LoneRangeFinder Loc: Left field

Could be that that AF works behind the "menu scenes" to select some "ideal focus".... (One could also just manual focus.) I just know if I select single point AF I can locate where in the frame I place it that "single point".

EG, I was out trying to shoot BIF one morning--and this frustrated the bleep out of me. My solution was to change to BBF and a higher number of focus points so maybe part of my solution here was actually locking in the focus with BBF so that depressing the shutter did not "refocus".

I'll have to do more trial on this.

amfoto1 Loc: San Jose, Calif. USA

BBF should be usable with both.

Nikon calls it AF-S and AF-C... Canon (which I use) calls these focus modes One Shot and AI Servo. I can answer your question as it pertains to the Canon cameras I use... But I suspect the same is true for Nikon.

AF-S or One Shot is designed for use with stationary subjects. It's great for that purpose... achieves focus, then stops and "locks". If you move or the subject moves, or both, focus will be off. You have to lift off the button, then reapply it to make the camera re-focus.

AF-C or AI Servo is a continuous form of AF that never stops and locks that's intended for use with moving subjects. It just keeps updating, detecting, measuring and adjusting focus, so long as you keep the button pressed. This can be problematic, though, with some techniques (such as focus and recompose), unless you use BBF.

Without BBF there are times when it's not a good idea to use AF-C or AI Servo. Using BBF allows one to make AF-C or AI Servo their "default" AF mode... to use it for both moving and stationary subjects.... and to be better prepared for either situation (not have to stop and change focus modes).

So, while BBF enables using AF-C for more things... it should also work fine with AF-S.

Another thing... I don't know if that 50-500mm is a parfocal or varifocal zoom. A parfocal zoom will maintain focus when you zoom, changing the focal length. A varifocal lens won't and will need to be refocused after any zooming to a different focal length is done.

Back in the days of manual focus, there was a strong need for parfocal zooms and most were designed that way. But varifocal designs are less complex and don't need to be as carefully calibrated, allowing them to be more competitively priced. To some extent, autofocus cameras and lenses offset the need for more expensive parfocal zoom designs. So some modern zooms now use varifocal design.

If you are using AF-C, it won't matter if it's a varifocal zoom. So long as it's running, the AF system will immediately correct for any focus error that you cause by zooming the focal length. But, if you are using AF-S... or if using BBF with AF-C and lifting off the button once focus is achieved... and then change the focal length after focusing... focus will be off if the lens is a varifocal design.

So it effects how you use the zoom, whether it's a varifocal or parfocal design. If you can't find info about it, you can test it yourself by focusing, taking a shot, zooming the lens without re-focusing and take a shot.

It also is possible that a parfocal design might get out of calibration over time.... with use, wear and tear... and no longer maintain focus perfectly when it's zoomed.

amfoto1 Loc: San Jose, Calif. USA

That's possible... but in those examples you were using 1/2000 shutter speed, which really should eliminate any camera shake blur.

Usually camera shake blur effects the entire image, too... not just part of it, as in these examples.

If using focus stacking technique that I mentioned in a previous response, you probably would want to use a tripod and take some time to make the multiple shots.

Using 430mm focal length for a shot like this is rather odd... Personally I'd most likely use a 90mm to 105mm macro or even a Tilt-Shift lens.

Rather than shooting it at an angle, it would be better if you oriented yourself so that the sensor plane of the camera was close to parallel to the ground, too. That would minimize problem with too shallow depth of field. Shooting this way would be a whole lot easier to do with a shorter focal length and smaller size lens that's able to focus closer.

Here's an example of extremely shallow depth of field (shot with a 180mm macro lens near that lenses highest level of magnification... I forget what aperture, though). As you can see, the sharp area of focus is only a few millimeters deep and is sort of a "plane of focus" that cuts across the image....



Here's another close-up example, though this time I used a 100mm macro lens stopped down to f/16 and carefully oriented myself to the rather flat subject, so that the entire frame would be sharply in focus....



And here's another, where moderately shallow depth of field was deliberately used and the subject was shot from an angle (much like your examples) so that both foreground and background are softer, while the center of the image is rendered sharp (100mm macro lens at it's largest f2.8 aperture)...

speters Loc: Grangeville/Idaho

Front and/or back focusing seems to be a common problem with the 50-500!

bdavis

Lone Rangerfiner said: "So, it was the combination of the focal length, the aperture AND the AF option selected." Howlynn said: "With the focal distance being 2.5m approx 98" this appears to be very close to the minimal focal distance of this lens."

These are the major contributing factors. Wherever the DOF ends with that long lens with the aperture open, the areas beyond will go out of focus quickly. The space in front of and behind the DOF gappear compressed. The aperture could have been smaller with a slower shutter speed (though not too slow with that lens). CO recommended AF-S. If you had done that and you selected for the sand along the "Rule of thirds line" closer to the bottom (1/3 of the way up from the bottom of the frame) you would have had most if not all in focus.

zigipha Loc: north nj

Agree with narrow aperature, the front/back distribution can be skewed

jimmya Loc: Phoenix

What occurs to me is if you're using full auto and all the focal points that go with it you'll get a result like this. Another thing is light. If your iris was stopped down to 3.5 or below you could have DOF problems. The photos you sent look like DOF might be your culprit.

I would consider going to single focal point - dead center and for shots such as these boost your ISO to compensate for the lack of light. Good luck.

TriX Loc: Raleigh, NC

It was mentioned earlier in the thread that it was shot at f13... DOF ~ 1 inch at the stated distance of 98".

CraigFair Loc: Santa Maria, CA.

Sigma does it again.
Craig

CLP1943 Loc: Wisconsin

Why don't mirrorless cameras have these problems?

LoneRangeFinder Loc: Left field

Seems like an unsubstantiated claim to me. I'd love to hear some proof or logic behind this claim. So call me a skeptic….

CO

Mirrorless cameras use contrast detection autofocus, There are no focusing errors with contrast detection because the camera adjusts the focus until it achieves the highest contrast at the sensor. DSLR cameras use contrast detection autofocus when in live view mode.

DSLR cameras have both contrast detection and phase detection autofocus. When using the viewfinder, the camera is using its phase detection autofocus. A small portion of the light entering the camera is split into two beams and directed to the AF modules near the bottom of the camera. The components of a phase detection system have to be very precisely aligned to be accurate. Also, because of manufacturing tolerances, you can have camera and lens combinations that will back focus or front focus.

LoneRangeFinder Loc: Left field

Thanks.

oldtigger Loc: Roanoke Virginia-USA

This becomes a non-issue :
"because the image sensor is different from the focus sensor, there is a chance that they are not aligned and something considered focused by the focus sensor is not focused on the image sensor ... this is why phase-detect autofocus is faster but more prone to front-/back-focusing issues ... enthusiast/high-end cameras have a micro-adjust feature to address this issue ..".
http://www.dpreview.com/forums/post/41290730

CJsFotos Loc: Cambridge Ontario Canada

From reviews I have read , any f stop smaller then F11 on this lens focus does fall off , sweet spot is F8