BetterPhoto Q&A
Category: New Answers

How to adjust f-stop

I wish to control the DOF of my photos, using aperture-priority mode. My aim is to focus on a person and make the background blur.

My questions:

(1) When I adjust the f-stop, it won't go beyond the range between F4 and F32. Is the f-stop preset by the lens?

(2) When I took portraits for my girlfriend, I used the widest aperture, i.e. F4 with my 28-80 mm lens. But the background does not become blur. How to get the desired outcome?

(3) The DOF preview button does not show the end result. How to make it work?

(4) The marks on the lens, e.g. 28, 35, 50, 80, is not helpful at all. How to improve?

Many many thanks!

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May 15, 2004

(2) f/4 is not particularly wide or "fast" for that range of focal lengths. To get more background blur you have to get closer to your subject, put more distance between your subject and the background, or get a faster lens (wider maximum aperture). All else being equal (though it rarely is) longer focal length setting will give you less DoF than shorter wide angle settings.

(3) Focusing and metering are always with the lens at its widest aperture (shallowest DoF). The aperture blades do not close down until the mirror flips up and the shutter opens. So if you have selected the widest aperture and pressed the DoF button there won't be any difference. If you've selected a smaller aperture, like f/8, then the aperture will stop down to that setting. Though the view will darken, let your eyes adjust and you'll be able to see the increase in DoF.

(4) The marks listed are the focal lengths available on the zoom, in mm. 28mm is a moderate wide angle view, 50 is a "standard" or "normal" view, 80 is a slight telephoto.

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May 15, 2004

I think I do not have the right type of lenses for the kind of things I enjoy shooting: (1) portraits that have a blur background (2) patterns that take in as much as possible (3) night city scenery that has an extensive DoF.

I have a standard zoom AF 28-80mm f/3.3-5.6G and high-power zoom AF 70-300mm f/4-5.6G.

Kindly please advise what type of lens I should acquire and use to give the best results for my 3 purposes stated above. Can I buy non-Nikon lenses if it does not have the required specifications?

Thanks a lot.

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May 15, 2004

Of course there are better (and more expensive lenses available), the two lenses you have are pretty well regarded as consumer/hobbyist zoom lenses. I don't quite know what you mean by (2), but stopped down to f/8 to f/16 (for deep DoF & city scenery) these lenses are nearly as sharp as $$$$ pro lenses. If your retailer and budget will allow, you might consider exchanging the 70-300 G for Nikon's 70-300 f/4-5.6D ED which has a little better optics, but that's not a must.

For shallow depth of field in portraits you might consider adding an 85 f/1.8 or 100 f/2 prime. A 50 f/1.8 would be very sharp, give shallow depth of field, and are very inexpensive (usually $100 or less), but its focal length is a little short for head & shoulder portraits. A 90 or 100 or 105 f/2.8 Macro would be very sharp and great for extreme close ups of insects/flowers/etc. and can also be a nice portrait lens - though some tend to "soften" it's sharpness in this use with soft-effects filter or a DIY piece of nylon hosiery.

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May 15, 2004