Super Ikonta III backfocus

[syfa]

Hi all,

I've recently acquired a Zeiss Super Ikonta III 531/16, with a Tessar f3.5 lens. The vendor told me it got CLA'd in 2009.
However, in my first few rolls I've noticed a consistent back focus using large aperture. It's not as clear in this resize, but the tree in the picture is sharp, while I focussed the RF on the girl.

Is there an easy diy way to fix this issue?

Many thanks.

 

[hanskerensky]

You first have to establish what causes the backfocus. Is it the rangefinder or the taking lens or maybe a combination of both ?

Did you check out the rangefinder on a clear object some (measured) meters away ?
Did you check it also at infinity (on a far away object) ?

Collimating the taking lens on a SI III on infinity is fairlly straightforward.
I normally use an auto-collimator but you might try using frosted tape on the filmgate and a magnifyer to check the image on it.

You might have a look at my Flickr sets :
http://www.flickr.com/photos/29504544@N08/sets/72157613202905483/

http://www.flickr.com/photos/29504544@N08/sets/72157613088050471/

http://www.flickr.com/photos/29504544@N08/sets/72157632954083827/

 

[Sarcophilus Harrisii]

Hans has given some excellent advice and speaks from much experience. I can only re-iterate that you must first establish where the discrepancy lies. Check the focus at the film plane. Adjust it, if necessary. Then, and only then, make adjustments to the rangefinder focus, if required. This is the only sure path to achieving the correctly matched focus of both systems that is needed to produce good results on film.
Cheers
Brett

 

[syfa]

Did you check out the rangefinder on a clear object some (measured) meters away ?
Did you check it also at infinity (on a far away object)?

Many thanks for the useful tips and photos, I'll check these things out and report back. 🙂

 

[GaryLH]

I would check focus by focusing w/ the rf at three distances on a tripod
- inf (first)
- 15-20 ft range
- closest focus
At each distance, check the real focus at film plan by using a piece of ground glass (or substitute like simple scotch tape) w/ the back open. If it is not in focus at inf, then everything will be off.

Gary