# Thread: How To Properly Determine Infinity For a Lens?

1. ## Re: How To Properly Determine Infinity For a Lens?

Originally Posted by reddesert
The problem with trying to start at 2 meters is measuring 2 meters from what? From the lens, the film plane, or some property of the lens like the front principal plane? I don't know exactly what the camera maker measured when they engraved the focus scale. However, the camera maker and I can agree on infinity.
Well, normally you measure from the film plane. 35mm SLR's (digital and film) all (AFAIK) have a mark on their body indicating the film plane. Looks like a sort of plimsoll mark on top of the body.

2. ## Re: How To Properly Determine Infinity For a Lens?

Originally Posted by reddesert
I don't really understand what the argument is here.

To set the infinity stops, Linhof doesn't focus on the Frauenkirche. They presumably use an autocollimator to produce a virtual target at infinity. Most of us don't have an autocollimator (although there is a Rick Oleson article about using an SLR to imitate one, if you have an SLR whose focus is known good). Without one, you can start by focusing a faraway target on the ground glass, like a utility pole, a streetlight, or the Frauenkirche. You focus back and forth to find the best focus, as with any target. It doesn't matter that the focus is "acceptable" at the near distance - you're finding the best focus. Now you know the location of infinity for that lens, so you know where to put the infinity stop.

After that, you can proceed to focus at some other distance, say 2 meters, and check between the ground glass and the rangefinder.

The problem with trying to start at 2 meters is measuring 2 meters from what? From the lens, the film plane, or some property of the lens like the front principal plane? I don't know exactly what the camera maker measured when they engraved the focus scale. However, the camera maker and I can agree on infinity.
LInhof has an indicator on its back frame that indicates the film plane position.

3. ## Re: How To Properly Determine Infinity For a Lens?

Originally Posted by reddesert

The problem with trying to start at 2 meters is measuring 2 meters from what? From the lens, the film plane, or some property of the lens like the front principal plane? I don't know exactly what the camera maker measured when they engraved the focus scale. However, the camera maker and I can agree on infinity.
f5.6, 150mm, circle of confusion some mediocre 0.089mm, distance aperture to object 2,00m, bellows extension 12.162mm, distance film plane to object 2,16m. http://www.erik-krause.de/schaerfe.htm#top The distance film plane to object seems to be reliable, since the often belittled, because expensive Technika has a dedicated film plane indicator on the top of the technical back, as others mentioned quicker than me. At 1,18m your calibration will be even more exact with only 3cm dof and fit the 1m indication on your distance scale. If the closer range is right, and if the cam matches both the lens and the camera, we don't even have to think about infinity anymore, in my opinion, but i am not a camera builder. But this is how I "adjusted" the Horseman 985 6x9 with 4 cams and their matching Topcor lenses. Btw. every bigger stroke brings the Horseman range finder out of alignment - so it is useful to know how to adjust it yourself. - On the other hand your Linhof works with reliable precision even under the toughest conditions.

Good luck!

4. ## Re: How To Properly Determine Infinity For a Lens?

Since the thread title does not specify Brand, I post this link, I have fooled with this manytimes

My best usable RF finder is the one one I put a laser inside, but that's an old thread

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