Ok, quick and dirty test. MFD on tripod. Focused at f/2 with magnified view, then took 2 other shots at 2.8 and 4 without changing the focus. Here are 100% crops:
1. The 35/2 does have focus shift.
2. It is somewhat negligible because the point of focus remains sharp.
3. The direction of focus shift is backwards consistently with other lenses known to have this problem.
Interesting. It seems different than i thought, since I no longer have the test picture, I will do another test with my m9 to confirm.
But, I am not sure #2 is valid depend on the lens. If your copy optimized at f2.8/f4 like I have on my M9, then f2 wil be front focus, it is not negligible at this DOF. If your copy optimized at f2, then I would say yes
Agree with you, zhangyue. I still have to take the same shots with my Ikon to see what aperture is it optimized for. Obviously on the GXR focusing with LV I do not have such problem as I normally focus at working aperture.
To me, this is quite significant focus shift. And you can see why I need compensate. BTW, for your #3, the direction also consistent with other lens have focus shift problem. My sonnar behave almost the same.
Again, this is strong focus shift, the only reason is not as severe concern as Sonnar is its wider focal length which DOF does cover it if optimized at f2. I think yours should be OK on IKON film body.
Indeed, zhangyue, your results are in line with what I had in mind. It seems the 35/2 is optimized for 2.8-4 as you mentioned earlier. I also read somewhere, probably at Lloyd Chambers that all ZM lenses slightly front focus with digital M cameras, because the sensor plane and film plane do not coincide exactly. This might add to the focus shift on your lens/camera combination.
That said, there's indeed a focus shift out there but it's just minimal.
I just happen to learn that there's a focus shift on the C-Sonnar 50/1.5 on digital body.
Do you guys know why the Zeiss lenses are being calibrated differently for both film and digital cameras? Is there any different design against the body?
edwardkaraa wrote:
Hi Zhangyue,
This is the answer from Zeiss:
Dear Mr Karaa,
Thank you for your inquiry to Carl Zeiss.
The amount of focus shift of lenses like the Biogon T* 2/35 ZM is so small that it does not play any role in practical use.
Sincerely,
Bertram Hoenlinger
However, they failed to mention if the focus moves forward or backward as I stop down. I will do my own test even though it will be more difficult to see on film and post the result over here.
Re: F2
Wow, you focused at 4th Batt. I thought you did it at the 1st one. That's really a significant focus shift, man. The one at F4 seems to be more solid.
p.2 #10 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
The focus shift may look significant for you, but only at MFD. It will get better furhter away. Also there are many inaccuracies in lens/camera calibration that may increase or decrease the effect, hence it is not important for everyday use.
Zeiss lenses are calibrated for the Zeiss Ikon film camera. The Leica M sensors seem to be on a slightly different plane, causing a slight front focus. That is if your RF and lens are perfectly calibrated which is rarely the case.
dannylin wrote:
That's interesting.
That said, there's indeed a focus shift out there but it's just minimal.
I just happen to learn that there's a focus shift on the C-Sonnar 50/1.5 on digital body.
Do you guys know why the Zeiss lenses are being calibrated differently for both film and digital cameras? Is there any different design against the body?
p.2 #12 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
Well, the fact is, there are plenty of people using Zeiss and Voigtlander lenses on their Leica M film and digital. I don't think there are any issues, except with some known lenses like the Sonnar for example.
p.2 #13 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
edwardkaraa wrote:
Well, the fact is, there are plenty of people using Zeiss and Voigtlander lenses on their Leica M film and digital. I don't think there are any issues, except with some known lenses like the Sonnar for example.
My experience is that ALL Zeiss and Voigtländer lenses for M mount focuses fairly accurate at MFD, but are often way off at larger distances. Some of them never even reach optical infinity when the rangefinder patch lines up at the infinity hard stop. This is extremely annoying and has been the case with two M8 bodies and two film bodies.
The reason that most people don't experience this is probably because they only use short DOF for closeups, while I like it at ~3-7 meters distance or so.
The problem is of course much less noticable on film, due to lower resolution and perhaps the thickness of the emulsion.
p.2 #14 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
Makten wrote:
My experience is that ALL Zeiss and Voigtländer lenses for M mount focuses fairly accurate at MFD, but are often way off at larger distances. Some of them never even reach optical infinity when the rangefinder patch lines up at the infinity hard stop. This is extremely annoying and has been the case with two M8 bodies and two film bodies.
The reason that most people don't experience this is probably because they only use short DOF for closeups, while I like it at ~3-7 meters distance or so.
