Need photo critique

[gossamer]

Hi, I have a Nikon D300 with a 16-85mm f3.5 (always shooting raw) and have a couple of questions about some pictures I took today. I was using the polarizer for the later part of the day, although I probably shouldn't have been.

I set the camera up for aperture-priority and 32mm focal length, and the shutter was at 1/60th, f5, with 250 ISO. The picture is bright and a bit overexposed. This was my staging shot for the scene.

I then somehow changed the focal length to 30mm, which changed the shutter speed to 1/320th, f5, still at 250 ISO. This picture is clearly underexposed.

The third picture was my best attempt at fixing it post-production with the few photoshop/camera raw skills I have.

My questions are, why would the picture be overexposed or underexposed when I was in aperture-priority? Should it automatically adjust the shutter speed to prevent this very problem from happening?

I also don't understand why the background is not blurred. The aperture was only at f5, which is typically low enough with this lens to create the blurred background effect. This may be a topic for a completely separate post, but I can't figure out why the preview button on the front of the camera doesn't perform as I expect. Every time I press it, it makes a click like it's going into aperture preview, but there's no visual difference.

Sure would appreciate any ideas you might have on the differences between these pictures!

 

[KmH]

For C&C:
Photography Beginners' Forum
Don’t be shy. Use one of the forums in the - Photo Galleries - Photos submitted by members for general display or critique - section of TPF if you want C&C improvement tips on some of the photos you have taken. For equipment specific questions, use one of the forums in the Camera Forum section of TPF. Brushing up on some of the basics? The Beginner's forum is for asking basic technical photographic questions about things like shutter speed, aperture, ISO, white balance, metering modes, focusing modes.

The background is not blurred because of how far from the camera the point-of-focus (PoF) is.
Lens aperture is not the only factor that determines depth-of-field (DoF). PoF, lens focal length, and image sensor size also contribute.
To get a shallow DoF and a blurred background you have to be closer using that focal length.
Understanding Depth of Field in Photography
Camera Exposure: Aperture, ISO & Shutter Speed

1/320 is about 2.5 stops less than 1/60. A stop faster shutter speed reduces the amount of light getting to the image sensor 2x.
Two stops means 4x less light gets to the image sensor
Two and a half stops means 10x less light gets to the image sensor.
Three stops means 16x less light gets to the image sensor.

What is A Stop?
A stop is a fundamental photography concept.

A 'stop' is a doubling (2x) or a halving (0.5x) of the amount of light that reaches the recording media be it film or an electronic sensor.
A stop change in exposure can apply to shutter speed, lens aperture, and/or ISO.

Since exposure is a triad of adjustments (shutter speed, ISO, lens aperture) you can change 1, 2 or all 3 of the triad settings.

If you want 1 more stop of exposure (brighter) you can adjust just one of the 3 by 1 more stop.
Or, you can change 2 of the 3 by 1/2 more stop each for a net gain of 1 stop of exposure.
Or, you can adjust all 3 by 1/3 more stop for a net gain of 1 stop of exposure.

You can also change the triad of settings and have no change in the exposure.
If you change 1 of the 3 settings by 1 stop more exposure and change a 2nd setting by 1 stop less exposure the net change is zero.

Suppose you subtracted a stop of shutter speed to help stop subject motion, you could add a stop of lens aperture to keep the exposure the same. However, adding a stop of aperture will also affect the total DoF by a small amount. So, if you don't want the DoF to change you would add a stop of ISO instead, however, adding a stop of ISO will increase by some amount the image noise in the photo.

Note: DSLR cameras are set by default to adjust the exposure settings in 1/3 stop increments.
Most DSLR cameras let you change that to 1/2 stop or 1 stop increments.
However, the advantage of 1/3 stop step increments is more precise control of exposure.

 

[gossamer]

The background is not blurred because of how far from the camera the point-of-focus (PoF) is.
Lens aperture is not the only factor that determines depth-of-field (DoF). PoF, lens focal length, and image sensor size also contribute.
To get a shallow DoF and a blurred background you have to be closer using that focal length.

Okay, I suspected this was the case. I guess I was looking for something more specific.

1/320 is about 2.5 stops less than 1/60. A stop faster shutter speed reduces the amount of light getting to the image sensor 2x.
Two stops means 4x less light gets to the image sensor
Two and a half stops means 10x less light gets to the image sensor.
Three stops means 16x less light gets to the image sensor.

I understand this. However, I don't understand why my camera didn't automatically adjust the shutter speed properly when I was in aperture-priority to compensate for the changed focal length. Instead, it choose a faster shutter speed, lessening the amount of available light, making the picture darker.

The camera was in aperture-priority, so I don't understand why it didn't produce a properly exposed picture.

Note: DSLR cameras are set by default to adjust the exposure settings in 1/3 stop increments.
Most DSLR cameras let you change that to 1/2 stop or 1 stop increments.
However, the advantage of 1/3 stop step increments is more precise control of exposure.

Maybe this is why. Would that explain the difference here? I'll have to check the camera in the morning. Sure wish I could go back and take the shot again.

I wish there was an exposure meter in the same way there is with manual focus. Had I not been a hurry (we weren't supposed to be taking pictures there and everyone was in a hurry to leave), I would have shot in manual, framed the picture better, and had no one to blame for a poor exposure but myself...