Does shutter slap exist?

[PaulC]

My Nettar's Compur Rapid (virtually unused) shutter has a particularly strong spring to cock the fastest speed of 1/250. I've noticed that several negs shot at this speed show a definite double image and none of them produce quite the sharpness that I get from my 6x4.5 folder (which has a much less powerful spring in a different shutter).

I would expect 1/250 on a 105mm lens to be fast enough to freeze motion on film, even with a medium format neg (I've hand-held slower speeds on other 6x9 folders without getting this result). It has got me wondering whether the force with which this particular shutter opens is enough to deliver an lens-jarring jerk.

Has anybody encountered such a thing with this type of shutter? Was that a problem with these cameras when they were new and the springs were unused? I believe this camera has only had about five films put through it.

"Shutter slap" is mentioned in various internet sites but many of these references seem to refer to what is really mirror slap and, in any case, they are not dealing with this kind of shutter.

[Sevo]

On long times, the spring tension is decreased - there usually is one step below 1/100 or 1/200s where a extra strong spring is added to the tension, and one above 1/10 or 1/8s where the shutter switches from springed to the clockwork type long time governor.

Shutter slap issues and mechanical tension limits are the reason that very large leaf shutters never were made in the common Compur/Prontor design - they were pneumatic (Compound type) up until electromechanical shutters took over.

[PaulC]

That's it then, thanks.

The shutter goes about halfway from 100 to 250 on the normal tension spring, then the high tension one takes over.

[Nesster]

Yes, that seems to be the reason.

However, some shutters are set up very strong even at the lower speeds -the Compur on my Rollfilmkamera is one such, which I feel limits its resolution, the damn shutter's too strong!

[PaulC]

I guess the nettar gets up to 175 or 200 before switching to the stronger spring, unfortunately the timing isn't marked at that point, so I will have to try limiting my exposure time to that and see if it boosts the IQ.

I thought Compur Rapids were meant to be the best of the folder shutters, but Prontors and humble Klios have not caused such problems.

[Esox lucius]

I have two Ikontas, Compur Rapid (1/400s) and Synchro Compur (1/500s) shutters. Both are CLA'd two years ago. The Synchro Compur goes to 1/250s until the tension gets tougher (but not bad) when you set it at 1/500s. Never had problems with camera shake even at the fastest shutter setting.

With my Compur Rapid I have, it is very stiff and I have noticed that I get the occasional camera shake exposure even with high shutter speeds.

[Farside]

[PaulC]

Does that mean it has no timer? Do you have to work in seconds rather than fractions of a second? That would be a significant limiting factor.

[Sevo]

The lower one might have no timer - timer-less shutters were common on process cameras, where exposure was in the order of tens of seconds. The upper is pneumatic - see the small cylinder on top...

[Farside]

[scsambrook]

Back in the 1960s, I used to have a Super Ikonta, 11-on-120, f2.8 Tessar, Compur-Rapid shutter. When you set the top speed (I think it was 1/400th) and cocked the shutter, the extra spring tension was most noticeable. When you fired the shutter it certainly felt different to the other speeds, but I never found any problems with shake or vibration. The "Focal Guide" that I had with the camera warned against engaging the top speed AFTER cocking the shutter, and also against moving the shutter off the top speed once cocked, but it didn't spell out what disaster would occur if you did so.

I've never previously heard of Compur blades "bouncing open", but then there's lots I don't know about!

[PaulC]

I don't think bouncing open is quite the right expression, it's more about recoil from the spring as it is released. I was surprised because I thought the forces inside the shutter would be balanced and give no overall kick, but it seems that in some cases that isn't so.

The camera shake must also be a lot more obvious now that negs get scanned at very large sizes rather than printed at modest ones. I routinely check 6x9 photos at 72dpi at around 20MP, which is really like taking a microscope to them. Later I downsize to whatever seems reasonable, depending on the image quality. I might be able to see shake in some of your 1960s negs if I put them through the same extreme examination.

[scsambrook]

Paul - you may be right about today's relatively enormous degrees of enlargement showing up hitherto not noticed problems. Be interesting for those who've been into photography for a long while and now have good modern scanning kit to make some similar experiments.

But I'm puzzled how "spring kick" can actually cause the trouble - I'm no scientist though! The mass of the shutter blades is very small relative to the camera itself, and the spring energy surely can't be particularly high. How does the effect occur? That there is an effect seems to be beyond doubt and I'm not disputing that - are we looking at something like a "twitch" in the user's hand, a bit like "snatching" the trigger on a rifle or pistol? I can't remember if the actual release pressure on the Super Ikonta was any different on the top speed - maybe I had to press harder to fire the shutter. If so, any roughness in the release linkage might cause a jerk as the shutter opened. Intriguing problem!

[PaulC]

I also wondered if it was old-fashioned camera shake, caused by jerking the release button. But from what Sevo said it was a known issue in the industry. Add to that the fact it is apparent at the highest shutter speed - albeit only 1/250 - and it seems unlikely to be my button-pressing technique.

I guess (not sure) that the old formula of the shutter speed being the reciprocal of the focal length to avoid motion blur needs to be modified on a neg that is 2.6 times wider than 35mm, but even then 105 x 2.6 = 273, which is not far from 1/250. And I'm not even certain that the principle I am applying there is true ... but again, the starting point is pre-pixel-peeping.

On the other hand, my Beirax, which has a top shutter speed of 1/150, gives me razor-sharp 6x9 negs.

I suppose cable release and with a tripod at 1/250 would be the ultimate test for the Compur Rapid.

[Nesster]

Yes, when I mounted the strong-springed rollfilmkam on a tripod and used a cable release, it was much better. Actually even better at night when I used T

[Farside]