Zeiss Nettar Focus Discrepancy

[cobbu2]

Hello All,

Not long ago, I acquired a cosmetically nice Zeiss Ikon Nettar 515 (for a very low price). I took it out for a spin and upon processing the film saw every frame was out of focus; I'm not new to zone focusing and on several frames, I knew the exact distance and the focus ring was exactly where it was supposed to be.

So I conducted a test, shooting an entire roll with the lens wide open of an object exactly 12.5 feet away, starting with the focus ring at closest focus (about 3.5 feet) then with succeeding frames focused at regular distance intervals with the last frame (number 16) focused to infinity.

As it turns out, the sharpest frame was when the focusing ring was set to 5 feet.

What could be the problem since appearance wise, the front lens seems positioned properly and turns on its helical to both the near and far stops as it should? Thanks in advance, Allan

 

[summicron1]

someone took the lens off and put it back on wrong, would be my guess. Front-focus lenses need to be assembled the same way or they don't focus correctly. Fortunately, a piece of frosted glass on the film plane and some trial-and-error patience on your part can fix it.

 

[ciniframe]

There should be 3 tiny grub screws on the focus ring. they can be loosened slightly to set the ring to the right position when the lens is focused to infinity. You will have to use a frosted flat surface at the film plane. Do what you did at first with the shutter on 'B' and held open with a locking cable release. Then set the camera at a known distance so that the image appears sharp on the ground glass surface. Then set the focus ring to that distance and tighten the grub screws (careful. they are very tiny, so not too tight).

 

[gone]

I suspect that someone had the lens apart and didn't start the helical threads at the right place. Or if you're lucky, the bezel on the front has slipped due to the screws backing out a little, and is not where it's supposed to be. Either way you need to loosen the grub screws (over a towel or a box just in case they fall out), then see if you can get infinity w/ a gg on the film plane.

A 50mm SLR lens makes a handy loupe if you don't have one, and tautly stretched Scotch Magic tape will do for a GG if you don't have one of those. I usually use a focus screen from a TLR, but anything that works is fine.

If you can't get infinity, which generally on those cameras is 100' to 150' or so, or if the lens seems to be in the wrong place for that (i.e. screwed in too far or out too far) you'll have to screw the lens all the way out and restart it in different places to get it right. Be sure to make a little mark at which places you restart it, or you could be there a while :] When you get it sorted out, you'll discover that they take wonderful photos!

 

[John Koehrer]

I doubt the helical is an interrupted thread type with multiple starting points. Those are found on SLR's.
Because it's a continuous thread, there's only one start point.

Most likely cineframe's got it right. the focusing ring has moved. Sooo. do as he suggests with a GG or tape focusing screen.

 

[cobbu2]

Thanks everyone for your excellent responses! I have to say, those grub screws are really REALLY tiny, a 3/64" screwdriver (the smallest I have) was barely small enough to work. So far, so good... I used the Magic Tape method as I have no easily available ground glass and it seemed to work fine. Everything is back together now, I plan to give it a test today and share the results!

 

[pdeeh]

If you find yourself sucked into fiddling about with cameras, and have the need for one more than once, a ground glass is easy to make following Ian Grant's instructions here:

(there was a url link here which no longer exists)

 

[PCC]

I doubt the helical is an interrupted thread type with multiple starting points.

Though I don't own a Nettar, my experience is with a front focusing Schneider Kreuznach Radionar that came with my ~1948 Franka Rolfix that is front focusing. It has a four start thread on the front focusing assembly.

 

[wombat2go]

I agree with the comments that a glass element might be flipped.
I sent my Nettar with "Nettar Anistigmat1:6,3 f=10,5cm" for shutter cla, and ultrasonic cleaning of the hazy elements.
The camera would then take sharp photos close in, but everything distant was out.
I sent the repairer the example jpgs below and he identified the problem and the camera was returned and corrected.

Edit: Here is the Nettar with its lens and shutter all refurb and correct. Ektar 100
https://app.box.com/s/2vvkg62b2gt3lavig368

 

[cobbu2]

Thanks to everyone for the informative replies, including the ground glass instructions! The Nettar is definitely a single point thread, it was easy to get it started.

Well, I think I was successful, or at least it seems about right. I ventured to a local lake this morning and took these on TMY:





The close to mid ranges look good, but I can't help but think infinity is still slightly off; or maybe it's just my imagination with some lens flare and slight fungus evidence present!

Cheers, Allan