Canon 70-300 is f4/5.6 usm 60d blurry and soft photos

[Robodot]

I brought this up a few weeks back without any real solid answer so I thought i would provide one to anyone who might be interested in putting a full frame lens on a crop sensor camera like i did.

I independently came to a conclusion by testing further, this lens was only sharpest at 300mm with F9+. I recently found out that many, many, many people who own this lens came to the same exact conclusion. as I did.

So i dug a little more (trying to decide to keep Canon or go to another brand) this is what I discovered:

When you use a full frame lens (EF) on a crop sensor camera, not only do you multiply the crop factor for the focal length, you also must "multiply the aperture" by that crop factor.

So on my lens, instead of being a f4/5.6 as Canon states is really a F6.3 / F9.

what does this mean in the real world, you will not be able to separate the subject from the background or use in lower light levels without noise.

[ebiggs1]

"When you use a full frame lens (EF) on a crop sensor camera, not only do you multiply the crop factor for the focal length, you also must "multiply the aperture" by that crop factor."

I think one of the most misunderstood thing about crop factor, a term I wish had never been invented, is the word "equivalent".  The lens itself does not change by mounting it on a different format body.  It is simply how the camera sees the lens' AOV. A lens can not change its physical characteristics once it is ground. A Pentax 645 has a 'crop factor' of .8 but you never hear people referring to that. The big Hassie is .64. Again you rarely hear anything about its equivalent values.  The term stuck for APS-C bodies.

Another silly part of all this is nothing is actually 'cropped'. You have to be thinking 35mm to think it is. It is as FF as any FF camera is.  The AOV is what changed.  Simple isn't it?