Is there a relationship between...

[GrantH]

when a fast lens, say for example sake a 10-20 f/2 is used at f/2 and when its used at f/8 as far as quality in the lens? Is it best to use these lenses closer to the f# number they are rated at rather than high in the range?

 

[Bitter Jeweler]

Lenses *tend* to be softer at the ends and sharper in he middle.

Read reviews of specific lenses to find their sweet spot.

 

[480sparky67 66]

Agreed. From a technical standpoint, each lens is going to have an aperture where things like CA and coma are at a minimum. Knowing where each of your lenses are in this manner can make a slight improvement in your images.

 

[RockstarPhotography]

Lenses have a "sweet spot" that gives the sharpest image. The only real way to find it is to shoot the same scene on a tripod with a remote release at the different apertures and looking at them at 100%. A general rule of thumb you can use though is the "sweet spot" is usually around 2 stops lower then the highest (lowest f stop) aperture setting.

 

[djacobox372]

Typically the "sweet spot" for a lens is two stops down from it's maximum aperture (f5.6 for an F2 lens).

But that's just a guess--some lenses are amazingly sharp at their widest apertures, so much that very little if any improvement is seen when stopping down.

All 35mm lenses start losing sharpness at f16 and smaller due to diffraction.

 

[kundalini]

when a fast lens, say for example sake a 10-20 f/2 is used at f/2 and when its used at f/8 as far as quality in the lens? Is it best to use these lenses closer to the f# number they are rated at rather than high in the range?

The lab results from places like photozone.de can be quite useful for the techie side of your question.

 

[jth]

Usually I choose the aperture value based on how much I want depth of the field in the picture but I quess thats not the pint in here. I agree with above messages usually range between f/4 to f/8 is sharpest and from photozone you can really find useful info on lenses.

 

[KmH]

when a fast lens, say for example sake a 10-20 f/2 is used at f/2 and when its used at f/8 as far as quality in the lens? Is it best to use these lenses closer to the f# number they are rated at rather than high in the range?

There is no f-number they are "rated at".

The f-numbers in the lens description only tell what the maximum aperture of the lens is.

 

[mikehaugen]

Typically the "sweet spot" for a lens is two stops down from it's maximum aperture (f5.6 for an F2 lens).

But that's just a guess--some lenses are amazingly sharp at their widest apertures, so much that very little if any improvement is seen when stopping down.

All 35mm lenses start losing sharpness at f16 and smaller due to diffraction.

wouldn't it be f4 for an f2 lens?

 

[KmH]

Yes.

f/2 to f/2.8 is one full stop.
f/2.8 to f/4 is the second full stop.
F/4 to f.5.6 is the third full stop.

Each full stop smaller is times 1.1412. each full stop larger is divided by 1.4142.

1.4142 is the square root of 2.

 

[480sparky67 66]

wouldn't it be f4 for an f2 lens?

Not necessarily. It could be closer to f/2.8, it could be f/5.6. Since the manufacturers don't specify this information, it's up to testing labs & users to figure it out.

Get a nice big lens test chart and set your camera up on a tripod and take test shots at various f/stops and do your own investigation.

 

[mikehaugen]

I was just speaking of the reference that he made about it being 2 stops lower than maximum, not to say that f4 was automatically the "sweet spot"

 

[Derrel]

"Some" lenses are exceptionally good closer to their wide-open apertures, and perform less-well in the f/8 to f/11 range....mostly supertelephotos, but also other very fast (meaning wide-aperture) lenses that were optimized by their designers to perform very well at wide apertures. Nikon's 400mm f/3.5 and 200mm f/2 AF-S VR-G for example, are near their best wide-open. In the case of the 400mm f/3.5 its image quality is optimized for wide-open or nearly so,and that lens' image quality DECLINES, markedly, when stopping down from f/4 to f/5.6. The same type of behavior can also be seen in shorter lenses like 35mm f/1.4 or 50mm f/1.4 lenses--which are typically optimized for good optical performance when shot at wide apertures. With newer and higher and higher megapixel count sensors, diffraction can often prevent a lens from resolving more detail at the smaller apertures. With a 12-14 MP sensor of 1.5x to 1.6x size, it's very possible that your 70-200 f/2.8 professional zoom lens will perform "best" at something like f/4.5, and not f/8.

 

[djacobox372]

Typically the "sweet spot" for a lens is two stops down from it's maximum aperture (f5.6 for an F2 lens).

But that's just a guess--some lenses are amazingly sharp at their widest apertures, so much that very little if any improvement is seen when stopping down.

All 35mm lenses start losing sharpness at f16 and smaller due to diffraction.

wouldn't it be f4 for an f2 lens?

Correct, thanks. But that's just a guess, each lens varies.