I just need to bounce this off someone who may know the scoop. I have had my Sigma 150-500 for about a year and a half, and have had mixed success with it (with my Canon 6D). Shooting handheld has been, for the most part, a complete failure (regardless of the shutter speed), so I shoot primarily on tripod with shutter release. I've come to the conclusion that if the subject is over 100 feet, my success of getting a sharp image is around 10%, and if it is a bird, probably less than that (I seem to have a bit better success with larger animals). Inside of 100 feet I have gotten some very good, very sharp images. So the question is, is this fairly normal? I've done the focus calibration thing, and it seems to be good. I primarily use AF, single point, and have tried establishing focus on bodies, eyes, edges, etc. with no appreciable difference in success. OS is turned off. Is this just the difference between a 1K lens and a 8K lens? Any other thoughts would be appreciated. ( I have included a recent example for your review. This was probably at about 125 ft, tripod, remote release)

Yes. you can either shoot at your current settings and use a lower ISO for less noise, more dynamic range and better color, or you can combine slightly lower ISO with slightly higher shutter speed / smaller aperture.

Are you using a Sigma lens or a Canon. Your listing is confusing.

If you have the Canon lens, and it is this one:

http://www.photozone.de/canon_eos_ff/558-canon70300f456isff?start=1

Then you have a great lens, so upgrading the camera is a good way to go. But I would go for the 5D MkIII which is a far better piece of equipment - I just found one with low miles (3000 clicks) doing a casual search on ebay with a buy-it-now price of only $1400. You should be able to find a nice one for anywhere from $1400 to $1800 and you will be quite happy. At some point in the future after a successful trip to Las Vegas, you can get the expensive fast glass.

I always read these BBF conversations with a bit of interest AND with a grain of salt!
TOO many of these conversations start to sound like those of the manual mode shooters, as if BBF is somehow inherently better.
As with a lot of this, BBF is better for some shooting but not for others.
I of course only know how this relates to Canons, and higher end Canons at that.
To start with, unless you have actually set some custom functions, the BB and the Shutter Button(SB) are exactly the same. The BB doesn't do ANYTHING any different than the SB.
For me personally, I have found that if I have a 1/4 of a second to pick up my camera and get a shot I can find my SB way faster than my BB and much more likely to actually land that shot! The SB is just WAY more ergo, more than 3/8 " in dia. and the ONLY button on the front of the camera versus that tiny row of 1/8" buttons along the back of the camera.
To use BB means you are using TWO buttons which WILL double your rate of error, since you HAVE to use the shutter button as well in conjunction with BB.
I find that FOR ME it's way easier to use the shutter button with smaller lenses, say up to a 100-400, then using the BB with bigger lenses as they get harder to handle!
My conclusion is that just as with priority modes, which and how I set up my BB depends on what I'm shooting and how I'm shooting it! And I can set up my preferred BB situation on my Custom Modes so I can switch it in and out as I switch lenses.
As to the CoC question, that's a whole nother BBQ! ;-)
SS

The back button focus doesn't hold any parameters. When you release the BBF it simply stops focusing - period. So if your subject doesn't move farther or closer to your lens, in theory your focus should be fine. But if your hand is touching the focus ring, or your f/stop is such that you have a shallow DOF, then you might experience out of focus shots. You have to know what you DOF is, and you must know for sure that your subject hasn't moved closer or farther. The good news is that you thumb should be resting on the BBF so you can just press it if you see a change. Keep practicing.

Hi, I have been using BBF for a little while but still have this question. Steve Perry says as long as your subject stays on the same focal plane you are locked in. Steve shows in his video a cartoon of a deer moving laterally and staying in focus because the focal plane hasn't changed. My question is what type of range will stay in focus. If the deer moves 10 feet laterally am I still in focus? There has to be a limit here. What about if the deer moves 2 feet closer, or two feet back, the focal plane has now changed correct? I guess am asking what kind of parameters does back button hold? Thank you.