Auto-focus isn't working on my prime lens

C

Child

New member
I purchased a Nikon 50mm f/1.8G AF-S Autofocus Lens from Adorama in "used but excellent condition" this month for my D5100. I have previously only used kit lenses.

I generally shoot in manual mode (as opposed to A, S, P, or Auto) and in manual focus (as opposed to AF-C, AF-S, or AF-A) with the lens switched to M/A (not M) on my kit lenses. This allows me to choose a point for the camera to focus on, and let the lens focus in automatically on my assigned point. I've got bad vision and can't trust my eye to focus tight enough.

But those settings don't work with this prime lens. Even with the lens in M/A mode, the lens will not auto-focus as long as the camera is set to Manual Focus mode (MF) - I have to manually adjust with the lens ring. The lens will happily auto-adjust if I'm in any of the AF modes, so I know the auto setting is working.

Is this just how the lens is built? Is there a setting I can change to allow me to focus manually and adjust the lens automatically? Or is the lens defective? Ultimately, should I buy a different lens?

Thanks guys!
Mckenna
 
BF Hammer

BF Hammer

Senior Member
Is there a AF/MF switch on the camera body, below the lens release button? (Where the D7xxx bodies have it)
Edit: I just looked, not there. But then I noticed you mentioned the camera is in manual-focus mode. So I do not expect the AF to work at all in that condition. When an AF mode is active, then the AF will work in the A-M position and allow you to manually override the AF the camera wants to do.

Unless I totally misunderstood you. Is it an active AF box you want the camera to choose here? You do that manually also by moving the joystick on the back of the camera to the focus point you want.
 
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Clovishound

Clovishound

Senior Member
If you have the camera in manual focus mode, it will not autofocus regardless of whether you have the lens switch set to M/A or not. If you have the camera set to an autofocus mode, and the lens switched to M, it will not autofocus. The When in autofocus mode, the camera will autofocus when you half press the shutter, but while in half press, you can turn the focus ring and change the focus and then fully press the shutter to take the picture. That is how the system is designed to work. This is what the M/A on the lens switch refers to.

I looked at the 18-55 kit lens I have, and it doesn't have a switch for manual/autofocus. That means it will stay in autofocus mode unless you change it to MF in the camera.

If you are trying to get the camera itself out of MF mode, press the i button and look for the AF-M selection. Press it and choose AF-A, AF-S, or AF-C, depending on what mode you want. All three of these will give you autofocus operation. Be sure the lens selector is in the M/A setting.

I got this from the Pup's D5600, but it should be the same for your D5100.
 
B

benhasajeep

New member
With Nikon if your lens has M/A or A/M position you can manual focus without turning off AF in the body. They have manual focus overide function.

But if the lens only has A position and M position, they do not have the overide feature. You must use body switch if you have it, or menu.
 
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