Sigma 18-35mm 1.8 autofocus issues

[shiron00]

I have a Canon T7i and have recently bought the Sigma 18-35mm f1.8 because I’ve heard great things about it. The problem is, once I started using it, I kept getting soft/blurry shots 50% of the time (action photos) because the autofocus seems to be off. I did some research and apparently this lens isn’t that great at focusing on fast moving subjects. I even just purchased the calibration dock and tried some focus settings from YouTube but to no avail. So I have two questions:

Apparently live view produces better image quality whilst shooting moving subjects, is this true?

Would anyone be willing to share their focus setting numbers if they’ve calibrated this lens (and it focuses well) for the Canon T7i?

Any help is greatly appreciated!

[deebatman316]

Is this lens front or back focusing on things. It sounds like you need an AFMA (Autofocus Micro Adjustment). I don't believe this camera supports it. Only higher end cameras support this feature. 

-Demetrius

Current Gear: EOS 5D Mark IV, EF 16-35mm F/2.8L III USM, EF 24-70mm F/2.8L II USM, EF 50 F/1.8 STM, EF 85mm F/1.8 USM, EF 70-200mm F/2.8L IS III USM, 470EX-AI & 600EX II-RT

Retired Gear: EOS 40D & Sigma 17-50mm F/2.8 EX DC OS HSM

[jrhoffman75]

Live View focuses using the exact image that the sensor is seeing. The optical viewfinder uses a separate focusing system that needs to be calibrated so that when the system says the subject is in focus it is also in focus on the sensor.

If there is a calibration issue with the optical viewfinder focusing system the Live View will produce an in-focus shot while the OVF will not.

There are also other reasons for the focusing results to be off. The OVF system has fewer focusing points, so if you are having difficulty keeping a focus point on the subject you could get poor focusing.

One thing you could do to check: set the camera up on a tripod and focus using the OVF. Switch to LiveView and see if the image looks in focus (don't touch any buttons that could cause focusing) Next step would be to focus using LiveView. Then switch off LiveView and press the shutter button. If the lens moves then the two focusing systems are out of sync.

[ebiggs1]

"It sounds like you need an AFMA (Autofocus Micro Adjustment). I don't believe this camera supports it."

It doesn't matter if the camera has micro focus adjustment or not the Siggy can use the Sigma dock to adjust several settings. I believe all Sigma Art lenses can use the dock which is an inexpensive tool. You can update FW with it at home too which is a good thing. Whether the lens needs adjustment is another question. A lot of folks jump to that conclusion when the problem lies in user technique and not a faulty or misadjusted lens. As JRH says, "...if you are having difficulty keeping a focus point on the subject you could get poor focusing."  It might be wise to set up a little test using a tripod and just the center focus point. Also turn off Ai-Servo and use One Shot. Try several distances and examine the results.

[deebatman316]

I didn't know Sigma had a dock that allowed AFMA. I only have one older Sigma EX that doesn't support the dock because the lens is too old.

-Demetrius

Current Gear: EOS 5D Mark IV, EF 16-35mm F/2.8L III USM, EF 24-70mm F/2.8L II USM, EF 50 F/1.8 STM, EF 85mm F/1.8 USM, EF 70-200mm F/2.8L IS III USM, 470EX-AI & 600EX II-RT

Retired Gear: EOS 40D & Sigma 17-50mm F/2.8 EX DC OS HSM

[Waddizzle]

Can you post a sample photo?  One that has not been cropped?