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Old Jul 3, 2007, 10:05 AM   #11
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Kjell - my A*300 does also (like you, I don't know why). Since it's manual focus anyway, I just pay attention to the viewfinder because I can see the focus change. I wouldn't be using it for fireworks and don't particularly use it in the dark so it doesn't bother me. I used to do the "crank until it stops" with with all of my M lenses - they would all stop at infinity.
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Old Jul 3, 2007, 12:58 PM   #12
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bilybianca wrote:
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VTphotog wrote:
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The reason lenses sometimes focus "past infinity" is simply because autofocus mechanisms tend to overshoot a bit, and then reverse direction. There has to be a little bit of slack available for them to do this.
There has to be another reason as well. I've got two A* lenses (200 & 600 mm), manual focus,that do this.There's nothing wrong with the lenses, it's even mentioned in the manual. I don't know for what purpose, but as I understand this is some kind of "pro feature".

Kjell
i read recently that with the longer lenses like my 500mm and your 600mm that the reason is because of the thermal qualities of the lens. makes sense because of the contraction and expansion in different tempertures.
i have several small lenses that do the same. don't know why.

roy
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Old Jul 3, 2007, 2:46 PM   #13
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From this point on I'm going to think of past infinity as the 'Buzz Lightyear effect'.. 'to Infinity..and BEYOND!'



"I tried to focus on infinity for these but they're still blurry!"

"Dang, you Buzzed the focus, man."


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Old Jul 5, 2007, 5:39 AM   #14
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robar wrote:
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bilybianca wrote:
Quote:
VTphotog wrote:
Quote:
The reason lenses sometimes focus "past infinity" is simply because autofocus mechanisms tend to overshoot a bit, and then reverse direction. There has to be a little bit of slack available for them to do this.
There has to be another reason as well. I've got two A* lenses (200 & 600 mm), manual focus,that do this.There's nothing wrong with the lenses, it's even mentioned in the manual. I don't know for what purpose, but as I understand this is some kind of "pro feature".

Kjell
i read recently that with the longer lenses like my 500mm and your 600mm that the reason is because of the thermal qualities of the lens. makes sense because of the contraction and expansion in different tempertures.
i have several small lenses that do the same. don't know why.

roy
Apparently, I have have just read that focussing past infinity on the smaller lenses allows the use in specialist films e.g. Infra-red.



Darren


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