Cosina 100-400 on 400d

[Bend The Light]

Hi all,

I bought a lens in a charity shop. Knew it was cheap and cheerful, but thought it would do me ok as a long lens for birding when I'm in Wales during the holidays (going to visit the red Kite centre, for one).

The lens is a Cosina 100-400 f4.5-6.7. Push and pull to zoom. But, I have a problem...

I can focus, autofocus works, and the zoom works well, and I can take a shot when on manual focus. But when I swithc to autofocus, it does the focussing, but then doesn't take the photo. The shutter won't go! The focus confirmation light (green dot on bottom right of viewfinder) flashes slowly when the shutter is depressed, but no shutter actuation.

anyone had any issues like this? Is it Cosina? I don't get the Err99 that you sometimes get with non-genuine lenses on the 400d, so it's not that...

 

[oldmacman]

Is the camera reading a focus lock? When auto-focusing, my camera won't actuate if there is not enough contrast to lock the focus. If that occurs (usually lower light) I switch to manual. So, have you tried the lens in different lighting conditions or are you experiencing the issue even when you're not expecting to?

 

[Bend The Light]

Thanks. I just tried focussing on a light shade with the light on...should be good for a focus lock. Nothing happening.
One thing I have noticed is that, when I press the DoF preview button, nothing changes...it's as if the aperture is fixed...when I do the same with my kit lens - the aperture closes down when I hit the DoF preview. Wonder if I have a fault - the aperture is not moving?

 

[penfolderoldo]

I think that means it's micro adjusting the focus.

 

[Bend The Light]

Well, I went outside, found a decent edge, opened the aperture rigt up, and it takes a shot, but only with very slo shutter.
Checked the aperture by closing it down, and then with the DoF preview, and it MADE NO DIFFERENCE. Did the same thing with the 75-300 canon lens, and the aperture closing can be seen clearly when the DoF preview is pressed. So, conclusion, the aperture is not being controlled. It is closed down at f22 (minimum, I think) and doesn't respond when changed on the camera. So, either a communication fault, the lens is not compatible, or there's a mechanical fault with the aperture blades. Any which way, it don't work!