Cosina 100-400 on 400d

Bend The Light

Bend The Light

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Name
Craig
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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...
 
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! :(
 
manualfocus-g said:
Normally the camera will give an err message if the lens isn't compatible, but the shutter should still fire even if the blades are stuck...weird!
Click to expand...

The shutter does fire at maximum aperture (as stated on the camera) but at a very slow speed, making me think that the aperture is stuck closed at f22. When I tell the camera to go to apertures above the minimum (say 5.6 at 100mm) it gives an Err99 message. So, it only shoots at maximum open aperture, but the lens doesn't actualy open to that aperture.

:(
 
manualfocus-g said:
When held to the light, are the blades closed then?
Click to expand...

Blades closed...pointed directly at the bulb in the house lamp...kit lens gives 1/160th, at 5.6. Set the cosina to 5.6, and point to the same, and get 1/2 second. Aperture is not opening up.
 
manualfocus-g said:
If the blades are shut then either they are stuck or the camera can't open them as the lens isn't compatible :(
Click to expand...

I googled, and some people say they used this lens on a 400d, so it ought to work. I looked over the lens...it's clean, no obvious dents or scratches, and the glass is good. What I can see of the aperture blades, they look "straight" and not like they have been bent, or anyhting.

Ah well, put it down to experience...:(
 
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