Focusing ZM C Sonnar 50/1.5 on Leica M240

KEH

KEH

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Friends,

I am having real problems with back focus on a new C Sonnar attached to my M240. I have searched a bit on the forum and it seems most of the shooting with this lens is on film bodies or non-Leica digital bodies.

Popflash include a warning about the lens as follows:
  • all production since 1997 is focus optimized at f/1.5 for film based cameras to a FFD distance at 27.86mm.
  • this adjustment works well for film based cameras, but causes a noticeable shift on digital rangefinder cameras - since their FFD is longer than film-based M-mount cameras (basically they do not meet the standard M-mount spec). When the optimized lenses are tested with digital rangefinder cameras at a close focus distance of 0.9m and at f/1.5, they front focus by about 2cm
  • because of the differences between film and digital rangefinder cameras - which we cannot control - it is impossible to have a focus optimized C Sonnar for both systems.
for customers who want their lens adjusted for digital rangefinder cameras, Zeiss Germany have set the FFD to a distance of 27.90. This provides good results on digital cameras, but will cause a focus shift on film cameras for the reasons mentioned above.

I find I can adjust for the back focus, but not reliably because it seems to vary with aperture.

Has anybody had a similar problem, and have you sent it to Zeiss for the 'adjustment for digital' bodies mentioned by Popflash? The Zeiss website makes no mention of any such service.

Any help appreciated. Lovely lens, but I can't use it reliably at the moment.

Cheers,
Kirk
 
The popflash statement is extremely misleading.

Focus shift is inherent in the Sonnar lens design.
The film vs digital issue is largely moot as focus shift dominates.

For this lens, the point of focus calibration is only valid for one aperture.
If you send it back to calibrate at f/1.5 the focus shift at e.g f/4 is so bad that depth of field does not cover you.

I have a 2010 lens with f/2.8 calibration.

I continue to read that shipping lenses are still optimized at f/2.8 as that is the best compromise, but with this front focus at f/1.5 is implied and cannot simultaneously be calibrated.

At least with the M.240 you have an EVF which should reveal all.
 
I personally prefer the lens to be calibrated for 2.8. I can deal with 2 cm front focus at MFD when shooting wide open. Correcting for back focus is more difficult for me. Unfortunately my copy was calibrated for 1.5 so I sold it and kept the planar.

PS. Pop flash have no idea what they're talking about. All ZM lenses are calibrated for Leica M mount exactly like Leica's own lenses. They are interchangeable between digital and film bodies as I have used mine on Zeiss Ikon, M6, M9 and M240 and they behaved exactly the same.
 
Popflash's statement seems to be there to reduce the number of sales returns.

I recently picked up a used ZM 1.5 Sonnar and have no problems focussing wide open with my M-E. Right now it's on my M5 so I'll see how it does w/ film (I'm testing it with an ND filter so all shots can be at 1.5)
 
Haven't you got a camera with a live view? Then focus the lens on a straight line and observe what happens as you stop down. This will show you at which aperture you get things right. My guess is, you have the f2.8 version, which should focus more or less correctly from f 2.8 onwards. Enjoy - f 2.8-4.0 range is the most useful one with this lens.
I have done the comparison of the different versions of C Sonnar- you will find it here:

http://www.rangefinderforum.com/forums/showthread.php?t=51742&highlight=comparative+focus+c+sonnar
 
Friends,

Many thanks - all very useful input.

I take it from mfogiel's test that you have to choose the desired application and match the lens calibration to the application. As he suggests, the alternative is using the live view viewfinder. I was hoping to avoid this (relying only on the optical viewfinder), but this will not work in all cases.

I guess I either sell the lens or bring the evf...

Cheers,
Kirk
 
Dear Kirk,

Or just focus and then rock backwards or forwards a tiny bit (typically 4-8 inches) according to the focused distance. Takes a fraction of a second. This suggestion comes from Dr. Nasse at Zeiss and has worked perfectly for me since I got the lens some years ago. Beats the EVF hollow for both speed and accuracy (and yes, I've tried both).

Cheers,

R.
 
