pauljolee
newbie
Reged: 20/05/2008
Posts: 8
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Hi guys sorry if this is a stupid question but I am a newbie to this and cant find any answers.I have a Sigma 50-500 lens on my E410 and it is set to autofocus for the simple reason that I have an interest in airshows and it is impossible for me to zoom,focus and pan at once.But when I click down halfway to autofocus while panning the lens goes from its current focus position all the way to the other end and back again which as you can imagine is hopeless and causes me to lose track of the planes.Is this normal or is there something I could do to rectify this.
Cheers Paul
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9463
Loc: Sussex-by-the-Sea
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Are you setting the AF to a single point? In this situation I find it best to fix the AF to one point, normally the centre which is the most sensitive/accurate, and stick with that. There are a number of 'intelligent' AF tracking systems on the market but unfortunately they are fairly new and often fitted only to the highest spec cameras. Fixing the AF point means that you know which one is the one to keep on the subject and the camera is less likely to be confused by trying to decide for itself which point to use.
Even then a lot is down to technique and you will need to practice as much as possible to be able to keep the target squarely under the AF point. Focus hunting is not uncommon and usually happens if the target drifts from the AF point or light and contrast is poor - especially as the lens hasn't got the fastest aperture range. Most AF systems work best at maximum apertures of 5.6 or better so at f6.3 the aperture is probably on the limit of what the AF can handle. This is a big heavy lens and at a 35mm equivalence of up to 1000mm camera shake is a potential issue - possibly enough to blur edges sufficiently to reduce contrast and affect AF accuracy.
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Nigel
Completely BSRIPN 
ElSid Gallery
A camera in the hand is better than one in the cupboard........
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pauljolee
newbie
Reged: 20/05/2008
Posts: 8
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Sorry for the delay in answering Nigel;yes I am using single point AF but now you have mentioned it I should try auto as I am thinking that I am missing the subject while panning or it is outside the AF area but in shot,thanks m8
Paul
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