Zeiss Ikon Nettar 6x9 focus issue

Agulliver · May 24, 2021

I bought this beauty of a 6x9 Zeiss-Ikon Nettar with the f4.5 lens and telma shutter. However when I tried turning the focus, instead of stopping when the "peg" hit the focus indicator, it just went round and round until the front lens elements just unscrewed all the way off.

So...in order for it to focus correctly, how should I screw it on? Is there a specific starting point? I've screwed it back in place successfully but placing tracing paper in the film plane and opening the shutter suggest the focus is not accurate.

Nicholas Lindan · May 24, 2021

Well, you have found the wrong starting point. Unscrew it at try the next starting point. There maybe 3 or 4, keep going until it works.

At the proper point the front ring should look like this at infinity and close focus:

John Koehrer · May 24, 2021

Older cameras/shutters like that may have only one helical thread. The problem of starting point comes in aligning double helicals.

Nodda Duma · May 25, 2021

Best way to make sure is to open up the back and put some scotch tape in the plane of focus. Point the camera at an object a long ways away and examine the focused imaged while you put the lens back on. If it hits focus, then you installed it correctly. The thread starts are far enough apart that it’ll be obvious if it didn’t line up correctly.

takilmaboxer · May 25, 2021

If you really want to do it right, use a tiny screwdriver to remove the focus scale ring from the brass lens assembly. Find the correct infinity focus by the usual methods. There may be a scratch on the brass rings, marked at the factory, designating infinity. Then install the focus ring in the correct position (post #2) and tighten. Viola!

Ces1um · May 25, 2021

Anyone ever have issues with the lenses of these folders not being parallel to the plane of the film? I have one and on opening my lens passes the parallel plane to the film and keeps going another 3-5 degrees (just eyeballing. It's visibly off. It could be more off, I didn't break out the protractor). There doesn't seem to be a way to easily adjust how far it opens as everything seems to be riveted in place rather than having adjustable screws.

Nicholas Lindan · May 25, 2021

Ces1um said:
Anyone ever have issues with the lenses of these folders not being parallel to the plane of the film?

I have seen out of line folders and the cause has always been bent linkages from being dropped when opened. My take was to find out what part got bent and straighten it as best I can - usually results in a workable camera.

hsandler · May 25, 2021

Ces1um said:
Anyone ever have issues with the lenses of these folders not being parallel to the plane of the film? I have one and on opening my lens passes the parallel plane to the film and keeps going another 3-5 degrees (just eyeballing. It's visibly off. It could be more off, I didn't break out the protractor). There doesn't seem to be a way to easily adjust how far it opens as everything seems to be riveted in place rather than having adjustable screws.

Yes, this is the main problem with folders, especially 6x9. Even an exceedingly small misalignment will show up at the edges of the frame at open apertures.I have found that Zeiss folders seem to have the most sturdy mechanism though.

Helge · May 25, 2021

hsandler said:
Yes, this is the main problem with folders, especially 6x9. Even an exceedingly small misalignment will show up at the edges of the frame at open apertures.I have found that Zeiss folders seem to have the most sturdy mechanism though.

That’s why pull out, non self erecting folders are mainly just curiosities.
They will always be woefully misaligned compared to self erecting folders or strut folders.

Of those more expensive self erecting ones, the Voigtländers are the worst.
Even if they aren’t visibly bent out of shape, how do you know it’s not a little bit out of alignment from rough handling in the past?

A rigid and precise folding mechanism is far more important to start off with, than what kind of lens is on there.
Of the European ones Zeiss Ikon and Agfa reigns supreme in that regard.
The rest I suspect were involved in the usual patent malarkey that made certain manufacturers chose idiosyncratic variations on mundane mechanisms, like film advance and folding doors. Often to the detriment of operation and durability.

Helge · May 25, 2021

Agulliver said:
I bought this beauty of a 6x9 Zeiss-Ikon Nettar with the f4.5 lens and telma shutter. However when I tried turning the focus, instead of stopping when the "peg" hit the focus indicator, it just went round and round until the front lens elements just unscrewed all the way off.

So...in order for it to focus correctly, how should I screw it on? Is there a specific starting point? I've screwed it back in place successfully but placing tracing paper in the film plane and opening the shutter suggest the focus is not accurate.

