[Sylvain]

Hello guys, 
Back after a few years of silence ! I had a lens question and I thought this could be a good place to ask.

so...

I've been the lucky owner of a Minolta CLE and its rokkor m 40mm f/2 pair for a year now and recently acquired a zeiss 28mm ZM biogon to complement my kit.
Sadly, I've shot a couple of rolls (ektar 100 and portra 400) and have found the results to be extremely soft. One great joy of that lens should be hyperfocal shooting so I set it at f/8, set the focus scale infinity mark on f/8 and thus I was supposed to get 1.5m to infinity DOF, theoretically. Light was plentiful and shutter speed high.
But... shots are awfully soft. Evenly so, so it reassured me it wasn't a knocked out element or so.

I had this idea to test it on a M10 to confirm and indeed I got results as bad as the developed CLE shots, when using the focus scale. But I could confirm I'm getting super sharp results when actually focusing on the subject, which here was in the 10 meters range or so. All this was performed at f/8.
It seems to be performing normally when set to focus on short range, wide open...it's not displaying a massive bias using the rangefinder (altough I'm aware there might be coupling issues).

So in summary :
-set to distant object : sharp, super sharp actually, center to corners
-set to close object : sharp
-When set using the focus scale, focus is between 2 and 5 meters : soft;

Is this kind of "midrange" softness something that seems likely when both short & long range are sharp ? or am I missing the focus scale use completely ? I'll probably send it for inspection to Zeiss but I'm curious about your possible experiences.

Thanks in advance,
S.

[Brightcolours]

I do own have a Zeiss Biogon 28mm f2.8, and do not have my/any 28mm f2.8 with focus scale at hand, but here are a few questions and some thoughts.

If I understand correctly, when you disregard the DOF scale stuff, and really focus at 2 meters on a subject, at 5 meters on a subject, or anywhere in between, you get out of whack results?
Or, you only get soft results when not focussing on something through the view finder, but when you try to guess the distance and set the distance via the focus scale things look soft?

You might get better results not using hyperfocal distance (regardless of which lens) and instead focus at infinity (with an appropriate aperture choice).
https://luminous-landscape.com/digital-focusing-part-two/

[Sylvain]

I do own have a Zeiss Biogon 28mm f2.8, and do not have my/any 28mm f2.8 with focus scale at hand, but here are a few questions and some thoughts.

If I understand correctly, when you disregard the DOF scale stuff, and really focus at 2 meters on a subject, at 5 meters on a subject, or anywhere in between, you get out of whack results?

Or, you only get soft results when not focussing on something through the view finder, but when you try to guess the distance and set the distance via the focus scale things look soft?

You might get better results not using hyperfocal distance (regardless of which lens) and instead focus at infinity (with an appropriate aperture choice).
https://luminous-landscape.com/digital-focusing-part-two/

A familiar name :-)
It's hard to give you a hard confirmation because that's precisely the thing I could not formally test. Poor testing protocol on my part as I was not very comfy with their olive M10 Safari in the streets of a so so area.
I've ordered an m to mft adapter to be able to do further digital testing of that but in the meantime, I'm curious as if this sort of "in between" dud was normal as a defect (thus not by design, where it is sometimes known that a lens perform poorly at some ranges of focus/zoom). I may be naive but I don't quite see how just the mid range could be defect but I sure hope zeiss didn't design it this way.

My assumption was that, given hyperfocal properties, I could indeed set the focus mark between 2 and 5 (use case was street photography) and eventhough in most case, subjects would still lie further than 5 meters, they'd still be sharp thanks to hyperfocal shooting.

I understand your question about the rangefinder but it's not strictly a rangefinder issue I'm afraid. Close distance and infinity tests indicate no notable bias.
As for getting better results at infinity, it's true that given the dof scale, it would still be rather workable (and indeed the digital tests shots at infinity were plenty sharp up to close enough : still getting DOF from inf to 3-4 meters at f8 but I'd find that a bit disappointing in practice.



Thanks already for the first input (and interesting article),

[mst]

Welcome back Sylvain

I have used the ZM 28 in the past, but not for very long, since 28mm is simply not a focal length I feel very comfortable with. However, I know the close siblings (from 25 to 50 mm), some of which I still use today.

I have not noticed the behavior you describe with any ZM lens so far. However, something I have occasionally experienced with ZM lenses is mechanical wear, usually resulting in some play on the focus ring or the lens tube. Is that something you notice on your sample? If so, the softness you see might be a result of partial decentering due to mechanical play.

