July 25, 2014, 07:13:47 PM

Author Topic: Sharpest f stop for a lens?  (Read 7428 times)

sanjosedave

  • Canon AE-1
  • ***
  • Posts: 76
    • View Profile
Sharpest f stop for a lens?
« on: September 14, 2013, 09:31:16 PM »
So, I'm watching Rod Goodman's video on B&H about headshots.

He said the reason he shoots at 5.6 is that a lens is sharpest two stops from wide open, he shoots with the 70-200 2.8

Is this a myth or true? I have never heard of such a thing before

canon rumors FORUM

Sharpest f stop for a lens?
« on: September 14, 2013, 09:31:16 PM »

neuroanatomist

  • CR GEEK
  • ********
  • Posts: 13546
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #1 on: September 14, 2013, 09:35:28 PM »
It's true for many lenses (perhaps even most) that they're sharpest 1-3 stops down from wide open. 
EOS 1D X, EOS M, and lots of lenses
______________________________
Flickr | TDP Profile/Gear List

takesome1

  • EOS M2
  • ****
  • Posts: 245
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #2 on: September 14, 2013, 09:37:11 PM »
So, I'm watching Rod Goodman's video on B&H about headshots.

He said the reason he shoots at 5.6 is that a lens is sharpest two stops from wide open, he shoots with the 70-200 2.8

Is this a myth or true? I have never heard of such a thing before

Both myth and true, it isn't necessarily 2 stops. Stopped down most get sharper. Some you do not have to stop down as much or very little. Some lenses are sharp wide open and only have a bit of improvement, like most of the big white telephoto's.
Also you get a wider DOF and some might interpret that as being sharper, at least makes it seem sharper.

pwp

  • 1D X
  • *******
  • Posts: 1455
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #3 on: September 14, 2013, 11:28:33 PM »
So, I'm watching Rod Goodman's video on B&H about headshots.
He said the reason he shoots at 5.6 is that a lens is sharpest two stops from wide open, he shoots with the 70-200 2.8
Rod Goodman, while simplifying his case, is pretty much right. While QC is usually pretty good, being mass produced items, YMMV with any lens. My current 70-200 f/2.8isII looks sharpest at f/4.5-f/5. Others I've had may have a sweet spot at f/5.6. As a general rule of thumb, it's the middle apertures in the f/5.6-8 range that most photographers will report as being a lenses sweet-spot for maximum edge to edge sharpness.

I know it sounds crazy, but my new 24-70 f/2.8II is so good I can barely distinguish between infinity focused shots at f/2.8 or f/5.6. All pin sharp edge to edge. Extraordinary. Let's hope this is the new standard. It's definitely not the norm.

For the most part, few lenses are going to deliver maximum sharpness wide open or shut right down to f/16 or F/22. Some macro lenses may be optimized for good sharpness at F/16.

Prove it for yourself and run controlled tests, tripod mounted, with your different lenses. Lock onto the same focus point and run through the apertures in one-stop increments. Be sure you're shooting fast enough so there is no camera shake. Don't use AI focus for this test. Be very careful and sure with your focus lock. You'll learn a lot about lenses in general.

-PW

neuroanatomist

  • CR GEEK
  • ********
  • Posts: 13546
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #4 on: September 14, 2013, 11:37:52 PM »
Prove it for yourself and run controlled tests, tripod mounted, with your different lenses.

The Pro version of Reikan FoCal has an Aperture Sharpness test that plots sharpness over the aperture range for your lenses.  Pretty handy, especially since it tells you about your own copy, not a different copy of the lens which someone else tested.
EOS 1D X, EOS M, and lots of lenses
______________________________
Flickr | TDP Profile/Gear List

Pi

  • 1D Mark IV
  • ******
  • Posts: 937
    • View Profile
    • Math and Photography
Re: Sharpest f stop for a lens?
« Reply #5 on: September 14, 2013, 11:45:39 PM »
Pretty much a myth. The sharpest aperture for quality primes is around f/4 - f/5.6 but closer to f/4. For some superfast lenses, it can be a bit to the left of f/4. Look at the Zeiss primes, the f/1.4 and the f/2.8 ones differ very little with respect to the "sweet spot".

