NIKKOR-P.C: Contax or Nikon?

[johnphoto]

Please forgive a newbie question, but when looking for an 85/105/135 Nikon-S lens on ebay or elsewhere where the seller clearly does not know that there's a critical difference? Does a 'C' stamped on the side of the barrel mean Contax, and the absence of a C stamp mean definitely for Nikon?

 

[NIKON KIU]

Yes!

Welcome!

Kiu

 

[Jan Pedersen]

As far as i know Nikon never made any S series lenses for Contax.
The P is an earlier version than the P.C. The P.C. are Double Gauss lenses and if not mistaken the P are Sonnar designs.
I have an old 105 P.C. and it is a phenomenal lens

 

[jim_jm]

That's correct. The lenses made by Nikon for Contax mount clearly have a 'C' stamped on the barrel. On my 105/2.5 Nikkor, it's located on the focusing ring, about 1.5 inches to the left of the infinity mark. On other lenses it may be in a different location on the barrel, but not hard to see at all. The "P" or "P-C" markings on the front lens ring have nothing to do with the lens mount type.

 

[Jan Pedersen]

I stand corrected. Thinking SLR and not rangefinder 😱

 

[marcr1230]

Yes - "c" on the barrel means Contax

It's critical for lenses greater than 35mm

The DOF on the 35 covers for the different flange to film plain distance

 

[johnphoto]

Thanks for the info. I'm looking at an 85 and a 135 on ebay; seller says they came with a Contax, and that there are no Cs stamped on the barrels. What would you do?

 

[marcr1230]

If they don't have a "C" on the barrel - the focus will be off by enough to be rather annoying

 

[marcr1230]

The "S" is the common term for Nikon S mount , which physically is the same as the Zeiss Contax RF mount. the problem is the film plan to lens flange distance - slightly different.

There are multiple theories as to why - I have my pet theory. but for 50mm and up lenses - you will have increasing problems if you don't get the one made for your camera.

There is one 8.5cm Nikkor on ebay now stating it is for both systems - that not possible

 

[johnphoto]

I should have mentioned: they are to be used with my newly acquired Nikon S2. (The ones on ebay right now are the ones I'm looking at; I already wrote to seller saying they cannot be for both; he wrote back saying no C stamp but they came to him with a Contax).

 

[jonmanjiro]

Yes - "c" on the barrel means Contax

It's critical for lenses greater than 35mm

The DOF on the 35 covers for the different flange to film plain distance

Nikon did not make any 50mm lenses for Contax, so we can say that the "C" on the barrel is critical for any lenses that are 85mm or longer (85mm, 105mm, 135mm).

The "S" is the common term for Nikon S mount , which physically is the same as the Zeiss Contax RF mount. the problem is the film plan to lens flange distance - slightly different.

The film plane to lens flange distance is IDENTICAL for both Contax and Nikon-S cameras when the lens is set to infinity. Even the pitch of the focus helicoid on the body is the same. The focus problem starts to occur and increases as you focus closer because:

* The focus helicoid on a Contax camera rotates 270 degrees to focus from infinity down to the minimum focus distance of 0.90m

* The focus helicoid on a Nikon S-mount camera rotates 260 degrees to focus from infinity down to the minimum focus distance of 0.90m

This means:

* When you stick a Contax lens on a Nikon S-mount camera and focus to minimum distance on the camera, the lens still needs to rotate another 10 degrees to reach its real minimum focus distance > resulting in back focus.

* When you stick a Nikon S-mount lens on a Contax camera and focus to minimum distance on the camera, the lens has already rotated 10 degrees past its real minimum focus distance > resulting in front focus.

The problem is there with all focal lengths, but depth of field covers the error with lenses 35mm and wider.

 

[marcr1230]

I'd never disagree w Jon, but....


The flange to film plane distance is a characteristic of the body alone
Focus for diffent distances involves moving the lens assemble closer or further from the film plane

Because the flange to FP distance is different, the lens assembly must be slightly forward or rearward in one model vs the other.

