How Do You Get The Focus/Un-Focused Effect?

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markyg

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I`ve noticed a lot of photos on the forum where the main subject is highly in focus but the background is out of focus. I tried to do this this morning but I suspect my camera (Fuji FinePix A101) isn`t up to the job. Is it a camera effect or is there someway to pull this off?

Cheers as per!!

Case in point!

Winter006Small.jpg
 
Welcome to the world of Depth of field!!!

i will let someone who can articulate the answer into a concise reply, rather than the really long ramble i will probably come out with!
 
markyg said:
I`ve noticed a lot of photos on the forum where the main subject is highly in focus but the background is out of focus. I tried to do this this morning but I suspect my camera (Fuji FinePix A101) isn`t up to the job. Is it a camera effect or is there someway to pull this off?

Cheers as per!!
Click to expand...


WHat you need to read up on is "depth of field". Basically, the area of aceptably sharp focus behind and in-front of the object you have actually focused upon. This changes with focal length and aperture. If you're using an automatic camera, you may have little control over this.

Basically assuming a standard 50mm lens is used on a 35mm camera, to obtain the effect you describe, you need to shoot at a wide aperture.. say F2.8. If you closed the aperture down to say f22, then the blurred background will be much sharper. On a manual camera, you would also have to adjust the shutter speed to compensate.

To fully learn how to use depth of field, you need to learn about reciprocity law. Ok.. don;t panic.. this is easy... a diagram will help.

reciprocity.jpg


Now... look at that table.. you will see apertures down the left, and shutter speeds down the right. Notice something? As the aperture gets wider (lower f number) the shutter speed gets faster! This is the reciprocity, or relationship between aperture and shutter speed. 1/1000th of a second at f2.8 is the same as 1/8th of a second at f22. The same amount of light reaches the film, or chip... the exposure is the same!! So why have the ability to control these two things independantly? For control over things like depth of field, that's why.

As stated earlier, a wide aperture (low number) gives shallow depth of field... your background will be blurred, and a small aperture (high f number) will give a deep depth of field.. sharp background. Howerver, you cant just choose a f number at random, as your exposure has to be correct. If you knew that your correct exposure should be 1/30th at f16, then if you want to shoot at f2.8, you just work it out....

1/30th at f16
1/60th at f11
1/125th at f8
1/250th at f5.6
1/500th at f4
1/1000th at f2.8

You need to increase your shutter speed by 5 stops, and you open up the lens by 5 stops... one balances the other.... The Reciprocity law. The exposure will be identical for all those combinations, but your depth of field will change dramatically.

Other things effect depth of field too. Focal length primarily. Long lenses have inherently shallow depth of field, even when stopped down to max, whereas wide lenses, such as a 18mm on a 35mm camera, has depth of field so deep when opened up, that you hardly even need to focus... so to get the effect you describe, a long lens, with a wide aperture would have been used.

Having a manual camera, or at least manual control over your camera is pretty essential for this. Cameras that allow you to adjust the aperture and then the camera adjust the shutter to match are called aperture priority auto cameras, and lots of auto cameras allow this too.. you need at least this latter option to have full control over depth of field.

Hope I haven't confused you too much.
 
in laymans terms,

the point you focus at is split into thirds,
two thirds are in focus behind the shot, and one third in front
so if you focus at 10 meters away, and at the right depth of field ( blured/unblured) , it could be 2 meters behind and 1 meter in front in focus, and the rest is blurred,

now,, the higher the Fstop also known as aperature the smaller the distance between the focusing points, the larger the fstop,the greater the distance and more is in focus, another way of saying it would be that the depth of field is bigger.

this can be set on ' simple ' cameras by choosing the shooting options , for example, you will have a portrait mode, closeup mode, and mountain( landscape ) mode,
the closeup and portrait will give the blurred effect on anything around 3-7 meters away, the landscape mode will have everything in focus ( pritty much )

hope this helps

MyPix
 
thanks for that Pook, very nicely explained!
 
The simplest way I can think of wording this very tricky subject is to tell you that a lower number of F stop (usually referred to as aperture) will also reduce the distance from front to back of your subject that will be in focus(usually referred to a Depth Of Field) D.O.F.

So basically you need a camera with an aperture priority mode, select a low F stop, ensure that you have the focus spot on your subject and shoot.

There is a lot more to it that this as Pook has touched on, but that’s the basics.

The good news is that if your Fuji doesn’t have aperture priority mode, your new Canon A95 definitely does.
 
Okaeydoke I got most of the above explanations.....the benefits of an engineering degree. So it seems I definately need a better camera if I am to improve my picture quality. Now the question is how much to spend........got £1k coming soon.......ho hum

Thanks again guys, quick explanation and concise!!! Very impressed!
 
This may just cause some (circle of) confusion :wink: but I produced a spreadsheet which you can get here that will give you the depth of field at different focal lengths and apertures.

There are a few assumptions in it, and I would take it with a few grains of salt, but it's fun to play around with different values and see the results.

