AF focus issues due to lens?

[Cluster]

I have been researching macro lenses that I might like to try.
Reading a pro review, it was said that the Sigma 105mm was "a bit hit and miss" with its focusing.
I'm confused about this.... doesn't the camera body demand that the lens focuses this way and that until the body is happy with the focus, unless the body has only a short time to achieve a focus before it gives up. Can a lens cause "hit and miss" focus issues?

 

[welshwizard645]

Depends on what generation that Sigma lens is, I've had some which required substantial calibration in camera, and some of the older lenses don't quite communicate with the camera body - I sold an EX 180/3.5 macro a few years ago that ceased to function on the D810 I had at the time following a firmware upgrade.

 

[sk66]

Can a lens cause "hit and miss" focus issues?

Yes, for a few reasons.
One is simply the accuracy of the focus sensor in use; but this would apply to all lenses. However, if a lens is not as sharp wide open (where AF occurs with SLR's) you can have less accurate/optimal images being compared for phase position. Similarly, if a lens is at all decentered it can cause issues as the images compared for phase come from opposing regions of the objective element.

Also, if a lens is not particularly sharp wide open it can suffer from focus shift when it stops down to actually take the image. How much it shifts depends on how far the lens is stopped down.

And finally, there is a tolerance built into everything (e.g. focus mechanism, lens mount, etc) and so there has to be an "acceptable focus" tolerance as well... otherwise a less sharp lens might never be considered "in focus," and a sharper lens might continually hunt for optimal focus.

 

[ancient_mariner]

From an experiential point of view some lenses are useless while others fantastic on the same body. With my current Sony A7, the Sony 50 f1.8 was borderline unusable compared to a Samyang 50 f1.4 that had a bad reputation for focusing but was actually much better. Others have reported their budget macro lens was also poor to focus. With my previous Nikon system it struggled to find focus in n low light with a couple of lenses, yet the focus confirmation light would let me nail focus manually every time.

It's not 'obviously' logical but it happens.