Focus Question

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Scubabix - 12 Nov 2006 16:33 GMT

I have recently purchased a Sigma 70-300 for my Canon 30D. I intend to
shoot airshows when I can and have a focus question. Since this type of
shooting is quick, would it be feasible to set the focus manually at the
farthest range and shoot to avoid the AF searching as you're trying to shoot
a jet going by at 300kts?

Rob

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Ed Ruf (REPLY to E-MAIL IN SIG!) - 12 Nov 2006 18:33 GMT

>I have recently purchased a Sigma 70-300 for my Canon 30D. I intend to
>shoot airshows when I can and have a focus question. Since this type of
>shooting is quick, would it be feasible to set the focus manually at the
>farthest range and shoot to avoid the AF searching as you're trying to shoot
>a jet going by at 300kts?

Not in my opinion.

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Ed Ruf (Usenet2@EdwardGRuf.com)
http://edwardgruf.com/Digital_Photography/General/index.html

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Nursey - 12 Nov 2006 19:48 GMT

> I have recently purchased a Sigma 70-300 for my Canon 30D. I intend to
> shoot airshows when I can and have a focus question. Since this type of
> shooting is quick, would it be feasible to set the focus manually at the
> farthest range and shoot to avoid the AF searching as you're trying to shoot
> a jet going by at 300kts?

Most airshows that I have shot usually have the aircraft going across
you so the autofocus shouldn't have to hunt that much.

I personally set to manual and then set to inifinity (not to the end of
the focus as this is slightly past infinity), checking on something else
in the distance, take a couple of test shots of the aircraft flying past
and have a quick check on the LCD.

If all appears well, then I shoot away happily.

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Scubabix - 13 Nov 2006 20:16 GMT

Thanks Ed and Nursey for the input.
Rob

>> I have recently purchased a Sigma 70-300 for my Canon 30D. I intend to
>> shoot airshows when I can and have a focus question. Since this type of
[quoted text clipped - 11 lines]
>
> If all appears well, then I shoot away happily.

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Ed Ruf (REPLY to E-MAIL IN SIG!) - 13 Nov 2006 21:55 GMT

>> I have recently purchased a Sigma 70-300 for my Canon 30D. I intend to
>> shoot airshows when I can and have a focus question. Since this type of
[quoted text clipped - 4 lines]
>Most airshows that I have shot usually have the aircraft going across
>you so the autofocus shouldn't have to hunt that much.

Correct.

>I personally set to manual and then set to inifinity (not to the end of
>the focus as this is slightly past infinity), checking on something else
>in the distance, take a couple of test shots of the aircraft flying past
>and have a quick check on the LCD.
>
>If all appears well, then I shoot away happily.

Well I'm more than happy to let the AF on my D70 and D200 "work it's magic"
with either of my telephoto lenses. Some older sots taken with the Nikon
70-200mm f/2.8 VR with a 2x TC can be seen at:
http://edwardgruf.com/Digital_Photography/dSLR/airshow/index.html
I wouldn't want to waste checks shots using your method and there's not way
my eyes were good enough to use the lcd for really good focus checks.

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Ed Ruf (Usenet2@EdwardGRuf.com)
http://edwardgruf.com/Digital_Photography/General/index.html

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Scubabix - 13 Nov 2006 23:27 GMT

> Well I'm more than happy to let the AF on my D70 and D200 "work it's
> magic"
[quoted text clipped - 4 lines]
> way
> my eyes were good enough to use the lcd for really good focus checks.

I agree about doing a focus check using the LCD. I also got to thinking
that if I left it in manual and was working the zoom, more than likely I'd
end up moving the focus ring too. I think I'll trust the money I put into
my camera and let it "work it's magic". Thanks again everyone for your
input.
Rob

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Roger N. Clark (change username to rnclark) - 15 Nov 2006 14:55 GMT

>>Well I'm more than happy to let the AF on my D70 and D200 "work it's
>>magic"
[quoted text clipped - 11 lines]
> input.
> Rob

I disagree about focusing with the LCD. The LCD has only about
1/40 to 1/20 the pixels of the camera, so sharp on the LCD can
be horrible on the image. While some cameras, like the 30D, allow
you to zoom in and check focus, you can't do that with action.
Action requires accurate focus in a small fraction of a second.

DSLRs like the 30D in servo mode will actually track the focus of
the subject and project the focal point to the time the shutter
actually fires, compensating for the delay from when you push
the button to when the shutter actually opens.

A good lens will autofocus on the 30D and not hunt. An issue
with accurate focus tracking is smooth subject distance. If you
hand hold, the motion translates to the autofocus sensor moving,
and potentially to different focus distances, thus making the
autofocus system try and track those movements, usually
resulting in focus errors.

For action work you'll get the best results with a good lens
with image stabilization.

Roger
Photos at: http://www.clarkvision.com
(For action photos check the birds and bears galleries.)

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