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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 27 Aug 2006 (Sunday) 15:48
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Focus to infinity

 
Stump
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Aug 27, 2006 15:48 |  #1

It's a common thing I hear. I had prosumer cameras like the Pano Fz30 and Sony f828 that dont work that way but just got my Rebel XT. I tried some star pictures lastnight and was gonna focus to infinity, I tried focusing all the way both directions and never got the stars in focus like that. I'm wondering about this mostly for lightning pictures that I'll be taking later on. Thanks


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phylet
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Aug 27, 2006 16:25 |  #2

ah yes, i had this issue with my XT when i first had it,
lenses have some built in extra-focus, that lets you focus PAST infinity, focusing to infinity is the right thing to do, but going all the way to the end is wrong, just let the AF do it, its easier on a lens with no markings.


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fatdeeman
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Aug 27, 2006 17:13 as a reply to  @ phylet's post |  #3

That's always been one thing I've found annoying about my 350d and it's lenses.

When I used to use film in college you couldn't go past infinity so you could just turn the focus ring all the way around and know you have the right setting.


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phylet
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Aug 27, 2006 17:42 |  #4

indeed deeman, but what if your lens contracts from cold? you'd not be able to reach infinity! or if it was hot, you'd have to focus before the infinity stop anyway!


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fatdeeman
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Aug 28, 2006 06:49 as a reply to  @ phylet's post |  #5

Well the seemed to get by in the days of old!


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chris ­ clements
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Aug 28, 2006 09:19 as a reply to  @ fatdeeman's post |  #6

fatdeeman wrote:
When I used to use film in college you couldn't go past infinity

Yes you could ; the lenses aren't different.
How else would the lens compensate for both Antarctica and the Amazon?

Sound like autofocus is causing some of us to lose the use of our eyes :)




  
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fatdeeman
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Aug 28, 2006 09:22 as a reply to  @ chris clements's post |  #7

Well I've got an m42 practika lens right here in my hand that doesn't go past infinity


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chris ­ clements
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Aug 28, 2006 09:51 |  #8

Sorry, but in normal temperatures the lens MUST be focussed past infinity when up against the end detent, even if it's not clearly obvious in the viewfinder or final print.
The expansion coefficients may well be less for ancient heavy metal ( ;) )than with modern engineering plastic, but some leeway must still be there.

* what would lead you to believe that what's at the lens' plane of focus (film or chip) would make a difference?




  
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fatdeeman
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Aug 28, 2006 11:39 |  #9

Oh well that's fair enough, I wasn't saying it was a case of digital being different, it's just when I use a NEW lens I can see the distance scale go past infinity but on this old m42 lens it only turns to the infinity symbol and wont go any further


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steved110
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Aug 28, 2006 16:00 as a reply to  @ fatdeeman's post |  #10

fatdeeman wrote:
Oh well that's fair enough, I wasn't saying it was a case of digital being different, it's just when I use a NEW lens I can see the distance scale go past infinity but on this old m42 lens it only turns to the infinity symbol and wont go any further

Praktica lenses are fairly basic/ low level in terms of spec.

If it is a fairly wide lens eg 28mm or wider, and used with a stopped down lens then the inherent DOF will be enough to compensate for the lens stopping dead on the infinity mark.

But every lens should focus past infinity - especially a manual lens - can you remember how to focus manually with a split focus screen? You twiddle the focus back and forth so the subject pops in and out of focus, settling on the position that to your eye at least looks best. So if your praktica M42 does not allow this, then it is quite frankly broken.


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chris ­ clements
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Aug 29, 2006 07:55 |  #11

No-one has yet quoted from the indisputable expert on this topic.
I refer of course to Buzz Lightyear.




  
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Focus to infinity
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