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Dud lens? (no focus)

zeiss lens focus problem

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#1 bradley hayman

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Posted 11 September 2017 - 08:49 PM

so my issue is my Zeiss 8mm lens isn't focusing at all.  Not clear, not sharp-- moving the focus ring does nothing at all.  The focus ring moves smoothly and stops at both ends but nothing changes.  Unfortunate since I was hoping to use it for a big project this week.

 

Details:

Lens: Zeiss 8mm with Arri standard mount

Camera: Eclair NPR

adapter: Calkovsky arri to c mount adapter

 

The shop where I bought the lens is convinced it's the adapter, and while I still have a lot to learn about these things, it still seems like moving the focus ring should do something.  Is this incorrect?   At this point I'd be encouraged if adjusting the focus made it worse, just so I'd know something is happening. 

 

Calkovsky has been working with me trying to figure this out but we haven't got it figured out yet.  He mentioned it's possible I might need a tiny tab to lock it in position.  

 

I have been able to at least get a clear image in the viewfinder if I hold the lens myself up to the camera maybe within a few millimeters of the mirror but that image does not change if the focus is set to infinity or to 12 inches.  No changes at all.

 

Any thoughts?


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#2 Adam Frisch FSF

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Posted 11 September 2017 - 09:19 PM

You have three possibilities:

 

1. Your lens is most likely mounted to close to the film plane. When a lens doesn't focus anywhere, that's what's happened. If it had been mounted to far from film plane, it would focus closer (like a macro lens) but not reach infinity.

 

2. There are exceptions to 1: If the lens is broken internally and one element is out of whack. A very easy way to test this is to just hold a piece of paper behind lens (where the film plane would be). If the lens focuses an image on the paper, nothing is wrong with it and scenario 1 is most likely in play.

 

3. There is a third possibility with film cameras - that the viewing ground glass is out of whack. They way to test this is, open the gate, put a piece of diffusion or white paper in the gate. Focus the lens on it. If it produces a sharp image on the diff/paper but not in the viewfinder, your ground glass is misaligned and needs adjusting.

 

Wide angle lenses are notorious for scenario 1, so that's most likely it. And on wide angle lenses, the internal focus is barely visible and moves the lens very little.

 

Good luck.


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#3 bradley hayman

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Posted 11 September 2017 - 09:46 PM

thanks Adam.  I've sent quite a few emails today to multiple parties and I feel like your response is shedding some light.  

 

#2 I can see images on the paper when I put it behind the lens so I guess that's ok

 

I hope it's not #3 since I just had the camera serviced and other lenses appear to have no problem

 

#1 sounds interesting.  I noticed that once the lens is mounted onto the camera, objects within 1 or 2 inches appear sharp (regardless of the setting of the focusing ring), while everything else is blurry.  But that's if the rear end of the lens is very close to the film plane.  


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#4 Dom Jaeger

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Posted 11 September 2017 - 09:55 PM

Photos are always helpful.

 

There are two different types of Standard mount lenses, the early ones had the focus scale section connected to the rear mount section, and were designed to rotate inside the camera mount while a tab locating into the inner part of the lens kept that part from rotating, so that it screwed in and out as the focus ring (and outer mount) was turned.

 

Later Standard mount lenses had a separately moving focus ring, and the rear mount part would stay fixed in the camera mount. The tab still located in the rear, but kept the whole mount as well as the inner part from rotating.

 

You can easily tell the two apart by holding the lens by the mount and trying to turn the focus ring. Older types won't turn because the focus ring and mount are one piece, and the inner section can only be rotated via the tab slot.

 

Cheap Standard mount adapters just clamp the outside of the mount, so won't work with the older style lenses.

 

From memory, the 8mm Zeiss should be the newer version, and so work with cheap adapters that simply clamp the rear with grub screws. It sounds like this is the case as you are describing the focus turning smoothly.

 

In this case, there may be a problem with the lens. You should see the inner section move in and out as you turn the focus ring. If it's not shifting there could be a part missing. A photo of the rear of the lens will help.

 

 


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#5 Dom Jaeger

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Posted 11 September 2017 - 10:00 PM

Just saw your last post, if it's only focussing one or two inches away the lens is sitting too far from the film plane. Either it's not seating properly in the adapter, the adapter is way off, or the lens has been screwed too far out. I'd say option 3 could be a possibility. If someone has tried to dismantle it, they may have re-assembled it one revolution too far out.


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#6 bradley hayman

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Posted 11 September 2017 - 10:27 PM

thanks for the post Dom.  Maybe we're getting somewhere...

