Lens problem at Thruxton BSB

rogan200

rogan200

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Rogan
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I got a nearly new Sigma 100-300 f/4 a few weeks back, and gave it an outing at the FIA GT meeting at Silverstone - got some shots I was happy with though my panning needed much improvement! Noticed a slight issue though that has reared its head far more frequently at todays BSB meet at Thruxton.........

Found panning with the bikes hard, but was not helped by my intermittent problem - every few shots when panning i'd AF on a part of the bike, pan... and then the lens would suddenly jump focus as i release the shutter. The focus is fine in the viewfinder, and as i release the shutter suddenly it goes way out and i can see it happening in the viewfinder. Some shots are then completely blurry, others just slightly so. Is this likely a lens, camera (D80) or user error? (i'm sure its not me as it happens when i'm sure the AF point has stayed locked on the bike). :bang:

Any help or ideas on this would be much appreciated! Thanks.....

P.S will be posting decent photos from my outing when i've had a chance to sort them tomorrow).

(is this in the correct section?)
 
rogan200 said:
when panning i'd AF on a part of the bike, pan... and then the lens would suddenly jump focus as i release the shutter.
Click to expand...

Do you keep the shutter button 1/2 depressed while panning or do you press it from nothing to full click? And what AF mode are you using?
 
Post some images so that we can ascertain what the problem is. For now, all I can offer you is... motorsport photography...one hard cookie to master.
 
Thanks for the replies.

I'm using continuous Af mode, half depressing the shutter to focus, then panning and then releasing the shutter.

Here is an example of an image where it jumped focus as i released the shutter:

3584433283_70ef48cba3_o.jpg


I have posted this as it was not a difficult pan. the rider was on his slowing down lap and so going relatively slowly, so i doubt panning technique is at fault. As you can see nothing in the frame is in focus so i can be focusing on the wrong thing!
 
Use the AF-ON button instead! Just hold it down then click the shutter release...
 
Thanks for the answers but not sure i'm convinced of them........

neil_g said:
got it on the center AF point? if its set to all points it might suddenly try and refocus on something in the background/foreground etc.
Click to expand...

Yes it was center AF in this shot - with the motorsport i always use a fixed AF point - not always the center one but a fixed one.

desantnik said:
Use the AF-ON button instead! Just hold it down then click the shutter release...
Click to expand...

Had a look at my D80 and i don't think it has an AF-ON button?

neil_g said:
ah yes missed that, if youre half pressing youll lock focus at where the bike WAS unless you move the focus lock button (no idea how to do that on nikon, sorry).
Click to expand...

But surely if I have the camera set to AF-C (which i'm assuming to be AF-continuous) it will continuously refocus as i pan with the shutter button half depressed? I'm pretty certain it does do this as i can see the shot is sharp until i release the shutter fully.

Again thanks for your advice but i was hoping someone might have an idea of what Technical fault this may be rather than user error.
 
I don't think anyone is actually suggesting a technical fault...

Simple to test though, just take a shot of a static thing with it in AF-C. If the static thing is ok in the test shot there is nothing wrong with the camera...
 
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