Distance from subject???

kitkatdubs

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Okay so here's my question. I understand aperture, ISO, and shutter speed. But I am trying to figure out is distance from my subject. For example, if I'm shooting a family of 4 at a f/1.8 ; how far away from them do I need to stand in order for them to be in focus?

Also, what the ideal f/stop for shooting 1 person, 2 person, 3 persons etc- so everyone is in focus? I seem to always be getting someone out of focus in my photos at a low f/stop. I have see DOF calculators, but they just don't make much sense to me.

Today, I am shooting my first maternity shoot and want to make sure that her whole body is in focus... so would I use the focus points and JUST focus on her face or would I use the focus points that focus on all of her body??

Thanks so much!!
 

KmH

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How far depends on the focal length of the lens you're using.
You also need to consider the point-of-focus distance as it relates to depth-of-field.

Few maximum aperture f/1.8 lenses deliver their sharpest focus at f/1.8.
Generally the lens needs to stopped down 2 or so stops before the lens will produce it's sharpest focus.

A Stop
A stop of exposure 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.

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.
 

astroNikon

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but at f/1.8 on a 50mm lens
in a nikon crop camera

and you want to get 3 people deep at say about 4 feet deep of focus
you'l have to be about 21 feet away
assuming you Focus on a subject that is essentially in the middle of that 4 feet deep of focus.
A Flexible Depth of Field Calculator
 
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kitkatdubs

kitkatdubs

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Okay so it's all based on perspective is what I gather? So for my maternity shoot, I'm going to use my 24mm f/2.8 fixed lens. If I'm taking maternity photos of just the woman, would it be best to like a 5 to make sure she is in focus? What about when her two daughters join her in the photos? I just still don't understand how far away I should be from her to make sure she is fully in focus...
 
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kitkatdubs

kitkatdubs

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Also, when shooting multiple people, should I be focusing on the middle of the photo? Or should I use all focus points?
 

astroNikon

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All Focus points ?

When I shoot portrait - I'm no Pro - but I use Single Point Focus Point and I select someone's eye. Shooting at a shoulder level.

I never let the camera decide any thing if indoor.

here's an idea

go get a couple tape measures
Put them as a + on the ground.

set your camera on a tripod
take photos at every other F stop (or each if you want) at f/1.8, f.2.8, 5.6, 7.1, 8, up to 22 etc with a Single Focus point right where the 2 tape measures cross

Then first compare the f/1.8 to the f/22 photos. Notice the out of focus areas
then start comparing them more closely together.

It's hard to explain, unless you yourself start experimenting and seeing the results.
The articles I posted show that same thing but you have to look at the pictures, otherwise experiment with it yourself.
 

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When DOF is critical, I'd prefer manual focus. That puts the point of focus exactly where I want it.
 
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kitkatdubs

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Thanks for the image above! Very helpful... wasn't aware of the distortion. I love my 50mm lens but not comfortable with it yet so I was going to use my 24mm today for the maternity shoot b/c I seem to know how to use it better for some reason, maybe b/c its wider.
 
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kitkatdubs

kitkatdubs

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Obviously experienced photographers don't use DOF calculators so is this something that is just learned over time- like how far away to stand from a subject when shooting at certain f/stop???
 

astroNikon

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Obviously experienced photographers don't use DOF calculators so is this something that is just learned over time- like how far away to stand from a subject when shooting at certain f/stop???
take one test shot, then zoom into it on your LCD
then repeat until the DOF is the way you want it.
it does becomes easier over time

some cameras also have a DOF button next to the lens, which helps a little
How to use the depth-of-field preview button on your dSLR - CNET
 

SCraig

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Obviously experienced photographers don't use DOF calculators so is this something that is just learned over time- like how far away to stand from a subject when shooting at certain f/stop???
Why "Obviously"? I use them frequently, even have one on my phone.

Lenses used to have DOF scales engraved on them so one could get an idea of the depth of field by looking at the scale. Not so common these days though since all one has to do is look at the LCD and see if everything they want to be in focus is in focus.
 

480sparky

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I must be experienced as I've never used a DOF calculator in the field. At least not when actually out shooting.

I do, however, use one on occasion to do 'what if' games.
 

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Thanks for the image above! Very helpful... wasn't aware of the distortion. I love my 50mm lens but not comfortable with it yet so I was going to use my 24mm today for the maternity shoot b/c I seem to know how to use it better for some reason, maybe b/c its wider.

A 24 mm lens, even on a crop body, will give lots of distortion, particularly when the subject is close and fills the frame.
 

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