Two suggestions that have worked for me:

1. For close focus at wide aperture: Test by using a tripod and photographing a slanted ruler. On my M9, my Sonnar is 'optimized' neither at f1.5 nor 2.8, but at f2 and 2.2. So that's where I use it if I'm up close and need a wide aperture.

2. After you've figured out your best close/wide aperture, skip everything between that and f6.3 (or whatever the Zeiss 1/3 click stop is after f5.6). Pretend the f-stops with focus shift problems just aren't there.

I have no problems my Sonnar shooting this way. And it's not a unique problem of the Sonnar – my pre-aspherical Summilux works the same way.

Kirk
 
Roger Hicks said:
...Or just focus and then rock backwards or forwards a tiny bit (typically 4-8 inches) according to the focused distance. Takes a fraction of a second. This suggestion comes from Dr. Nasse at Zeiss and has worked perfectly for me since I got the lens some years ago. Beats the EVF hollow for both speed and accuracy (and yes, I've tried both)...
Click to expand...
Roger's suggestion is a good one, and i have used this method. My C-Sonnar came optimized for f/2.8. Later, I sent it to DAG for coding and adjustment, and it came back optimized at about f/2. Now I make no compensating movements and in "real world" shooting (M8, M240) notice no focus issues other than my own mistakes! 🙄

If you'd like to see some examples, look at my gallery (RF collection) for Hawaii pics about a year ago, all shot with this lens on an M240. Hope you enjoy yours!

Doug
 
Mine is meant to be optimized for 1.5. I tried some tests with film but my notes and the lack of sharpness of my tiny prints, when thwey arrived, made the whole thing too difficult. I had a nice set up with the M9 and determined that mine is optimized for about f2.4. This means that I am front focussed at 1m by about 1-1.5cm, and the minor degree of back focus at f2.8 and f4 are negated by the depth of field. I find the lens very useable on the M9 and the Monochrom.

Here's the link (to the link) to my test: http://www.rangefinderforum.com/forums/showthread.php?t=118838
 
EdwardKaraa said:
I personally prefer the lens to be calibrated for 2.8. I can deal with 2 cm front focus at MFD when shooting wide open. Correcting for back focus is more difficult for me.
Click to expand...

+1 I have owned the C-Sonnar for nearly 5 years, optimized at f/2.8 as (1) I shoot most often with this lens at f/2.8 where its DOF close-in works best for me and (2) I find it easiest to deal with its focus shift at f/1.5 by leaning slightly toward the subject.

My recommendation would be to determine at what aperture you will most frequently use the lens and then have Zeiss optimize the lens for that aperture. If you optimize at f/1.5 then you will need to learn to lean back slightly when shooting at f/2.8. If you optimize at f/2.8 then you will need to learn to lean slightly toward the subject when shooting at f/1.5, as I mentioned above.

The need for the lean in/out workaround is only needed at near distances, approximately 1-3 meters.

If the lean in/out workaround isn't for you, then Doug's suggestion to split the difference and have the lens optimized at f/2-2.2 will minimize the impact of the focus shift close-in at wide apertures.
 
I just checked my test files again and am further convinced that you have to do your own test with tripod and slanted ruler.

I mentioned above that my 1.5 Sonnar was optimized at closest distance and widest aperture at f2.2 and 2 – on M9.

But I just re-checked the files I'd made with my MM, and it's 'right on' at f2.8. So mileages do vary a bit with camera bodies. On MM I'd have to lean forward to compensate at f1.5 and F2; lean back at f4 and f5.6; or stop down to f8 to cover the focus shift with DOF.

The 50 p-a Lux that I mentioned is 'right on' at f2 on MM, but DOF doesn't cover focus shift until f8.

Kirk
 
I found my Sonnar really frustrating on my 240 ... I was getting more misses than hits but never had this issue on my M2. It seems to me that digital sensors have zero margin for error.

I now use the lens with the EVF which slows your shooting down because of the post exposure blackout you get with the EVF ... but it does allow me to get my focus exactly where I want it when it counts.
 
Friends, again, many thanks.

