New to M. Question on lens

[ALScott]

Advertisement (gone after registration)

32 minutes ago, Jeff S said:

First thing is a good eye exam to assess not just distance, but astigmatism, and correct for each as needed. I use glasses to correct for both, as I don’t want to be taking my glasses on and off when the VF isn’t to my eye.

 

Regular eye exams for years and years.  Got Lasik maybe 10 years ago...  eliminating all distance issues.  Only possible issue is near from getting old!  Better than the alternative I always say.

[Jeff S]

37 minutes ago, ALScott said:

Regular eye exams for years and years.  Got Lasik maybe 10 years ago...  eliminating all distance issues.  Only possible issue is near from getting old!  Better than the alternative I always say.

So, if you’ve ruled out any astigmatism, then I’d recommend experimenting with some diopters as I described.  Math aside, I find it’s the easiest way to determine optimal focusing… for you.

Jeff

[LocalHero1953]

2 hours ago, streetrattakesphotos said:

Actually, even with the moon. Don't know if the M11-P was the OP's first camera, but with the telephoto RF 100-500mm for my R5, the moon is not at infinity. I have M lenses that don't do very much of this, and they're the ones without much throw at that end of the focus ring, so that it's fairly hard to tell.

I went back to basic Newtonian optics on a spreadsheet (1/u+1/v=1/f). This works just for classic simple lens cells, no floating elements, no internal focusing, no zoom.....

• For a 50 mm lens, the difference between infinity and the distance to the moon corresponds to a focusing movement of 6 billionths of a millimetre. For an aircraft at 35,000 feet, the movement from infinity would be 0.2 microns. For infinity to the horizon on a flat plain for a tall person (5km) it would be 0.5 micron. For a portrait (2m) it would be 1.3mm, and to the Leica close-up point, i.e. the full rack of the helicoid, (0.7m), it would be 4mm. The last figure matches the reality I can measure on a handy 50mm lens.
• For a 135 mm lens, the corresponding movements from infinity are (moon) 47 billionths of a millimetre, (aircraft) 2 microns, (horizon) 4 microns, (portrait) 10 mm, and (theoretical close up) 21 mm.
• For a theoretical 500 mm lens, the corresponding movements from infinity are (moon) 650 micron, (aircraft) 23 microns, (horizon) 50 microns, (portrait) 167 mm, and (theoretical close up) 1.25m.

For those of you still awake, I suspect the difference between the moon and infinity (or the stars) is negligible for a Leica rangefinder lens, even if it is not so for a 500mm lens.

As to whether a church spire at 5km or a house at the end of the road at 500m can substitute for infinity, that would depend on how precisely engineered the helicoid is: if a slight movement of the focus ring translates precisely and repeatably into a micron movement of the focusing cell, then you'd need to pick the more distant object. Making this work is Leica's forte.

Edited October 25, 2024 by LocalHero1953

[250swb]

3 hours ago, ALScott said:

Regular eye exams for years and years.  Got Lasik maybe 10 years ago...  eliminating all distance issues.  Only possible issue is near from getting old!  Better than the alternative I always say.

As @pedaes says, if you are indeed using hyperfocal distance to focus the image then it's an average of whatever you consider 'acceptably sharp' by your own rules and nothing to do with the lens or rangefinder. With an M11 and it's already well known problems of soft images (because of the higher pixel count) using hyperfocal distance to 'focus' is going to exaggerate any mis-focus which is the essence of hyperfocal distance, it's just a way to kind of get as much of the image more or less in focus without actually turning the focus scale to do so. So you will be guaranteed that whatever you are interested in getting sharp won't be perfectly sharp, just 'sharp enough' (hopefully).