in this case.

Yes, the different metering modes will account for the difference in exposure with these scenes.
 
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#16
According to the EXIF data, the metering modes aren't the same in 7401 (matrix) and 7402 (centre weighted). You are using the 'Auto (Flash Off)' Scene mode. I assume this has switched your metering mode. If you use 'P' mode instead, this should leave the metering mode alone (and won't change ISO unless you also turn Auto ISO on). But you may be better off with matrix metering, which seems to have done a better job in this case.
Ok I did not consider/realize that the metering modes were changing between these modes. Point taken, will keep this in mind.

Mind you, I'm not happy with the matrix one either it's still too dark.
 
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#17
Your always going to get some whacky exposure shots if you let the camera do any of the thinking lol.
 
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#18
Your always going to get some whacky exposure shots if you let the camera do any of the thinking lol.
I think it depends on the camera and its metering system, a high-quality DSLR from one of the top makes will probably get the metering right on auto more often than the operator will get it right on full manual (unless using a hand-held high-quality spot meter and knowing how to use it), and the camera will certainly do the job of metering a lot quicker than a person can!

I use old film cameras on a regular basis and find the matrix metering system on both a Canon EOS-3 and EOS 30 (two advanced cameras from the end of the film era) get things consistently right in 'P' mode in all but strongly backlit situations, within the limits of the exposure latitude of the film I'm using (think dynamic range with digital). My Canon 6D also does a really good job of getting the exposure right in P mode, so much so that I don't usually bother with centre weighted metering options. If shooting an air show then depending on the lighting conditions (and how much of the frame the planes were filling) I'd probably stick to matrix metering and dial in a bit of exposure compensation to ensure the planes in flight came out correctly exposed. However, this isn't something I photograph regularly so some of the air show specialists on here would probably be able to advise you better.
 
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#20
You’ll always struggle if you keep concerning yourself with metering modes, camera exposure modes etc.

And you’ll succeed if you step back and use logic.

How does your meter work?
What’s it looking at, what’s it assuming about what its looking at?

What does Spot metering do? It looks at a circle of <5% of the viewfinder and assumes it’s 18% grey.
What does Centre Weighted metering do? It looks at the whole scene but weights it’s measurement in the central 65% and assumes it’s 18% grey
What does Centre Weighted metering do? It looks at the whole scene and assumes it’s 18% grey, but it uses patterns it’s been trained to spot where there’s areas of light or dark to try to not be fooled.

None of those methods will get you a perfect exposure all the time. And expecting them to is a fools errand.

So step 1: engage brain and look through the viewfinder, what’s it looking at? What is your chosen metering pattern measuring? Is it actually about 18% grey?

Step 2: If it is, the centre of the meter will be perfect, if it’s brighter (the sky) you’re going to need + exp comp, if it’s darker then you’ll need - exp comp (assuming you want/need to show the scene as your eyes saw it).

Step 3: shoot

Step 4: check your image and histogram; is the amount of comp correct? If not adjust and repeat steps 3&4
 
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#24
I assumed this meant a situation where (e.g.) you've locked down two of shutter speed, ISO and aperture (say in a semi-automatic mode like A or S) and the third can't be adjusted far enough to get a correct exposure. The OP knew this wasn't the explanation because the meter would have warned of over or under exposure.
 
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