Zm 21mm..Problem????

[D&A]

Hi All,

I purchased a new Zm 21mm f2.8 lens a couple of weeks ago and am finially getting around to testing it. I'm currently using it on an Epson RD1 body. I noticed something that for me was quite strange and it appears to be the lens rather than the body (I can test on a Leica M body later next week).

Lens Issue: If I put rotate the focusing ring to the minumum distance (which is 0.5m) and then walk the lens/body forward towards an object (can also do this with the camera on a tripod to keep position) till the object is in correct focus ( via the rangefinder). At this point if I begin to roate the focusing ring away from minimum distance (towards infinity), no change in the rangefindeer patch or indication that the lens is now moving away from "correct focus" can be seen in the rangefinder untill approx. a I go through an approx. 10 degree turn in the focusing ring till if reaches the 0.6m (2 foot) mark. At first I thought it might be the RD1's "cam" but when I dimounted the lens and took a look, this is what I noticed:

There is the usual "cut out" on the rear of the M mount of the lens where the focusing cam in the body interacts (hence the rangefinder coupling). While holding the lens in my hand and turning the focusing ring from infinity to minimum siatnce I notice a black sleeve starts to decent lower down the lens till the top of this sleeve is even with the bottom of the cutout for the rangefinder cam on the mount of the lens. At this point the lens is focused at the 0.6m (2 foot) mark. If I continue to turn the focusing ring towards the minium distance mark of 0.5m, then this sleeve will go well below the the cutout for the rangefinder cam, and this is why it haas no effect on the rangefinder patch in the RD1. None of my other rangefinder coupled VC lenses has this issue and with all of them, the sleeve reaches "even" with the cutout cam on the back of the mount just as the focusing ring reaches it's minium distance. Unlike the Zm21mm lens which has a dead spot between 0.5m and 0.6m in regards to the rangefinder patch not moving...all other VC lenses remain coupled to the rangefinder patch throughout it's focusing range.

Is this well known in the Zeiss 21mm f2.8 lens and designed this way for a reason. I apologize in advance if this is something simple and I'm not aware. Thanks in advance.

Dave (D&A)

 

[D&A]

Just took a look at my post above and I'm truly sorry for all the syntax and spelling errors. Thats what happens when I try typing at 3:00am and don't use spell check. I hope the post is clear enough to understand what I was trying to get across. Thanks!

Dave (D&A)

 

[oscroft]

The rangefinder in the RD1 is only coupled from 0.7m to infinity, so the 0.5m to 0.7m part of the lens focus range will not engage it.

RD1 spec here

 

[D&A]

Hi Alan,

Thanks for your prompt reply and I wasn't aware of this spec for the RD1 (though I should have been.

What I still don't understand is how for example if this lens was mounted on say a Leica M6 or M7, since the sleeve I described (that rises and falls as the focusing ring is turned) falls below the level of the mount cutout for the rangefinder cam, how could the cam on the M6 or M7 even reach or touch it so that it's rangefinder patch could respond (move) when in the range between 0.5m and approx. 0.6m (when the sleeve is well below the cutout? Not sure if my question and description is explained clearly. Thanks!

Dave (D&A)

 

[oscroft]

What I still don't understand is how for example if this lens was mounted on say a Leica M6 or M7, since the sleeve I described (that rises and falls as the focusing ring is turned) falls below the level of the mount cutout for the rangefinder cam, how could the cam on the M6 or M7 even reach or touch it so that it's rangefinder patch could respond (move) when in the range between 0.5m and approx. 0.6m (when the sleeve is well below the cutout?

That's a good question, and I'm afraid I have no idea (and, sadly, I do not possess a Leica that I can examine).

My only guess might be to wonder if the rangefinder cam is thin enough to descend into the lens when the focus sleeve thing retracts? I've just checked the cam on my Bessa-R, and that wouldn't be thin enough to do it even if it focused that far, but the thin cams on my FSU rangefinders might do it (again, if they had the range).

Or then again, maybe it doesn't couple that close on an M6 or M7 either - are you sure it does?

