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Is lens calibration the answer?


Keelo 17 18 Australia
11 Aug 2006 5:52AM
Hi all

Just wondering if anyone has had a lens recalibrated. I have a Canon 17-35L lens, and from what I have read on the net and in magazines, its nowhere near as sharp as the later version, the 16-35L. My question is, will calibrating help improve sharpness or am I throwing good money away, don't get me wrong, I've had this lens for a number of years and its served me well (most of the landscape shots in my PF were shot using it) but I can't help thinking it can be better. Images at small appetures like f16/f22 are Ok but below that, things like tree foliage at medium distances, 50 feet or so start to look mushy. Also theres the topic of chromatic abberation, will calibration help with that? Your thoughts and experiences would be most helpful.

Cheers
Mark
keithh 17 25.7k 33 Wallis And Futuna
11 Aug 2006 8:36AM
well I wouldn't say it was nowhere near as sharp, just not as...are we not getting Depth of Field confused with sharpness here.

I know for a fact, because I had one, that the 17-35 was not as sharp at f22 as it was at f11. What you're seeing is the difference in applied DOF and how sharp things appear outside of it. Mid and distance objects will appear softer, out of focus, purely because they are outside the focal plane of your chosen aperture, no amount of calibration will alter that. I always found that the 17-35 was at it's best for landscape work at f16.

Having the lens re-calibrated will only improve - if it was needed - the lenses ability to focus. You could always have the focusing checked...and it would be cheaper.
User_Removed 17 17.9k 8 Norway
11 Aug 2006 12:03PM
You might also find this article very enlightening when it comes to image sharpness Mark. Be aware that to get the maximum benefit from the interactive demonstration, you will need to have 'Java' installed. This has changed my approach to matters pertaining to DoF and overall image sharpness.

HTH's...
Keelo 17 18 Australia
11 Aug 2006 8:42PM
Thanks for the replies chaps, Keith, you're probably right, lens sharpness and depth of field,are two diferent things, although I was always under the impression that with a wide angle lens and small aperture, depth of field would extend from the hyperfocal point to infinity and everything would appear sharp. However saying that,Mike I found the article in you're link very good, adding lens difraction, airy disks and circles of confusion into the debate has actually helped me understand it all a bit better, although I will have to read it a couple of times to get my head around it. Any way thanks again for taking the time to reply.
Mark
nikon5700ite 17 1.8k
11 Aug 2006 10:10PM
Depth of field is a subjective assesment and one of the parameters is the degree of magnification. So if you are closely examining your results you are quite possibly pushing the magnification way above that which the DoF tables/markings apply to.

Greater magnification equals less DoF becuase the circle of confusion is being enlarged and becomes a circle instead of appearing as a dot to the viewer's eye.

Magnification is not only the size of the print but also the distance from which it is being viewed.

Move back and all will be well Smile
User_Removed 17 17.9k 8 Norway
12 Aug 2006 7:44AM

Quote:I will have to read it a couple of times to get my head around it.


You're right about that Mark - took me a couple of reads to get my head round it! Very worthwhile though...

Glad to have been of help.

Mike

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