Super Ikonta III focus shift?

[noci]

dear friends,

doing a lot of almost-low-light work with my ZISI III, I often seem to get some noticeable focus shift at f3.5.. or perhaps it's just my technique? I doubt it, though, as I can focus i.e. a Canon 50 1.2 accurately in low light, and the ZISI patch is actually really good in low light (and it appears to be accurately calibrated, as I get consistent results from f4 or f5.6 and up).

Have any of you noticed anything similar and might be able to advise on whether to back- or front focus?
(I'll just have to test it out, otherwise..)

best wishes & thanks,

Max

[ZeissFan]

Oh good lord. Here comes the focus shift issue with other lenses.

But seriously though, are you sure that the lens has been collimated correctly?

I've never heard of focus shift on the older Tessars, but anything is possible.

[noci]

yes, I believe it to be collimated properly... hurm, perhaps I'm the problem after all--- *introspects*. without me, the camera would never have to focus. perhaps it's trying to tell me that.

m

[ZeissFan]

You can check collimation quite easily using an SLR and medium telephoto lens.

I have instructions on my site (http://elekm.net/zeiss-ikon/repair/collimate/).

A lens can focus past infinity.

The more I thought about this, the more I would be inclined to check the collimation of the lens.

There is also the possibility that the linkage between the actuating arm under the lens and the rangefinder assembly is damaged.

One other thing: When turning the focusing ring, ensure that the lens itself (look at the name on the lens face ring) also turns in tandem.

Finally, check to make sure that the last four or five digits of the serial numbers on the front and rear lens elements match.

I've not encountered a Tessar that misfocused, because it's not that complex of a lens -- just four elements.

[noci]

thank you for your advice, I'll follow the leads you pointed out and will post back here once I know what's up!

x
M