Another question about Canon MTF charts, Sir/ Madam.

[surapon]

Dear friends and Teachers.
I have go back to Photography school/ Local Technical College more than 15 Classes in past 8 years, Start from The Beginning of Photography---To the Advance Photography, Wedding Photography and Studio Light Photography.
Many of my dear teacher teach me that, Most of the Lenses in this world have a sweet spot F. stop between F = 5.6 to 11.0, And the best sharpest corner to corner = F 8.0 , That Why Canon company use F/8.0 as the Blue Curve Line on their MTF chart, and Compare to the Most not too sharp in Black Curve line at the Maximum/ Widest aperture ---as the Black Curve Line on MTF chart.
---- QUOTE from Canon "
Here’s a breakdown of how to identify the different curves in a Canon MTF chart:

Black curve lines: lens performance at maximum, widest aperture.
Blue curve lines: MTF curves with lens stopped-down to f/8.
Thick lines: MTF data showing contrast — measured with thicker line sets on test target.
Thin lines: MTF resolution data — tests measure performance rendering thinner lines on test target.
Dashed lines: Lens’s MTF performance with harder-to-reproduce Meridional line sets.
Solid lines: MTF performance with Sagittal lines, arranged parallel to a diagonal from image center to corner."
And from the link:
http://www.learn.usa.canon.com/resources/articles/2013/reading_MTF_charts.shtml

Yes, I know that all MFG.s use difference MTF chart and difference setting, BUT, THE QUESTION IS =as my teachers teach me that Most of the Lenses , have the Best Sweet spot/ Sharpest F. Stop at 8.0 ----That still True ???.
Thanks you, Sir/ Madam.
Surapon

 

[Loswr]

BUT, THE QUESTION IS =as my teachers teach me that Most of the Lenses , have the Best Sweet spot/ Sharpest F. Stop at 8.0 ----That still True ???

It varies by lens. For example, based on photozone.de's tests for the two you listed, both lenses peak for center sharpness at f/4 and for mid-frame and corner sharpness at f/8 and f/5.6, respectively:

 

[mackguyver]

Surapon, since you shoot with L lenses, most of them are optimized to be at their best wide open or 1 stop down. This is generally true with all of the f/2.8 and f/4 L lenses, while the series II super telephotos are usually best wide open. The really fast lenses, f/1.2 and f/1.4, are usually best around f/5.6 or f/8, and some of the older lenses like the 135 f/2 are best around f/5.6. Most lenses have sharp centers wide open, and the center will improve some, but the biggest improvement will be in the corner sharpness.

Besides sharpness, vignetting is nearly always going to be reduced by stopping down, and that usually improves CA as well. Distortion isn't really affected by stopping down.

 

[surapon]

BUT, THE QUESTION IS =as my teachers teach me that Most of the Lenses , have the Best Sweet spot/ Sharpest F. Stop at 8.0 ----That still True ???

It varies by lens. For example, based on photozone.de's tests for the two you listed, both lenses peak for center sharpness at f/4 and for mid-frame and corner sharpness at f/8 and f/5.6, respectively:

Thousand thanks , dear Teacher, Mr. neuroanatomist.
Your Answer which make me very clear understanding , Now.
Yes, Sir, If I do not know, and do not ask the expert like you and our friends---I will stupid until I die----Thanks you, Sir.
Have a great day.
Surapon

 

[surapon]

Surapon, since you shoot with L lenses, most of them are optimized to be at their best wide open or 1 stop down. This is generally true with all of the f/2.8 and f/4 L lenses, while the series II super telephotos are usually best wide open. The really fast lenses, f/1.2 and f/1.4, are usually best around f/5.6 or f/8, and some of the older lenses like the 135 f/2 are best around f/5.6. Most lenses have sharp centers wide open, and the center will improve some, but the biggest improvement will be in the corner sharpness.

Besides sharpness, vignetting is nearly always going to be reduced by stopping down, and that usually improves CA as well. Distortion isn't really affected by stopping down.

Thank you, Sir, Dear Friend Mr. mackguyver.
I will learn from you , And memorize in every time that I take a snap shot , from now on.
Thanks again, and have a great day, Sir.
Surapon

 

[Mt Spokane Photography]

It is a general rule of thumb, that if you want border to border sharpness, f/8 is going to be best.

Many high end lenses will be sharpest in the center, but weaker on the edges and corners at wide apertures. That's not a issue for many images, but for those needing sharpness across the frame, f/8 is a good place to start.

 

[surapon]

It is a general rule of thumb, that if you want border to border sharpness, f/8 is going to be best.

Many high end lenses will be sharpest in the center, but weaker on the edges and corners at wide apertures. That's not a issue for many images, but for those needing sharpness across the frame, f/8 is a good place to start.

Thousand Thanks, my Dear Teacher, Mr. Mt Spokane.
Yes, To day my Day of Learning from Every CR. Members, include You too, Sir. The Sharpness that we want , at Center up to the corner of The Photos start from 1 stop down from the wide open of F. Stop to , Maybe 1 Stop, smaller hole from 8.0---That Depend on the Shallow DOF that we want
Have a great day, Sir.
Surapon