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Canon 18-200 versus Sigma 70-200
Apr 5, 2013 00:33:14   #
abc1234 Loc: Elk Grove Village, Illinois
 
I am comparing a Sigma EX DG APO HSM 70-200mm F/2.8 without image stabilization to my Canon 18-200 kit lens. I have shot a brick wall with both lenses, with and without a tripod, over a range of focal lengths, apertures, ISO's. I am not seeing any significant difference in sharpness between the two lenses.

My question to all of you is this: do you think the parity of the two lenses is due to viewing the pictures on a monitor or that the two lens are really the same optical quality?

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Apr 5, 2013 04:32:14   #
Leicaflex Loc: Cymru
 
My personal opinion is that you cannot compare optical quality and resolution by viewing your images on a back-lit monitor. My I suggest that you print out your two test shots, if you can to A3 size and then compare the two lenses.

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Apr 5, 2013 09:10:31   #
abc1234 Loc: Elk Grove Village, Illinois
 
Leicaflex wrote:
My personal opinion is that you cannot compare optical quality and resolution by viewing your images on a back-lit monitor. My I suggest that you print out your two test shots, if you can to A3 size and then compare the two lenses.


Thank you. That was my gut feeling.

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Apr 6, 2013 09:17:27   #
ole sarg Loc: south florida
 
The canon has some wide angle capabilities the sigma does not. what do you shoot and what do you need to accomplish that need?

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Apr 6, 2013 09:23:01   #
FredB Loc: A little below the Mason-Dixon line.
 
Comparing images on computer monitor is pointless. Unless you're using a $20,000 Sony studio monitor, both shots are being reduced to the same basic resolution.

You need to print them out at a size commensurate with their dimensions, at a decent printer DPI, one after the other, on the same type of paper. 5x7 is probably the smallest size I would ever use to compare two shots, and more often I'd go to 8x10 or even larger. If there is a visible difference, that's where you'd start to see it.

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Apr 6, 2013 09:35:09   #
abc1234 Loc: Elk Grove Village, Illinois
 
ole sarg wrote:
The canon has some wide angle capabilities the sigma does not. what do you shoot and what do you need to accomplish that need?


That is always the question and so many people here ask what to buy without knowing how they want to use it. Not just lenses but many other things.

The Canon 18-200 is excellent for what it does. What it does not do well is interior basketball games, concerts, events and other challenging lighting situations. I have too many shots with camera and subject movement, even at ISO 6400. Two solutions exist: buy a camera with higher ISO's or a f/2.8 lens. The camera is out due to cost and bulk and I am willing to shell out money for those two stops faster than what I have.

Sarge, you can stick in your two cents now. Thanks for the good question.

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Apr 6, 2013 10:06:57   #
abc1234 Loc: Elk Grove Village, Illinois
 
FredB wrote:
Comparing images on computer monitor is pointless. Unless you're using a $20,000 Sony studio monitor, both shots are being reduced to the same basic resolution.

You need to print them out at a size commensurate with their dimensions, at a decent printer DPI, one after the other, on the same type of paper. 5x7 is probably the smallest size I would ever use to compare two shots, and more often I'd go to 8x10 or even larger. If there is a visible difference, that's where you'd start to see it.
Comparing images on computer monitor is pointless.... (show quote)


Fred, Leicaflex got to me first. After a number of hand-held shots of a brick wall, I mounted the camera on tripod and shot the same wall at different focal lengths, ISO's, and apertures. I then sent the uncropped, unadjusted files to Costco for 8x12's. Next, I ranked the prints for a given focal length by sharpness. And, finally, I went back to the files to identify which lens and aperture belonged to each print.

From normal viewing distance, I am hard pressed to say a significant difference exists between the two prints when comparing the same relative aperture. When looking close up, the Sigma prints do look sharper but I do not know if this is due to the greater contrast or superior optics. I do know that post-processing will make all these prints look the same. I know that some readers will disagree with me strongly and I would like to hear their opinions.

The bottom line is I will buy the Sigma because I expect the faster lens to improve those low light shots. Any other benefits will be frosting on the cake.

Both lenses showed some spherical distortion. The appropriate lens profiles in Lightroom fixed them perfectly.

Fred, thank you for your interest.

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Apr 6, 2013 11:23:41   #
imagemeister Loc: mid east Florida
 
Technically speaking, it should be no contest - the Sigma better ! But you may have to go bigger than 8X12 to see it !

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Apr 6, 2013 11:51:51   #
abc1234 Loc: Elk Grove Village, Illinois
 
imagemeister wrote:
Technically speaking, it should be no contest - the Sigma better ! But you may have to go bigger than 8X12 to see it !


I agree with you. Bear in mind that the larger you make the print, the greater the viewing distance. The distance cancels the size so that the apparent sharpness is the same.

For how I intend to use the Sigma, I usually do not crop more than 50% and print only to 8x12. That is hardly pushing the lens.

Thanks for the comment.

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Apr 6, 2013 12:18:42   #
imagemeister Loc: mid east Florida
 
At 2.8, the Sigma should also focus quicker and more accurately .....which will figure into the apparent sharpness....

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Apr 6, 2013 12:45:57   #
abc1234 Loc: Elk Grove Village, Illinois
 
imagemeister wrote:
At 2.8, the Sigma should also focus quicker and more accurately .....which will figure into the apparent sharpness....


The two lenses did not appear to differ in speed and accuracy.

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Apr 6, 2013 13:36:45   #
imagemeister Loc: mid east Florida
 
At lower light levels they should .....

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