Zeiss Ikoflex Tessar questions

[hsandler]

I have just acquired a Zeiss Ikoflex Favorit, last of the line. It has a Tessar 75mm f3.5 taking lens which displays a faint pinkish hue in reflected light.

First question: I have seen photos of Favorits with a lens marked Tessar T (The T in red) and Opton. Mine does not say T or Opton on it, just Zeiss Tessar. I know the red T means it's got a certain coating. Would mine therefore be uncoated or have a lesser coating? The lens serial number is about 1100000. On some online list, which I can't find again, this seemed to indicate a manufacture date of about 1953; however, the Favorit was not introduced until 1957.

Second question: The first test roll I shot looks good when the lens was stopped way down, but shots at more open apertures, even f8 indicate a fair bit of defocusing on the left side of the frame relative to the centre and right. Would this indicate an element in the lens is tilted or could it be in a plane parallel to the film but not centred? If the entire front lens standard is tilted I would be able to see the defocus in the ground glass, right?

I would be willing to unscrew the front bezel, but not willing to try anything more invasive, as the camera and shutter otherwise work fine.

 

[shutterfinger]

It has a Tessar 75mm f3.5 taking lens which displays a faint pinkish hue in reflected light.

Likely a coating. T series did not come into existence until later, possibly multicoating.
Serial number is at the beginning of a range that runs 1953-1959.
Reference: A Lens collectors vade mecum.

The first test roll I shot looks good when the lens was stopped way down, but shots at more open apertures, even f8 indicate a fair bit of defocusing on the left side of the frame relative to the centre and right

Likely the front standard not parallel to the film plane. Use a digital caliper or ruler with fine graduations and check each side of the front standard to the film plane, both side must be the same distance at all focused distances. 0.01mm will be noticeable at f3.5 on fine detail.
Zeiss tessar lens diagram:

light travels the direction of the arrow, rear cell is a cemented pair.

 

[hsandler]

Thanks shutterfinger. I don't have a precision ruler, but the front standard "looks" in plane, and the front cell of the lens "looks" centred. When I unscrewed the front cell, the only possible thing I found was there is a spacer that had ridden up a fraction of a mm on the head of a flat positioning screw which was supposed to be centred in a notch in the spacer. If just a fraction of a mm will do it, I'm hoping that is the cause. Here is a full-size scan of a shot at f8. Focus point was the corner of the greenhouse, which is sharp. The right side shows the expected fall off with distance due to depth of field. The left side is noticeably defocused, more than limited depth of field would cause. I also did a "brick wall" shot at f3.5 of a flat wall parallel to the film plane with defocus on the left side.

Greenhouses by Howard Sandler, on Flickr

 

[shutterfinger]

Yes, a shim or spacer in the front cell mounting being off will certainly cause problems. The focus error is obvious. Time to test with some more film?
I was thinking your camera was a folder but being its a TLR you can take a business card or similar and adjust the focusing so that the card will just fit between the front standard and body on one side then check the fit on the other.
Both sides must be the same.