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Message: <blockquote data-quote="a.dancy" data-source="post: 1326015" data-attributes="member: 25708">Attached is a sequence of shots of shelduck in flight using Sigma 300 f2.8. note the numbers on the frames which is a testement to the Canon 20D as well as the lens's autofucus, with the bird flying toward me<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />: each shot is a 50% crop. You should be able to read the exif data which should indicate f5. Forgive the minor blowout of the white on the leading edges of the wings...I'm not perfect<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" /> . The shutter speeds are relatively slow for BIF.The white headed duck is a huge crop taken using 40D ( 75% crop ) non of the images have been sharpened or processed other than resizing, so there is a loss of sharpness/quality in compression.The canon is the superior lens having distance limiters and IS. The sharpness at F5.6 and above is close to the Canon's. You will have difficulty telling them apart. Wider open the Canon does perform better but you still get razor sharp images at f2.8. but remember you will not want to shoot with such shallow DOF frequently.The Sigma 300 f2.8 is sharper than the 120-300 zoom and any reference to the contrary is utter tosh ( internet myth started off by a salesman) but the zoom is still very sharp.The Sigma 300 with 1.4X converter performs very well indeed and you should get razor sharp shots. With a 2X converter not so well but you may expect that. You can still get acceptable images fit for publication. You will need to boost contrast and you may get a touch of CA where you get white highlights...but not all the time. You can still have this problem with the canon but either way it can be sorted in PS. A tripod is nearly always a must when needing a 2X converter. Check out some of my wheatear shots in the gallery where I have used the 2X converter.Check out my gallery grey heron shot where I have used a 2X converter and 1.4 stacked.As stated the Canon is the superior lens in every way but to put things into perspective I believe the 300 prime is the most under rated lens there is. The lens is of solid construction. The focus wheel is a touch stiff but no problem. Yes, I would like the Canon but I am very happy with the Sigma. If you you are thinking of continually using longer focal lengths then get a longer lens.The Canon 300f4 is an excellent choice. It is far easier to carry about and is very sharp.I disagree about the Canon being over priced and of old technology. It is probably the sharpest lens in the pack but you still get a lot of  bang for your bucks with the Sigma in my humble opinion.As with any lens you must use what ever lens you have and take advantage of that lens's specific qualities and attributes. If you do not you do no justice to yourself or the lens. AD</blockquote>

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