Procedure to adjust IIIf shutter spped

[tony.m]

Hello - i tried to learn how to CLA and repair. I was able to adjust slow shutter speed. But need help adjusting higher speed. The camera I have had around 1/300 at 1/1000. I read that hi-shutter speed can be adjust by changing curtain tension (the two screws on the bottom). I am wondering if there is a good direction on how to get the right tension? I have been doing trial and error and get the speed up to around 1/600, if I adjust higher, that curtain seem to be opened unevenly.

i am using home made LED/photodiode hooking to an oscilloscope. (which I assume it worked well, when I tested it with my M6 that just came back from CLA).

 

[Sarcophilus Harrisii]

Welcome to Rangefinder Forum.

How are you ascertaining the accuracy of each speed setting?

[EDIT: OK, missed that, sorry—if it's set up correctly, an oscilloscope could work quite well, but you still need to be able to measure the exposure at different parts of the film gate—otherwise you won't be able to establish if the curtains are running at the correct speeds across the gate.]

In order to get a focal plane shutter correctly adjusted it's imperative you have some way of checking the effective exposure across the film gate. Otherwise you'll find it very hard to get consistent, even, exposure across the entire negative.

I'm not so sure upping the curtain tension is necessarily such a good idea unless you are certain it is needed. Assuming the shutter was correctly tensioned at some point, even if that was when Leitz made it, there ought not to be a need to substantially vary these settings. If the times are way off at present, it indicates a need for cleaning and lubrication, replacement curtains, slit adjustment, or all of the above. It is folly to believe all causes of poor accuracy may be cured by simply fine tuning curtain spindle tension. Almost invariably, this should need minor adjustments, unless someone else has badly maladjusted things.
Over to you.

 

[Mr_Flibble]

Both curtains need to run at exactly the same speed. On the IIIf the curtains should move across the film plane in 1/30th of a second.

If the running speed of the curtains is correct, any deviation in exposure times would be due to gap between the curtains being too wide or narrow.

 

[tony.m]

Hi - thank you both for replying. Is there any test method to measure 1/30 of the moving shutter? If my camera is accurate at 1/25, can I assume that they are correct? How do I adjust curtain gap if that's the case. Thanks.

 

[Sarcophilus Harrisii]

If you have an oscilloscope and sensor assuming you have an appropriate light source it ought to be possible to measure 1/30. I seem to recall the IIIf red dial versions had a 1/50 sync speed though?

A good 1/30 time is only a starting point, it certainly does not guarantee that faster times will be good. And there's not much point trying to adjust the mechanism unless it has been cleaned and lubricated and the curtains are in good repair. A IIIf is old enough now that there's a fair chance its curtains are no longer serviceable anyway.

The starting point for getting accurate speeds is a clean, lubricated mechanism, running curtains that exclude light satisfactorily and are supple enough to spool onto their drums willingly. Given this, curtain tension can be incrementally adjusted to get exposures reasonably even. Decent 1/30 or 1/50 times are a good starting point because although the second curtain release, (obviously) has to trip the curtain to end the exposure, the entire gate is fully exposed. It's easier to isolate the effects of curtain run time on exposure at one of those speeds because you're not dealing with slit width as well as curtain speed, hence, it is not a bad setting to begin tensioning curtains from scratch. So if you don't have access to a sophisticated tester with the ability to measure the curtain velocities, getting a decent "full gate" time out of the shutter gets you, if not in the ball park, then, at least, heading down the right street, to get to the ball park...

The goal, in the first instance, is to get consistency of exposure across the film gate. The 1/30 or 1/50 (depending on model) is merely a stepping stone. If that measures good, you can try 1/100, 1/200 or even 1/500. As each time shortens, the tolerances for precision tighten. Depending on the resolution of your tester, you might have the mechanism giving 0% tapering at 1/50. But when you set 1/200, you're still off a bit. And so on. All this means is that the curtains are starting to run together, which is good: but they're still not quite right. The process is incremental. So you are less likely to wander off the garden path and get each curtain hopelessly out of range, this way.

The Leitz manual, using their drum tester, stipulate starting at 1/500 and adjusting the slit patterns. My suggestions above, do not contradict their instructions in any way and are not set in stone. They're simply based on years of experience in getting good results using less sophisticated equipment.

What is non-negotiable (repeating my comment above for clarity) is that there are two aspects to an accurate focal plane shutter: curtain run time and slit width. You can't correct a mechanism that needs release timing correction with only tension adjustments. Similarly, you can't correct the times of a shutter whose curtains are not running at the right speed by changing the release timing. Both have to be optimum.

The sequence, then, is to get the curtains running in harmony at the correct velocity (aka travel time). Once this is achieved, if the effective exposure is long or short, 1/50-100 to 1/500 times can be dialled in by correcting the second curtain release, and 1/1000 may then be further calibrated, in isolation, if needed. Slow times are adjusted via the escapement.

