Lens won't focus.....what is the problem?

02/29/2008 01:29:42 PM · #1

Today my Sigma 18-200mm f/3.5-6.3 DC for Canon stopped autofocusing. My other lenses work fine. I also noticed that when I look through the viewfinder with that lens it looks darker than it really is. Any suggestions on how to fix it? Thanks.

02/29/2008 01:33:44 PM · #2

Does it still attempt to focus and can't lock on, or is it locked up (not moving to focus at all)?

Canon EF 16-35mm f/2.8L USM

02/29/2008 01:34:29 PM · #3

Originally posted by glad2badad:

Does it still attempt to focus and can't lock on, or is it locked up (not moving to focus at all)?

It is trying to focus but won't lock onto anything.

trevytrev

Canon EOS-5D

02/29/2008 01:44:55 PM · #4

Originally posted by KarenNfld:

Originally posted by glad2badad:
Does it still attempt to focus and can't lock on, or is it locked up (not moving to focus at all)?

It is trying to focus but won't lock onto anything.

Sounds like the apature isn't opening up in order to focus easier and allow more light in for you to see. Seems like you could have an apature issue, just a guess.

cpanaioti

Canon EOS-40D

Canon EF 70-300mm f/4.5-5.6 DO IS USM

02/29/2008 01:47:07 PM · #5

Too close, not enough contrast?

Try shining a light on the area you want to focus on.

02/29/2008 01:49:41 PM · #6

Sounds like what trev says...especially with it appearing darker thru the viewfinder.

BTW - Probably a silly question, but you didn't do a firmware upgrade or anything to your camera did you?

Silly question #2, most likely it's the lens, but can you verify for sure with another camera body? Just a thought.

02/29/2008 01:54:05 PM · #7

Originally posted by glad2badad:

Nope, no upgrades. I will try to test the lens on my friend's camera. So if it is the lens, does that mean it's kaput?

Gordon

RIM BlackBerry Curve

Canon EF 85mm f/1.8 USM

02/29/2008 01:55:56 PM · #8

Does your camera have a depth of field preview ?

If so, you should be able to switch the camera to aperture priority mode, stop it all
the way down f22/f32/ whatever that lens does, and press the DoF preview button.

It should get darker when you look through the viewfinder.

You should be able to look into the lens from the outside and actually see the aperture close
up and open up as you press/ release the DoF preview button.

Try it with another lens to get an idea of how it should look.

If your lens isn't doing that, then the aperture is stuck (which is what it sounds like)

02/29/2008 01:57:17 PM · #9

Originally posted by KarenNfld:

... So if it is the lens, does that mean it's kaput?

If it's the lens, it doesn't mean it's kaput - may just need some TLC. Are you out of warranty now? Even if you are, I'd contact Sigma as their service is pretty decent (at least the one time I needed to go that route).

Canon EF 16-35mm f/2.8L USM

02/29/2008 02:24:28 PM · #10

Originally posted by Gordon:

I had no idea if my camera had that or not so I called my partner Joe. He told me how to test it, and by pressing the button I guess it unstuck the aperture, and now it is focusing again!!!! Thank you!!

trevytrev

Canon EOS-5D

02/29/2008 02:34:00 PM · #11

You may still want to have it looked at and cleaned, I hear that oily blades can cause this. Not sure if it is cost effective though.