Generally speaking, the Canon EF 100mmis a great lens. The bokeh is fine. The lens is pretty fast. f/2.8 to f/22 is useful as a creative range. The optics are sharp and the all-time focusing is a boon. So what’s not to like? Well, here’s the thing. The Canon EOS50D, which I use, has the ability to use the viewfinder in “live preview” mode, and when doing so, will allow you to zoom in on your focus point (or anywhere else, but that’s irrelevant to my point here) such that you can see extremely fine detail. At which point you can manually focus the lens so that it is exactly right. Marvelous, right?
It would be. But the lens has some mechanical backlash problems. Let me explain backlash; if you’re not familiar with it, it takes a bit of describing.
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The 






![fyngyrz posted a photo: The map location here shows where I was when I took the photo, rather than the photo itself. I was looking west (obviously) from the north end of the church parking lot which itself is north of Bonnie Street, and south of Airport Road. I jockeyed around until I had the sun completely behind the radar housing, and then shot a few shots at different exposures, hoping that the 50D's dynamic range would catch the gradation in the sky; it did ok, but I still wish we had another couple of high quality bits of dynamic range. Maybe the next camera generation will go there. Canon EOS 50D [modified IR response in Hα range], hooded Sigma EF-S 30mm ƒ/1.4 EX DC HSM prime [ø62mm] w/B&W 62mm IR/UV cut filter #65-014691; RAW to JPEG conversion and editing in Aperture 3. fyngyrz posted a photo: The map location here shows where I was when I took the photo, rather than the photo itself. I was looking west (obviously) from the north end of the church parking lot which itself is north of Bonnie Street, and south of Airport Road. I jockeyed around until I had the sun completely behind the radar housing, and then shot a few shots at different exposures, hoping that the 50D's dynamic range would catch the gradation in the sky; it did ok, but I still wish we had another couple of high quality bits of dynamic range. Maybe the next camera generation will go there. Canon EOS 50D [modified IR response in Hα range], hooded Sigma EF-S 30mm ƒ/1.4 EX DC HSM prime [ø62mm] w/B&W 62mm IR/UV cut filter #65-014691; RAW to JPEG conversion and editing in Aperture 3.](http://farm5.static.flickr.com/4078/4912161604_6cd46bace2_m.jpg)



