How close do I have to be to a subject for it to be in focus at f/1.8?

[madisonofriel]

If I wanted to use low apertures (like 1.8-2.8) how far away can I be for it (the persons EYES) to still be tack sharp?
I know that It make the DOF much smaller, But I have no idea how to calculate what distance I should be from the subject. I have tried DOF calculators, but they don't really help.
Please help me clear this up.

 

[MOREGONE]

Lenses have a minimum focusing distance. I am not sure if it is always, but most lenses have the range right on the lens that it can focus on, from Infinity to 0.30 meters for example.

It will change from lens to lens so check out each of your lenses. Macro lenses can get really close for example while some others like large zooms can like be 3ft/1m.

Check out this article by Nikon and it should give you some additional info

Nikon | Imaging Products | DSLR Camera Basics | Minimum Focus Distance

 

[astroNikon]

IF they are standing perpendicular to the camera it should be kinda easy to get both eyes in focus.
If they are at an angle you have to know the distance to cover both eyes.
Of course, their nose and hair may be out of focus in the perpendicular one

use this calculator to determine the Depth of Field. ==> Online Depth of Field Calculator

You enter the camera type (basicallly the sensor size)
focal length you are using
f stop
and distance away, as that can vary the focus depth greatly too

here's another good calculator with a in-depth explanation ==> A Flexible Depth of Field Calculator

Pull out a tape measure and start testing on a ruler or stuffed animal so you can practice and see the OOF and In-Focus areas dependent upon subject angle, distance, aperture and how it correlates to the calculator.

 

[weepete]

Ninjaed!

Also tack sharpness is about more than being in focus.

 

[Braineack]

If I wanted to use low apertures (like 1.8-2.8) how far away can I be for it (the persons EYES) to still be tack sharp?

the closer you are, the narrower the DOF becomes.

assuming the subject is directly face on to camera, you can maintain tact sharp eyes from the min. focus distance all the way back to the horizon line.

 

[madisonofriel]

Ninjaed!

Also tack sharpness is about more than being in focus.

?? Yes I know. But its pretty important.

 

[madisonofriel]

If I wanted to use low apertures (like 1.8-2.8) how far away can I be for it (the persons EYES) to still be tack sharp?

the closer you are, the narrower the DOF becomes.

assuming the subject is directly face on to camera, you can maintain tact sharp eyes from the min. focus distance all the way back to the horizon line.

Even at 1.8? I have not been able to do this successfully. Say I'm like 10ft away from a person... Can I use 1.8?

 

[madisonofriel]

Lenses have a minimum focusing distance. I am not sure if it is always, but most lenses have the range right on the lens that it can focus on, from Infinity to 0.30 meters for example.

It will change from lens to lens so check out each of your lenses. Macro lenses can get really close for example while some others like large zooms can like be 3ft/1m.

Check out this article by Nikon and it should give you some additional info

Nikon | Imaging Products | DSLR Camera Basics | Minimum Focus Distance

This really helps... But how do I figure the MAXIMUM distance I can be away?

 

[Braineack]

yes.

on my camera, if I was standing 5ft from you and wanted to take your picture at f/1.8 with a 35mm, my total DOF would be about half an inch. enough to just have the plane of your eyes in focus if you stared DIRECTLY at me. if you were on any sort of angle to me, only 1 eye would be in focus.

If I stood back to 10ft, the DOF at the same 35mm f/1.8 would be increased to 1.7ft, so now your entire head should be in focus. it will be VERY small in the frame, but it will be sharp.

 

[The_Traveler]

use dofmaster.com and its online dof calculator and all your questions will be answered exactly.

 

[KmH]

The focal length of the lens is as important a factor as the lens aperture when wanting to figure the distance you to need to be.
To get the same DoF you need to be 2x further away with a 100 mm lens than with a 50 mm lens to get the same DoF from both lenses with a small lens aperture like f/1.8.