I've written about this in some detail recently in this discussion.
https://www.rangefinderforum.com/forums/showthread.php?t=173917

Hi - thank you both for replying. Is there any test method to measure 1/30 of the moving shutter? If my camera is accurate at 1/25, can I assume that they are correct? How do I adjust curtain gap if that's the case. Thanks.

With respect: Given the sorts of questions you are asking, I'm doubtful you are ready to do these sort of adjustments to your Leica. It's essential to have a sound understanding of the basic concepts involved in adjusting the shutter. This forum certainly has a few members who have become skilled in servicing Leicas and various other vintage rangefinders, so, yes: you may be able to learn to do this. I'm not trying to discourage you. But if you do not understand how the curtain gap is set, it sounds like you may be in over your head at this point. You may wish to consider getting an experienced technician to service your IIIf. It's a fine camera that's surely worthy of the investment.
Cheers
Brett

 

[tony.m]

Brett - thanks a lot. Your reply is very helpful to me. Yes, I didn't know how the camera works and I should have started with that. The reason I jumped into that was because, the slow shutter speed is straightforward to adjust, and I was able to get it very accurately (assume that my instrument worked properly, and probably need to check if it is the same cross the plain) at most speed up to 1/50 (1/5 and 1/10 is about 10% off). 1/75 is started to be off more than 30% and the rest is pretty much way off. So, I thought, must be adjusting curtain tension would help base on some instruction I found but I think I was totally wrong.

I tried to lubricate the camera before I started troubleshooting shutter speed (from: https://www.youtube.com/watch?v=gTb94H0AGng). I may have missed some parts, especially around curtain, I tried to avoid.

With your explanation, I think I may be able to improve the way I measure the shutter speed by having three sensors (left/middle/right) instead of one. This way, I may be able to measure, approximately both slit width and velocity base on the distance between sensors and timing. Not sure if it will work as I thought, but I am going to give it a try this weekend.

 

[tony.m]

I was able to get the hi-shutter speed to work! First, I found that the 1st curtain is running slow, it's about 1/38 and it seems not consistent so I started adjusting the first curtain so that it's approximately 1/50 (I have red dial). When it got to about 1/50, the timing (from 1st sensor to 2nd sensor and from 2nd sensor to 3rd sensor) became consistent (first picture is what it was before adjusted at 1/100). Then I found that, like you said, the shutter speed (opening time) is not even across the plane shutter. So, I started adjusting the second curtain and was able to make it almost 1/50 measuring from left, middle, right.

Then, I found that above 1/50, the speeds are still uneven and still off (e.g. 1/500 is about 1/350). So, I started to adjust second curtain again starting at 1/500 as suggested by the service manual. I tried to set the speed measured from the middle sensor to 1/500, however, the left and right sensors reading are off (1/490, 1/500, 1/540). I, then, found that, by lowering speed a bit, the gap between the speed at all 3 positions are become closer. When I set speed from middle sensor to around 1/480, all three speeds become very close. So, I moved on to adjust 1/1000. With 1/1000, adjustment seems to be even more sensitive (I think you mentioned this as well). But it started off very close already, so I adjusted a bit and closing the gap between all three. Now, rechecking 1/500, the speed different between all 3 sensors are increasing. So I switched back and forth between 1/1000 and 1/500 to make sure that the errors are smallest.

After that, I checked, 1/200, 1/100, 1/75, 1/50, they seems consistent and not require adjustment. So, I was able to get shutter speed from 1/50 up with about 10-20% and the different across the shutter plane are about 2%-5%. (I tried to get it consistent across the shutter plane, but it's like wack a mole, so I kept the best average across shutter speeds).

..

However, ..., now, I was not able to get slower shutter speed to work. 1s was about 1/1.3, 1/2 was about 1/2.2, 1/5 was about 1/6, however, 1/10 and 1/15 were about 1/3. I guess, I will try to remove slow governor, dip it into acetone, relube and try again. Please let me know if there is any else I can try for the slow shutter speed.

UPDATED: was able to adjust slow shutter now. It was the front plate lever out of place.

 

[Sarcophilus Harrisii]

I was able to get the hi-shutter speed to work! First, I found that the 1st curtain is running slow, it's about 1/38 and it seems not consistent so I started adjusting the first curtain so that it's approximately 1/50 (I have red dial). When it got to about 1/50, the timing became consistent across 3 sensors (first picture is what it was). Then I found that, like you said, the shutter speed is not even across the plane shutter. So, I started adjusting the second curtain and was able to make it almost 1/50 measuring from left, middle, right.

