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Contax N Vario-Sonnar 24-85 autofocuses on Sigma SD14


To the best of our knowledge this is the first Zeiss lens to have autofocused on a Foveon-based camera

View attachment 826

About half a year ago we completely redesigned our parts so as to adopt the same screw pattern as the Sigma SA mount. I just got a SD14 yesterday and perhaps this comes as no surprise to any of you the Vario-Sonnar 24-85 just autofocused and stopped down as it should.

I put together the details of the conversion here:



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Hi Conurus,

this is again really good news. Although not possible with all N-lenses.

On your site you wrote about some N-lenses:

The thicknesses of brass shims vary from lens to lens and the chance of success of a SA-mount conversion is noted in the above table.
Here is an example picture of what a brass shim is (but these are obviously not of a lens):

View attachment 827

So this is really a pitty. It means that the Canon conversion is a "more secure" choice than a Sigma conversions, because there are more lens choices with Canon mount and the risk of having not enough brass shim in the N-lens is also pretty high (55%)...

I am mentally crying because of the no-go for the N70-200... :z04_motzer:

Best wishes


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Are there any downsides to the conversion...??

Do you have issues with the lenses....and if you buy a converted lens from you what type of warrantee..??
Have you seen any image degradation when it is converted...or do you get ghosting...??
Are all the AF functions present...

Thanks for the answers ahead of time.

Tony C.
Yes, it autofocuses just like any autofocus lens. Most of the Contax N series lenses support full time manual (FTM) except 28-80 and 70-200. Some of the Contax N series lenses are equipped with ultrasonic motors: 50/1.4, 24-85, 70-300, 17-35.

There is a plastic piece that we are not able to fit into the Sigma SA mount. This picture illustrates the difference: the left is in Canon EF mount and the right is Sigma SA:

View attachment 877

You may be able to dremel the plastic piece a little bit to fit - then there will be no difference between SA and EF. However, we are not able to do that in a cosmetically satisfactory way and therefore we are not able to do that for you.

The black plastic piece is supposed to shield stray light coming from outside of the frame (that's why the hole is rectangular). It is there for a reason or else Contax would not have put it in but we are not sure about the impact of omitting it in the real world (this is so new that we have not yet tried field testing).

We have a one-year ultrasonic motor warranty on all lenses we sell or convert. We test every outgoing lens carefully. We are just a small shop and we know each customer by name. The N series has all been discontinued and not that many of them were made to begin with (see statistics below) and we expect only a small percentage will ever be converted to EF mount, and even fewer to Sigma SA.



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Hi conurus,
sorry, but we do not allow links to images or copy/paste image into the forum. The reason is, that after a while the links are broken and all discussions about images are worthless.

We want to have meaningful discussions within our forums also for new users in i.e. 3 months from now. This is only possible, if we have the images here uploaded on our forum server without external links.

Therefore all images for image discussions have to be uploaded directly here in the forum on our server. We delete all other links to images. The same counts for for links to the images on our CI gallery.

Thanks for your understanding in advance

I corrected it for you ;), so just click on the image and it opens in lightbox

Best wishes
Thank you very much! I will keep that in mind in the future and upload images instead of linking to them. (You can be sure I will have field test photos very shortly. :) )