Zeiss 521/16 Compur Rapid Shutter  

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Courtesy of Mike Kovacs photo.net and the  Classic Cameras (pre-1970) Forum

Ikonta 521/16 Lens/Shutter Overhaul


What I am presenting here is a lens and shutter overhaul on a Zeiss Ikon Ikonta 521/16 with an uncoated Opton Tessar lens and a non-synched Compur Rapid shutter. This camera had a jammed shutter and foggy optics. Many folders, their lenses and shutters are alike in many ways, so I hope the presentation will also be of use to people wishing to repair different cameras. This camera turned out to be more difficult than the average repair case but Iím going to go slow and show lots of pictures as encouragement to those that wish to begin in camera repair.

Tools and Materials Used:

      Jewelers screwdrivers


      Spanner wrench w/ slotted and pointed tips

      Rubber pad

      Ground glass


      Ronsonol lighter fluid

      Rem gun oil

      Optical cleaner


Click on Thumbs to enlarge:


To start, we will remove all of the optics from the front and rear of the shutter. The first step is to remove the infinity stop. On many cameras, this is nothing more than a threaded post (circled) which can be removed with a slotted screwdriver.



Once removed, you can rotate the lens past minimum focus and continue to unthread it. When you do this, go slowly while pulling outward slightly. Note the position of the focusing ring when it comes free. If it was set right when you started and you put it back on the same way, then the focus should be correct upon reassembly. Weíll deal with the focus in detail later.



Sometimes when doing camera repair, you come across evidence of a previous repairmanís handiwork. In this case, someone had bored a large hole (circled), probably to free a stuck element. On this camera, the 2nd lens element was tight and required a rubber pad to provide enough friction to free it. Some cameras will also have slots or holes for a spanner wrench on the 2nd element. Remove the 2nd element and set it aside.


Next, we will remove the rear optical group, a cemented doublet on a Tessar lens such as this. Flip the open camera over and remove the rear element using a spanner wrench on the inner pair of slots (circled). Set the group aside.


Now that we have the optics out and set safely aside, we can begin to tackle the shutter. On this Compur Rapid, there is a screw with two holes for a spanner wrench. Turn the screw so the flat side faces the center of the shutter. Other shutters open in different ways but most either copy the Compur design, or use a threaded nut in the center that needs to be loosened.
Once the flat side faces inward, you can rotate the nameplate CCW to line up the bayonet with the 3 scoops on the shutter housing. Lift the nameplate off and set it aside. Under the nameplate is the speed ring. Carefully rotate the speed ring without lifting it out and note how there is a cammed surface on the lower right. This is changing the speeds, as is another surface that puts the pallet on the slow speed escapement in and out. There is also a space that the booster spring slides into for 1/500 speed. Once satisfied with this, wiggle the speed ring off and set it aside.
Here is the view under the speed ring. Note the booster spring, the release mechanism below it, the slow speed escapement and the cocking ring. Do not attempt to wind and fire the shutter or the cocking ring is likely to fly out. Have a good look at the cocking ring and note how it makes contact on top with a slot that locks it when fully cocked, how it rides against the pallet arm on the right side of the slow speed escapement, the release delay on the left side of the slow speed escapement, and the shutter release latch. It is not as bad as it sounds but it will not sit flat after reinstallation until all these conditions are satisfied.
If you are lucky, this is as far as you will need to go. Carefully place a drop or two of lighter fluid on the slow speed escapement, replace the speed ring and fire the shutter until the lighter fluid is dry. Try to hold the camera at an angle that prevents excess lighter fluid from draining onto the shutter and aperture blades. In many cases, this will bring a slow shutter back to life. I would try it 3-5 times before giving up and moving the next step.
Life is not always that simple. On this shutter, the escapement will have to come out. Remove the mainspring from its post on the left side of the slow speed escapement and wiggle the cocking ring and the spring out. The slow speed escapement is attached to the shutter housing with two screws. Under these screws are oblong holes that allow the position of the mechanism to be adjusted. Moving the pallet (right side) closer to the inside makes the shutter run faster. Carefully mark the position of both screws in relation to the escapement, remove them and lift the escapement out of the shutter. I normally soak mine overnight in lighter fluid. The escapement should run smoothly without lubrication in many cases. If it still doesnít run, I use a pin and dip it into Rem gun oil to obtain a tiny drop. I apply a drop to the pallet shaft (the rocking arm) and the star wheel shaft (the gear the pallet rocks against). That should be enough to get most escapements running smoothly. Donít over-lubricate them or you are asking for trouble later when the excess oil attracts dirt.