Then, I found that above 1/50, the speeds are still uneven and still off (e.g. 1/500 is about 1/350). So, I started to adjust second curtain again starting at 1/500 as suggested by the service manual. I tried to set the speed measured from the middle sensor to 1/500, however, the left and right sensors reading are off (1/490, 1/500, 1/540). I, then, found that, by lowering speed a bit, the gap between the speed at all 3 positions are become closer. When I set speed from middle sensor to around 1/480, all three speeds become very close. So, I moved on to adjust 1/1000. With 1/1000, adjustment seems to be even more sensitive (I think you mentioned this as well). But it started off very close already, so I adjusted a bit and closing the gap between all three. Now, rechecking 1/500, the speed different between all 3 sensors are increasing. So I switched back and forth between 1/1000 and 1/500 to make sure that the errors are smallest.

After that, I checked, 1/200, 1/100, 1/75, 1/50, they seems consistent and not require adjustment. So, I was able to get shutter speed from 1/50 up with about 10-20% and the different across the shutter plane are about 2%-5%. (I tried to get it consistent across the shutter plane, but it's like wack a mole, so I kept the best average across shutter speeds).

..

However, ..., now, I was not able to get slower shutter speed to work. 1s was about 1/1.3, 1/2 was about 1/2.2, 1/5 was about 1/6, however, 1/10 and 1/15 were about 1/3. I guess, I will try to remove slow governor, dip it into acetone, relube and try again. Please let me know if there is any else I can try for the slow shutter speed.

UPDATED: was able to adjust slow shutter now. It was the front plate lever out of place.

Well done. I think you've done very well, indeed. It sounds as if the mechanism is in good order, given those reported times.

It's important to slide the front cover plate into the shutter assembly in such a way that the pallet control lever is correctly positioned. The small access port in the plate is provided to permit this to be inspected when the plate is re-installed.

A friend liked my own IIIf so much, he acquired one of his own. I've spent some time this weekend servicing his. So I've just done the same process again. I had more problems getting the fast speeds correctly adjusted than I did with my IIIf, but got there eventually.
Again, congratulations, and well done.

 

[tony.m]

Thanks!

Just curious, when I adjust curtain tension, it seems that I was adjusting speed of the curtain. If the first curtain is fixed at 1/50, there must be a sweet spot for the second curtain tension so that the slit opening is consistent across the shutter plane. Then, is there an adjustment that changes the slit opening itself? (though, service manual say, adjusting second curtain tension changes slit opening).

 

[Sarcophilus Harrisii]

Thanks!

Just curious, when I adjust curtain tension, it seems that I was adjusting speed of the curtain. If the first curtain is fixed at 1/50, there must be a sweet spot for the second curtain tension so that the slit opening is consistent across the shutter plane. Then, is there an adjustment that changes the slit opening itself? (though, service manual say, adjusting second curtain tension changes slit opening).

Altering curtain tension on one curtain will ordinarily have some effect on slit size at faster speeds although not necessarily across the whole film gate. The goal in the first instance is to have the curtains running across the gate in harmony so that exposure is consistent across the negative. For clarity you can't control the slit width across the whole gate simply by balancing the running speeds. The slit is created by the release mechanism that holds the second curtain back after the first begins to move. How much that is, of course, varies depending on the exposure time set. At 1/1000 the second curtain fires almost immediately after the first. At 1/500 it holds back a little more, more again for 1/200 and so on; until 1/50 (or 1/30 in the case of a IIIf black dial), it waits until the first curtain has fully exposed the gate.

So, when adjusting the curtain speed, the goal in the first instance isn't to get accurate exposure times in itself. You certainly want the effective time to be in an adjustable range (if the curtains are running at the right speed and the mechanism is clean and well adjusted, this should not be an issue). You're simply trying to get the curtains balanced and running together for the same amount of exposure.

Once you've got that, if the amount of exposure is for instance 30% more than nominal; the curtain release adjustments on the release latch are used to change the release delay (and hence the slit width) until the exposure is good.

The National Camera manual, for the IIIf, when calibrating tension from zero (Eg after new curtain installation) recommends taking up all the slack in the curtain/ribbons until they are both fully drawn across the gate (with the shutter fired, obviously). With the first curtain fully spooled around its take up roller and the second curtain ribbons similarly spooled up but no tension on the rollers they suggest 1 3/4 turns of tension for the second curtain adjuster, and 3 turns for the first. (Those are turns of the gears on the shaft ends, not of the adjusting worm screws themselves which would be many more turns).

Once you've added 1 3/4 turns to the second adjuster that should be sufficient. All further adjustment should be done with the first curtain until a balanced exposure across the gate is achieved.

If you take a step back this all makes sense. At the faster times the exposure is controlled by altering the slit for each speed. If that is not right the slit can be adjusted. But it's impossible to adjust a slit that changes across the gate. Hence; curtain tensions are calibrated to get the exposure consistent. Release timing is then calibrated to alter the slit, and get the exposure accurate.
Cheers
Brett

 

[tony.m]

That makes sense. Thanks!