The only way to truly know is to run a cheap roll of film through it and shoot some test targets that you have measured out exactly.

I little bit off at full open center, at the closest setting is within the acceptable margin.
It will be quite clear if something is off at close distance.
Never use infinitely as the arbiter of correct focus. Most front cell focus lenses are optimized for 40X the focal length of the lens. So 4.2 meters in this case.
Infinity is easy to hit well enough.
Tolerances of DoF are huge at infinity, and you’ll often stop down significantly when shooting at infinity.

There are more than two entry points for the helical AFAIR.
The pic posted by Nicholas above is very helpful. It will be visibly off from those distances to the shutter speed ring if you screwed it in wrong.

takilmaboxer · May 25, 2021

I've always loved landscapes. So I set the lens as accurately as I can at infinity, and then shoot a test roll to find out exactly where 10 feet (3 meters) falls on the focal scale.
The problem with using a closer distance to set the lens, is that allows for the possibility that the lens is unable to reach focus at infinity. In a view camera, if the lens is too close to the focal plane, you can't reach infinity at all. If it is too far away, stopping the lens down will produce a sharp "infinity". Same with folders but it's the rotation that changes the focal length, so it's harder to visualize.

Ces1um · May 25, 2021

Nicholas Lindan said:
I have seen out of line folders and the cause has always been bent linkages from being dropped when opened. My take was to find out what part got bent and straighten it as best I can - usually results in a workable camera.

This could easily be the problem. I was given this camera for free from the Halifax Camera Repair Centre before it closed down. Who knows why it was there in the first place. People tended to donate old gear, which they would occasionally fix up and sell. It may have seen some level of repair or maybe it saw no attention at all. It looks too cool to throw out but it's not worth running film through unless you're needing a little front shift in your composition.

Helge · May 26, 2021

takilmaboxer said:
I've always loved landscapes. So I set the lens as accurately as I can at infinity, and then shoot a test roll to find out exactly where 10 feet (3 meters) falls on the focal scale.
The problem with using a closer distance to set the lens, is that allows for the possibility that the lens is unable to reach focus at infinity. In a view camera, if the lens is too close to the focal plane, you can't reach infinity at all. If it is too far away, stopping the lens down will produce a sharp "infinity". Same with folders but it's the rotation that changes the focal length, so it's harder to visualize.

That seems like a good idea. But there are two problems with that.
1. It’s actually quite hard to find a good and reliable source of infinity. Stuff very far away often has problems with aerial perspective and glare/veiling against the sky.
Collimators are expensive, and not trivial to DIY.

2. As said, infinity is quite easy to do “well enough” (read: As good as any reasonable person could expect). Close focus not at all.

The lens threads will only have so many possible starts. So unless you plan on doing a fine adjustment with shims and bending of metal (which I’d strongly advise against for a number of obvious and not so obvious reasons), you will only have one correct setting for the lens.
The lens is made to be optimal at the 40X focal setting. With a lot of leeway either side.

Once you get inside about one meter the approximation breaks down and needs too much stopdown to be really useful (an old trick is removing the stop for “macro” and then stopping way down. You need to be really diligent about not losing the screw of course). That’s why most FC focusers are conservative in only having markings to 1.2 or 1.5 meters.

Things are much different on the other side of the “optimal” distance. There’s is a tonne of slack even with moderate stop down, after about ten meters.

With view-cameras you have the ground glass which makes all of the difference in being able to adjust. But of course also slows the shooting way down.

So even if you plan on shooting nothing but hard cranked infinity, which sounds kind of improbable and boring to be honest, there is no real reason or even possibility of “optimizing for infinity” really.

Nodda Duma · May 26, 2021

To your comment above, if the lens is too close to the film plane then you are able to achieve — and go beyond — infinity focus position. It’s when the lens doesn’t get close enough is when you have problems getting to that infinite conjugate. Short focus, lens is farther. Long focus, lens is closer.

For these simple designs, with a scale already etched on the lens barrel, you only have to check at one distance. Infinity focus (really, anything beyond a couple hundred meters) is convenient because you can also check range of travel — that's what the factory shims are there for. You can tell whether you started the lens on the correct helical even at shorter distances (I use the top of a tall tree across the street). You can also check at, say, 2 meters or 5 meters or whatever, if you have a tape measure.

