# 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

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

Related but can someone help me understand where to pull the front standard out to?
Sorry basic question I know.

I don’t really understand.
The very earliest is for wide angle, as it denotes 90mm
The middle says 180mm
Then the very front says 135mm

If I have a 210mm lens where do I put it?
I tried to read the manual but it didn’t really do a good job of explaining.

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

The distance markings are designed to work with that little arrow indicator / black triangle when the lens is set to infinity at "stops" that you must be missing. Ignore them, especially since you aren't using those lenses. Set your camera up on a tripod with the focus racked all the way back and locked, with the sliding extension at the normal, not extended or retracted (like in your picture) position. Simply move the front standard till "infinity" is in focus, and there is your infinity position, roughly. If you want you can use a marker to add a mark to the bed of the camera. I would fudge it a little in towards the body so that you are past infinity, so you have some room to focus to infinity.

Also don't forget that unless you are using the RF this really doesn't matter much as long as you aren't wildly out of position. When I shoot my Linhof MT for landscape I just pull the lens out till it's kinda almost in focus and then use the focus knob to get it in focus.

PS: you should probably find an old Technika users manual online and read it, and then simply practice with your camera. It's not a complex camera, but if you don't understand all of the extensions and accessories and etc., especially if you are a new LF user, it might be daunting. The manual should from the Technika IV, V, or Master models will work fine - you have one of those models it looks like to me.

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