Focus at infinity

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Focus at infinity

Postby biggerry on Sun Sep 27, 2009 10:50 pm

I have a 100-300mm old school lens that I use quite often, I learnt early on that with the focus barrel rotated all the way to the infinity stop the images of things in the horizon, and even the moon, are not terribly sharp, however, backing the focus off the stop just a fraction really improved the sharpness and i guess that point is the real focus for infinity.

Has anyone else experienced this with other nikkor lens? It is not of real concern for me, but I am curious if anyone else has had the same issue.
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Re: Focus at infinity

Postby Big Red on Mon Sep 28, 2009 12:11 am

AF lenses are more likely to do that as they need room to "go past" the focus point so they can then turn back the other way.
i have one that is exactly on the mark and in certain weather conditions it gets stuck there as it can't turn back because it is still trying to go forward.
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Re: Focus at infinity

Postby aim54x on Mon Sep 28, 2009 1:02 am

A lot of my lenses focus past infinite....but I have never noticed them AF-ing past infinite nor have i noticed them being not as sharp as infinite.
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Re: Focus at infinity

Postby Matt. K on Mon Sep 28, 2009 8:46 pm

Many zoom lenses focus beyond infinity because this position changes as the focal length changes. (I'm pretty sure I've got this right!) :D :D :D
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Re: Focus at infinity

Postby ATJ on Tue Sep 29, 2009 9:22 am

I think that is true of most lenses. It is just more noticeable with longer lenses as the magnification is greater and depth of field is less.
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Re: Focus at infinity

Postby Photopotamus on Tue Sep 29, 2009 10:21 pm

Seems to me I recall reading somewhere that the tolerances beyond infinity were to allow for "environmental changes" (ie: temp, humidity, etc..), that would cause minor variations (expansion/contraction) in the lens construction.
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Re: Focus at infinity

Postby Mr Darcy on Wed Sep 30, 2009 1:02 am

Dare I admit that I have been caught by this on more than one occasion. Usually on a night shoot. "Arr it' a long way away... I'll just turn the focus ring all the way...She'll be right" :oops:
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Re: Focus at infinity

Postby Willy wombat on Wed Sep 30, 2009 10:45 am

Its a trap - I learnt the hard way that screwed out all the way is not infinity, (its just back a bit)
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Re: Focus at infinity

Postby biggerry on Wed Sep 30, 2009 11:18 pm

AF lenses are more likely to do that as they need room to "go past" the focus point s


yeah, all my AF lens do this, however my 105mm f2.5 stops smack on the infinty point and seems to be in focus, quite handy when you just want to bang it out to infinty without worrying about the horizon or whatever not being in focus.

Dare I admit that I have been caught by this on more than one occasion.


yep, been done on this as well, however only on the AF units when doing manual focus.

When I get a spare 5 minutes i will take some sample shots for interests sake...
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