The reason the 270vs 260 degrees is because the actual focal length of the nominal Nikon 50 is slightly longer than the 50 Zeiss if I remember, Nikon was building lenses for Leica cameras which had that standard. The 50s have no helical - depending on the camera body to move the lens fore and aft

My theory is that Nikon went with the Leica standard 50, and adjusted its flange distance and throw of the focus mechanism. This created a problem at 85mm - requiring 2 versions, differing not in the optics but the relative distance to the lens mount on the body

Jon - please jump in and correct my analysis

 

[marcr1230]

Jon - this is actually some text I wrote out a few years ago when I was thinking about this:

On the Nikon site http://imaging.nikon.com/products/imaging/technology/history/rhnc09s-e/ - they mention that the actual focal length of the Nikon 50mm was the Leica Standard 51.6mm
and the Zeiss Sonnar was 52.3mm, that is to say the 50mm designation is more customary than meant to be exact. Nikon may have made lenses for Leica apparently and didn't redesign the optics

There is an optical formula 1/S1 + 1/S2 = 1/f ( http://en.wikipedia.org/wiki/Focal_length ) , where S1= distance from front nodal point, and S2 = distance from rear nodal point, so that if the film plane is at the rear nodal point distance the image will be "in focus"

I then built a spreadsheet varying the distance from effective infinity to 0.5 meters, and for any focal length and distance to subject , you can see how far the rear nodal needs to be
from the film plane for that distance to subject to be in focus

What I found is that , while you can position either lens so that inifinity is in focus on the Nikon, or close up is in focus, you can't do both with the same helical and 2 different focal lengths

in fact, with the longer focal length, the close focus distance of the rear nodal point to the film plane is greater than a slightly shorter focal length

What this means is that at some level the offsets of distance markings on the Nkon/Contax barrels (you have to turn the Contax more degrees to focus at the same close up distances as the Nikon) make sense, to close focus the Sonnar, you need to extend the lens just a wee bit more than you would for the presumably shorter focal length Nikon Lens.

The helicoid travel is the same, i.e if you move the barrel the same degrees, the lens will move the distance forward/backward on each mount

I also know that the lenses have a certain depth of field, probably on both rear focus plane and subject side, so within reason you can use some lenses not specifically designed for the camera with
good results

the focusing helical and rangefinder are obviously linked, and with other than 50 mm lens, the in camera helical will not move the lens the correct distances to be in focus, so the external mount lenses have their own built in helicals which step up or down the focusing travel to the needs of the specific lens

Since this is my first day as an optical engineer - I should probably stop here 🙂

 

[aoresteen]

Here's a picture of the C that is engraved:

Nikon made 85mm (f/2 and f/1.5), 105mm, and 135mm lenses for the Contax. I do not believe that they made any 50mm lens for the Contax. I use a Nikkor 105mm lens with my Contax IIa.

Wideangles (35mm or wider) can interchange with no practical issues. I use a CV 25mm S lens on my Contax IIa with no problem.

 

[jonmanjiro]

You're pretty much spot on Marc!

On the Nikon site http://imaging.nikon.com/products/imaging/technology/history/rhnc09s-e/ - they mention that the actual focal length of the Nikon 50mm was the Leica Standard 51.6mm
and the Zeiss Sonnar was 52.3mm, that is to say the 50mm designation is more customary than meant to be exact. Nikon may have made lenses for Leica apparently and didn't redesign the optics

That's exactly what happened. Nikon reworked the Contax mount to suit the Leica standard of 51.6mm because they were already making that focal length in screw mount. Consequently, all Nikon 50mm lenses have to be 51.6mm or close to focus properly on an S-mount body.

What I found is that , while you can position either lens so that inifinity is in focus on the Nikon, or close up is in focus, you can't do both with the same helical and 2 different focal lengths

True. That's why non 50mm lenses are external mount and have their own helicoid built in. An exception is the external mount 50/1.1 which was made in external mount because of the extra support the external mount provides. The Nokton 50/1.5 and Skopar 50/2.5 are also external mount of course, so we have three external mount 50mm lenses for the Nikon S system.

The helicoid travel is the same, i.e if you move the barrel the same degrees, the lens will move the distance forward/backward on each mount

True. But as you stated, the RF mechanism is calibrated to move from infinity to minimum focus with 270 degree rotation of the helicoid on a Contax vs 260 degree rotation of the helicoid on a Nikon, and that's where the problem occurs - in the linkage with the RF system.

Here is a table taken from the Bessa R2S/C manual that shows what you can expect when using Contax mount lenses on a Bessa R2S or Nikon S-mount lenses on a Bessa R2C. It only covers 50mm and 85mm because Cosina/Voigtlander only made those focal lengths for S-mount. As you can see, focus is fine at infinity for all apertures (the Japanese use "O" in the same way as a tick mark is used in English).

 

[farlymac]

Thanks for the info. I'm looking at an 85 and a 135 on ebay; seller says they came with a Contax, and that there are no Cs stamped on the barrels. What would you do?

