Brightness Curve

[Arjung]

I have taken 2 sets of images at different apertures. My camera settings are Matrix metering and Aperture Priority. In both cases the shutter has halved as I move from 5.6 to 8. The brightness curves are very different with 5.6 appearing much brighter than 8.

Why is this happening?

Nikon D800, 28-300 3.5-5.6
1st image: 5.6, 1/500, ISO 1600, Matrix
2nd image: 8, 1/250, 1600, Matrix
3rd image: 8, 1/500, 3200, Matrix, -0.3 EV
4th image: 5.6, 1/1000, 3200, Matrix, -0.3 EV

[Shadowman]

Nice shots.

[Arjung]

Thanks John, my dogs are my subjects for me to improve my photography. I am particularly fond of wildlife photography, these subjects are perfect to practice on.

Any thoughts on why 5.6 is brighter than 8?

[Shadowman]

Thanks John, my dogs are my subjects for me to improve my photography. I am particularly fond of wildlife photography, these subjects are perfect to practice on.

Any thoughts on why 5.6 is brighter than 8?

Hi Arjun,

1 stop of light difference. Check out the link below and play around with the chart.

http://www.photonhead.com/beginners/stops.php

[Manfred M]

Matix metering examines the light of the whole scene, not just the subject. The one thing that one sees is that the camera shifted a little between each set of shots, so the light that the metering system was evaluating would have been a little bit different from shot to shot.

Had you taken the shots in rapid succession (so that there are no changes in the lighting) using a tripod and not varied the scene at all, the results should have been "identical" so far as the exposure is concerned.

One thing that puzzles me a bit is that you used negative exposure compensation of 1/3 stop in the second set. Why did you do that? Nothing in the scene suggests to me that this would be necessary.

[Mike Buckley]

The brightness curves are very different with 5.6 appearing much brighter than 8.

The histograms of the first pair of images are almost exactly the same. The histograms of the second pair are only a little different.

In addition to everything Manfred mentioned, keep in mind that the combination of matrix metering and aperture priority is very good though not perfect. When using a tripod in a studio situation, when photographing inanimate objects, when using the exact same lighting and when leaving the focus point in exactly the same place, on very rare occasions I've experienced that the exposures are not consistent from image to image.

When I used to follow this stuff, many Nikon cameras were reported to create different exposures of the same scene if a single point of focus was used and if it was changed from landing on a dark spot in the scene to landing on a bright spot. As an example, this was well documented for the D80 (which I paid attention to because I owned one) but I don't remember how much of a problem it is for your D800.

[Dave Humphries]

Hi Arjun,

In the first pair, I think it is uncorrected vignette effect caused by the lens, which, at f/5.6 is approaching wide open when the focal length 210mm.

It is probably the same in the second pair, albeit shot at 180mm - and I say this because if viewers switch between the shots, you'll note the grass at both edges of frame is darker in the f/5.6 shots than the f/8 ones (and the centre brighter).

Also at play might be Nikon's D-Lighting, I couldn't tell from the EXIF data if that was in use.

To my mind, the metering method is irrelevant, if the EXIF is to be believed* whether it was shot Auto, Manual or whatever, if the exposure ought to be the same because the ISO is unchanged between a given pairs and the aperture and shutter speed change by one stop in opposite directions, it should be the same - you'd think

* However, shutter speeds (especially) are not always consistent, sometimes this is visible in EXIF (e.g. 1/250 may also be shown as 1/256), but the differences are usually a few percent and unlikely to result in a noticeable brightness variation.

Another possibility is that the lens isn't accurately giving you those apertures because the iris is sticky, but I doubt it is this, since you might expect the f/5.6 one to be darker.

I expect you wouldn't get the same result with a zoom lens with narrower zoom range than 28-300mm (f/3.5-f/5.6) and the effect is one of the lens' design compromises.

That said, I have seen inexplicable differences between some of my shots too, on odd occasions (and not with that lens), but have ignored it.

Enjoy, Dave

[Arjung]

Yes I do agree that the camera has shifted ever so slightly as my focus mode is AFC Single Point. So if the dog moves, chances are I have followed his eye.

I use negative EV to do get a slightly higher shutter speed and avoid pushing up the ISO to 6400 which generates more noise, unless necessary. When I see wildlife (dawn & dusk are some excellent times) I push the ISO to 6400 and get down to -0.7EV.

One of the drawbacks of a high megapixel camera is the minutest of camera shake, the remedy for which is either using support or if handheld a higher shutter speed. The dogs move around at high speed and are often in the shade, where the shutter halves. Ideally in action I look for shutter of at least 1/1000 to freeze. As I am shooting in RAW, I feel 0.3 is an acceptable compromise for higher shutter.

