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Fix for CZ Vario Sonnar 35-70 3.4 infinity focus problem
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PostPosted: Tue Nov 05, 2013 9:02 pm    Post subject: Fix for CZ Vario Sonnar 35-70 3.4 infinity focus problem Reply with quote

Occasionally I see reports on the Internet about infinity focus problems with the Vario Sonnar 35-70 f3.4 for C/Y mount.
Often a bad adapter is blamed for the problem, but I've never heard of anybody who actually fixed the "adapter issue".

Some time ago I bought a 35-70 and found that its focus plane was off and oblique, so infinity was like at 100meters the left side and 5meters at the right side, really bad. Since the lens had a bad ding on the filter thread I thought it was caused by an accident and tried to figure out if some parts of the lens were displaced by the blow and if there was a way to compensate this.

I found that the lens body is not directly attached to the mount. The mount is made of the aperture ring and an additional ring that is held by 3 screws, and I found this group to be oblique - easy fix, loosen the screws and put the mount into a correct position.

But I also found that there is a mechanism that allows to change the register of the lens to a small degree (about 1-2 mm). It is some kind of adjustment ring under the aperture ring.

I've made a few photos to explain how the mechanism works, but the important photo is photo 7, which shows what you actually have to do.

The original C/Y MM as well as the Leitax adapter mount that I use are attached to the black ring that gets visible when you remove the mount (photos 1 and 2).




Once you take of the aperture ring, you see 3 screws that connect it to the main lens body (photo 3).



If you remove the screws (not necessary to fix focus!) you can take the ring off (photo 4), but you don't have to do this. The ring is actually 2 rings, an outer one with the screw holes, and an inner ring with a thread and a number of dents (photo 5).




The inner threaded ring can be rotated and slowly moves out of the outer ring until it comes off completely (photo 5, bottom row, and photo 6). This is how the height of the ring combo is changed, thereby changing the distance to the film/sensor.


To adjust the distance, you do not have to take the ring out. You just need to loosen the screws of the adjustment ring, lift it so you can rotate the inner threaded ring, and rotate the ring at the dents (photo 7). Now you just need a little patience to repeat this procedure until the lens focuses to infinity at the infinity setting.




I use that lens on a D800.
It is very sharp and may even cause Moire in the corners (!), but you need to stop down to at least 5.6 because it has a tendency to purple fringe badly wide open (not talking about axial or lateral CA, the latter of which are very very low for a zoom).
Contrary to common belief, the lens is parfocal.

Cheers,
Amir

(this may very well be my one and only post on this forum)


Last edited by Amir on Tue Oct 07, 2014 7:32 pm; edited 1 time in total


PostPosted: Tue Nov 05, 2013 9:13 pm    Post subject: Reply with quote

odd, I can only see the photos if I reply to my posting...

And I forgot: turning the ring clockwise will make the lens "focus closer", that is, the lens will focus past infinity.


Last edited by Amir on Tue Nov 05, 2013 9:16 pm; edited 1 time in total


PostPosted: Tue Nov 05, 2013 9:16 pm    Post subject: Reply with quote

welcome Amir
very interesting, I hope it will not be your last post


PostPosted: Thu Oct 02, 2014 6:15 pm    Post subject: Reply with quote

I am not sure why I cannot see the pictures. Could you perhaps re-post them?


PostPosted: Thu Oct 02, 2014 9:17 pm    Post subject: Reply with quote

A lot of pictures embedded in the site were lost recently when the site crashed.


PostPosted: Tue Oct 07, 2014 7:33 pm    Post subject: Reply with quote

uploaded them again.
Cheers
Amir


PostPosted: Tue Oct 07, 2014 8:41 pm    Post subject: Reply with quote

I wonder if similar arrangements can be found in other lenses? That's a very good way of adjusting a lens.

Thanks for uploading the pictures again, it's useful information.


PostPosted: Thu Oct 31, 2019 11:27 am    Post subject: Reply with quote

I have some additional information WRT this.

All lenses have infinity focus adjustment. This lens has it under the naming plate with the engravings, three screws as usual. As this lens focuses by moving the front group.

This lens additionally has an adjustment to adjust the distance from the rear element to the camera, shown here, which is nice and very good info. Thank you.

Both these adjustments can be seen as equivalent but they aren't:

If you know that your adapter is not of the correct width and that the infinity focus of the front group is spot on you can do this. Otherwise you are uncalibrating the lens. I was lucky that I marked the previous position on mine before doing anything.

If you know that your adapter is correct then you can adjust the lens as is shown here, but you don't need to mount and remount the lens as many times. You can just remove the mount and remount it without the aperture ring. Then the 3 screws and the dented ring are accessible with the lens mounted on the camera. Once you are done then you remove the mount and set everything again.


PostPosted: Thu Oct 31, 2019 12:38 pm    Post subject: Reply with quote

I am using both of my Zeiss C/Y zoom lenses 35/70 and 28/85 without any problems with an K & F adapter! No Sweat!