[Kerrowdown]

the technical violation...

Does this carry a custodial sentence?

[MJSfoto1956]

"sweet spot" also refers to the specific focal lengths that a zoom is best at. It is not uncommon for zoom lenses to be "best" at either wide or long but more often than not, rarely both. There are of course exceptional lenses that are "best" across the entire focal lengths (the new Sigma 18-35mm appears to be one of these). But in general your zoom will indeed have a sweet spot where it performs very well. Or put another way: it pays to know where your lenses are best and where they are weakest and then take that into account when shooting.

YMMV.

Michael

[Na Horuk]

I think sweet spot is the aperture and (on zoom lenses) focal length that gives the best measured results. Highest resolution, lowest CA. But this also depends on the specific lens. Some zoom lenses are better on one end, others in the middle. Best aperture is usually one or two stops from wide open, but below f10. Some Pentax cameras have an MTF mode that chooses the aperture with the highest resolution for that specific lens (only works with Pentax lenses). You can find out the "sweet spot" of your lens by looking at online reviews or just by studying your photos. If you can't notice a difference, its probably not important anyway Its just good to know that a lens at its lowest f-number or above a certain f-number, at certain focal lengths might not perform as well is it could. This explains why sometimes a photo appears a little fuzzy, even though there is no motion blur and the focus is good.
I would only worry about this if a) I was taking a photo where technical quality is important, like a product photo for a client and/or b) I was using a really bad lens with quality so low that only the "sweet spot" is acceptable. You can usually shoot raw and use lens profiles to digitally correct vignetting, distortion, and CA quite well. You can even add some sharpening and clarity, to make the photo appear more detailed and sharper.

Oh, and sometimes people refer to the sweet spot as crop sensor. Lenses tend to perform better in the middle of the frame than in the extreme edges. Since crop sensors are smaller than FF sensors, some say they only record the "sweet spot" of the lens' image circle, provided the lens projects a bigger image circle.

[todd]

Does this carry a custodial sentence?

Yikes maybe! I'd better hurry and go strip the exif! Or just keep an eye out for the Exif Sheriff...

[mgvh]

Lens sweet spot? Well, first, sweet spot doesn't matter if there are limitations on what I can do (e.g., low light requiring open as possible) or what I'm trying to accomplish (e.g., landscape w/ as much depth of field as possible). But, if I do have some flexibility, each of my lenses does have a certain length/f-stop where I have tested them and found that I can get the best pictures. So, I have created a little chart to help me recall. It's based on my observations of sharpness, contrast, and chromatic aberrations. Here's what it looks like:

Sigma 10-20

• Avoid 10mm if possible; best @ 20mm; use ~f8 @10; ~6.3@15mm; 5.6@20mm

Pentax DA 18-135

• Use f5.6>8 at wide end; f8-11 at long end

Pentax DA 21 f3.2 limited

• f3.2 ok but improves to 5.6-8 for best

Pentax DA 35 f2.4

• Great at f2.4 but improvement at f3.2-8; best at f4-5.6; still good at f8

Pentax F35-70

• Fine open but use f8

Pentax A50 f1.7

• Use f2/2.8 at minimum; best at f8; may need +1/3 or +2/3 EV

Pentax DA50 f1.8

• Use f2.8 at minimum < 4 < 5.6-8 > 11

Pentax DAL 55-300

• Best at f8/11 & even f16 @ long end for far

[houseofstyles]

Concerning diffraction, discussion seems to centre around F11 as being the start of this problem. But if diffraction results from light passing through a small hole, isn't this then a function of focal length, since F11 is a small opening in a 15mm lens, yet quite a large opening in say a 300mm lens?

[Imageman]

The term sweet spot has been used in golfing terms for longer than I care to mention, it refers to a spot on the club head that the ball flies sweetly and generates the best shot while feeling effortless, club manufacturers advertised large sweetspots in hollowed out irons.


I think this is just example of uneducated people using expressions out of context and trying to visualise lenses in the way they visualise golf clubs, as devices that have a magical property in one particular place.


There really isn't a sweet spot, a lens is sharpest in its center and stopping down uses proportionally more of the centre of the meniscus in each element, that's why lenses sharpen up the smaller the aperture until diffraction comes in at around f11.


Ive never in 50 years of photography heard that a lens is sharpest a couple of stops below widest aperture until very recently, and its certainly not supported by any real life tests that ive seen and ive seen plenty.


