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...

ThatCanonGuy

If the light is flashing and it won't take the photo, it means the lens hasn't locked focus. This may be a problem with the lens, it may be that your subject is low-contrast and therefore hard for the AF to lock onto, or it might be the lens just not performing well. Try letting the AF lock onto a high-contrast subject, like black against white. If this doesn't work, then it's probably the lens.

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?

ThatCanonGuy

If the lens is already at maximum aperture, then nothing will happen. However, if it's stopped down then it may have a fault. Maybe your camera shows a stopped-down aperture, but the aperture isn't moving. Try taking a photo with the aperture set to maximum, composing so you can easily tell how much DOF there is. Now stop way down... to like f14 or something. Are the two images the same, or does the second one have a lot more depth of field? If they're the same, sounds like your aperture blades aren't moving.

Bend The Light

I think the aperture blades are not moving...:(

ThatCanonGuy

If you take a shot at maximum aperture (so the blades don't have to move), does it still not shoot? Maybe something else is wrong with it too

Bend The Light

It IS shooting at maximul aperture now (lowest f-number). It's f4.5 when at 100mm, and f6.7 at 400. It shoots at both, but as soon as I stop down a notch, it gives Err99.

ziggy53

Bend The Light wrote: »

It IS shooting at maximul aperture now (lowest f-number). It's f4.5 when at 100mm, and f6.7 at 400. It shoots at both, but as soon as I stop down a notch, it gives Err99.

That sounds like an older third-party lens that is not compatible with newer dSLR camera bodies. Typically, it's because the communication rates for the lens do not match the communication rates for the body. You may be able to use the lens on an older Canon film body or a "very" old Canon dSLR, like a D30 or D60.

It could also be a newer lens that is broken.

If you have no use for the lens only at wide open aperture then I suggest selling the lens.

Bend The Light

Thanks Ziggy.

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!