I had rented a version from Lensrentals in order to give the lens a try, and the copy I rented worked very well from f2.8 on up, with 'reasonable' (and presumably correctable through leaning) results at f1.5.

I just heard back from Lensrentals and they are fairly sure that the copy I had was optimized for f2.8 -- they will verify once it's back from another rental.

If the Lensrental copy is f2.8, then that is what I will ask Zeiss to do for my copy.

This was service above and beyond by Lensrentals. Those guys rock (as do all the responders to this thread).

I will post the end of the story, since there seems to be some interest on the forum.

Cheers,
Kirk
 
MCTuomey said:
+1 I have owned the C-Sonnar for nearly 5 years, optimized at f/2.8 as (1) I shoot most often with this lens at f/2.8 where its DOF close-in works best for me and (2) I find it easiest to deal with its focus shift at f/1.5 by leaning slightly toward the subject.

My recommendation would be to determine at what aperture you will most frequently use the lens and then have Zeiss optimize the lens for that aperture. If you optimize at f/1.5 then you will need to learn to lean back slightly when shooting at f/2.8. If you optimize at f/2.8 then you will need to learn to lean slightly toward the subject when shooting at f/1.5, as I mentioned above.

The need for the lean in/out workaround is only needed at near distances, approximately 1-3 meters.

If the lean in/out workaround isn't for you, then Doug's suggestion to split the difference and have the lens optimized at f/2-2.2 will minimize the impact of the focus shift close-in at wide apertures.
Click to expand...

Apart from the leaning forward trick that works very well, I find it also easy to slightly focus backwards with portraits. Instead of the near eye I focus on the nose ridge for instance, or in frontal portraits, focus on ears instead of eyes. For long distance shooting, it's easy to learn how much further to go from optimal focus with some trial and error. With the RF it's very consistent. After the images coincide, I slightly rotate the focusing ring further by 1-2 mm.
 
Kirk,

I have a Sonnar that I got from BH in June. No issues with my M240 at all. In fact, I was surprised how well it works. I had some obvious front and back focus issues on 3 Voigtlander lenses. So, as I read about all the "focus shift" issues with the Sonnar I thought it was going to be terrible and I would probably return it. However it worked fine. I did not send it for adjustment either.

However, I don't obsess too much about how dead-on it is. If the photo looks good, I'm happy and don't try to pixel peep 100%. (Thats what the Planar is for.) But I have not experienced focus being so far off it's clearly OOF on my intended spot.

If you can return the lens, I'd try another sample. Or try sending it to Zeiss to see if they find something out of spec.

Here is a crop from a slightly larger file. RF Focused on her eyes. Probably f1.4 to f2...
L1004065%20-%20Version%202.jpg

Another crop, focus on the girl's eyes, f1.4 I'm pretty sure.
L1004090%20-%20Version%202-X2.jpg
 
filmtwit said:
Pick up the Olympus AV-2 finder, you should get live view then to do focus work.
Click to expand...
Yes, that can solve the matter. I bought an Olympus VF-2 primarily for using SLR lenses on the M240... I did use it once to check that it actually worked.

But, y'know, I paid a lot to get a fine digital rangefinder camera, and putting the VF-2 on it turns it into just another EVIL camera. And I have a dSLR to use those lenses on anyway. 😉

Fortunately, I've made peace with my C-Sonnar, working well for me.

Doug
 
I did some further testing on my M240 prior to sending off to Zeiss, taking some test shots at 5 feet.

First, here is the C Sonnar focused at f2.8 with the optical VF:
20141118-L1000735.jpg


Next is the C Sonnar focused at f2.8 with the EVF:
20141118-L1000736.jpg


Finally, here is the Summicron 50 at f2.8 with the optical VF:
20141118-L1000737.jpg


Sorry for the large sizes. Comparing the first two we see severe backfocus for my copy of the C Sonnar. The Summicron shot shows that my M240 is certainly in the ballpark on focus accuracy - some back focus, but that could be operator error 🙂

John Connolly at Zeiss USA says that the C Sonnar currently shipping is optimized for f2.8. Not my copy, obviously. Off it goes to Germany for adjustment.

Thanks again for all the inputs.

Kirk
 
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