 

[sebastel]

both R-D1 and leica M rangefinders are specified to couple up to 0.7m. due to construction and assembly tolerances, the coupling will work a little bit further. how much further will depend on your actual camera.

as soon as the focus is shorter than the minimum distance, the coupling arm will simply lift off, because it cannot turn more, either because it hits the lens mount, or some other limiter.
focusing on longer distance will return the focus coupling ring of the lens closer to the cameras focus coupling arm until it engages.

and that's it.
very "simple", and hence quite reliable.

cheers

 

[D&A]

Hi Sebestal & Everyone,

Thanks for the explanantion. Just from examining it yesterday, the retractable lens sleeve that comes in conatct with the coupling arm (the cam), it's seemed that once the sleeve retracted below the cuout on the rear of the lens, there was no way the cam could reach it or be affected by it (unless some M camera mount body had an ultra thin cam to continue contacting the retractable sleeve.

This brings me to a few questions:

1. You mentioned in your post (copied below) that the RD1 and M rangefinders are specified to couple up to 0.7m or a bit further (it seems the RD1 goes to 0.6 with the Zm 21mm lens).....then why did Zeiss design this lens to continue focusing further to 0.5m even though it de-couples from the focusing arm (cam) other from the obvious that it gives the user the closest possible focusing distance with a given lens even though at some point it decouples from the rangefinder?

2. Is there any M mount camera than can actually keep "rangefinder coupled" to the Zm 21mm lens throughout it's range down to it's minimum focusing distance of 0.5m?
Possibly the current zeiss rangefinder camera or maybe one of the Bessa models?

3. Do any of the other Zeiss or possibly Leica lenses do this too where part of their close focusing range becomes de-coupled from the focusing arm (cam?). I can't recall using any other rangefinder lens thhat fits an M mount camera doing this but them again most of you have used more lenses than I have.

Thanks again for taking the time to respond.

Dave (D&A)

both R-D1 and leica M rangefinders are specified to couple up to 0.7m. due to construction and assembly tolerances, the coupling will work a little bit further. how much further will depend on your actual camera.

as soon as the focus is shorter than the minimum distance, the coupling arm will simply lift off, because it cannot turn more, either because it hits the lens mount, or some other limiter.
focusing on longer distance will return the focus coupling ring of the lens closer to the cameras focus coupling arm until it engages.

and that's it.
very "simple", and hence quite reliable.

cheers

 

[SDK]

The Zeiss ZM 21mm, 25mm and 28mm all focus to 0.5m, but no M body can go all the way there. Leica Super Angulon M 21mm/3.4 lenses focus to 0.45M and decouple exactly the same way. You have to measure with a tape or give it your best guess when these lenses are set below the coupling range.

 

[Chaser]

You could always measure out your camera strap to 0.5m and then use that to measure your close ups.

 

[SDK]

A marked camera strap is a good plan Chase. Hey how's the 28mm Biogon working out?

 

[D&A]

I truly thank everyone for their observations and explaanaantions. I had no idea that there were other lenses (besides the Zeiss Zm's mentioned that also decoupled in the same fashion. Thats why at first I became a bit alarmed while focusing at very close range and all of a sudden the rangefinder patch stopped moving even though I was still turning the lens barrel. The camera strap as a sort of impromptu measuring device is a good one and I'll have to try that out.

Again I appreciate the lesson learned here! Dave (D&A)

 

[Chaser]

A marked camera strap is a good plan Chase. Hey how's the 28mm Biogon working out?

I honestly love it. I think it was made to be perfectly matched with a Minolta CLE.

 

[x-ray]

The Zeiss ZM 21mm, 25mm and 28mm all focus to 0.5m, but no M body can go all the way there. Leica Super Angulon M 21mm/3.4 lenses focus to 0.45M and decouple exactly the same way. You have to measure with a tape or give it your best guess when these lenses are set below the coupling range.

This is correct about a number of lenses. My 21 3.4 SA was exactly that way. My new 35 f2 asph summicron focuses slightly closer than the MP body that it came on.