For distance focusing, you’ll get the widest depth of focus by setting the lens to the hyperfocal distance. The position for that vs infinity on a typical f/3.5 or 4.5 6x9 folder is so slight that you actually don’t know what distance “infinity” corresponds to — true infinity to somewhere closer to the hyperfocal distance? It’s in the tolerances. In real cameras, two different cameras of the same model will no doubt have two different “infinity” focus settings but the images will look the same.

takilmaboxer said:
I've always loved landscapes. So I set the lens as accurately as I can at infinity, and then shoot a test roll to find out exactly where 10 feet (3 meters) falls on the focal scale.
The problem with using a closer distance to set the lens, is that allows for the possibility that the lens is unable to reach focus at infinity. In a view camera, if the lens is too close to the focal plane, you can't reach infinity at all. If it is too far away, stopping the lens down will produce a sharp "infinity". Same with folders but it's the rotation that changes the focal length, so it's harder to visualize.

Helge · May 26, 2021

Nodda Duma said:
For these simple designs, with a scale already etched on the lens barrel, you only have to check at one distance. Infinity focus (really, anything beyond a couple hundred meters) is convenient because you can also check range of travel — that's what the factory shims are there for. You can tell whether you started the lens on the correct helical even at shorter distances (I use the top of a tall tree across the street). You can also check at, say, 2 meters or 5 meters or whatever, if you have a tape measure.

What does “range of travel” mean in this context?

Trouble with infinity, as implied, is that it has a very large range.
One “perfect” infinity, may be different from tomorrows, and has huge implications on whether the rest of the scale matches up.

6x9 has incredible potential resolution compared to any digital camera, so don’t listen to would be experts on the dark side, waxing lyrical about performance at infinity of this or that lens.
You won’t be able to see the difference between straight-on infinity and 50 meters, even full open, on even the largest most well made print.

gone · May 26, 2021

I always set my lenses to achieve infinity around 100', or less. "Infinity" is a concept, not a distance. I had an SLR lens that couldn't get to infinity, but it didn't matter because it was normally used stopped down, and the shots were plenty sharp.

But back to your lens alignment. You should try to fix that somehow because if it's quite off, sharp prints all the way across the frame will be impossible. 6x9 covers a lot of real estate, and will show a misalignment more than a 6x6 camera will. On folders like yours where there's no real way to adjust the lens plane by adjustment, you'll just have to rebend whatever is bent.

What I do in such a case is open the folder's back (or take it off if needed) and set the camera on a table that is level w/ the back open and the camera pointed toward the ceiling. Then take a steel rule or something similar that is very straight and lay it on the lens. You might have to take the distance scale off to get an accurate measurement on the 4 compass points. Place a bubble level on the rule in the center, and look at what needs to be bent where, and by how much. If you get it in the center of your bubble your prints will be sharp.

Nodda Duma · May 26, 2021

Range of lens travel, Helge, to ensure the lens reaches infinity as well as short focus.

Agulliver · May 27, 2021

Thanks for all the advice. I think I'll try a test film this weekend if possible. The range of travel does look roughly like that in post #2 but if my attempts at focussing on electric lights about 6-10 feet away are in any way telling, it's not focussing correctly at close focus. But....maybe my method isn't that accurate as the tracing paper isn't as good as ground glass. If I had some of that Scotch tape rather than the completely transparent British Sellotape I'd try that, seems a great idea. Might pick some up anyway.

Helge · May 27, 2021

Agulliver said:
Thanks for all the advice. I think I'll try a test film this weekend if possible. The range of travel does look roughly like that in post #2 but if my attempts at focussing on electric lights about 6-10 feet away are in any way telling, it's not focussing correctly at close focus. But....maybe my method isn't that accurate as the tracing paper isn't as good as ground glass. If I had some of that Scotch tape rather than the completely transparent British Sellotape I'd try that, seems a great idea. Might pick some up anyway.

No one really seems to know where the plane of focus is in a folder.
Seriously, do a search.
Is it on the rollers? On the guide rails? The pressure plate? Etc.
That’s why it’s almost impossible to do the ground glass check.
The only test that really matters, is a rigorous test with film.
Set up some precisely measured, high contrast, flat targets and shoot some frames on different settings to make good use of the roll.
Any B&W film will do.

