topic Re: 1 pt autofocus is inaccurate in EOS DSLR & Mirrorless Cameras

EOS 70D focus inaccurate outside of center AF point

Andysdn — Tue, 30 Apr 2024 14:25:48 GMT

I have an EOS 70D with an EF-S 18-135 1:3.5–5.6 IS STM and EF lens 50mm 1:1.8 lens.

I typically shoot in 1pt autofocus and have realized that various points are inconsistent. For instance, when I place the camera on a tripod with the 18-135 and shoot using the center point my shot is sharp. However when I focus using an outside point the subject is completely out of focus.

I tried this same test with the 50mm and it’s better but but it still seems to be less sharp on the outside, just not nearly as bad as the 18-135.

Is the 18-135 lens faulty or is there a camera setting that will fix this? At this point I’m ruling out technique as a the culperate.

Re: 1 pt autofocus is inaccurate

Andysdn — Thu, 11 Jan 2018 05:16:12 GMT

I should also note that I’ve always had focus issues with this lens. I only recently tested each point for accuracy

Re: 1 pt autofocus is inaccurate

ebiggs1 — Thu, 11 Jan 2018 15:33:07 GMT

When you are not using center point "only" which is what I use 90% of the time, the cameras focuses on the closest thing. Whether it is your intended subject or not. I suspect that is what you are noticing. In other words what you think is in focus is different than what the camera thinks.

If you want precise focus on something turn off all the other focus points and use just the center.

Re: 1 pt autofocus is inaccurate

Waddizzle — Fri, 12 Jan 2018 00:37:35 GMT

@Andysdn wrote:
I have an EOS 70D with an EF-S 18-135 1:3.5–5.6 IS STM and EF lens 50mm 1:1.8 lens.

I typically shoot in 1pt autofocus and have realized that various points are inconsistent. For instance, when I place the camera on a tripod with the 18-135 and shoot using the center point my shot is sharp. However when I focus using an outside point the subject is completely out of focus.

I tried this same test with the 50mm and it’s better but but it still seems to be less sharp on the outside, just not nearly as bad as the 18-135.

Is the 18-135 lens faulty or is there a camera setting that will fix this? At this point I’m ruling out technique as a the culperate.

Are your subjects moving or stationary?

I suggest that you use One Shot mode, not AI Servo mode to take test shots. Then, use DPP to see where the active AF point was located in the frame. The center AF point is also the most sensitive and most accurate. I would rather lock focus, and recompose the shot than use the center in One Shot mode.

Re: 1 pt autofocus is inaccurate

RobertTheFat — Fri, 12 Jan 2018 16:20:48 GMT

@Waddizzle wrote:
@Andysdn wrote:
I have an EOS 70D with an EF-S 18-135 1:3.5–5.6 IS STM and EF lens 50mm 1:1.8 lens.

I typically shoot in 1pt autofocus and have realized that various points are inconsistent. For instance, when I place the camera on a tripod with the 18-135 and shoot using the center point my shot is sharp. However when I focus using an outside point the subject is completely out of focus.

I tried this same test with the 50mm and it’s better but but it still seems to be less sharp on the outside, just not nearly as bad as the 18-135.

Is the 18-135 lens faulty or is there a camera setting that will fix this? At this point I’m ruling out technique as a the culperate.

Are your subjects moving or stationary?

I suggest that you use One Shot mode, not AI Servo mode to take test shots. Then, use DPP to see where the active AF point was located in the frame. The center AF point is also the most sensitive and most accurate. I would rather lock focus, and recompose the shot than use the center in One Shot mode.

That doesn't make sense to me. Did you mean to say "I would rather lock focus and recompose the shot than use anything but the center in One Shot mode"?

Re: 1 pt autofocus is inaccurate

Waddizzle — Fri, 12 Jan 2018 23:10:43 GMT

“That doesn't make sense to me. Did you mean to say "I would rather lock focus and recompose the shot than use anything but the center in One Shot mode“

You are correct. It did come out backwards, I meant exactly what you wrote. Bad eyes failed me again.

Re: 1 pt autofocus is inaccurate

stlimages — Mon, 29 Apr 2024 22:07:57 GMT

I don't understand. If the one-point autofocus points other than the center point aren't accurate, why are they there at all?

I just finished a major concert shoot with the top middle point on the singer's face. Her face was out of focus in almost every shot, but the top of her dress was pin sharp.

Re: 1 pt autofocus is inaccurate

kvbarkley — Mon, 29 Apr 2024 22:43:48 GMT

You don't tell us the camera, but you can use several combinations of focus points.

The camera will use all the selected focus points and choose the one that is closest to the camera. In this case, it appears that the dress was closer.

Re: 1 pt autofocus is inaccurate

stlimages — Mon, 29 Apr 2024 23:07:01 GMT

Thanks for the quick response. I shot with a Canon 80D. Selected only the middle focus point on the top row. Went back and looked at it in camera. It shows the red square on the right half of the singer’s lips. That’s where I thought I was focusing. Her entire face is in soft focus — too soft to use. But a portion of her dress roughly 10-12 inches below where I focused is tack sharp.

steve levine

stl.images

Re: 1 pt autofocus is inaccurate

wq9nsc — Mon, 29 Apr 2024 23:28:44 GMT

There are a couple of possible issues:

1. Did you calibrate the lens to the body using the built in micro-focus adjustment (it is under the AF menu)? If you are using a lens in a situation where the depth of field is shallow (typically a wider aperture telephoto but will also occur with any lens when shot close enough to the subject), then it will need to be calibrated to the camera. It is quick and easy so first make sure that the lens is properly dialed in for the center focus point so do this first before further testing

2. Some lenses will have various optical imperfections where it has lower sharpness in some parts of the frame and I suspect that could throw off the AF system. If you consistently shoot with a specific point not in the center of the AF array, then you could try doing the AF microfocus adjustment using that point instead of the center point to see if that works better for you. I have a bunch of lens and bodies, many of which are very wide aperture telephoto glass with a very shallow depth of field and I have never run into issues using any available AF point after dialing in the calibration using the microfocus calibration.

Rodger