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Re: [OM] General Autofocusing Question [Very OT]

Subject: Re: [OM] General Autofocusing Question [Very OT]
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Wed, 06 Jan 2010 13:45:04 -0500
What Jim said.  Inexpensive Nikon bodies have done away with the 
mechanical screw drive in the camera body which was used in earlier 
autofocus lenses.  These lesser bodies only have provision for 
electronically driving newer lenses which have a focus motor in the 
lens.  Canon has only ever used in lens focus motors but I believe 
you'll find the same split between in-lens motors and mechanical screw 
drive from the body in both newer/older Pentax and Minolta/Sony.

When you first asked your question I thought you were asking the 
difference between phase detection autofocus (SLRs) and contrast 
detection (point & shoots and continuous live view).  Contrast detection 
has, until very recently, been much inferior to phase detection but 
Panasonic has made major strides there with their micro 4/3 stuff.
<http://en.wikipedia.org/wiki/Autofocus>

Chuck Norcutt


Jim Couch wrote:
> Boris,
> 
> Most Nikon lenses focus via a 'screw drive' motor that physically move 
> the focusing mechanism. Many newer lenses use an ultrasonic or similar 
> focusing mechanism. The real problem with the D5000 is that you will be 
> limited to manual focusing most of the autofocus lenses. Only the newer 
> lenses from Nikon that are designated AF-S will autofocus on the D5000, 
> sigma HSM and Tamron NII lenses will also autofocus. You can use the 
> other autofocus lenses, but will need to manual focus them with the 
> D5000. If you have any other questions on Nikon DLSRs contact me off 
> list. I shot with them for a couple of years until switching to the 
> Olympus E-620 this summer, so i can probably answer most questions you 
> might have.
> 
> Jim Couch
> 
> Willie Wonka wrote:
>> How does autofocusing work?
>>  
>> I have permission to spend some money on a new camera.  Stumbled upon the 
>> Nyk*n D5000 at Target.  Nothing to be excited about, but it looks like a 
>> useful tool...apparently the autofocusing motor is removed, but how does it 
>> autofocus without it?
>>  
>> Curious Boris
>>
>>
>>       
>>   
> 
-- 
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