Using a DSLR camera (especially Nikon D3000) how i can focus two or more objects at a time? Suppose a group of 4 people are there, how I can get the focus on all the 4 peoples eye ? Any body please answer.
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What you have is a Depth of Field (DOF) problem. Three factors affect DOF:
1) The focal length of the lens.
2) The f-stop (aperture) chosen.
3) Subject distance.
Obviously I’ve no idea of how you’d be posing the 4 people in your question so I’ll just use this as an example and pose them in a 4 foot x 4 foot square so that side to side and front to back they are 4 feet apart. I’ll choose a 50mm focal length and focus on the people closest to us. By referring to the DOF Calculator we find:
50mm @ f16 focused at 10 feet our DOF is from 2′-9″ in front of our subject at 10 feet to 6′-3″ behind our subject. All 4 of our subjects will be in focus.
50mm @ f16 focused to 9 feet our DOF is from 2′-4” in front of our subject at 9 feet to 4′-9″ behind our subject. Again, all 4 of our subjects will be in focus but we have less margin of error for our 2 subjects at the rear of our 4 foot square. If 1 of them moved to 5 feet that subject would be out of focus.
As you can easily see, the closer we get to our subject the less DOF we have. If we chose a shorter focal length lens then we’d have to be concerned with possible distortion of our subjects and the ones at the back would look smaller than the ones in front. If we chose a longer focal length we’d need to be much farther back than 10 feet. We could probably get good results with a 35mm lens but any shorter of a focal length can cause the aforementioned problems.
Of course, if we group our 4 subjects closer together it becomes easier to get all 4 in focus even with a longer focal length lens or a larger f-stop such as f11 or even f8.
So go to the referenced site and play around with the DOF Calculator.
On the top dial switch to A(aperture priority) mode. Use a high f/number, to keep more objects in focus.
Note: It’ll still appear to focus on one in the viewfinder, but the final image should have the other 4 in focus. Nikons keep the aperture wide open no matter what the set aperture is when the viewfinder is in use, and goes down to the set aperture when the shot is taken.
Both answers could be right, depending on their intentions. Use a smaller aperture (larger number) to increase your depth of field. For example, use the largest number for the aperture that your lense allows such as F/22 (or F/32 if you have it).
The other answer is backwards use a smaller aperture for greater depth of field.
Use a wider aperture. More depth of field.