If the shutter blades have oil on them, you can often remove that by gently dabbing them with a tissue soaked with lighter fluid. Keep changing tissues and wiping until they are clean.


However, this will not be enough for this shutter. When I hold open the blade actuator, see that extra piece sticking out? You might also note in the earlier photos that the shutter is not stopping down all the way light tight. If you see something like this, or the blades are still fouling after the tissue cleaning, then the rear of the shutter must be removed and the blades individually cleaned.  
In the rear of the camera, there is another nut with 4 spanner slots. This is the shutter nut. Remove it and the shutter will come free from the lens standard.
The aperture controls are removed with a single screw. Remove the screw and set the aperture controls aside.

On the rear of the shutter are three screws.  When they are removed, you can separate the back (aperture) part of the shutter from the front.  You must be aware of a few things before proceeding.  First, the shutter release will drop out when you open the back as will the booster spring.  You can remove them before starting or deal with them as you open the back.  The release arm has a hairspring that goes into a slot on the case.  This is easily dealt with after the shutter halves are joined back together.  Second, you want to keep the front of the shutter facing down and lift slowly.  The 5 blades are loose and it's good to get a photo of their arrangement before they drop out.  Remove the three screws and carefully separate the two halves.


Here you see how the blades work. Sometimes there will be a blade with a tip that curves in or out. Sometimes (less often) there will be shims. Document the arrangement carefully before proceeding. If you carefully push the blade actuator, you can actually see how the blades pivot about a fixed pin. Remove the blades and clean them individually with lighter fluid. To reassemble, lay one on top of the other and keep at it until you get them all back on. This is exacting work that requires a steady hand and patience. Before reassembling, you can stop the aperture down and give that a good cleaning with plenty of tissues and lighter fluid. Carefully lay the rear of the case back on, make sure that it's properly lined-up and replace the three screws.

    Once youíve gotten this far, it's pretty much a matter of proceeding in reverse.  If the shutter fires smoothly and reliably, pat yourself on the back and put it back together.  Remember I mentioned the speed adjustment?  If you have little in the way of equipment, a PC with a microphone is more than good enough to check the 1 sec Ė 1/10 timings.  I am also in the process of building a photodiode-based shutter tester that interfaces through a sound card.  You can move the pallet in and out to get a good 1 second timing and the rest of the speeds should fall into line.   Mike inspired me to post my Tester Sound Card Shutter Tester

 I clean the optics with tissue or Q-tips and an optical cleaner. If you have a blower, itís a good idea to blow them first, then to clean. For really foggy lenses, a freshly laundered T-shirt with a light touch will remove the fog. Follow up with optical cleaner and air puffs. Early coated (mostly WWII vintage) lenses have extremely delicate internal coatings so do take care in such a rare case. I have not seen such a lens on a folding camera yet.

    The last step that you need to complete is the focus setting. If it was good to begin with and you install the focus ring starting at the exact spot that it came off, then it should still be good. To get the focus back in the same place, start by placing it on a little bit past your marked spot, go backward applying light pressure and feel for the "pop" when it goes over the start point. It's when you feel the "pop" that you should reverse directions and screw the ring back on.

If you have a ground glass, take your camera outdoors and focus on an object far in the distance, e.g. a radio tower. Make sure the coarse side of the screen is facing the lens and that it sits in the inner film rails. If infinity lines up on the dial with your focus on the ground glass, reinstall the infinity stop and you are finished. If not, there are usually set screws on the focus dial. If you back them off, you can reset the position of the dial without moving the focus on its thread, then tighten the set screws and replace the infinity stop. For a more elegant way to bring infinity indoors, see the links below. Or see how Dave dose it on the cheap AGFA towards the bottom of the page.

I normally also spend some intimate moments with my folder in the closet with a flashlight. Check carefully for holes in the bellows and patch them if necessary. The Zeiss folders I work on have not yet required any patching, even after 50-70 years of service.

I hope this is of some use to would-be camera tinkers. Happy snaps!

Helpful Links:

Rick Oleson - http://rick_oleson.tripod.com/index-27.html - bring infinity indoors, tech notes

Daniel Mitchell - http://daniel.mitchell.name/cameras/index.html - excellent notes on many shutter types

Thanks to Mike Kovacs


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