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clarification
I was reading a post by someone heres the thread - http://forums.dpreview.com/...ums/readflat.asp?forum=1034&thread=28769356.

And Im not sure why it was recommended to shoot at a low f number. I thought one would get a sharper pic by reducing the apperture rather increasing it by using the lowest f number? could some one advise me? thanks..

I always thought that a higher f number wld give a more sharper pic. Is this wrong?..

Comments (9)

SXW wrote:.

I was reading a post by someone heres the thread -http://forums.dpreview.com/...ums/readflat.asp?forum=1034&thread=28769356.

And Im not sure why it was recommended to shoot at a low f number. Ithought one would get a sharper pic by reducing the apperture ratherincreasing it by using the lowest f number? could some one advise me?thanks..

I always thought that a higher f number wld give a more sharper pic.Is this wrong?.

A low f-number = a wide aperture (lets in more light, so useful in low-light situations). The query in the thread you mention was from someone who was trying to take pics in low light of her daughter doing gymnastics, and had ended up with a slow shutter speed ( = blurred pictures due to the fact that gymnasts don't stand still)..

If you use as wide an aperture as possible, to let in a lot of light, then the shutter speed can be shorter, giving you more chance to freeze the motion..

You may be getting confused the depth-of-field issues. At a narrow aperture (large f-number) the depth of field is greater, such that objects a greater distance in front of and behind the focus point are sharp. At a wide aperture the depth of field is narrow, and anything much in front of or behind the distance you focussed at will be blurred (because it is out of focus, not the same as motion blur)..

In the gymnastics situation, sure you could stop the lens down to f/16 so that everything form three feet in front of you to infinity is in sharp focus. but that is no good if the shutter speed ends up at 1/4 second when you really need 1/500 to freeze the rapid motion of the gymnasts..

Best wishesMike..

Comment #1

Mike703 wrote:.

SXW wrote:.

I was reading a post by someone heres the thread -http://forums.dpreview.com/...ums/readflat.asp?forum=1034&thread=28769356.

And Im not sure why it was recommended to shoot at a low f number. Ithought one would get a sharper pic by reducing the apperture ratherincreasing it by using the lowest f number? could some one advise me?thanks..

I always thought that a higher f number wld give a more sharper pic.Is this wrong?.

A low f-number = a wide aperture (lets in more light, so useful inlow-light situations). The query in the thread you mention was fromsomeone who was trying to take pics in low light of her daughterdoing gymnastics, and had ended up with a slow shutter speed ( =blurred pictures due to the fact that gymnasts don't stand still)..

If you use as wide an aperture as possible, to let in a lot of light,then the shutter speed can be shorter, giving you more chance tofreeze the motion..

You may be getting confused the depth-of-field issues. At a narrowaperture (large f-number) the depth of field is greater, such thatobjects a greater distance in front of and behind the focus point aresharp. At a wide aperture the depth of field is narrow, and anythingmuch in front of or behind the distance you focussed at will beblurred (because it is out of focus, not the same as motion blur)..

In the gymnastics situation, sure you could stop the lens down tof/16 so that everything form three feet in front of you to infinityis in sharp focus. but that is no good if the shutter speed ends upat 1/4 second when you really need 1/500 to freeze the rapid motionof the gymnasts..

Best wishesMike.

Quoted for truth..

THE Brandon Paith and his Nikon D80...

Comment #2

So in essence, the lower F number was to compensate for the low lighting since he wanted a faster shutter speed in order to freeze the action?.

I have another question - if I were to focus on say an object and use a low F number, that object would still be in-focus right? assuming object is not moving fast. if so, If I were to take 2 pics one with a lower f number VS one with a higher f number (using same shutter speed) would the pic which I took with the higher f number come out more sharper?..

Comment #3

SXW wrote:.

I always thought that a higher f number wld give a more sharper pic.Is this wrong?.

Yes. While that thread had to do with shutter speed, there is still the issue of diffraction to consider. View this thread for a discussion and examples....

Http://forums.dpreview.com/...ums/readflat.asp?forum=1014&thread=28721235..

Comment #4

SXW wrote:.

So in essence, the lower F number was to compensate for the lowlighting since he wanted a faster shutter speed in order to freezethe action?.

Exactly. For action, a fast shutter speed is the most important thing when choosing exposure settings - hence, wide aperture (small f-number)..

I have another question - if I were to focus on say an object and usea low F number, that object would still be in-focus right? assumingobject is not moving fast. if so, If I were to take 2 pics one with alower f number VS one with a higher f number (using same shutterspeed) would the pic which I took with the higher f number come outmore sharper?.

Depends how deep (from to back) the object is. If it were flat, then yes, it would be in focus at any aperture. But with a very wide aperture (like f/1.4) the depth of field can be very narrow - a couple of inches. So if you focussed on somebody's eyes for a portrait shot, the tip of their nose (in front of the focus plane) or their ears (behind the focus plane) might be out of focus. At f/11 in contrast everything several feet in front of and behind the person would be in sharp focus..

