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Ideal aperture for portraits?

chrisgeary

Prominent Member
What's the ideal aperture for a portrait at, say, 100mm and 200mm?
 

senu

Distinguished Member
Im sure answers will come but in my limited experience I think it would depend a bit more on distance to subject and what sort of "bokeh" effect you are trying to achieve.
Certainly I think one of the benefits of Digital is the ability to try several "permutations" and see which turns out best
 

Brammers

Banned
There's no answer to that question! It depends entirely on what you're trying to do. Do you want selective focus? What angle is the face at? What's the background like?

All you can do is say after the shot 'needed more DoF,' needed less DoF' or 'just right!'
 

salubrious_k

Established Member
Well I'd agree that it all depends on your distance to the subject. You need to play around and get a feel for it. You know that your aperture is too wide when the cheeks are in focus but the nose isn't... unless your shooting someone with a really long nose (c;
 

chrisgeary

Prominent Member
Hmm ok. Let me put it in context... I have been using my Sigma 70-200/2.8 for a while now. I am struggling to get subjects in focus with it. I usually capture candidly so distance and pose varies. But what is clear is using 2.8 as the aperture at typically 150-200mm produces a very shallow depth of field, which consequently makes it harder to get the face front to back sharp. Yes, I do want lovely bokeh but what I'm trying to work out is whether I *need* a 2.8 lens to achieve this as its rather heavy!
 

Peakoverload

Established Member
Chris,

You need to do a bit of reading on depth of field and what affects it. I recommend you take a look at this page http://www.dofmaster.com/dofjs.html

Enter a focal length and an aperture and see how much depth of field you will get. Now change the aperture and you'll see how the depth of field changes.

The problem with your original question is that there is no correct answer as no two portraits are the same. Some people will want a very limited dof to have, for example, one side of the face soft with the other sharp. Others will want the dof deep so that all the face, front to back, is pin sharp but the aperture that they use will, as you will see from the link I gave you, vary depending on their focal length, distance to subject and distance of subject from the background.

For the 'traditional' portrait you may find that a lot of people use f/8 as this is typically the aperture where the lens is at it's sharpest. Others on the other hand will use f/4 because it will produce a softer background but it really depends on their focal length and how far the subject is from the background so these are a very, very rough rule of thumb.
 

chrisgeary

Prominent Member
Thanks... you've confirmed my thoughts. and thanks for the link.. that is very useful!

So I'm wondering what the benefit of a heavy 2.8 telephoto lens is now. Its not quite long enough for those trips to the zoo and 2.8's DOF is too shallow for portraiture over about 150mm which is quite often what I end up shooting at.

The great thing about the Sigma is, when I do get it right, it produces really sharp images with very little to no CA and its bokeh is very nice indeed.

If I changed to, say, a Nikon 70-300/4-5.6 VR, would I still get nice enough bokeh? I appreciate that at, say 200mm, I'm likely to be at least at f5 so at 3m distance I'll be looking at 4.2cm DOF.
 

Peakoverload

Established Member
Thanks... you've confirmed my thoughts. and thanks for the link.. that is very useful!

So I'm wondering what the benefit of a heavy 2.8 telephoto lens is now. Its not quite long enough for those trips to the zoo and 2.8's DOF is too shallow for portraiture over about 150mm which is quite often what I end up shooting at.

Go back and have a look at the dof calculator. Put in 200mm as your focal length, f/2.8 as your aperture and set your distance to subject as 10 meters. This gives you a dof of 26cm which is quite a lot and just about deep enough for the average head. Now change the distance to 30m. BAM! Suddenly you have a dof of 2.41m! Okay YOU aren't going to stand 30m away from your subject when shooting a portrait but what if you are shooting wildlife or are at some kind of race meeting, photographing planes in the air etc etc. THAT is the point of f/2.8 at such focal lengths.
 

chrisgeary

Prominent Member
Right. So lesson learned today is DOF changes not only with aperture but also with focal length AND distance to subject. I hadn't realised those two things. Thanks for your help :)
 

Radiohead

Prominent Member
This demonstrates how distance to subject affects DOF. Both shots here are with a 70-200 at 200mm, f3.2. The first shot was with the little girl about 5 feet away and zoomed right in for a close crop (you're seeing it as shot with no cropping afterwards):

442616514_246d9832be_o.jpg


Her left eye is in focus but the other side of her face is dropping away quite fast - it works for me because of the hair covering the other eye.

This second shot was from about 25 feet (IIRC) - same focal length and aperture but a much greater distance to subject has meant she's sharp from front to back, but still throwing the background out nicely:

442616426_de2c4b808e_o.jpg


The same is true for this shot moments later:

442620007_51c353a0a0_o.jpg


I cannot over-estimate how good and versatile the 70-200 is for shooting people and candids.
 

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