Focus multiple points

[Droid04]

Hy everyone!

Last day I wanted to make a photo of a chess table complete with pieces. Single light source above - normal indoor lamp. The chess table & pieces are all shiny & highly reflective.
I used Nikon D5000 + Nikkor 70-300 on tripod. Settings : f 4.5/ f8/ f11, 3D focus mode, center weighted light mettering.
10 seconds timer.

So, in viewing the pictures on large screen I noticed that many had a focus problem.
I shot in manual focus and alternatively with auto focus and both seemed to have problems, regardless of apperture.
Probably due to the reflective surfaces, it was hard to lock on.
Also how do you focus on more than one object (beside increasing DOF) ?

Ideeas/ sugestions for focusing on reflective objects/ others ideeas?

Thanks!

 

[tirediron]

Posting images would help in troubleshooting.

In general: You can only focus on one point (that is, a specific distance) at one time. Using smaller apertures increases the depth of field or the area that is acceptably sharp, but you cannot focus on a near area here and a far area there; optics simply don't work that way. What you may have to do is what's known as stacking focus, that is, taking a number of images with varying points of focus and combing them in software (such as ZMCombine) to produce a single image with 'impossible' depth of field. Essentially the focus equivalent of HDR. With respect to your lighting, the only way is going to be to diffuse your light sources and use flags and scrims to control the light. You can learn all about that in the lighting bible.

 

[KmH]

The camera can only use 1 point of focus (distance).
Focus stacking is a technique used to expand DoF beyond what a camera/lens is capable of.

That point of focus defines a plane pretty much parallel to the plane of the image sensor. If you tilt the camera up/down/sideways you also tilt the image sensor and the plane of focus.

Depth of Field determines how far in front of and behind that single point of focus the focus will be acceptably sharp.

The nature of your question indicates you do not yet have a solid understanding of how focus and DoF are related.

 

[Droid04]

@ tirediron : Thank you! I've never tried stacking focus points. I'll give it a try and see what's it like. I deleted the pictures that had bad focus clarity.. next time I'll keep them for referencing.

@KmH : You are correct - I don't know exactly how focus and Dof work together You've also answered another question I had: so focus point is not actually a point (or a small zone near the focus point) but rather a narrow horizontal plane. But if that's the case then why the camera manufactures make focusing points matrix and not small plane area-like zones ? Is the focus point also defined by the vertical or just by horizontal ?
I'll look more into it, thanks !

 

[Designer]

The area of acceptable focus is not a "narrow horizontal plane" as you wrote, but rather is parallel to the sensor, which in most cases is more vertical (you are holding the camera upright, not pointing it down toward the ground). Cameras cannot display such a plane in the viewfinder.

The multiple points are so you can select which one point you want the camera to use for focusing (ignoring the other points).

For the greatest (deepest) depth of field, use a smaller aperture. With a sufficiently small aperture, you can get most of your scene in focus (acceptably).

 

[KmH]

Camera makers include multiple focus points so photographers don't have to 'focus and recompose' as much, and to facilitate AF features like 3D Tracking..

The focus point indicators in a DSLR viewfinder define an area that contains the focus point, but the focus point itself is not shown.

There are 2 types of focus points - regular and cross-type.

Regular focus points detect horizontal or vertical edges in a scene. Horizontal focus points detect vertical edges and vertical focus points detect horizontal edges.
Cross-type focus points detect both vertical and horizontal edges. Cross-type focus points usually have greater sensitivity to light than regular focus points.

Your D5000 has Nikon's Multi-CAM 1000 auto focus module and has 11 AF points. The center AF point is a cross-type AF point. (See your D5000 specifications, page 226 of the user's manual)

Nikon's D5200, D5300, and D7000 has Nikon's Multi-CAM 4800DX AF module that has 39 AF points, the middle group of 9 being cross-type AF points.

Nikon's D7100 and all the higher level Nikon's use Nikon's Advanced Multi-CAM 3500 AF module that has 51 AF points, the central 15 AF points being cross-type AF points.

http://www.cambridgeincolour.com/tutorials/camera-autofocus.htm
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

 

[rambler]

With the camera on a tripod, do not change any settings, and take multiple photos each focusing on another point on your image using auto focus each time. Focus on all the areas of the image that you would like to have in sharp focus in one final photo.

Using software called Helicon Focus, load in all your images, select "render". Wait a bit as the software combines all the images you included into one final all-focused image.