By the way, most lenses that have f/1.8 as their maximum aperture need to be stopped down a couple of stops to about f/3.5 before they start to deliver their sharpest focus.

 

[astroNikon]

Also, how are you focusing ?

Is your focusing system (what kind of camera?) on an AUTO mode so that the camera identifies what it is going to focus on
Or are you using a Single Focus Point so YOU can identify where it is going to focus ?

To do this stuff you really need to be in Single Point Focus Mode so that you identify exactly what point should be in focus.

 

[enzodm]

If I wanted to use low apertures (like 1.8-2.8) how far away can I be for it (the persons EYES) to still be tack sharp?
I know that It make the DOF much smaller, But I have no idea how to calculate what distance I should be from the subject. I have tried DOF calculators, but they don't really help.
Please help me clear this up.

I try another road, since it seems to me that you suppose there is a link between aperture and distance.
Aperture is not constrained by distance: you can use 1.8 at any distance, from the minimum allowed by the lens to infinity. You are in one place, your subject is at another one, and that's almost all.
To have eyes on focus, you need to focus on (one of) them, and DOF will be around them (from slightly in front, to slightly back). DOF calculators give you how much in front and how much on back (or the sum of both). As told by others, if eyes are not parallel to the sensor, at those small apertures there is some risk that one is out of focus, because outside the DOF limits.

 

[madisonofriel]

If I wanted to use low apertures (like 1.8-2.8) how far away can I be for it (the persons EYES) to still be tack sharp?
I know that It make the DOF much smaller, But I have no idea how to calculate what distance I should be from the subject. I have tried DOF calculators, but they don't really help.
Please help me clear this up.

I try another road, since it seems to me that you suppose there is a link between aperture and distance.
Aperture is not constrained by distance: you can use 1.8 at any distance, from the minimum allowed by the lens to infinity. You are in one place, your subject is at another one, and that's almost all.
To have eyes on focus, you need to focus on (one of) them, and DOF will be around them (from slightly in front, to slightly back). DOF calculators give you how much in front and how much on back (or the sum of both). As told by others, if eyes are not parallel to the sensor, at those small apertures there is some risk that one is out of focus, because outside the DOF limits.

So, let me see if I have this straight...
As long as you're the minimum away from the person facing you, and you focus on the eyes, You can use whatever aperture you want?
It makes sense, but I cant seem to be able to do it.
For example, this was taken at 1.8 in a low light room... and it is blurry as heck.
How can you make sure it is focused on the eyes?

 

[astroNikon]

How can you make sure it is focused on the eyes?

If you are doing portraits you want to be at f/5.6 - 7.1 for simplicity

You have to learn about your focusing modes on your camera. See my post above
To focus specifically on an eye you have to be in a Single Focus Point mode and thus focus on ONE eye. You CANNOT be in an Auto mode because you are then letting the camera do the thinking.

This does not mean that both eye will be in focus. This is dependent upon your Depth of Field which is based on your distance and aperture .. see the DOF calculators about that.

You might want to tell us what camera you have .. then someone can give you more info on your focusing modes and how to change them.

Keep in mind. just because you have a lens capable of f/1.8 does not mean f/1.8 is the best setting for what you are attempting to do. At some point you may have to ADD more light if you are taking a picture of people

- You can raise the ISO which makes the camera more light sensitive, but may introduce noise.
- You can lower the shutter which may introduce movement if too low. But generally try to stay above 1/120
- you can use a lower f/1.8 which allows more light in but gives you a shallow depth of field (the problem here).
- or you add light - brighter room or flash

Generally. With the proper DOF (aperture) selected, the proper shutter speed. Then a good ISO that doesn't introduce too much noise. If it's still dark then you have to add Light somehow.

In the photo you have alot of light coming in on the side, which is a different problem. You could use a reflector to reflect the incoming light back onto the front of the subjects, adding more light.

But you still need to know how to properly select a focus point for proper DOF