Ive seen countless enlargements and 100% crops that show sharpness increasing all the way to f8 and sometimes beyond. This supports the traditional view, stop down for sharpness and keep stopping down for greater sharpness until you hit diffraction.


Large format lens use was always compose fully open then stop down to f32 or f64 for maximum sharpness where was this sharpest is 2 stops below maximum aperture for the 150 years of photography that recommended f64 as the aperture for sharpness.


I think this is a spurious rule that has been recently made up that sounds right but in fact is nonsense.


Maybe some very modern lenses are sharpest at f4, but I seriously doubt it. Im happy to be convinced if someone has some crops supporting sharpest 2 stops below maximum, but this is not supported by any lens theory or real world experience that ive seen.


I keep hearing it though so can anyone prove this has any foundation in fact. It would be good to see some evidence of it because newbies are being told it as though its true, and they believe it.

[yusuf]

sweet-spot often doesn't make sense & and it also doesn't mean sharpness. Lens is sweet if it' usable across my aperture range and meets the criteria for that aperture.

For example, I would expect shallower DoF and nice smooth rendering at wide open even if the lens is less sharp. So a lens producing sharp but weird rendering at wide open (for example Nikon AIS 28 f2) is not in the sweet-spot even though it's sharp.

Also, I agree with post above, lens remains sharp whatever aperture you select, it's the apparent sharpness which varies because of focus, contrast, & the diffraction.

[zoolander]

I sometimes hear people on the board here refer to a lens "sweet spot"...

I am not a noob, but more information on specifically what this really means would help (as well as how to determine this information for my specific lenses).

I assume the 'sweet spot' is the aperture range where the lens is most sharp? Of course each lens has it's own personality as to where it's best. Or is it more than that?

I think it would be useful to write down and have this information for my particular lens collection. Mainly so I can use what I am being told and try to better self evaluate and examine my shots so in the end I can make better photography decisions.

Here is my lens list. DA 15mm, DA 21mm,F28 f2.8, FA 31mm, DA 40mm, FA 43mm, F50 f1.7, DA 70mm and a Tamron 70-200 f2.8 (I don't know if zooms have a sweet spot as much as primes do because of the varying focal length and aperture combination)

List away!

Here's what I plan on doing as an example: Go to Ephotozine or where ever: HD PENTAX-DA 15mm f/4 ED AL Limited Lens Review

Scroll down to the sharpness graph, take a printscreen> open it in windows paint> crop it> then colour print it> then laminate it> then attatch it to the lens with a rubber ban.

Each time you put that lens on, you'll have a little flip card showing the sweet spots of all your lenses. It could be infringing on copyright though to print somebody else's work.

[lytrytyr]

Im happy to be convinced if someone has some crops supporting sharpest 2 stops below maximum, but this is not supported by any lens theory or real world experience that ive seen. I keep hearing it though so can anyone prove this has any foundation in fact. It would be good to see some evidence of it because newbies are being told it as though its true, and they believe it.

For a textbook example, take a look at the Imatest resolution test of the DA 40 Ltd on the K5 here (Photozone):

Pentax SMC DA 40mm f/2.8 Limited - Review / Lab Test - Analysis

In general, the "sweet spot" in this sense
means the best balance between stopping down to minimize aberrations,
but not getting to the point where diffraction destroys the benefit.

It may be actually be fully open for an 8mm lens, yet f/64 in large format as you mention.

[6BQ5]

For a textbook example, take a look at the Imatest resolution test of the DA 40 Ltd on the K5 here (Photozone):

Pentax SMC DA 40mm f/2.8 Limited - Review / Lab Test - Analysis

In general, the "sweet spot" in this sense
means the best balance between stopping down to minimize aberrations,
but not getting to the point where diffraction destroys the benefit.

It may be actually be fully open for an 8mm lens, yet f/64 in large format as you mention.

I agree! Most of my modern lenses are sharpest from f/4 to f/6.3. Beyond that I get increased DoF but diffraction slowly begins to take over. When I say "most" that means I have "some" that are indeed sharpest starting at f/8 and keep getting sharper up to f/16. It all depends on the lens and it is something one needs to learn about their lens. In the digital age it's plenty easy to experiment. Put your camera on a tripod and snap a picture of a flower, a car, mail box, etc at different distances and different aperture settings. If it's a zoom then try three different focal lengths: wide, middle, and tele. Don't get too bogged down in it though.