[toni-a]

All lenses after some use will need servicing no exceptions, some might need it more frequently though.
if you have some patience, and dexterity and tools you can try yourself, while video filming the whole process to be able to go back in case anything happens.
you will also need a digital body with video output to a screen and a test chart.
mount the lens on the digital body and check for imperfections in the projected image and check the behavior, very often the problem will become obvious after that you can try repairing it yourself:
progressively de-assemble the lens (while filming the process) , check for any loose elements or free pieces of elements or screws or dirt inside the lens, clean dirt, put back free or loose screws where they are and retest, if everything fine done, otherwise it will become more complicated: most lenses have chims to adjust elements positions, in Canon lenses they are in the rear just under the mount and electronics circular plate, on other lenses each element has its own chims check for them and try to repair otherwise you will need professional help which in your case will cost as much as the lens...

[Sylvain]

Welcome back Sylvain

I have used the ZM 28 in the past, but not for very long, since 28mm is simply not a focal length I feel very comfortable with. However, I know the close siblings (from 25 to 50 mm), some of which I still use today.

I have not noticed the behavior you describe with any ZM lens so far. However, something I have occasionally experienced with ZM lenses is mechanical wear, usually resulting in some play on the focus ring or the lens tube. Is that something you notice on your sample? If so, the softness you see might be a result of partial decentering due to mechanical play.

Hi Markus ! thanks 

Good point ! Actually, I acquired the lens second hand with indeed a little play in the focus ring. I completely overlooked to mention that as I somehow discarded this issue as both close & far focus seem to produce sharp results. I would have thought that mechanical play wasn't coupled to the actual element but you seem to indicate it is a cause.  I will add too that the softness seems even across the field.
 
Markus, I have a lens spanner wrench and I see the rear element has the notches. From your experience, is that "play" DIY fixable?

Toni-a, thanks but I wouldn't venture too far doing this myself ...

[mst]

I honestly don't know if the play in the mechanics could affect the centering quality (due to wobbling of the whole tube). In the two cases where I had that kind of play, I sent the lenses to Zeiss and their analysis and cost estimate mentioned the play and centering issues in both cases.

Also, in both cases, parts were replaced to fix the play. So, even if you manage to successfully open and reassemble the lens, I'm not sure there's much you could do about the play yourself without replacing parts. Also, in addition to all the warnings from Toni: some lenses feature unexpected surprises for those fearless enough to just grab the necessary tools and exploring disassembly. Like, spring loaded screws, bolts or shim rings, for example, usually way too small to ever find them again after their ballistic flight across the whole room... I learned myself the hard way

Since you mention the softness is equal across the whole frame, I guess the best approach now is to check the lens on a digital camera, preferably one with live view, as Toni already suggested. That should give you a good idea if the softness is a general issue of the lens or a result of front or back focus.

Practically all ZM lenses (with the exception of the 50/1.5 maybe) are great performers, so you should not see noticeable softness in any case, especially not on film.

[Sylvain]

I honestly don't know if the play in the mechanics could affect the centering quality (due to wobbling of the whole tube). In the two cases where I had that kind of play, I sent the lenses to Zeiss and their analysis and cost estimate mentioned the play and centering issues in both cases.

Also, in both cases, parts were replaced to fix the play. So, even if you manage to successfully open and reassemble the lens, I'm not sure there's much you could do about the play yourself without replacing parts. Also, in addition to all the warnings from Toni: some lenses feature unexpected surprises for those fearless enough to just grab the necessary tools and exploring disassembly. Like, spring loaded screws, bolts or shim rings, for example, usually way too small to ever find them again after their ballistic flight across the whole room... I learned myself the hard way

Since you mention the softness is equal across the whole frame, I guess the best approach now is to check the lens on a digital camera, preferably one with live view, as Toni already suggested. That should give you a good idea if the softness is a general issue of the lens or a result of front or back focus.

Practically all ZM lenses (with the exception of the 50/1.5 maybe) are great performers, so you should not see noticeable softness in any case, especially not on film.

Yes, I wouldn't attempt the repair all things considered. I have an M to MFT adapter coming but I don't think I'm going to learn much else from it. Best I send it back to Zeiss for a proper repair indeed. Remember how much it costed you ?
thanks

[mst]

Last time it was around 270 EUR for a ZM 25/2.8, around 3 years ago. That should give you a rough estimate only, though, the actual costs might of course vary with the kind and number of parts that need to be repaired.

I don't know if their customer support is available right now. Most manufacturers continued to offer repair services over the last weeks, but Leica for example didn't. So, you should maybe get in touch with them first.

[toni-a]

270 EUR a repair!!! Unless a lot of spare parts are needed, repairs here cost a fraction of that