The problem is of course much less noticable on film, due to lower resolution and perhaps the thickness of the emulsion....Show more →
I do not have any digital M but I had an M6 and also use a GXR-M, and all lenses were accurate at infinity except the 35/2. I sent it to Zeiss and they said the focal flange was slightly off and they calibrated it free of charge and it is now perfect. I can confirm all this on the GXR-M as all lenses reach infinity exactly at the infinity hard stop. That is my experience, but I don't doubt yours. There are so many variables in this business.
p.2 #15 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
dannylin wrote:
Zhangyue,
Re: F2
Wow, you focused at 4th Batt. I thought you did it at the 1st one. That's really a significant focus shift, man. The one at F4 seems to be more solid.
That test itself lead two thing:
1. at f2, the lens front focus. PLUS
2. with f2.8 and f4 test, it proves there is focus shift.
If on film body, you might be OK if lens and body perform as it should be.
Martin, Edward, all my Zeiss and Film leica lens incude 50cron and 35cron are front focus at MFD. Since Sonnar and biogon both have focus shift, it actually helped with sonnar.
It could be my body, though I doubt it I will send my body and 50lux soon to Leica get my 50 lux fixed for focus error in mid-range. I will know after it.
For shooting 3-5meter zone, for urban object, this is most likely no issue but not for portrait at or close to MFD.
p.2 #16 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
edwardkaraa wrote:
I do not have any digital M but I had an M6 and also use a GXR-M, and all lenses were accurate at infinity except the 35/2. I sent it to Zeiss and they said the focal flange was slightly off and they calibrated it free of charge and it is now perfect. I can confirm all this on the GXR-M as all lenses reach infinity exactly at the infinity hard stop. That is my experience, but I don't doubt yours. There are so many variables in this business.
What Martin wrote is my experience with the ZM50 Planar on the M9. Accurate focus near, front focusing becoming increasingly more noticeable as the distance to subject increases. Infinity is not sharp until f/4 and is best stopped down past f/5.6. Interestingly, I don't experience this with the GXR.
p.2 #17 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
That is very interesting. I can understand that focus inaccuracy at mid-distances may be caused by the RF or the lens to RF coupling. But at infinity both M9 and GXR should give a similar result, unless the flange distance is not exactly the same, which is not the lens' fault IMO.
p.2 #18 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
edwardkaraa wrote:
That is very interesting. I can understand that focus inaccuracy at mid-distances may be caused by the RF or the lens to RF coupling. But at infinity both M9 and GXR should give a similar result, unless the flange distance is not exactly the same, which is not the lens' fault IMO.
I'd guess the GXR M module has a tad to short flange-to-sensor distance just to get rid of possible problems of not reaching infinity. It's always better to be able to get past infinity than to never reach it.
One must realise that all older, fast lenses does shift focus (forward upon stopping down) and that the M system was designed by someone knowing this. If something in the system is off, you better get the camera calibrated with a reference lens, first of all. Then you can get the lenses calibrated and collimated, which is possible for any brand. The trouble is to get someone to do it. Leica will probably not touch a Zeiss lens.
For lenses with severe focus shift, calibrating them (not the camera!) for accurate focus closed down one or two stops is probably a good idea. If your Sonnar is spot on at f/1.5 and infinity, it will focus beyond infinity stopped down!
For all these reasons, I haven't got an M9 yet. But when I do, I'll probably try to use modern Leica lenses if they are to be fast, and that's terribly expensive.
p.2 #19 · Zeiss ZM Biogon 35/2 or C-Biogon 35/2.8?
Makten wrote:
I'd guess the GXR M module has a tad to short flange-to-sensor distance just to get rid of possible problems of not reaching infinity. It's always better to be able to get past infinity than to never reach it.
One must realise that all older, fast lenses does shift focus (forward upon stopping down) and that the M system was designed by someone knowing this. If something in the system is off, you better get the camera calibrated with a reference lens, first of all. Then you can get the lenses calibrated and collimated, which is possible for any brand. The trouble is to get someone to do it. Leica will probably not touch a Zeiss lens.
For lenses with severe focus shift, calibrating them (not the camera!) for accurate focus closed down one or two stops is probably a good idea. If your Sonnar is spot on at f/1.5 and infinity, it will focus beyond infinity stopped down!
For all these reasons, I haven't got an M9 yet. But when I do, I'll probably try to use modern Leica lenses if they are to be fast, and that's terribly expensive....Show more →
How could I know if the lens reach infinity or not? I did some test but all it shows it get sharper and sharper once slow down the lens.(especially on corner) How can I tell if it is not reach infinity or just nor as sharp as stop down?
Another tricky part is even the lens doesn't reach infinity, the DOF cover it if it can reach close to infinity, make it hard to judge.
