Lens won't af while zoomed

[aBuze88]

So Im new to photography and decided on a T7i. Using my EF-S 55-250mm lens today while zoomed in on my girlfriends face it would never focus in. However, zoomed in on the television it was able to focus almost fully zoomed. Is this just a lighting situation, doing something wrong, or possibly have something wrong with the lens?

[RobertTheFat]

---

@aBuze88 wrote:
So Im new to photography and decided on a T7i. Using my EF-S 55-250mm lens today while zoomed in on my girlfriends face it would never focus in. However, zoomed in on the television it was able to focus almost fully zoomed. Is this just a lighting situation, doing something wrong, or possibly have something wrong with the lens?

---

Sounds like a lighting situation.The lens will focus only if it has enough light. The TV set provides its own light.

[Tronhard]

How far away was it to:

The television

Your Girlfriend's face

The longer the lens the further away its minimum focusing distance.

thanks

[kvbarkley]

Sometimes AF can get confused. Sometimes focusing on something else closer to you and then back on the subject can kick it in the pants.

[aBuze88]

Thanks for the responses. The television was actually closer than she was. Her face would be in focus but has i zoom in it became out of focus. Pressed the shutter in half way to focus and it only blurred out more. I thought maybe it was the lighting but with flash on it didnt focus and then once i zoomed out l, it had no problem auto focusing.

[kvbarkley]

Was there anything closer than her face when you were focusing? Canon's algorithm will focus on the focus point with the closest object, which is not necessarily what you want:

[aBuze88]

Once i was zoomed in nothing was on the screen but her shoulders and face. There were no other objects in the frame.

[ebiggs1]

This lens will not maintain focus when zooming.  That is normal.

Varifocal and Parfocal are two different types of zoom lenses.  Varifocal lenses do not maintain focus when you change the focal length.

[Waddizzle]

The MFD on some lenses can vary as you change focal length.