AF hunting with Sigma 150-600mm f/5-6.3 DG HSM contemporary lens beyond 300mm

[Man Mohan Khullar]

Dear all, any suggestions/advise will be highly appreciated. I am really struggling.

[Sudhir Shivaram]

Dear Mohan Khullar,

Can you please explain what exactly is the AF issue you are facing? Also need answers to below:
– What is the AF point you are using on Canon 90D.
– Can you please share images where you are facing issues.
– Are you using One Shot mode or AI Servo?

AF hunting happens due to multiple reasons including:
– low lighting
– Distractions in the scene
– Subject not properly visible to lens
– If you are using any kind of filters to the lens

And to be honest, the Sigma 150-600mm is not a fast lens to get you good AF.

Rgds,
Sudhir

• This reply was modified 1 week, 6 days ago by  Sudhir Shivaram.

[Man Mohan Khullar]

Dear Sudhir Ji, Thanks a lot for the revert. My answers to your queries are below inline.

Can you please explain what exactly is the AF issue you are facing?

[MMK] – Whenever I go beyond 300mm there is continuous pulsing/hunting of AF and camera does not focus at all. I eventually have to use manual focus.

Also need answers to below:
– What is the AF point you are using on Canon 90D.

[MMK] – I tried both; ” One point AF” and “Spot AF”. Issue persists in both options.
– Can you please share images where you are facing issues.

[MMK] – Since camera does not focus at all so I do not have such pictures. I am using MF to take pictures.
– Are you using One Shot mode or AI Servo?

[MMK] – I tried both options but problem persists.

AF hunting happens due to multiple reasons including:
– low lighting

[MMK] – yes I am aware so I tested in bright day light.
– Distractions in the scene

[MMK] I tried on bigger distant objects like street light masts to rule out distractions like tree twigs and leaves. But it did not focus on bigger and clear objects.
– Subject not properly visible to lens

[MMK] I think this is not the case in my testing.
– If you are using any kind of filters to the lens

[MMK] – No.

And to be honest, the Sigma 150-600mm is not a fast lens to get you good AF.

[MMK] – I would like to share one more observation. In EXIF data the focal length is always coming as 175mm irrespective of the actual position of the lens whether it is at less than 175 mm or more than 175 mm till the full range of 600mm. Is there a communication issue between lens and camera and can this be the cause of AF hunting?

The lens might be slow but it should AF some time. It does not do at all beyond 300mm. Your guidance is highly appreciated.

Or may be I put my money on wrong lens.

Thanks and Regards,

Man Mohan Khullar

[Sudhir Shivaram]

Ok, going through your reply, looks like there is an issue with the lens and you need to take it to service centre. What you have explained – that’s not common and is definitely not how a Sigma 150-600 behaves.
As an alternative – I would recommend you to try and test with a different Sigma 150-600 (if you can rent it) and compare the results.

Rgds,
Sudhir

[Man Mohan Khullar]

Thanks so much for a very quick revert and advising the way forward.

Best Regards,

Man Mohan Khullar