M240 lens focus test

[stump4545]

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what is the easiest way to test if your M240 and lens are calibrated properly and your RF focus is in perfect alignment.

 

 

If I use my EVF to focus on something maybe at 10ft away with focus peaking, and then quickly switch to my optical viewfinder to see if the image in the optical viewfinder is in perfect focus?

 

 

Would this work?

 

 

If image in optical viewfinder is not in perfect focus, how do I know if it is the lens that needs calibration or the m240 body?

 

thank you

 

 

 

 

 

[pop]

The most useful resource (FOC) is this: http://www.dphotojournal.com/focus-test-chart.pdf

Even if it is about other cameras, you still learn a lot. The actual testing of your camera begins on page 13.

 

If the picture and what you see in the RF do not agree, there is no way to tell which one - if any - is correct.

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[jaapv]

stump4545, on 24 Feb 2016 - 16:48, said:

what is the easiest way to test if your M240 and lens are calibrated properly and your RF focus is in perfect alignment.

 

 

If I use my EVF to focus on something maybe at 10ft away with focus peaking, and then quickly switch to my optical viewfinder to see if the image in the optical viewfinder is in perfect focus?

 

 

Would this work?

 

 

If image in optical viewfinder is not in perfect focus, how do I know if it is the lens that needs calibration or the m240 body?

 

thank you

Not always - it depends on the lens, focus peaking is not always the most reliable way of focusing. You will need a tripod too. With one lens-one camera it is impossible to determine whether the camera or the lens is off. Reason why Leica usually wants to see both for calibration issues. Even a whole system can be off-standard.

[MT0227]

Here's some additional guidance I received, asking the same question. 

 

CheshireCat, on 26 Feb 2016 - 00:37, said:

 

 

 

This is the procedure:

 

- Camera on tripod.

- Lens wide open (some lenses do shift focus by design when stopped down, so this is very important).

- Put a lens focus test chart at 45 degrees with respect to the sensor. Something like this one: https://ziebaphoto.f...rchecker111.gif

 

For each focus distance (I usually test MFD, 1m, 2m, 3m, 5m):

- Focus with RF on the chart target.

- Enable LV, with max zoom, and verify that the target is in focus on the sensor.

- If not in focus, achieve critical focus with LV, then look into the RF to see if still in focus within your eye tolerance.

- If not, lens needs to be calibrated, which requires Leica or an expert ($$$). That is what I call "a lemon" 

 

Finally, test infinity:

- Set the lens to infinity.

- Use a very far object, like a distant building (antennas are good targets).

- Enable LV, with max zoom, and verify that the object at "infinity" is sharp.

- Fine tune focus (just very slightly turn the ring back and forth) to see if infinity matches with the focus ring hard stop.

 

Note that some lenses focus a little past infinity to accommodate for temperature changes. This is ok, but should not be eccessive. For example, my Summicron 75 focuses past infinity a bit too much, and for critical sharpness wide open I have to fine tune with LV. I will send it in for calibration eventually.

In any case, the real problem you want to check for is the lens not being able to reach infinity.

 

That's all. You could do something like this without LV, by taking a lot of photos, but you will never be able to see the critical focus popping out as you turn the focus ring in realtime. This is particularly important for the infinity test.

[trent]

Stump,

 

Since what one sees through the viewfinder (not LV) and what the lens projects on the sensor are two different things, it is good to double check the calibration.  I rigged a simple test to put my mind at ease. 

 

The target is a scrap of wood with finishing nails spaced an inch apart.  Placed it on my mantle and with my camera on a tripod and using a timed release, I took images (after carefully focusing!) with the lens at maximum aperture.  In this situation, the 75MM @ f2.0 doesn't give one much to play with.  I was please to find that at 6 feet the calibration was spot on as well as at minimum focus. Beyond that, increasing DOF will help.

 

Good luck.

 

Trent

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[byroncheung]

On top of what other suggested, i'd also say having a viewfinder magnifier will also help to be sure the rangefinder is focusing on what you're trying to focus on to, minimizing error from our eyesight.

 

But to be honest, if you're asking this question, very likely either the lens / rangefinder is not spot on (this mechanical system is notorious to get out of line overtime anyway...) if it were me I'd just send it out to DAG for him to check them out and re-calibrate if necessary, I've done that couple of times in my leica-life-time...

[jaapv]

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Actually, a magnifier magnifies errors as well... It will only improve accuracy after one has eliminated them as far as possible. Mostly my cameras hold their calibration for years, even decades, so i cannot place "notorious", unless it applies to the learning curve associated with the system.