 

I am wondering if someone took it apart, cleaned it, and reassembled it incorrectly or just poorly.  Partly because one of the tiny screws that holds in the focus 'wings' just fell out with little to no provocation.  Also, when I hold the lens tightly and lightly shake it, I can hear something rattling around inside.  

 

for what it's worth, here's some pics of the lens.  Forgive the sizes (and my lack of manicure), I'm tired lolet5jy0.jpg24113kg.jpg

 

1e8k1x.jpg10elq9f.jpg


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#7 Dom Jaeger

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Posted 11 September 2017 - 10:39 PM

OK, well the other possibility with that adapter is that it's not allowing the lens to seat properly because of the sloping inside section that may be hitting the back part of the lens. The lens seat is the flat surface just behind the focus scale. If you measure the distance from adapter to front of lens when fitted and set to infinity you should be able to measure whether the lens is properly seating on the flat surface inside the adapter or whether it's hitting the sloping part.  Or try fitting the lens when set to minimum focus (when it's screwed away from the film plane), lock the grub screws, and try to shift focus towards infinity. If it's hitting the adapter the focus will jam before it reaches infinity. If it turns all the way then the lens may be incorrectly set.


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#8 Robert Hart

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Posted 12 September 2017 - 03:46 AM

Hold the wings and try to turn the very front of the lens barrel. Do not try to turn the lens barrel with the aperture ring. The Zeiss lens irises can be damaged by over-closing. If the lens barrel moves independently of the position of the "wings" and you can see at the rear, the inner body rotating inside the outer barrel, then that will have to be the method by which you focus it.

The focus marks will be pretty to look at but meaningless as they are with a couple of old ARRI standard-mount Cookes I have. I don't think the Zeiss lenses are set up like that but who knows?

That adaptor you have appears to be universal for the original ARRI standard and ARRI bayonet mount which were very similar. There may be interference between the rear of the lens body structure and the adaptor as suggested ikn a previous response. In the profile image, the lens appears to be riding forward in the adaptor by about 0.8mm but that may be my imagination or the flange face on the back of the Zeiss lens may have a small shoulder machined into it and thus a small apparent clearance seen in the image.


If you offer up the lens to the adaptor, without securing the grub screws, try moving the lens back and forth within the adaptor a small whisker to see if the image sharpens. If that adaptor is correctly machnined and there is no interference between the rear lens body and the adaptor, then that face immiedately to rear of the focus marks should be hard up against the front face of the adaptor. 

To check if there is interfence between the lens body and the rear inside of the adaptor, use a sharpie or whiteboard marker to ink the inside of the adaptor then assemble your lens into it with the lens set at infinity focus. Do not fasrten the grub screws. Rotate the lens inside the adaptor, take it out again and see if you can find any ink stripped from the inside rear of the adaptor. If there is, then that is a point of contact which may have to be dressed back by a machinist to permit working clearance.

 

Danger Will Robinson. The wall thickness of the adaptor may be insufficient to allow removal of enough material to achieve that clearance without breaking through to the outside of the adaptor body.

If you have an engineer friend with a vernier caliper, measure from the front of the adaptor to the flange face of the C-Mount section at the rear. The distance should be ( 52mm - 17.52mm ) =  35.48mm.

Please take heed of better and more qualified people than I who may critique my comments here.


Edited by Robert Hart, 12 September 2017 - 03:57 AM.

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#9 Robert Hart

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Posted 12 September 2017 - 04:14 AM

Footnote to above. If there is something loose inside of the lens, then a little metal key which engages in a slot in the moving structure inside may have become detached. In that event, the moving structure inside may be turning instead of being driven forward or rearwards by the helicoid thread. That could be a cause of failure to focus. When you move the focus "wings", have a look at the front or rear of the lens to see if the inner structure is rotating. If it is, try with then lens mounted to the camera or an assistant holding the lens by the mount, to turn the "wings" whilst stopping the inside of the lens from turning. You should be able to do this by shoving two fingers inside the corrugated anti-reflection surface inside the front of the lens or by grasping the inner rear section which may be rotating. If, when you have arrested the rotating movement of the inner structure, you can then see the front of the lens moving forward and rearwards in a normal focus movement, the key inside had likely come loose. It is the engagement of a key in a slot which stops the inner structure from turning with the focus ring in that type of arrangement. Another test may be to hold the wings from movement and attempting to rotate the inner structure by the inner front of the bit which sticks out at the rear which may show the same foreard or reverse movement. If the lube on the helicoid threads has become hardend and locked the threads, then the fastener of the key or the key itself may have broken off.

The best method of all will be if you can afford the cost, to have a lens tech examine the lens.


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