The classic rim-set Compur was a high quality shutter that was fitted to countless cameras ever since it was first introduced in the mid 1930’s. They were the best shutters of their era and because of their performance and reliability they were often used by camera manufacturers on their more expensive models. Simply said, if the vintage camera in your hands is fitted with a Compur, you probably have one of the high end models.
The Compur was available in three main variations, the Compur, the Compur-Rapid and Synchro-Compur. Additionally within these groups, there were many variants that were introduced over the years to meet changing needs of users and manufacturers. The Compur was most common version. It was fitted with three shutter blades and usually had a top speed of 1/250. The Compur-Rapid was, as the name suggests was faster. It was fitted with five shutter blades (which were smaller and lighter to reduce inertia) and had a faster top speed. The Synchro-Compur was pretty much the same as the Compur-Rapid but had the additional complication of a timing mechanism for the flash synch connector. The timer was controlled by a green lever and allowed the shutter to be used with either flashbulbs or electronic flash.
Although there are countless variations of these shutters, the basic operation remains pretty much the same due to the shared design architecture. That said there are differences that you should be aware of:
“T” & “B”
The first of these is the “T” & “B” settings. Usually if you see both of these on your Compur shutter, you won’t have to cock the shutter to use these setting. Simply set the shutter to T or B, push the shutter lever and the shutter blades will open and close accordingly.
If the shutter only has a single “B” setting. You’ll probably (but not always) have to cock the shutter first before being able to use that setting. A little experimentation will quickly reveal what you need to do.
The other shutter speed settings (with the exception of the fastest one)
For these shutter speeds you need to cock the shutter to use them. Once the shutter is cocked you can change the shutter speeds as needed. However this does not apply to the fastest speed on your Compur, Compur Rapid or Synchro-Compur shutter.
The fastest shutter speed setting
You cannot set any Compur, Compur-Rapid or Synchro-Compur shutter it to its fastest shutter speed if it’s cocked! If you try to force it you'll probably break something. You must select the fastest speed before cocking the shutter. You’ll also notice that if you decide to use this setting, it takes extra effort to move the speed selector ring to that position. It also take considerably more effort to cock the shutter. This is normal. This is because the fastest shutter speed engages a second, rather stiff spring to force the shutter blades to move as fast as possible.
Dealing with quirky Compur operating procedures
1 – There is an odd way of selecting the fastest shutter speed that is common to all Compur, Compur-Rapid and Synchro-Compur shutters. All of them depend on a second spring for the top shutter speed. As a result when using the fastest speed, you must select the fastest speed before cocking the shutter. If you change your mind and you want to use a slower speed afterwards, it is permissible to select a slower speed. This is because the second spring automatically disengages itself. However after this, the top speed can once again only be selected when shutter is uncocked. (See tip number 4.)
2 - Many Compur shutters were fitted with a built in self-timer. If it does have one, none of the Compur, Compur-Rapid or Synchro-Compur shutters will allow you to use it when set to the highest shutter speed. (This is because the additional pressure of the second spring is high enough to damage the self-timer.)
1 – Assuming your shutter has one, I recommend that you don’t use the self-timer if your Compur shutter hasn’t been serviced recently. Trying to use the self-timer on a camera that’s been laying around unused for 50 or 60 years is asking for trouble. They’ll often hang up or jam if you attempt to use the self-timer.
2- If your self-timer hangs up, you can try to resolve the problem by judiciously applying some extra pressure to the cocking lever to help it move along. (Be careful not to apply too much pressure!) If you’re lucky you may hear the self-timer ticking along sluggishly. Once it’s moved along far enough, the shutter will fire normally. After that, don’t use the self-timer again until it’s been properly serviced.
3 – On Synchro-Compur shutters, it’s best to keep the green “X”/“M” selector lever set to the “X” position. “M” is for flashbulbs and “X” is for electronic flash. (Some early Synchro-Compur shutters won’t allow you to use the top shutter speed if the lever is set to “M”.)
4 – If you need to select the fastest shutter speed and the shutter is cocked, you’ll need to uncock it first. If you don’t want to waste a frame of film, set the aperture to a small f stop and cover the lens casually with your hand to block out stray light. (Not super critical.) Then fire the shutter, using the accessory lens release. (On Zeiss-Ikon Ikonta and Super Ikonta cameras there’s a black tab near the lens stand that pushes on a chrome lever. This tab was intended for double exposures. It can also be used to un-cock the shutter if you’re putting the camera away for a longer period.)
5 – It’s not uncommon to come across a Compur or Compur-Rapid shutter that’s been fitted with a flash sync connector. Usually these connectors were set up to work with flashbulbs and won’t work correctly with electronic flash. (This is because the Compur and Compur-Rapid shutter predate electronic flashes.) However it can’t hurt anything to try use a flash. You may be lucky and have a shutter that was readjusted in the past.
6 - The only real advantage of the Synchro-Compur versus a Compur-Rapid (that happens to have a flash connector) is that the Synchro-Compur has a green lever that allows you to adjust the ignition timing to work with flashbulbs. Flashbulbs are filled with magnesium threads which need time to start burning and then a bit more time to reach optimum output. The time needed is quite short and is measured in milliseconds but it's enough to disrupt a flash photo. So setting the green selector lever to "M" advances the timing and allows the flashbulb to start burning early, so that the shutter blades open at the brightest moment of the burn.
Frankly none of this is relevant in the age of electronic flashes. Set a Synchro-Compur to "X" and forget it. And if your Compur or Compur-Rapid happens to be fitted with a flash connector, have a repairman test and readjust it to work with an electronic flash. (If you own one of our freshly serviced cameras, rest assured that we've already done this for you!)