Near the borders, things change, and f/5.6 or even f/8 may be the best.

BTW, this is of almost no practical use anyway unless you are shooting a chart.
« Last Edit: September 14, 2013, 11:53:06 PM by Pi »

takesome1

  • EOS M2
  • ****
  • Posts: 245
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #6 on: September 15, 2013, 12:05:48 AM »

BTW, this is of almost no practical use anyway unless you are shooting a chart.

Sure it is. We spend thousands of dollars on expensive gear to gain a little IQ that for the most part we only see if we pixel peak. Then if we ignore the sweet spot on our lens we ignore something that improves the IQ of our pixel peaking for free.

Personally I know the sweet spots of my lenses and balance it with the DOF I want to get the best results I can.

canon rumors FORUM

Re: Sharpest f stop for a lens?
« Reply #6 on: September 15, 2013, 12:05:48 AM »

privatebydesign

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 2057
  • Ermintrude says "moo"
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #7 on: September 15, 2013, 12:19:00 AM »
BTW, this is of almost no practical use anyway unless you are shooting a chart.

Unless you are using a TS-E, then knowing the "sweet spot" is very relevant.
The best time to plant a tree is twenty-five years ago. The second best time is today.

Pi

  • 1D Mark IV
  • ******
  • Posts: 937
    • View Profile
    • Math and Photography
Re: Sharpest f stop for a lens?
« Reply #8 on: September 15, 2013, 12:37:52 AM »

BTW, this is of almost no practical use anyway unless you are shooting a chart.

Sure it is. We spend thousands of dollars on expensive gear to gain a little IQ that for the most part we only see if we pixel peak. Then if we ignore the sweet spot on our lens we ignore something that improves the IQ of our pixel peaking for free.

No, it is not. DOF, noise level, subject movements, border performance, etc., are far more important factors for choosing an f-stop. I would never shoot with the 135L or the 85L at f/2.8 instead of f/4 or vice versa just because some test site tells me that one of the f-stops is 5% sharper than the other. It will be sharper in a tiny plane of focus anyway and it would not necessarily give the best overall look, unless you are shooting a chart.

Unless you are using a TS-E, then knowing the "sweet spot" is very relevant.

I am not sure what you mean. I would always stop down because you are never sure that you adjusted the tilt and shift well enough, and when using those functions, you are pushing the limits of the optics anyway. All those pretty charts tell you little about the performance with T&S. PZ has some data actually, which shows that you'd better stop down. If this is what you meant, then I agree.
« Last Edit: September 15, 2013, 12:44:39 AM by Pi »

MLfan3

  • Rebel T5i
  • ****
  • Posts: 109
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #9 on: September 15, 2013, 12:46:48 AM »
So, I'm watching Rod Goodman's video on B&H about headshots.

He said the reason he shoots at 5.6 is that a lens is sharpest two stops from wide open, he shoots with the 70-200 2.8

Is this a myth or true? I have never heard of such a thing before

it is correct , most of lenses are sharpest at f5.6 or f4.

takesome1

  • EOS M2
  • ****
  • Posts: 245
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #10 on: September 15, 2013, 12:48:55 AM »

BTW, this is of almost no practical use anyway unless you are shooting a chart.

Sure it is. We spend thousands of dollars on expensive gear to gain a little IQ that for the most part we only see if we pixel peak. Then if we ignore the sweet spot on our lens we ignore something that improves the IQ of our pixel peaking for free.

No, it is not. DOF, noise level, subject movements, border performance, etc., are far more important factors for choosing an f-stop. I would never shoot with the 135L or the 85L at f/2.8 instead of f/4 or vice versa just because some test site tells me that one of the f-stops is 5% sharper than the other. It will be sharper in a tiny plane of focus anyway and it would not necessarily give the best overall look, unless you are shooting a chart.

It all matters. If you ignore one, then two things they compound on your IQ. One may have a greater impact than the other but they all matter.

Sweet spot matters, two examples both I know by experience and using tests;

My 35mm the spot starts at about 1.8 to 2.2, any wider and the quality falls quickly. The narrow DOF of the 35mm is what makes it a really great lens, go less than 1.8 and the IQ falls quickly. Knowing this I can take full advantage of my lens.

