shay_ohayon Posted August 30, 2005 Share Posted August 30, 2005 Ok, so I'm burning with fever because I caught the cold, and I am quite bored at home - so I decided to do a comparison test between my two favorite lenses - Canon 70-200 F4L, and Sigma 24-70 EX.I mounted the two on a 300D + tripod, and set both to 70mm.Much to my surprise - the images I got were not the same. It seems that the image with the 70-200, set on 70mm has a larger focal length than the image I got with the 24-70 set on 70mm. I did not move the camera orientation or tripod position between shoots. Any ideas ?!?!?!?! And please don't tell me to throw away the Simga piece of junk, and buy the 24-70L, since I am short on cash... :) Shay Link to comment Share on other sites More sharing options...
idoy Posted August 30, 2005 Share Posted August 30, 2005 I think this thread is relevant: <a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00CbWY">http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00CbWY</a> Link to comment Share on other sites More sharing options...
shay_ohayon Posted August 30, 2005 Author Share Posted August 30, 2005 Hi Ido, Yep. That was the problem. I was focusing at a distance of 1.5-2m. BTW - they are both quite sharp at the middle of the frame, but the 70-200 defenitly win when I compare conrners. Both have nice results at F8. F22-32 turned bit blury, but I guess it's because the 300D doesn't have a mirror lock, and expsure was almost 3 sec. Shay Link to comment Share on other sites More sharing options...
jim_roof Posted August 30, 2005 Share Posted August 30, 2005 Your blurriness at small apertures is probably due to diffraction rather than not using MLU. I would avoid stopping down any more than f11 if it can be at all avoided. Every lens will degrade at f16-f22 due to this phenomenon. Link to comment Share on other sites More sharing options...
bobatkins Posted August 30, 2005 Share Posted August 30, 2005 See <a href="http://www.bobatkins.com/photography/technical/diffraction.html">this article</a> for examples of how stopping down too far results in decreased image sharpness due to diffraction. I'd recommend not stopping down past f16 with a 20D/350D if maximum sharpness is your goal. Link to comment Share on other sites More sharing options...
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