Aperture basic quesion

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ukranger

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Hi Guys

A quick & probably simple question to most but I'm a little confused:thinking:

I've been reading about aperture & it seems if I put the on max aperture & no zoom there's not a lot of blurred background but if I take a step back & zoom in to the subject there's much more.

Sorry if I've confused you guys & myself here lol

Is there something I'm missing or doing wrong here

Thanks in advance
 
Longer focal lengths produce a more diffuse background.
The different perspective of longer focal lengths means they include less of the background, so "stretch" the background over a larger area making it look more blurred.

I'm not describing it very well, I'm sure someone else here can link to a diagram/example so you can see what I mean :)
 
Yes thats right, longer telephoto lenses do produce a more narrow depth of field (DoF).

You're not doing anything wrong. This is why people like to do portraits with long-ish lenses. It flattens the perspective (more flattering, wide angle makes noses look big) plus the blurred out background makes a nice back drop.

Ade
 
Depth of Field is an effect of magnification combined with aperture size, the effects are the same or comparable whether one uses a a wide lens or a zoom or long lens

But the appearance of the out of focus areas on the zoomed image look diffused simply because ones closer to them… cropped into them if you like. (like a cropped sensor also does)

In effect making it look like theirs more oof when it is in fact the same (comparable ) as the wide image.

Try cropping into the non zoomed to match the size of the zoomed and you’ll see how it can become just as oof close up.
 
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Hi Rob,

I assume when you say "max aperture" you mean highest f number, so you're not missing anything. The higher the f number, the smaller the aperture and the greater the depth of field (i.e. more of the shot in focus)... and vice versa with smaller f numbers.

However, there is more than one factor that determines depth of field, which is why your DoF decreases if you take the same shot from slightly further back with a longer focal length using the same lens. You will also find that DoF is affected by distance between subject and background (e.g. the greater the distance, the less DoF) - and also distance between camera and subject (e.g. the shorter the distance, the less DoF).

Googling 'aperture depth of field' should provide you with loads of sites to help improve your understanding, and I would recommend taking some test shots (at different apertures, at varying distances and with multiple focal lengths) cos this will definitely help you see the results and ultimately may stick in your head. :)
 
Forbiddenbiker said:
I took max aperture to mean the maximum aperture. So a low fraction and the biggest hole. :thumbs:
Click to expand...

When you say "low fraction" I assume you mean the smallest denominator? Because that is actually the largest fraction
 
Maximum aperture = largest (f/1.8 for instance) = Less DOF
Minimum aperture = smallest (f/22 for instance) = Greater DOF
 
Your ok then.:thumbs:

Try viewing your own finger in front of your face. (say the eyes are a wide aperture) It doesn’t matter how long your lens and arms are, when you focus on your finger close up to the front of the lens/eye, the background is out of focus.…as you move your finger away the background starts to come into focus… and visa versa the closer the background is to your finger, the more quickly it comes into focus as you move your finger backwards.

So if you want max silky out of focus background you’ll need a wide aperture, subject nice and close and the background as far as possible.


:)
 
Thanks for that, just a quick question that's popped into my head after reading this thread.

Say you'd like to take a photo of someone from head to toe how would you get that blurred background effect as if your close that would cut out say the legs waist etc.

How would you overcome this?
 
Same way, but its not as easy ... like everything photographic a compromise is needed …your always going to be limited by the wide aperture abilities of any given lens, and by the distances and framing sizes of the subjects involved.

Take this shot. I’m shooting with a 28mm on a D70, which gives an approximate field of view that’s very like our own eyes. (= about 47mm or like close to a 50mm lens on a full frame) ..my maximum aperture is f2.8.

But in this shot I've chosen f3.5 because I want all of her and the bike in focus and the depth of field to end and start to blur the background just beyond the bike.
.. I’ve shot as close as is acceptable, focused onto the front mudguard/wheel to render the front wheel well within acceptable DoF ranges
…In this way I can separate the background from my subject and emphasise the subject and mostly the front tyre nice’n’sharp in doing so.

yvonnelavy3.jpg


So the blur in this photo is only subtle right ..but if you look deeply into the back of the lane at the far end you’ll see that the burr is far greater than the general scene ..simply because its further away.

However if I’ d shot this at f2.8, I would have rendered far more of the background as blurred as that deep bit
…But my depth of field would have narrowed greatly and Id have lost much of the in focus range along the back of the bike, leaving only her face distance and the front of the bike in sharp focus.

I chose all of the bike and less of the blur as you can see,
--

If say you only have f4 as your widest aperture, you’d have frame as close as is possible and place the subject at a considerable distance from the background to achieve good blur.
:thumbs:
 
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ukranger said:
Thanks for that, just a quick question that's popped into my head after reading this thread.

Say you'd like to take a photo of someone from head to toe how would you get that blurred background effect as if your close that would cut out say the legs waist etc.

How would you overcome this?
Click to expand...

Very large aperture or long focal length. And position the person where the background is reasonably far away.

Some of my favourite portraits I've seen on flickr were shot with 200 f/2's and 300 f/2.8's
 
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Nice answers! Good thread.

Tomorrow I am picturing my girlfriends graduation, and she wants me to get a pic of her and her friends. I'd like a blurred back ground, so I take it that I would need to go far back, zoom in, low DOF, and shoot? ( WiIth them not being close to a background)
 
With that lens in your Kit bag Joe?

Yes go the long end, with her near filling the frame or whatever compromise. what’s your min F3.5? you a cropped sensor?

Your going to need the background to be at some considerable distance or choose something unobtrusive, pretty perhaps.
Imagine cropping my shot above from the front wheel axel to her shoulders and matching at the sides...it would be about that blurred backwards if you get me.

Your not going to get much blur with that lens but choosing something subtle and randomly detailed will soften more easily.
Keep away from heavy lines, poles, contrasty stuff in the background because that will still look ugly even when slightly blurred or heavily blurred.
 
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