Optimal Performance for each lens


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drazic

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Apr 12, 2006
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#1
How to determine what aperture settings that gives the optimal performance of any lens ?
Example if i have a lens with f3.5 to 4.5 on each end, does it mean that the lens performance is at its best if i stop down 2 stops ?

same goes for prime lens example those with f1.8, does it mean its much sharper at 2.8 ?
 

ExplorerZ

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#2
drazic said:
How to determine what aperture settings that gives the optimal performance of any lens ?
Example if i have a lens with f3.5 to 4.5 on each end, does it mean that the lens performance is at its best if i stop down 2 stops ?

same goes for prime lens example those with f1.8, does it mean its much sharper at 2.8 ?
depends on each lens, but most are sharpest when stopped down 2 stops, can be more can be less. if you are unsure, just stop down 2 stops
 

smallaperture

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Jan 5, 2004
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#4
Why is there such an obsession with sharpness? As long as the pic look sharp, I am happy with it - there are a host of other attributes that are important as well like composition, colour, contrast, mood, feeling, depth of field, bokeh, etc, etc........
 

singscott

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#5
honda said:
mostly centre performance best at f5.6 to f8, border best at f8 to f11.
http://singaporephoto.blogspot.com
If you look at MTF graphs from lenes manufacturers. Indeed the sharpness peak at F-stops at the mid range. So F1.4 to F16 lens the optimal sharpness is at F5.6 to F8. Again a F2.8 to F22 lens the optimal sharpness is at F8 to F11. Sometime you don't have a choice but to use aperture at the ends range because of lighting situation or the in order to get certain DOF. Then again is good to know.
 

honda

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Nov 30, 2004
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#6
its more useful to take photos at the wide open aperture n see if it is sharp enough for u. most of the time u will find it is good enough. for example i find the kit lens 18-55 for 350 sharp enough wide open but the aperture is too small at 5.6 for 55mm compared to the sigma 18-50/2.8. sure there is a difference between wide open n optimal aperture but its not noticeable if u dont compare. anyway different lens have different image quality comparing different brands, different models n different settings on the camera n postprocessing make alot of difference.
http://singaporephoto.blogspot.com
 

wind30

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Mar 14, 2004
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#7
drazic said:
How to determine what aperture settings that gives the optimal performance of any lens ?
Example if i have a lens with f3.5 to 4.5 on each end, does it mean that the lens performance is at its best if i stop down 2 stops ?

same goes for prime lens example those with f1.8, does it mean its much sharper at 2.8 ?
actually it all depend on the lens your have and the body you are using.

Example my olympus 14-54mm on a 5MP E1 is sharp wide open. Stopping down has not much improvement as the lens is out resolving the 5MP res even wide open.

When I had a sigma 20mm f1.8 on 6MP KM7D, I had to stopped down to f2.8 or enven f4. It was really soft at f1.8.

Now I have a tamron 28-75mm f2.8 on a s3pro. It is a bit soft at 75mm f2.8, just stopping it to f3.3 improves a lot.

All depends on the lens and body you are using. So got to test it yourself. Furthermore depends on whether your lens copy is good also.
 

honda

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Nov 30, 2004
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#8
one objective way of looking at the lens performance is to go to the manufacturer website n study the mtf charts. the mtf chart tells you the lens contrast n resolution at the wide open aperture n sometimes optimal f8 aperture.
http://lewwl.zoto.com//galleries/singaporephoto
 

txv611

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Aug 20, 2005
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#9
Agree. MTF chart are useful as a GUIDE to learn about the characteristics of your lens. The curve on the MTF tells you the optimal working conditions. If comparison of MTF between lenses are necessary, they should be based on the same focal length.

Primes and 'L" lenses are almost certainly the winner in MTF charts. Of course there are more to sharpness and contrast. You cant see color tone characteristics on the chart so MTF charts are not always the determining guide in choosing your lens.

Note: On 1.6X bodies, you can ignore part of the drop off in the end of the curve in the MTF charts of full frame lenses (EF only, Not EFS) since they wont be capture by the image sensor.


honda said:
one objective way of looking at the lens performance is to go to the manufacturer website n study the mtf charts. the mtf chart tells you the lens contrast n resolution at the wide open aperture n sometimes optimal f8 aperture.
http://lewwl.zoto.com//galleries/singaporephoto
 

solarii

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Oct 20, 2005
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#10
txv611 said:
Agree. MTF chart are useful as a GUIDE to learn about the characteristics of your lens. The curve on the MTF tells you the optimal working conditions. If comparison of MTF between lenses are necessary, they should be based on the same focal length.

Primes and 'L" lenses are almost certainly the winner in MTF charts. Of course there are more to sharpness and contrast. You cant see color tone characteristics on the chart so MTF charts are not always the determining guide in choosing your lens.
Very true. Think its best to judge image quality of the pics taken by a lens as whole... sharpness is ony one criteria. Colour is an equally important factor that's often neglected since it can't be measured quantitatively.

Sigma makes quite a few lenses that are very "sharp", even better than the canon equivalents, but they lack far behind in terms of colour vibrancy. Sure, u can use PS, but its not quite the same.
 

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