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Photography Question 

Suzanne Colson
 

Test a lens for Sharpness


I finally splurged for a Canon L lens. I just got my 70-200mm f/4 IS lens a couple of days ago and have taken many shots and quite pleased. Appears very sharp, great colors and contrast. I think the images are quite sharp, but I hear of so many people having 'soft' copies that I would like to put the lens to a thorough test. I have 3 weeks to return and want to make sure. What is the best way to thoroughly test it.


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April 29, 2007

 

Christopher A. Walrath
  How about some sort of measuring device, tape measure large enough to see the marks further away. Lay it on the floor and just above the end of the tape or whatever, focus at 5 feet and see if the big '5ft' comes in 5 by 5. Try this for other distances and at various focal lengths. Make sure to make notes about which exposure relates to which distance.


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May 02, 2007

 

Pete H
  Hello Suzanne,

Lenese are tested all over the web. There are myriads of not only user reviews, but optical theoretics on all lenses.
Why not save time and read them?..That way you have more time to shoot subjects, rather than Ronchi gratings. LOL

http://www.fredmiranda.com/reviews/showproduct.php?product=14&sort=7&cat=27&page=2

http://www.wlcastleman.com/equip/reviews/300mm/index.htm

http://www.luminous-landscape.com/reviews/lenses/70-200is.shtml

http://www.popphoto.com/cameralenses/3855/lens-test-canon-70-200mm-f4l-ef-is-usm-af.html

http://www.kenrockwell.com/canon/lenses/70-200mm-f4.htm

All the best,

Pete


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May 02, 2007

 

Suzanne Colson
  I poured over those sites before the purchase and what I interpreted was a quality control problem with lens, not just Canon. Some copies can be very sharp and some can have focusing problems as well as not being as sharp as it should be. I am just hoping I didn't end up with one of these.


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May 02, 2007

 

Pete H
  True indeed, pro-sumer lenses have QC difficulties....whiich is why the cost is in the 100's, not thousands.

If you have concerns, there are many "test" patterns you can purchase...Or if you feel ambitious, make one yourself.

Generally, I would look at the len's sweet spot, usually around f/8-f/11.

"Softness" at f/4 isn't necessarily a bad thing...great for portraits of people.

Things of concern and what to look for:

1) Light falloff; esp at the edges.
2) Chromatic abberations..or false colors at the margins of a hard line.
3) Focus errors.

Shoot about 50 shots at the same subject, same "f" and speed. f/8 would be a good choice.

Scrutinize the images for consistancy.
A post processing histogram may be of help as you cycle thru the test images.

All len's have their strong AND weak points; so it is equally important to learn your lenses as well as your camera.

Pete


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May 02, 2007

 

John Rhodes
  Suzanne, it seems to me you have already performed a significant test as you said "...and have taken many shots and quite pleased. Appears very sharp, great colors and contrast. I think the images are quite sharp." What else matters?

John


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May 03, 2007

 
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