P.S. If you have £1000 to spend, the 350D was made for you. :D
 
To acheive a shallow DOF in the picture you posted, your camera should have a close up, or macro mode. Try that :)

Kimmett
 
silkstone said:
P.S. If you have £1000 to spend, the 350D was made for you. :D
Click to expand...

Nope if you have a grand, then a second hand 300d (body only for you), the change you can give to me to put to a 350d for me :)

Ta :)
 
Bod said:
silkstone said:
P.S. If you have £1000 to spend, the 350D was made for you. :D
Click to expand...

Nope if you have a grand, then a second hand 300d (body only for you), the change you can give to me to put to a 350d for me :)

Ta :)
Click to expand...


PAHH!!!.......spend it on a real camera like a Nikon D70 , lol

MyPix :wink:
 
Steve said:
The simplest way I can think of wording this very tricky subject is to tell you that a lower number of F stop (usually referred to as aperture) will also reduce the distance from front to back of your subject that will be in focus(usually referred to a Depth Of Field) D.O.F.

So basically you need a camera with an aperture priority mode, select a low F stop, ensure that you have the focus spot on your subject and shoot.

There is a lot more to it that this as Pook has touched on, but that’s the basics.

The good news is that if your Fuji doesn’t have aperture priority mode, your new Canon A95 definitely does.
Click to expand...

Quality - was curious about trying out DOF and this thread has been most useful - I now know how to (in theory at least) and that I can on my camera! :D
 
Good explanation there by Pook. Grasping the reciprocity relationship between shutter speed and aperture and their halving and doubling relationship to each other is the basic key to a good understanding of photography. As you progress you'll find photography is a contant battle and compromise between what you want to do and what the prevailing light will allow you to do. One of the biggest problems is that as the size of the aperture decreases and the shutter speed lengthens, camera shake starts to enter the equation. In other words as we select that small aperture to get everyting in focus from the foreground to the horizon, camera shake becomes more of a potential problem as the shutter speed lengthens. Us human beans are pretty crap camera supports when it comes to long exposures. :wink:


Hand holding the camera.

Grab hold of the thing. don't be afraid to cup your left hand under and around the lens. Pull the camera firmly into you face so that is firmly pressed against your cheekbone and brow. If you wear a neck strap, try winding the slack around your right hand so that it actually tightens the camera into your face Your elbows should stabilise the whole thing by being pulled down onto your chest. Your feet should be spaced for balance, and when you take the shot breath out gently like a marksman as you press the shutter. Practice the technique till it's second nature.

The minimum safe shutter speed for handholding with a 50mm lens is 1/60 sec. That's to eliminate just your movement, and takes no account of any movement in the subject. If you can go faster then you should, but 1/60 is the minimum. That's not to say you should miss a great shot for the sake of trying 1/30 or even 1/15 but it takes practice to achieve those speeds hand held and it's always a bit of a gamble.

The good news is there's a simple way to always know what the safe hand holdable speed is with any lens. ...

The safe speed is equal to the focal length of the lens in use - or the nearest marked equivalent. The longer the focal length of the lens, the more each tiny bit of camera movement will show up in your shots.

28mm 1/30

50mm 1/60 Nearest marked equivalent

80mm 1/125 Nearest marked equivalent

200mm 1/250

500mm 1/500

1000mm 1/1000

Remember these are minimum safe speeds- if you can go faster you should.

Bear in mind that as you vary the focal length on a zoom lens, the minimum safe shutter speed changes. - easily forgotten.

You can see why a good solid tripod (and remote release) is an essential piece of kit if you want to work in all conditions.

Wonder of wonders! we now have image stabilisition lenses (IS) which is something to consider when you're shoppig for glass. These actually give you 2 or 3 stops slower hand-holdable shutter speeds than none IS lenses. Very useful for available light work!
 
You can always cheat :wink: With a bit of care it could be done fairly well instead of this hash up. But you get the idea.

Winter006Small.jpg
 
CT said:
The good news is there's a simple way to always know what the safe hand holdable speed is with any lens. ...
Click to expand...

I've always used that as well but when I went for the 10D because of the 1.6 crop factor giving the impression that say a 50mm is an 80mm, I've also changed the "safe" speeds. Is that a fair assumption or just daft?
 
dod said:
CT said:
The good news is there's a simple way to always know what the safe hand holdable speed is with any lens. ...
Click to expand...

I've always used that as well but when I went for the 10D because of the 1.6 crop factor giving the impression that say a 50mm is an 80mm, I've also changed the "safe" speeds. Is that a fair assumption or just daft?
Click to expand...

Great question! It actually makes my head hurt thinking about this, and I'm still not sure. :LOL:

A 50mm lens only becomes an 80mm lens because we're thinking of it in 35mm film terms. It's actually still a 50mm lens as far the chip in our digital camera is concerned, so I think the old safe rule still applies, but I'm quite happy to be put right on that. If the focal length 'actually' changed then the max aperture would become smaller (effectively) too wouldn't it?
 
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