focal points

[deepakaa]

hi..
i m using Nikon D3100 ...18-55 lens...f3.5-5.6...
hve 2-3 basic questions...

1) while shooting portrait with more than 1 person in frame...how to focus on more than one face ?
how to get all the faces sharp ?
sometimes while shooting 2 or 3 persons in one snap, i get one face sharp and other faces lesser sharp ?
how to correct it ?

2) while shooting landscape...i dont want to focus on any one point...i want to keep everything focused..
so can i ignore the focus point (focusing on any point on the screen) and go on shooting with a larger f n° (11, 14,22,..) or there is a way to select manually more than 1 focus point..?

Many Thanks in advance for ur response.

 

[Trever1t]

DOF (depth of field) is really the question. The smaller your aperture the more DOF you will have. Works the same for questions 1 & 2

 

[Compaq]

You really can only get completely spot on focus at one distance from your sensor. Your focal plane is curved, if you draw a straight, horizontal line across your frame, everything that point will not be in focus. However, should you draw a line which has all points on equal distance from your sensor, then everything on that line will be in focus. Does that make sense? Have you ever seen portraits of groups in which the people are all standing in a curve? That's to get as many people sharp as possible.

If you at a short focal length choose a small aperture (f/11, /16, /22, /32), the chance is that you'll have pretty much everything in acceptable focus from one feet from your camera or something. Most of the landscape will rest at infinity anyway, so focus isn't really an issue.

About your focal plane, I'm sure someone more experienced than me can come with a better explanation

 

[Helen B]

You really can only get completely spot on focus at one distance from your sensor. Your focal plane is curved, if you draw a straight, horizontal line across your frame, everything that point will not be in focus. However, should you draw a line which has all points on equal distance from your sensor, then everything on that line will be in focus. Does that make sense? Have you ever seen portraits of groups in which the people are all standing in a curve? That's to get as many people sharp as possible.

We discussed that issue fairly recently. http://www.thephotoforum.com/forum/...r-images-focusing-families-2.html#post2273720

Best,
Helen

 

[Compaq]

We discussed that issue fairly recently. http://www.thephotoforum.com/forum/photography-beginners-forum-photo-gallery/244968-crustal-clear-images-focusing-families-2.html#post2273720

Best,
Helen

Right, nice find.

 

[Helen B]

Right, nice find.

Nice find? Jees, yes, finding one of my own posts from two weeks ago was a major challenge for me. Actually I got one of my nurses to do it for me.

 

[ann]

:lmao: your the best helen

 

[table1349]

Right, nice find.

Nice find? Jees, yes, finding one of my own posts from two weeks ago was a major challenge for me. Actually I got one of my nurses to do it for me.

ROTFLMAO!!!

 

[Compaq]

Limited info on iPhone app anyway, relevant find, then, m'lady

 

[SabrinaO]

Simple answers.... To get everyone in focus use a mid range aperture... F8 f11 to get everyone in focus. For landscapes... A much smaller aperture is needed to get the whole scene in focus... F11-f22

 

[deepakaa]

Thanks everyone...
for my first question ....ya i know about increasing f n° to increase DOF...but my question is more for smaller f n° to blurr background...
i recently shoot my portrait with my wife using a tripod camera was hardly 2 feet from us and i choose smaller f n° to blurr background i got a good sharp on my wife's face but my face was lesser sharp ..

for my second question...does this mean that there is no importance of focal point in landscaps ? as we use small f n° like f22 or so one and we want to keep everything in focas...so we can leave a focal point anywhere and shoot...??

You really can only get completely spot on focus at one distance from your sensor. Your focal plane is curved, if you draw a straight, horizontal line across your frame, everything that point will not be in focus. However, should you draw a line which has all points on equal distance from your sensor, then everything on that line will be in focus. Does that make sense? Have you ever seen portraits of groups in which the people are all standing in a curve? That's to get as many people sharp as possible.

If you at a short focal length choose a small aperture (f/11, /16, /22, /32), the chance is that you'll have pretty much everything in acceptable focus from one feet from your camera or something. Most of the landscape will rest at infinity anyway, so focus isn't really an issue.

About your focal plane, I'm sure someone more experienced than me can come with a better explanation

Compaq...i think you are making good sens but i am not sure to have understood completely your theory...could you pls elaborate more or give a reference to a tutorial or something ?

Thanks.

 

[Compaq]

The wider your lens is, the bigger DOF you will have. If at 18mm and f/16, your DOF will be very big, the chance is that your landscape will rest at infinity: that meaning autofocus will focus at close to infinity. Always pay attention to focus, of course, but it's not something you need spend much time perfecting on such a wide lens and such a large aperture.

See te thread Helen provided. I'm no expert on this.

 

[KmH]

With multiple subjects, and a close focal point it is very common to have focus issues related to a shallow DOF.


DOF (depth-of-field) is affected by 4 factors:

1. lens aperture
2. focal point to image sensor distance
3. lens focal length
4. focal point to background distance.

Play with some numbers using an online DOF calculator like the one found at www.dofmaster.com.

Wide lens apertures generally give a shallow depth-of-field when the focal poinbt is near the lens. With a wide lens aperture, as the distance to the focal point increases DOF gets deeper.
With a wide lens aperture and a close focal point distance, depth-of-field can get very shallow, like less than an inch. A person facing a camea directly can have the eyes in focus but the nose can be outside, or in front of the near limit of the DOF.