The scale on the lens assumes you measure from the front element BTW.
Many people don’t know this.

Nicholas Lindan · May 27, 2021

Helge said:
The scale on the lens assumes you measure from the front element BTW.

That's interesting. I'd always thought it was measured from the film plane.

takilmaboxer · May 27, 2021

Helge said:
No one really seems to know where the plane of focus is in a folder.
Seriously, do a search.
Is it on the rollers? On the guide rails? The pressure plate? Etc.
That’s why it’s almost impossible to do the ground glass check.
The only test that really matters, is a rigorous test with film.
Set up some precisely measured, high contrast, flat targets and shoot some frames on different settings to make good use of the roll.
Any B&W film will do.

Absolutely right. I use a cityscape in the distance for infinity focus. It is possible, using this method, to see the difference in negative sharpness with even a slight deviation from the true infinity point. Much more sensitive test than any lab test for infinity.
By the way, "true" infinity corresponds to the situation where the incoming rays are parallel. It is unambiguous.

Helge · May 27, 2021

Nicholas Lindan said:
That's interesting. I'd always thought it was measured from the film plane.

Front cell focusers for some reason often use the front of the lens ring as reference. It even says so in the Nettar/Ikonta manual.

Helge · May 27, 2021

takilmaboxer said:
Absolutely right. I use a cityscape in the distance for infinity focus. It is possible, using this method, to see the difference in negative sharpness with even a slight deviation from the true infinity point. Much more sensitive test than any lab test for infinity.
By the way, "true" infinity corresponds to the situation where the incoming rays are parallel. It is unambiguous.

It’s not.
What you might happen to hit in the far field or “infinity” will impact closer ranges by orders of magnitude.
If you shoot “the horizon”, you stop down to at least f16. That takes out any minute differences, if they are there at all.

Agulliver · May 28, 2021

I've always assumed focus is from the front lens element...I don't remember being taught that but if I was it would have been aged four or five. I do remember using a tape measure between the front element and the subject as an early way of determining focus when I took it upon myself to take portraits of all my teddy bears one morning.

Well this particular camera is loaded with Fomapan as a secondary camera on a quick camping trip over the bank holiday weekend. We shall see, as they say. I'll try a variety of long shots and closer portraits.

Nicholas Lindan · May 28, 2021

I think the confusion on the focus measuring point may come from a statement on the last page of the Zeiss Nettar manual https://www.cameramanuals.org/zeiss_ikon/zeiss_ikon_nettar_ii.pdf. Here Zeiss gives a table of distances when using their Proxar closeup lenses. The manual states "The distance of the object must be measured from the front edge of the supplementary lens mount." I couldn't find any other reference to camera to object distances in the manuals for either the Nettar I or the Nettar II.

The film plane is used as the reference for camera to object distance for both marked distances and for pictures taken with a closeup lens. This can be verified with an SLR and a tape measure. Set the lens to a distance of one foot, 0.5 meter (or some other convenient close distance), move an object so that it is in focus and then measure the object-to-camera distance - you will find it correlates to the distance from the object to film plane (location given by the -0- symbol on the top of most cameras).

Adding a +4 closeup lens will give a 0.25 meter (9 3/4") film plane to object distance when the prime lens is set to infinity; again this is verifiable with a camera, closeup lens and tape measure.

The camera-object distance, with the lens set to infinity is given by X = 1 / D, where D is the diopter of the lens and X is in meters. At other lens settings the formula is X = L / (L * D + 1), where L is the lens distance setting in meters. Interestingly the camera-object distance does not depend on the prime lens' focal length.

Zeiss made a mistake in the table in the above referenced manual. The distances given are for the film plane to object distance and not the lens to object distance. If they felt it would be easier on the user to measure from the front of the lens then they could have subtracted the lens to film plane distance from values given in table, but they didn't.

The back of the accessory shoe is often given as the location of the film plane if the camera doesn't have a '-0-' mark. The manual for the Agfa Solina https://www.cameramanuals.org/agfa_ansco/agfa_solina.pdf ($14.97 from Montgomery Ward https://www.collection-appareils.fr/x/html/appareil-3227-Agfa_Solina.html) states "The focusing distance is measured from the film plane (rear edge of the accessory shoe)!" on page 22.

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