My 500mm the sweet spot is 4.5, wildlife is wild and cropping images is the norm. You need every advantage you can take to have an acceptably sharp image when you do have to crop. A bit less sharpness can mean the difference between a usable image and not.

duydaniel

  • 7D
  • *****
  • Posts: 341
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #11 on: September 15, 2013, 01:03:29 AM »
usually the sharpest one is either:

- 3 stops from widest open
- half of your smallest aperture. for example if f22 is your smallest, then f11 is your sharpest

but if you want white paper... maybe take a look at DxO  ::)

Pi

  • 1D Mark IV
  • ******
  • Posts: 937
    • View Profile
    • Math and Photography
Re: Sharpest f stop for a lens?
« Reply #12 on: September 15, 2013, 01:07:07 AM »
It all matters. If you ignore one, then two things they compound on your IQ. One may have a greater impact than the other but they all matter.

Sweet spot matters, two examples both I know by experience and using tests;

My 35mm the spot starts at about 1.8 to 2.2, any wider and the quality falls quickly. The narrow DOF of the 35mm is what makes it a really great lens, go less than 1.8 and the IQ falls quickly. Knowing this I can take full advantage of my lens.

We are talking about different things. Of course, you have to know your lens. But the sweet spot for the purpose of this thread is somewhere between f/2.8 and f/4. And you are talking about narrow DOF and f/1.8-2.0. If somebody told you tomorrow that the sharpness across the frame is maximized at f/5.6, would you shoot at f/5.6 instead of at f/1.8 when you want that shallow DOF?  Or would you always shoot at f/5.6 for maximal sharpness even though your object is most likely not flat and not in the center only?

canon rumors FORUM

Re: Sharpest f stop for a lens?
« Reply #12 on: September 15, 2013, 01:07:07 AM »

takesome1

  • EOS M2
  • ****
  • Posts: 245
    • View Profile
Re: Sharpest f stop for a lens?
« Reply #13 on: September 15, 2013, 01:22:44 AM »
It all matters. If you ignore one, then two things they compound on your IQ. One may have a greater impact than the other but they all matter.

Sweet spot matters, two examples both I know by experience and using tests;

My 35mm the spot starts at about 1.8 to 2.2, any wider and the quality falls quickly. The narrow DOF of the 35mm is what makes it a really great lens, go less than 1.8 and the IQ falls quickly. Knowing this I can take full advantage of my lens.

We are talking about different things. Of course, you have to know your lens. But the sweet spot for the purpose of this thread is somewhere between f/2.8 and f/4. And you are talking about narrow DOF and f/1.8-2.0. If somebody told you tomorrow that the sharpness across the frame is maximized at f/5.6, would you shoot at f/5.6 instead of at f/1.8 when you want that shallow DOF?  Or would you always shoot at f/5.6 for maximal sharpness even though your object is most likely not flat and not in the center only?

Why do I have to say only the sweet spot matters, if I disagree with you that it does matter?
I would take all in to account and not ignore one. I am saying they all matter.
If you want to ignore all of these things we could just say "F/8 and be there"


Marsu42

  • Canon EF 400mm f/2.8L IS II
  • *******
  • Posts: 4356
  • ML-66d / 100L / 70-300L / 17-40L / 600rts
    • View Profile
    • 6D positive spec list
Re: Sharpest f stop for a lens?
« Reply #14 on: September 15, 2013, 02:13:04 AM »
Is this a myth or true? I have never heard of such a thing before

it is correct , most of lenses are sharpest at f5.6 or f4.


I'd prefer neuro's answer vs. absolute f-stop numbers - usually it's some stops down from wide open and might be different from center to corners. L lenses should be at least very usable wide open, but even this sometimes isn't the case - take the 50L/1.2, or for example the 17-40L/4 is sharpest @f11... the tdp widget is the best way to find out:

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=100&Camera=453&Sample=0&FLI=5&API=3&LensComp=100&CameraComp=453&SampleComp=0&FLIComp=5&APIComp=4

canon rumors FORUM

Re: Sharpest f stop for a lens?
« Reply #14 on: September 15, 2013, 02:13:04 AM »