Getting everything in frame in focus

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Corbus

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Sorry, second thread of the day but I need more guidance.

I have the option of auofocusing using single point, auto, dynamic area or 3D tracking (although that's only on AF-C mode).

I seem to be having problems getting focus on all faces when taking a group shot, even in groups of say 3 or 4. I use autofocus for this and single point for portraits of one person. However, although auto shows up various points of focus, I'm struggling to get the faces all in focus. One could be perfect and one could be quite blurred. My last attempt at this was indoors without flash, I was about 8 feet away and I had to use f/2.8 in order to get a good shutter speed.

Is there a general rule to say that U need to be at a particular f-stop at that distance to get everything in focus? I couldn't possibly have gone any more as I was already at a high enough ISO, any more would have brought a fair bit of noise. Is 2.8 far too wide open to achieve what I wanted?
 
f/2.8 would be ok if all your subjects were the same distance from the lens- it gives a shallower DOF so if one of the people was 5' from you and another was 10' away one or the other- or both would be OOF, thats where you eith have to use a flash, IS, really high ISO or a tripod.
 
topcatproduction said:
f/2.8 would be ok if all your subjects were the same distance from the lens- it gives a shallower DOF so if one of the people was 5' from you and another was 10' away one or the other- or both would be OOF, thats where you eith have to use a flash, IS, really high ISO or a tripod.
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I totally understand that part of it all, I should have mentioned that the subjects were side by side exactly the same distance away.
 
Remember that the focal distance is a curve - not a straight line.
 
Corbus said:
I totally understand that part of it all, I should have mentioned that the subjects were side by side exactly the same distance away.
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Depth of field can be very shallow at f/2.8 - see that DoFmaster link. A few inches either way could throw it out.

However, if your subjects are indeed all at exactly the same distance, yet some are blurred, then it's subject movement revealed by too long a shutter speed.

Post a pic and it will be easy to see what the problem is.
 
For groups you need to be shooting around f/8 - can you post a pic with EXIF data?
 
Suvv said:
This has come up a few times lately, have a look here

http://visual-vacations.com/Photography/focus-recompose_sucks.htm
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That link is wrong and is confusing two different issues - focus-recompose technique and field curvature.

The 'natural' focus of a basic spherical lens, eg magnifying glass or like the LensBaby, is to form a sharp image of a spherical subject on to a spherical surface (sensor).

The former characteristic is undesirable but usually not that critical (unless you photograph brick walls a lot) and is designed out of good lenses to a substantial degree, eg enlarging lenses are corrected to a very high degree, as they have to be.

The latter characteristic, which would need a spherical sensor, is obviously a complete no-go so that is highly corrected in a multi-element lens, often using aspherical glass surfaces.
 
OK, I'm no expert at all, but the way I've always understood is that if you want to shoot a group, you should go for a higher f-number. 2.8 is fine when all you want to focus on is at the same length, but that will never be with a group, there's always going to be someone that is a bith further away.

Moreover, if you are shooting a group, you usually have a longer focal lenght and this would make your depth of focus even tighter.

If you're shooting indoors, I would up the ISO (a decent DSLR can easily go with 800) and use a tripod. This should allow you to increase the f number.
 
never bother using a tripod to shoot people as anything you can't handhold they won't be still for (as a rule of thumb)

notable exceptions are lighting people with ocf using a long exposure to pull in sky detail and when you are using the tripod for image so as to look more professional
 
Ellekes said:
Moreover, if you are shooting a group, you usually have a longer focal lenght and this would make your depth of focus even tighter.
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Exactly the opposite - if you're shooting a group you're more likely to be using a WIDE lens - so you would have greater DoF for any given aperture.
 
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