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Author Topic: Correcting infinity focus  (Read 4586 times)

jljonathan

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Correcting infinity focus
« on: May 18, 2012, 12:57:19 PM »

I have a couple of Zeiss C/Y lenses that I am using on a Sony Nex 7. When I rack focus to infinity, the lens goes passed the infinity focus point; I have to nudge it back 1/4" turn to hit infinity. Is there a way to make an adjustment so that the lens focuses at infinity when fully turned?
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mouse

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Re: Correcting infinity focus
« Reply #1 on: May 18, 2012, 03:09:31 PM »

There is a way to adjust the infinity stop.  However, based on my reading, you may not want to make this adjustment.  The stop is (allegedly) set past infinity in order to allow room for dimensional changes that may occur with temperature. 
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Johnny_Johnson

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Re: Correcting infinity focus
« Reply #2 on: May 18, 2012, 03:58:19 PM »

Do both lens focus past infinity with the same adapter? If they do then the problem is probably an adapter that's too thin. If that's the case I'd try another adapter fron a different vendor.

Cya,
Johnny
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jljonathan

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Re: Correcting infinity focus
« Reply #3 on: May 18, 2012, 04:01:43 PM »

No, the 135 focuses short of infinity, but the 28 is right on.
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jgbowerman

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Re: Correcting infinity focus
« Reply #4 on: May 20, 2012, 10:13:04 AM »

I have a couple of Zeiss C/Y lenses that I am using on a Sony Nex 7. When I rack focus to infinity, the lens goes passed the infinity focus point; I have to nudge it back 1/4" turn to hit infinity. Is there a way to make an adjustment so that the lens focuses at infinity when fully turned?

I have understood all lenses will focus past infinity, but perhaps I am mistaken. Every lens I have used on Nikon cameras (Nikon and Zeiss glass) will focus past infinity in manual mode. Personally, I want that extra play in a lens. I'd rather it be my eye making the call and not a manufacturing specification.
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scooby70

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Re: Correcting infinity focus
« Reply #5 on: May 20, 2012, 10:26:50 AM »

I can't remember ever owning or using a lens that didn't go past infinity.
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mdarnton

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Re: Correcting infinity focus
« Reply #6 on: May 20, 2012, 11:19:58 PM »

I recently send a lens to Nikon authorized service. It went in stopping solidly at infinity, and came back with infinity at about 15 feet on the scale. I called to complain, and the service rep explained that some of the modern AF cameras won't give focus confirmation at infinity unless you go PAST infinity, first, so they are setting them slightly off to allow that. When I explained that I was on film, not digital, and often relied on the focus scale, he had the lens put back the way it had been sent to them. For a subsequent lens CLA I was certain to specify infinity at infinity.

I also remember when the first complex zooms and lenses with exotic elements came out in the 70s or 80s they were set to go past infinity to allow for temperature changes. I believe the 180/2.8ED Nikkor may have been the first lens I read about that did this.
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PhotoEcosse

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Re: Correcting infinity focus
« Reply #7 on: May 21, 2012, 12:37:52 AM »

Of course, focussing "past infinity" is an impossible scenario. But, yes, many modern AF lenses will turn beyond the infinity market and go out of focus as a result.

However, I am surprised that it is happening with non-AF lenses such as you mention.

The reason that AF lenses have "space" beyonf the infinity marker is to avoid jarring against the physical stop when the AF mechanism focusses at infinity.

But, as there is no such reason for your lenses to have been built that way, I suspect that the adapter problem may be the first thing to investigate.
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Petrus

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Re: Correcting infinity focus
« Reply #8 on: May 21, 2012, 02:57:39 AM »

Of course, focussing "past infinity" is an impossible scenario.

Optically speaking it is not an impossible scenario. The point of focus is approaching you from behind...
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Colorado David

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Re: Correcting infinity focus
« Reply #9 on: May 21, 2012, 01:13:10 PM »

I have nothing useful to add to this discussion and I apoligize in advance for merely using up bandwidth.  I couldn't help but hear Buzz Lightyear saying "To infinity and beyond!" ;D

scooby70

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Re: Correcting infinity focus
« Reply #10 on: May 21, 2012, 09:06:32 PM »

 ;D You're never too old to enjoy Toy Story :D

The newest lens I have is a Voigtlander 25mm f0.95 which is a manual lens for MFT and it goes past infinity, not much but enough to be able to see that it does.
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