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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 24 Jul 2006 (Monday) 16:56
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Why can lenses be set beyond infinity?

 
Raymate
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Jul 24, 2006 16:56 |  #1

Does it have a use?


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fivefish
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Jul 24, 2006 17:02 |  #2

You know what they say... "To infinity, and beyond!"

I think it allows you to look into the future, some time warp thingy. :)


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Raymate
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Jul 24, 2006 17:04 as a reply to  @ fivefish's post |  #3

fivefish wrote:
You know what they say... "To infinity, and beyond!"

I think it allows you to look into the future, some time warp thingy. :)

Think your right, as i typed the post i turned the lens and saw your comment before you posted it :)


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Big ­ WIll
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Jul 24, 2006 17:14 |  #4

Just incase you see something a little bit further than infinity! obviously!


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GyRob
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Jul 24, 2006 17:22 |  #5

Take no notice of the comments IT'S for further than infinity shots of cause ;)
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Mr. ­ Clean
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Jul 24, 2006 17:24 |  #6

I read something about DSLR's and focusing beyond the infinity mark...I don't remember what it was, something like focusing beyond the hyperfocal length and not necessarily beyond infinity of course


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Doom1701e
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Jul 24, 2006 17:26 |  #7

I've seen into alternate universes with my lenses set to beyond infinity. :-P


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flyingmachine
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Jul 24, 2006 17:29 as a reply to  @ Mr. Clean's post |  #8

I asked a similar question before, basically it allows the cameras autofocus system to focus at infinity. It needs to move past the optimal focus point then return to it. With the kit lens in bad liighting conditions it's pretty obvious.


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SkipD
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Jul 24, 2006 17:35 |  #9

The slight overtravel also allows for mechanical expansion and contraction of the lens focussing components without affecting the ability to adjust the focus at infinity, both automatically and manually.


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Raymate
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Jul 24, 2006 17:36 as a reply to  @ flyingmachine's post |  #10

flyingmachine wrote:
I asked a similar question before, basically it allows the cameras autofocus system to focus at infinity. It needs to move past the optimal focus point then return to it. With the kit lens in bad liighting conditions it's pretty obvious.


Thank You... now you say that it makes sense if the lens hunts it needs to go maybe go past it and then back again to lock


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Raymate
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Jul 24, 2006 17:37 as a reply to  @ SkipD's post |  #11

SkipD wrote:
The slight overtravel also allows for mechanical expansion and contraction of the lens focussing components without affecting the ability to adjust the focus at infinity, both automatically and manually.

This makes even more sense :)


Canon: EOS 5DmkII • 50D • 40D • 350D • 100 f2.8L IS Macro • 70-200 f4L • 24-105 f4L IS • 17-40 f4L • 50 f1.4 • 60 f2.8 Macro • 85 f1.8 • 430EX • 580EX II • ST-E2
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FlashZebra
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Jul 24, 2006 17:49 |  #12

Skip D's explanation is the vital one that has been in play, long before auto focus lenses were ever available.

As lenses get more massive and long (more potential to expand or contract due to temperatures), the need to have a bit of "extra infinity" increases.

A refractor 500 or 600mm lens at 30 degrees F is meaningfully shorter (in an optical sense) than the same lens at 105 degrees F.

But, the lens must focus at infinity in both conditions. This is the reason for the required infinity slop.

Enjoy! Lon


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steved110
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Jul 24, 2006 17:57 as a reply to  @ FlashZebra's post |  #13

All lenses can focus slightly beyond infinity, even the ancient manual everything lenses. the reason for this is two-fold - firstly depending on ambient temperature, things expand and contract, slightly, and this could affect focus if your lens came to a sudden halt at some arbitrary point.

Secondly, when focusing, the AF camera needs to see a phase contrast, and quite frankly so does the human eye - if you have ever manual focused or used a microscope you will realise that you always overshoot the focus then wind back and forth a few times to assess the focus - voila! you need to be able to focus beyond infinity.

Besides, it has a nice Zen thing about it.....


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fivefish
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Jul 24, 2006 18:02 |  #14

It's kinda like buying a guitar amp. You want to buy an amp that can go to 11.

I mean, why buy an amp that can only do 10 on the volume knob?

What do you do when you're playing in a concert and the drummer won't quiet down? And your amp can only go max at 10? You're doomed.

You need to kick it up a notch. Need to turn that dial to 11!


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JCR
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Jul 24, 2006 18:04 |  #15

someones been watching too much spinal tap :D


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Why can lenses be set beyond infinity?
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