Sometimes you want a narrow depth of field to blur out distracting backgrounds: portraits are often taken with a wide aperture for this reason. In contrast, for landscape or architecture shots, a narrow aperture is likely to be more useful so that everything from the tree in front of you to the horizon is in focus..

You can see the effect using the on-line calculator here:.

Http://www.dofmaster.com/dofjs.html.

Best wishesMike..

Comment #5

The larger the aperture you use (the smaller the f number), the less that will be in focus in front of and behind the point of focus. This could be an advantage OR a disadvantage depending on your subject and the effect you are trying to achieve..

Also, because lenses in the real world are imperfect, the larger the aperture the lower the resolution and contrast will be. Again, in the real world, the reduction in resolution may be more than compensated for by the reduction in motion blur the higher shutter speed achieves..

As an aside, lenses have an aperture at which they are sharpest and, as a rule of thumb, this tends to be two or three stops down from maximum. Going to a smaller aperture than this causes blurring due to DIFFRACTION which appears from about f11 and upwards on DSLRs. Diffraction by the way is unavoidable and occurs because of the physical laws governing light rays...

Comment #6

Chris59 wrote:.

As an aside, lenses have an aperture at which they are sharpest and,as a rule of thumb, this tends to be two or three stops down frommaximum. Going to a smaller aperture than this causes blurring dueto DIFFRACTION which appears from about f11 and upwards on DSLRs.Diffraction by the way is unavoidable and occurs because of thephysical laws governing light rays..

I am nit-picking but we might as well get this right, It is the sensor size and resolutioin that determines the f stop at which diffraction begins to have an impact on a camera lens. On the D40 it kicks in above f/16, on the D80 above f/13 and on the D300 above f/11. (These are not absolutes but a good rule of thumb)..

It is the physics of the lens design and not diffraction that tends to mean that a lens it at it's best two to three stops up from minimum. There is then commonly a plateau for a couple of stops before a gradual decline..

Lenses vary a little from this general statement. But by way of example the Nikon 50mm f/1.4 is at it's sharpest from circa f3.5 to f/6.3. By f/8 the 50mm f/1.8 lens is sharper which is why the (cheap) 50mm f/1.8 is often used on camparison tests on this site set to f/9..

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #7

Chris Elliott wrote:.

I am nit-picking but we might as well get this right, It is thesensor size and resolutioin that determines the f stop at whichdiffraction begins to have an impact on a camera lens..

Absolutely not right. Diffraction is an aberration of the lens, directly related to the actual size of the aperture opening. The same lens at the same aperture will cause the same exact diffraction pattern no matter what sensor size or resolution the image is projected on..

Sensor resolution may have an effect on how noticeable the diffraction is within the final image. However, some patterns will be noticeable on any sensor..

Http://en.wikipedia.org/wiki/Diffraction..

Comment #8

Chris Elliott wrote:.

Chris59 wrote:.

As an aside, lenses have an aperture at which they are sharpest and,as a rule of thumb, this tends to be two or three stops down frommaximum. Going to a smaller aperture than this causes blurring dueto DIFFRACTION which appears from about f11 and upwards on DSLRs.Diffraction by the way is unavoidable and occurs because of thephysical laws governing light rays..

I am nit-picking but we might as well get this right, It is thesensor size and resolutioin that determines the f stop at whichdiffraction begins to have an impact on a camera lens. On the D40 itkicks in above f/16, on the D80 above f/13 and on the D300 abovef/11. (These are not absolutes but a good rule of thumb)..

I understand this but didn't want to "nit-pick" because as you say, these are not absolutes..

In fact if we ARE nit-picking we could say that diffraction is ALWAYS the limiting factor in lens resolution and that the larger the maximum aperture, the less diffraction and higher resolution you could, in theory, achieve. In the real world however, lenses cannot be made "perfect" so a lens' shortcomings limit it's resolution at maximum aperture and by stopping down we remove the worst of the abberations caused by the outer parts of the glass until the lenses real world limitations are overtaken by the physics of diffraction - as you say - "diffraction begins to have an impact"..

In other words if we could design a lens that was theoretically perfect, it would give maximum resolution at maximum aperture and any reduction in aperture would also mean a reduction in resolution..

It is the physics of the lens design and not diffraction that tendsto mean that a lens it at it's best two to three stops up fromminimum. There is then commonly a plateau for a couple of stopsbefore a gradual decline..

True, but I was talking about the reasons for the reduction in lens resolution above this "plateau" - perhaps I wasn't clear on this..

Lenses vary a little from this general statement. But by way ofexample the Nikon 50mm f/1.4 is at it's sharpest from circa f3.5 tof/6.3. By f/8 the 50mm f/1.8 lens is sharper which is why the (cheap)50mm f/1.8 is often used on camparison tests on this site set to f/9..

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #9

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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