which lens for bird and flower photography?

Hi,

I am interested in photographing birds and flowers. Currently, I have the "Nikkor 28-200mm f/3.5-5.6G ED-IF" and "Nikkor 55-200mm f/4.0-5.6 AF G ED AF-S DX" lens for my Nikon D70s, but I found them to be not sharp enough.

Maybe this is due to my lack of photographic skills since I am pretty new to SLR. I shoot most of my photos on small aperture (large f-number ). This is because I read somewhere says that a large f-number will give me less depth of field which is great for isolating the subject from its surroundings. But the small aperture cause me to not able to use fast shutter speed.

What aperature do most people use for flower photography? Do I need a faster lens?

Thanks!

You have the effect of aperture on depth of field (dof) backwards. A small aperture (higher number) has a greater dof than a large aperture.
Another thing that will effect dof is the focal length of your lens. You will have more dof on the shorter focal lengths.
Use a tripod to allow slower shutter speeds when needed and use a higher ISO setting to keep the times short as possible. If the problem is movement of the flower from wind, try blocking the wind somehow. I used a friends kid for that last week.
Also lenses are sharpest generally a couple stops from full open.
Remember that the zone of acceptable focus is 1/3 in front of and 2/3 behind the actual focus point so focus partway into your scene, not at the closest or farthest part of the flower.

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Originally Posted by Chunk

You have the effect of aperture on depth of field (dof) backwards. A small aperture (higher number) has a greater dof than a large aperture.
Another thing that will effect dof is the focal length of your lens. You will have more dof on the shorter focal lengths.

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Thanks chunk!

One thing I don't understand is when I hit the DOF preview button on the camera, the view finder always looks darker at higher f-number and brighter at lower f-number.

Shouldn't a brighter view means greater depth of field? This is where I got confused.

Normally the aperture is wide open when viewing to allow the maximum brightness in the viewfinder. Because of this the depth of field you normally see is the narrowest for the focal length you are at. When you press the dof preview button, the aperture is stopped down to the actual size selected, letting less light through the lens and showing the scene as it will be captured. I know some people use that dof preview button to good advantage, but I always had trouble seeing the efect in the viewfinder and usually relied on experience and the dof range indicated on a lens.

Since it won't cost you anything but time with a digital camera, I'd suggest finding a subject like a picket fence running at an angle away from you and put your camera on a tripod. Hang something (camera bag?) on the fence in the foreground and focus on it for a picture while having the aperture wide open and a short focal length. Repeat this while stopping down by a stop or two until you are stopped all the way down. Then zoom in to a long focal length and repeat.
Then move the camera bag to a spot in the middle distance and repeat all the shots. Then a further distance.
Sounds like a lot of work but by the time you've evaluated how many pickets are in acceptable focus in all the different cases, you'll have a pretty good feeling for what you are going to get recorded with all the variations possible.

If you use a macro you could use a similar process with a low angle shot of a keyboard or perhaps a printed page.

Chunk brings up a lot of good points, but one part of having sharp images with digital cameras is software related. You do need to start with a good sharp image, but digital images are soft out of the camera. Cameras can be set up to sharpen (usually a couple different settings) at the time you take the picture, and/or they can be sharpened in Photoshop.

Scott Kelby's book (Adobe Photoshop XXX for Digital Photographers, insert whatever version you've got) has a whole chapter on sharpening. It's like anything else - basic sharpening is pretty easy but there are some advanced techniques you can try out too.

Chunk mentioned that most lenses are sharpest about 2-3 stops down from wide open. I've usually found that to be the case too, and some lenses stopped down all the way can be pretty soft. Generally, it's best to stop down only as far as you need to. In other words, don't stop down to f22 if f11 will get you the amount of DOF you need.