Look forward to your thoughts and comments

[Arjung]

Thanks for the inputs Mike.

I spend my time photographing wildlife and use AFC Single Pt focusing as I believe sharp eyes is one of the firsts to have a decent image. Composition follows. I would welcome your thoughts and comments on this

[Arjung]

Thanks Dave. Your inputs are very valuable. Rather than break my head on why the brightness curves are different, it may be more important to focus on the lighting and composition

[Manfred M]

I use negative EV to do get a slightly higher shutter speed and avoid pushing up the ISO to 6400 which generates more noise, unless necessary. When I see wildlife (dawn & dusk are some excellent times) I push the ISO to 6400 and get down to -0.7EV.

Sorry, things do not work this way and you are not using the exposure compensation (EC) function as it was designed.

Digital noise does show up at higher ISO values, but even more so in underexposed images, especially in the shadow areas. By using EC, you are effectively underexposing the shot and are likely getting more noise than if you shot at the higher ISO.

EC is designed to give the photographer a bit more control in situations where the lighting in the scene fools the reflective light meter in a camera. A camera will tend to overexpose scenes that are predominantly dark (for example night scenes) and underexpose predominantly light (for example, snowscapes) scenes.

[Mike Buckley]

This is to confirm Manfred's point that the ideal way to achieve the least amount of noise is to nail the perfect exposure. That's true even if doing so drives up the ISO. Keep in mind that you can lower the ISO by using a larger aperture.

My thinking is that most people are overly preoccupied with noise. If noise is present in my images but can't be seen when the image is viewed at 30% or less of the full-size display, I couldn't care less about the noise so long as I'm displaying at that size or smaller, which is 99% of the time for me. If I make a print that requires using an image file at greater than 30% of the full-size, I'll deal with the noise at that time and not before.

I agree with your priority of getting at least the near eye of an animal sharply in focus and making composition slightly less important. However, I would add to that that any concern about noise should be an even lower priority. Even so, if you want to make elimination of noise a higher priority, that indicates to me that nailing the exposure should be second only to achieving sharp focus.

[Arjung]

Manfred & Mike,
I will experiment with the ISO & EC (I shoot over 100 photos everyday for my learning) once I get my camera back from the service center. I dropped it and broke the viewfinder. Kicking myself for it. I will revert with my inputs as you guys are very knowledgable about photography. I believe the best way to improve your photography is to keep experimenting; once the theory is as simple as driving a car you can focus on the composition.

Mike, what you say is interesting about noise. I have a 20"x30" tiger photo hanging in my living room shot at ISO 6400 and 1/1000 walking towards me. Unless you are a foot or two away you cannot see the noise, that is in the dark areas only

[Manfred M]

I believe the best way to improve your photography is to keep experimenting; once the theory is as simple as driving a car you can focus on the composition.

Blind experimentation might be fun, but it can lead down false roads and can lead to frustration. Understanding, at least at a high level, the underlying technology and how it impacts your final image. A lot of people associate (sometimes incorrectly) that high ISO does impact digital noise, but they neglect other high ISO issues that are just as closely linked to high ISO, namely reduced dynamic range and reduced colour depth. When it comes to ISO, the best performance will be at base ISO, and these other factors will degrade as you increase ISO. The rule (which was there in film days too) is that the lowest ISO will give you the best image quality.

Mike, what you say is interesting about noise. I have a 20"x30" tiger photo hanging in my living room shot at ISO 6400 and 1/1000 walking towards me. Unless you are a foot or two away you cannot see the noise, that is in the dark areas only

The dark shadow areas are where you would expect to see the noise, so this is no surprise. Things can be done in how you shoot and afterwards in post-processing to somewhat mitigate the noise issues.

[Mike Buckley]

I have a 20"x30" tiger photo...walking towards me.

I would absolutely get rid of any photo that is walking toward me even if it displays no noise whatsoever.

[Manfred M]

I would absolutely get rid of any photo that is walking toward me even if it displays no noise whatsoever.

With your well established love of fine wines, I wonder if this is a "cause and effect" issue...

[Arjung]

Thanks Manfred,
Your points on ISO are well appreciated. But when I need to freeze action in low light I have to compromise and push up the ISO rather than get a blurry photograph

[Manfred M]

Thanks Manfred,
Your points on ISO are well appreciated. But when I need to freeze action in low light I have to compromise and push up the ISO rather than get a blurry photograph

I totally agree; the highest ISO setting on your camera might be the lowest ISO that you can use, under certain lighting conditions.

On the other hand, if you have good lighting conditions and are shooting a stationary object, you should not be shooting at ISO 6400, if you want the best image quality.