Wrong shutterspeeds with Copal/Sinar

[Jacob von Post]

Hello. I have a Sinar, and sometimes I use a Sinar/Copal shutter, which you place in be tween the front and the bellow. It has a lever at top where I can choose between different shutterspeeds. B, 1/60 - 8 sek. The problem is that the hole thing is quite a few years old, and the shutter speeds no longer are accurate. What shou ld I do? I have some very nice lenses with no shutter built in them, so I need i t sometimes.

One more feature is that I can adjust the aperature from this shutterpiece. But the levers at the lensplate that is supposed to forward the aperature-informatio n to the lens moves a bit slow/hard and the hole thing kind of jams up. Probably there is a way of lubicate this, but how and with what.

Excuse my english, (I'm from Sweden), hopefully someone have some good advice fo r me.

[Bob Salomon]

Why not let an experienced repair station fix it?

[Brian Ellis]

If you know the actual shutter speeds at each indicated shutter speed, and if they are off by the same amount every time, it's pretty easy to compensate when making the exposure time. E.g., if an indicated 1/30 of a second is consistently 1/15, just take this into account when setting the aperture or switch to a faster known shutter speed. If the speeds are inconsistent (e.g. if indicated 1/30 of a second is 1/15 one time and 1/2 another time and 1/4 another time) then you have a real problem. All I know you can do in that case is try to have the shutter repaired. If you don't know the actual shutter speeds you can buy a shutter speed tester from Calumet among other places.

[Per Volquartz]

Just went through a similar situation with an old Sinar Shutter.

Remedy: Send it to Sinar or to another qualified repair center. It sounds like it needs a major overhaul.

[neil poulsen]

I purchased a Calumet shutter tester and have been taking a lot of measurements. I have a collection of shutters, most of which date from the 70's and 80's. While not necessarily accurate, I was amazed at how consistent these mechanicl shutters are.

I've tested 7 shutters thus far, which makes about 63 shutter speed/shutter combinations. (7 multiplied by about 9 shutter speeds per shutter.) Of all these, only 3-4 were outside of plus/minus 0.1 stops. That's only one-tenth of a stop! About two-thirds of these shutter speed/shutter combinations were consistent to within plus/minus 0.05 stops. (Half of one-tenth stop.) While a couple of these were the fastest shutter speeds, others were a 1/15th and a 1/60th. For one of these shutters, the fastest speed was the most consistent.

Knowing that my shutters are remarkably consistent, I only care about how far off each speed is from it's target shutter speed. I collected 18 data points (10 is good) from each shutter speed/shutter combination and determined the difference (delta) of each data point from target in terms of stops. If "S" is the shutter speed data point (in seconds), and "T" is the target shutter speed (also in seconds), then I used the formula: Delta = Log10(S/T)/Log10(2). I averaged these 18 (10) deltas to obtain the average inaccuracy in stops. I have a small table that I include in my pack with shutter speeds across the top and lenses down the side that identifies my average delta for each shutter/speed lens combination. With this cross-reference table, I know how many stops (e.g. +0.6) by which to adjust the exposure to compensate for the inaccuracy of the particular speed that I'm using on the given lens.

Some may comment that my $90 shutter tester doesn't give accurate results. These inaccuracies result from the inherent inefficiencies shutter designs. However, given that one shoots LF at smaller apertures and usually for times exceeding 125th of a second, these tester inaccurcies aren't relevant. I double-checked my logic on this with Schneider's LF technical support.

[neil poulsen]

Post Script: Of course, it's always a good idea to get your shutter cleaned and serviced. But, in the event that inaccuracies prevail, one can do the above.

[John D. Clark]

I have the Calumet shutter tester like Neil -- it's a great deal at about $75. Almost all large format shutters are somewhat inaccurate (but precise) at long and short speeds. I keep tables of speeds in my field notebook, so I know that my 210 is +1/2 stop at 1/60, etc. I mark the range of shutter speeds that are accurate enough (within +/- 1/6 stop) so I know at a glance that my 210 is accurate between 1/2 and 1/30, and exposure need no additional adjustment. Of course, if the speeds are drastically out, it may need professional servicing.

JD Clark