What is the impact of physical distance to a photo taken with a fixed lens setting?

[mdodwell]

Hi All,

I was wondering the what the impact of the following is on a photo. I am very much a beginner and am trying to understand, bit by bit, the aspects of camera work etc work with each other.

I am basing this scenario on the equipment I have, a D3000 camera and a 15-55mm lens.

If I was to take a say, portrait photo and i set the lens at 55mm and an aperture of f/5.6, then proceed to take a series of photo's of the same subject, in the same pose, etc, but, after each photo took, say, a meter step back until I reach about 10m. If I kept the setting the same after each step, how would this affect the photo and why.

I will try this out over the next few days to experience first hand, but at nearing 21:00 its a bit dark to go out LOL.

Cheers
Matt

[Photosbykev]

Assuming you are shooting in automatic mode either shutter or aperture priority then as you move back the main subject becomes smaller in the frame and the metering system will start to be affected by the region around the subject. The metering system is always trying to produce an average exposure based on the the value of 18%, something like a mid gray in black/white terms or green grass.

If the background is very bright the camera will reduce the exposure and the main subject becomes underexposed if the background is dark the camera will increase the exposure and the main subject will be overexposed.

[teaking]

If im understanding correctly, and you lock your focal length at 55mm and lock your exposure @ F5.6 and keep the same shutter speed and focal point, pose etc etc

Every time you step back your just going to have a different point in focus and the person posing is going to get very blurry.

If you leave it set to auto focus and lock the exposure your subject is just going to be in focus further away.

If you only lock the aperture then your shutter speed may change a bit to.

To sum it all up its the same as a prime lens vs a telephoto you can still focus at different points on a prime only that you cant zoom in your limited to that focal length.

[OsmosisStudios]

Teaking: thats assuming the focus stays locked. if the camera focuses each time, then the image will still be in focus: the only thing that will change is that the subject will be smaller and smaller.

[teaking]

Os:

I knew there was an easier way to explain what I was trying to say... and you just did it haha
Thanks for the heads up.

[zona5101]

The depth of field will also increase. At f5.6 55mm the near to far dof is 2.15 feet at 20 feet it increases to 9 feet....

[edbayani]

another thing that will change is the size of the background in relation to the subject.
if there is an object in the bg. measure the size of that object against the size of the head of the subject. as you step back till you reach 10m. measure again the object against the head of the subject and you will notice the object in the bg is smaller.

[sybren]

Originally Posted by edbayani

another thing that will change is the size of the background in relation to the subject.
if there is an object in the bg. measure the size of that object against the size of the head of the subject. as you step back till you reach 10m. measure again the object against the head of the subject and you will notice the object in the bg is smaller.

That shouldn't be influenced. Indeed, both the subject and the objects behind her will get smaller as you move further away, but they should do so linearly. What you describe happens when you zoom out.

[edbayani]

if you zoom the lens only the image will get bigger but since you do not move farther from the subject, the bg object will remain the same.
try shooting and measuring
the bg object against the subject as you move away from the subject.
this is called perspective.

[sybren]

Originally Posted by edbayani

if you zoom the lens only the image will get bigger but since you do not move farther from the subject, the bg object will remain the same.

The background object gets smaller when you zoom out. If only your subject changes and the background stays the same, you're not looking through a camera but using some nice drugs.