Sweet spot on the lens

[pitkin2020]

I have heard people talking about the lens having a "sweet spot", from what i get it means a certain F number on that lens being the sweetest spot and producing the best results.

But how do you know, is it a mathematical answer like the exact half of the range of F stops or is it just from reviewing the photos and finding it that way? Or is it just complete rubbish lol.

 

[Donki]

Its usually two or three even four stops down from wide open on your lens, but this is different different depending on your lens. TBH I never really worry about a "sweet spot" I chose an aperture that will give me the DOF I want to create.

 

[BandyQuill]

I have heard people talking about the lens having a "sweet spot", from what i get it means a certain F number on that lens being the sweetest spot and producing the best results.

But how do you know, is it a mathematical answer like the exact half of the range of F stops or is it just from reviewing the photos and finding it that way? Or is it just complete rubbish lol.

this is normally to be found on the lenses with a wider aperture (lower F number) for example my 50mm F1.8 sweet spot is closer to F4 than 1.8, but this isnt practical for a dimly lit room or when i want a shallow DOF and the sweet spot isnt much better than an image anywhere else in the range, just slightly sharper...

 

[pitkin2020]

Thanks for the info guys, so basically the sweet spot isn't that important compared with the composure of the shot and the required DOF.

 

[Original Poster]

this is normally to be found on the lenses with a wider aperture (lower F number) for example my 50mm F1.8 sweet spot is closer to F4 than 1.8, but this isnt practical for a dimly lit room or when i want a shallow DOF and the sweet spot isnt much better than an image anywhere else in the range, just slightly sharper...

Interesting, I will try F4 out on my 50mm tonight!

 

[Donki]

Thanks for the info guys, so basically the sweet spot isn't that important compared with the composure of the shot and the required DOF.

Not in my opinion no, say you have a fast lens 1.4 or even 1.8, they have a very shallow depth of field when used wide open so you not going to get a sharp picture from centre to edge anyway. Plus you pay your extra money for the wide apertures you should be using them instead of pixel peeping on sharpness. . DOF if a great creative way to express yourself in photography and gives depth to images so dont restrain yourself looking for a certain range of apertures that you think are the sharppest.

 

[HoppyUK]

Thanks for the info guys, so basically the sweet spot isn't that important compared with the composure of the shot and the required DOF.

Generally, that's true. In the centre, almost any lens will be very sharp at any aperture.

As you raise the f/number, everything gets better, but the edges and corners far more than the centre. Usually, the middle area is much more important than anything else, but if you're shooting landscapes then edge detail can be just as important.

The sweet spot is the point where the aberrations that are improved by raising the f/number (ie most of them), cross over with those that get worse (ie diffraction).

With a good quality lens, on crop format this will be around f/5.6, and on full frame it will be around f/8. Smaller formats like compacts or Four Thirds will peak at lower f/numbers, as diffraction is format dependent. Diffraction is really bad at high f/numbers - I would never use f/22 on a crop format camera unless absolutely forced, and only f/16 at a pinch.

Some lenses have two peaks - first the centre will peak, but then the edges will continue to improve while the centre begins to drop off slightly. But you have to look damn close to see it.

 

[Digifrog]

Generally f/8, or thereabouts.