Strange behaviour of 35mm f2 lens

[Nigel Charlton]

I have just purchased a 35mm f2 from a respectable company for my XT 1. 

When the lens is on the camera it makes a hunting noise constantly. It also appears to zoom in and out which is odd for a prime lens. It also the back screen seems to get brighter and darker without touching the camera at all. 

Any advice? Is it the camera or lens? 

Regards 

Nigel

Edited March 21, 2020 by Nigel Charlton
Question it completed

[Greybeard]

Presumably the camera works OK with other lenses? (Which implies the lens is the problem).

What are the pictures like? Does the lens communicate with the camera (focus, aperture, metering and EXIF)?

Do the contacts look OK?

[rolf]

3 hours ago, Nigel Charlton said:

I have just purchased a 35mm f2 from a respectable company for my XT 1. 

When the lens is on the camera it makes a hunting noise constantly. It also appears to zoom in and out which is odd for a prime lens. It also the back screen seems to get brighter and darker without touching the camera at all. 

Any advice? Is it the camera or lens? 

Regards 

Nigel

The "hunting" noise is due to the lens continuously trying to focus .

If  PRE-AF is set to ON (in AF/MF >PRE-AF ), the lens will keep focusing CONTINUOUSLY  in S and C modes (even when the shutter is not pressed)

Turn it OFF , and see if that solves the issue

[Nigel Charlton]

On 3/21/2020 at 1:44 PM, rolf said:

The "hunting" noise is due to the lens continuously trying to focus .

If  PRE-AF is set to ON (in AF/MF >PRE-AF ), the lens will keep focusing CONTINUOUSLY  in S and C modes (even when the shutter is not pressed)

Turn it OFF , and see if that solves the issue

Thank you for your advice Rolf. All sorted now !