M9-P infinity check

[IWC Doppel]

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Any tips on ways to check if my M9-P needs adjustment at infinity ? I think I am seeing some softness when shooting distance shots (eg landscape or buildings from a few hundred M's) it could be me expecting more but I hadn't noticed this before tbh. I'm due for a sensor clean but don't want to pay for a service if I don't need one

[ockie50]

Focus on a flag pole or church top a minimum of 10 times the focal length away in meters, that is 50x10 = 500 meters for a 50 mm lens etc. The split image should overlap perfectly if your rangefinder is correctly adjusted.

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[250swb]

A few hundred meters is not infinity. You shouldn't be able to adjust focus on infinity, it is the end stop of the lens, it's the pylon five miles away.

 

True infinity is usually covered by DOF to make it sharp even with a lens wide open, and even if other things are slightly mis-adjusted. But other things can make objects at infinity look less sharp, like camera movement which is exaggerated with a wide angle lens just as it is using a telephoto, where a fractional movement doesn't show up on closer objects but is magnified as the relative angle of movement becomes greater at the horizon. The there is atmospheric haze which distorts objects at infinity and makes them appear softer. And of course detail and contrast are reduced the further you get away from things anyway, the lens can't resolve them.

 

So a few hundred meters or middle distance isn't infinity, but some things do remain the same, like camera movement is exaggerated at a few hundred meters, so try using a tripod if you don't already, keep the shutter speed up, use the best f/stop like f/8 so the lens is at it's most contrasty and at the peak of it's resolving power, and you can still get atmospheric haze softening the image especially in city's.

 

Steve

Edited March 22, 2014 by 250swb

[FPB]

I check my lenses on the M9 for infinity focus with a radio / cellular transmitter that is about 2 km away. A about 300 meters there is cross on a church and the next house is about 100 meter. All on the same image. Now 4 pictures are taken: 2x wide open and 2x at f5.6. At each f-stop one at maximum infinity of the lens and one with the focus ring / tab turned back a little bit. Maybe 1/3 of a mm. No more. If everything is ok, then you can see where the focus plane moves. This works with lenses down to 35mm and must be done with good weather conditions and on a stable tripod. Raw only.

 

Bill

[plewislambert]

"the M9 for infinity focus with a radio / cellular transmitter that is about 2 km away. A about 300 meters there is cross on a church and the next house is about 100 meter. All on the same image. Now 4 pictures are taken: 2x wide open and 2x at f5.6. At each f-stop one at maximum infinity of the lens and one with the focus ring / tab turned back a little bit. ......"

If you think the focus appears to be out, consider whether a heavier tripod, the use of a long cable release or extra care would yield an improvement. I noticed some image blur with my M9 on a tripod on some lens-comparison pictures. When I studied the fine detail it was clear the camera had moved during a very short exposure so I repeated the shot with a whole lot more care releasing the shutter. A sharper picture resulted.

Philip:)