Which aperture setting takes sharper images. f/8 or f/11?

[raaskohx10]

I have t2i (550D) and two lenses i.e. 18-55 mm and 55-250 mm. Any idea how to take sharper images of landscape by selecting a particular aperture setting? I read on a different forum that for sharper images f/8 or f/11 are the ideal settings. Any suggestions?

[cicopo]

Every lens is different but the general feeling is that the sweet spot is in that area. Use a tripod & shoot some carefully selected scenes to see how yours do.

[Samsen]

Yes every lens behave in its own terms but in general you get your softest image when lens is fully open and that significantly gets sharper as you close the F by 2 or 3 stops, on any instances only 1 to 2 stop.

So if in doubt just close 2 - 3 stop or run your own test.

[Samsen]

Also to answer your second part of question, between F 8 and 11, (That falls after 3 stop from wide open) probably there is no significant difference sharpness or lesser light and more DOF on F11.

[ebiggs1]

"...  two lenses i.e. 18-55 mm and 55-250 mm. ..."

Using either of these two lens mentioed I will guess F8 is best.

[ScottyP]

A lot of the "rules of thumb" out there are based on FF sensors.  You need to dial a lot of things back 1 1/3 stops for a crop sensor when it comes to depth of field.  I suppose that may include the sweet spot, although that is more to do about lens resolution/distortion than the sensor.

It should not matter all that much, as the difference would be slight.  If I were going to guess, I would set my "thumb" back to compensate and say f/8 is sharper than f/11 on a crop? 

As mentionied, I do know for sure that the depth of field you will get is affected by the crop, by 1 1/3 stops of deeper DOF.  Your f/8 will look like what photography authors would consider about f/12.7 or something.  Your f/11 will look like what they'd call f/18 or so.

[Samsen]

Seems this topic is having many hits so let me give some more info that might be useful to all:

When you need to know real detail analysis of a lens, there is no better place to check than:
PhotoZone

Specific to your question are the 2 links below. Just scroll down to MTF  or Modulation Transfer Function  also known as spatial frequency response (Way sharpness is measured objectively) That let you know exactly what you wanted to know about the sharpness. 

Link to EF-S 18-55mm IS

Link to EF-S 55-250mm

The site should be very useful for any one eager to know specifically a detail about any lens so enjoy.

[domina]

These lenses are good for general use, but if you want a very sharp lens then get the Canon EF 35mm f/2 (which costs about $260 I think), or the Canon EF 50mm f/1.8 (about $90), or find old manual-focus lenses like Jupiter-37A 135mm f/3.5 (about $40 but you'll also need an adapter). You can also emulate sharpness with software (Canon's Digital Photo Professional or in-camera processing), and make sure you use a tripod so there won't be any camera shake. Aperture numbers higher than f/11 or f/13 may produce unsharp images due to diffraction, while aperture number lower than f/5.6 may produce soft images due to the lens itself, so better stick with apertures between f/5.6 and f/10 for maximum sharpness. However, perceived lack of sharpness may be more related to very low depth of field (dof). To increase dof you can use higher f-numbers, as the softness caused by diffraction is less important than the softness caused by low dof. You can calculate the best dof to use by searching on-line for a depth of field calculator and then find the hyperfocal distance you need to use. (there are some smartphone apps for that).

[jdavis1877]

looks like the MTF on the 15-85 is 5.6 for almost all lengths, stay with 5.6 and 8 and you should be in sweet spot