Since you say they are to be used on an S-2, and you are happy with the price and condition, buy them. Without the "C" on the barrel, they will definitely work fine on your S-2.

PF

 

[enasniearth]

Nikon / contax

Nikon / contax

The flange to film distance for Nikon and contax are the same so all lenses are in focus at infinity .

Lenses shorter than 50 , will work equally well on both camera body's as depth of field eliminates any focus problems with both systems .
The exception may be the 3.5 cm 1.8 nikkor , due to its wide aperature there may be some focus error on contax cameras at close distances

When the Nikon was designed they took the best features from Leica and contax and combined them in one camera .

They selected the contax body shape with built in focus mount ,
From the Leica the horizontal shutter with coupled rangefinder were used .
Part of German reparations from the war voided Zeiss and leitz patents so this was up for grabs .

They used the Leica standard for the mount,
One problem was that the Japanese assumed the mount on the cameras was metric pitch , in reality it is based on an old English microscope standard of 26 threads per inch , metric is 25.4xx threads per inch .
Hense the rotation is off on the mount by a small degree .
The lenses marked 'c ' have taken this in to account and the focus cams are different .

The standard lenses are of different focal length standard , so wide open at 1.4 there is a focus error as the lenses are focused at closer distances on the the Zeiss and Nikon systems . Hense
Zeiss 5cm lenses on Nikon body's and Nikon 5 cm lenses on contax body's have some error at closer distances from the indicated rf setting

another item of confusion is that the red c on the front rim indicates coated ,
Many people think it means contax , in reality the only lenses for contax have the c marked as 'c' on the barrel near the focus scale .

One of the other problems is the finders , the one for Nikon are unmarked , the Leica ones have a L on the bottom of the shoe and are narrower .
The contax ones have an odd shoe with a semicircle cutout on the leading edge ,
Both the Leica and contax finders are a loose fit in a Nikon rf shoe .

 

[jonmanjiro]

One problem was that the Japanese assumed the mount on the cameras was metric pitch , in reality it is based on an old English microscope standard of 26 threads per inch , metric is 25.4xx threads per inch .
Hense the rotation is off on the mount by a small degree.

I think this is one of those Internet myths that resurface from time to time.

Amedeo's adapters for S-mount to M-mount and Contax mount to M-mount certainly have the exact same helicoid pitch.

 

[Highway 61]

I think this is one of those Internet myths that resurface from time to time.

Yes. As Marc and you have mentioned it above, the problem key resides in the native focal length of resp. the Zeiss and Nikon "50mm" rangefinder lenses. This is why there is no satisfying real solution for making either a Sonnar work on a Nikon RF body, or a Nikkor-S work on a Contax RF body. Shimming the lens or the lens mount will make the counterpart lens/body work correct at some pre-defined distances range only (close up to average, or average to infinity), but not through the entire focusing range. The only solution would be to modify the rangefinder gears pitch inside the body - which isn't feasable.

Some people seem to have quite successfully adjusted the Sonnar a way which modifies its native focal length, making it very close to the Nikkor "50mm" focal length, by adjusting the distance between some optical groups of the lens, though.

 

[enasniearth]

I think this is one of those Internet myths that resurface from time to time.

Amedeo's adapters for S-mount to M-mount and Contax mount to M-mount certainly have the exact same helicoid pitch.

Jon ,
In rotoloni s Nikon rangefinder system , there is an interview with masahiko Fuketa , the main designer of the Nikon one , quote
" the lens mount was very difficult to make . We thought we were the same as contax but after Nikon one production began we realized we were slightly different . At infinity they are the same but the 'travel ' was different . This caused long delays "

From dechert s canon rangefinder cameras quote
"All canon bodies from 1947 on onwards will accept Leica mount lenses , but a few of the lenses on such canons will not accurately mate with Leicas or canons made after 1952 . This is particularly true of many lenses mounted during 1946 and 1947 , and results from the fact at that time both canon and nippon kogaku engineers believed that the leitz flange pitch was exactly 1.0 mm , when in fact it is 26 threads per inch ."

I don't remember the source for the microscope standard of 26 tpi however it is an old English standard for Europe ,

It would be interesting to compare the pitch for a Nikon and contax helicoid ,
A half a thread per inch is not much however would cause the decrepacy of rotation , and the 3 ' marking being at different locations on contax and Nikon mounts .

I assume the travel referred to by Fuketa to be the amount the lens is extended with rotation of the mount ,
Perhaps I am mistaken or missing something here .