LCT said:
Yes sorry for misreading but it's perhaps that i don't comprehend well what may be a lens related misalignment. I've got some with Leica Ms from time to time and some more 🙄 with R-D1 and R-D1s but each time the misalignment was a RF problem. It did not change with lenses and it was not necesseraly related to accuracy. I mean an RF may be misaligned and (more or less) accurate or well aligned and inaccurate, does it make sense at all?
Yep, it does. We are dealing with several variables here:
1) Lens collimation plan vs lens-scale. Not all lenses area created equal (unfortunately), either by design, malfunction or sloppy production. A lens should focus on a defined plan (standard for a Leica-M and all optcally compatible mounts) when the lens scale indicates the correct distance for focus. If an object is 1m from the focal plane (film/sensor) and the lens scale is indicating 1m, then the image should be forming at the focal plane (film/sensor). Things get weirder as focal plane for some lenses can (and will) be curved and it can change with aperture. But let's ignore that stuff
🙁 for a while and focus on collimation only.
2) RF mis-calibration. AFAIK, a RF can be mis-calibarated in several "dimensions" (and it's combinations):
a) it can be vertically mis-aligned
b) it can be horizontally misaligned
b) it can be out-of-focus (the RF patch, that is) and
d) the base length may be off.
The a) problem is usually the most benign (alhough it impairs the ability to correctly focus on other patterns than vertical lines and cause focus errors! My Epson is like that right now and I sure feel it... :-() It's easily corrected on the Epson RD-1 but, apparently, not on the s (I have the s, damn it!). I tried it but it dind't work. The screw that was supposed to act on the vertical aligment turns loosely and does nothing on my RD-1s. I thought that was a problem with mine but some other people in this forum reported the same problem :-(
Problem b) is much worse and it's impossible to focus a lens correctly except relying on DOF. When a correctly collimated lens is focused on infinity (on the scale), the RF patch should coincide with the mais image. If it does not, the RF is mis-aligned. Mine was badly mis-aligned after a mild bump (my M3 had 10x worse bumps and never had a problem with RF...), more than 20% off at infinity. If all your lenses are ok, then it should happen to all of them. If your lenses vary, it could even happen that horizontal mis-aligment is beneficial for some of them...
🙂 Problem b) is also easily corrected on the Epson (I corrected mine myself, no sweat).
c) and d) are rarer. c) can still be corrected easily (without unmounting the cover) but will give you more work, as it can have impact on b). AFAIK, fixing d) requires unmounting the top cover, so it's not a DIY thing.
3) RF accuracy. That theoretically dependes on the effective base lenghth (base length and VF magnification) but IMHO depends on other stuff in practice (VF constrast, lens helicoid step, available light, eyesight, etc, etc). Of course, everything else being equal, it's obvious a larger effective BL will perform better than a smaller BL base. It's just that, in practice, not everything is equal...
🙂
So, we have at least 3 factors: lens collimation, RF aligment, RF accuracy.
My Epson RF is now vertically mis-aligned, but horizontally ok. This means that I am able to correctly focus correctly collimated lenses, within RF accuracy bounds (which, BTW, get smaller with vertical misaligment, unless you have some handy vertical lines to focus on the subject. More on this on the end of my post).
The problem is that "horizontal aligment" depends on the lens being well collimated. If mars's RD1 aligns correctly at infinity with other lenses that he believes are well-collimated (eg: new Leicas, as Leica quality control is good enough to rely on new lenses for that - old could be malfunctioning) and does not with the Elmarit, probably the problem is the Elmarit.
He _could_ align the RF so that it becomes correct for the Elmarit, but that would probably make it worse for all other lenses.
Nothing of this has to do with "accuracy" (in fact, he doesn't need to take a picture at all to test it and align it, alhtough it would be a good idea to check it out
🙂).
So, if mars has a collimated lens and an aligned RF, I would guess it would be accurate enough to get a fair share of sharp shots with a 90/2.8 wide-open, at least not much worse than a Leica M6 on the same conditions, if those conditions include low-light and bright spotlights (my M& TTL RF flared a lot in those conditions, making focus accuracy a lottery), low shutter speeds (camera shake), people moving (shallow DOF and people getting out of focus) and high speed ISO settings (lower resolution because of noise processing).
If he didn't, then maybe that's an accuracy problem. But what I found out is that I get a lot of focused shots with the 50/1.5 wide-open and at close range.
This is becoming long, sorry!
🙂 But this is something that has been bothering me for a while...
🙂
To finish: I bought a 35/1.2 CV Nokton and I was getting several out-of-focus shots at f1.2 and f1.4. More than with the 50/1.5 Nokton. I made some tests and it seemed like it was backfocusing a bit, nothing to be afraid of at f2 but showing at lareger apertures.
Two days ago, I decided to repeat the tests on the 35/1.2 but ensuring I had very good lighting AND thin but very visible vertical lines. The results were clear: it focus ok. Problem is that vertical mis-aligment does REALLY impair focus unless you have clear, thin vertical lines to focus on (large lines lead to some focus error, as DOF at 0.7m and f1.2 is razor-thin).
I can post the (boring pictures) that came out of the test, if that's useful.
BTW, the 35/1.2 Nokton (at least my sample) is amazingly sharp in the center from f1.2 and corners keep-up from 2.8. At f2 corners are a bit fuzzier, at f1.4 they are a bit worse. But that's a flat field.
On "practical" pictures, the 35/1.2 is as bit as good as the 50/1.5 Nokton and that is very good. SO, it looks like it will join the rest of the line-up on my signature and I'll have to post some rave about it!
🙂
Again, sorry for the long post that became a bit off topic!
🙂
