Front focus/back focus or dead on?

Not sure about this. What do you see?
RAW image converted with DPP4, no processing.

IanD wrote in post #17941579
Not sure about this. What do you see?
RAW image converted with DPP4, no processing.

Hosted photo: posted by IanD in
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forum: Canon Lenses

It is kind of hard to tell, but I'm thinking it is either correct or it might be a touch back.

well it is not front focusing

looks like you focused on the ball and then repositioned?

I suggest taking oodles of shots including the eyes of ducks or a pet, whatever is handy and enable to red focus point in your play menu so you can see where focus point was.. Maybe you can take shots of a ruler with a tripod - note where your center focus point is and see where focus end up - but not using live view.

Focus was dead on the brand name. Will okay around a little more under better lighting and temp conditions.

Looks dead-on to me. The brightness is killing your contrast though. A brick wall perpendicular to your (camera's) line of sight is a much better AF-testing target.

IanD wrote in post #17941579
Not sure about this. What do you see?
RAW image converted with DPP4, no processing.

Hosted photo: posted by IanD in
./showthread.php?p=179​41579&i=i230380065
forum: Canon Lenses

This is the perfect example of how AF actually works. It focused on the highest-contrast edge that was horizontal - the brown blade of grass to the left of the tennis ball.

skid00skid00 wrote in post #17942296
This is the perfect example of how AF actually works. It focused on the highest-contrast edge that was horizontal - the brown blade of grass to the left of the tennis ball.

Or the edge of the ball by the look of it.

The left edge of the ball is pretty high contrast as well. Probably best not to test on a round object anyway.

gjl711 wrote in post #17942310
Or the edge of the ball by the look of it.

If you look at 4 PM on the ball, you'll see that focus is behind the ball.

You'll want to click the link on the pic to see the full-res version, if you haven't.

skid00skid00 wrote in post #17943181
If you look at 4 PM on the ball, you'll see that focus is behind the ball.

You'll want to click the link on the pic to see the full-res version, if you haven't.

I was looking at the top edge between 9 and 12. The top edge looks to be in focus.

IanD wrote in post #17941606
Focus was dead on the brand name. Will okay around a little more under better lighting and temp conditions.

If the focus point was on the label then it is strongly back focused.

Assuming this isn't a heavy crop, the edge of the ball or the grass in front should not be close enough to the focus point to make a difference (and the texture of the ball and contrast of the lettering should provide plenty of detail for the AF to lock onto). That assumes, of course, that you used a single point AF. If you used multiple or all points then who knows what the camera is going to pick to focus on. If you are going to check front/back focus you want to eliminate as many potential confounding factors as you can.

gjl711 wrote in post #17943246
I was looking at the top edge between 9 and 12. The top edge looks to be in focus.

I wasn't specific enough, mea culpa...

At 4 o'clock, you can clearly see that the ground clutter is much sharper than the tennis ball, so it's backfocused, which guide me into believing that it focused on the brown grass leaf on the left of the ball, which prompts me to ask for a pic showing the AF point overlay - betcha it includes that blade.

Thanks for the input everyone. I was called out of town Sunday evening and have not had a great deal of free time.
to answer the question of where the lens was focused, it was right in the middle of the tents ball. I do not have the overlay image on my laptop but trust me, it was right in the middle.
While I have captured some great images with this lens, the one thing that is driving me nuts is the reverse of the "twist to zoom" as compared to my Canon zooms.
For that reason only, I have put the lens up for sale.
It is a great lens, for the price. It is not a short cut to a cheap 600 with Canon L results but it does produce very well if the shutter button presser does their part.
Again, many thanks.
Cheers.

Something else you have to consider is that the actual AF point is a fair bit larger than the box in the viewfinder. It's also very often not centered very well either. That is why it is always reccommended to to AF tests with a large flat AF target that is perpendicular to the sensor plane. Then use your 45 degree ruler at a decent distance from the actual target to judge the focus accuracy.

Three dimensional targets just aren't reliable enough to get a decent measure of the AF accuracy.

Alan