Shutter Speed Testing Focal Plane Shutters

[ic-racer]

Amazing the technology available to anyone today.

 

[albada]

I tested three different sensors and found this the be the best of them: Vishay BPW76

The spec's in the datasheet for this phototransistor (Vishay BPW76) look good. And it's cheap enough that buying a few won't empty the bank. Thanks.
And you're right about "Amazing the technology available to anyone today." Even the humble 8-bit microcontroller is amazing compared to what we had in the 1970's.

 

[snusmumriken]

Thanks for the link, it details the shutter tester i was describing on a previous post above.

Also, check out this British Intelligence report:

35. The timing of the fast range of the shutter is carried

out with the aid of a stroboscope of somewhat antique design.

By means of this the 1/200, 1/500 and the 1/1000 speeds are

checked. The stroboscope consists of a revolving drum placed

horizontally, with 33 horizontal slits in its surface,

illuminated from inside by a lamp of approximately 20 watts.

The drum is driven by a belt from an electric motor which may

be controlled by a rheostat. The drum is also coupled to a

speedometer in order that its speed may be set. The correct

speed for the drum to rotate at was 280 r.p.m. The camera

is held on a wooden block in such a manner that the light

from the rotating drum falls on the blinds of the focalplane

shutter. The shutter is then fired and a series of

stroboscopic lines are seen in the aperture. If the shutter

is correctly set these lines appear vertically but if the

shutter is incorrectly set the lines will curl down either to

the left or to the right according to whether the shutter is set

too slow or too fast.

36. The checking of the lower speeds was only carried out

on the 1/20 second and 1/4 second settings by means of a

revolving series of lights. The various speeds of the shutter

were not accurate to the measurements on the shutter control

knob and this fact was acknowledged by the Leitz executives.

who pointed out, however, that the results obtained were quite

good enough for all general requirements.

37. A metronome was used in checking the one second

escapement.

Source:

LEITZ INVESTIGATED BY BRITISH INTELLIGENCE 1946

I don't understand this description, even after viewing the other links. How does one see any pattern if the shutter is open for only 1/1000 sec? Can the eye recognise the pattern in so short a time? Please can someone explain?

BTW, this is a fantastic thread, and very timely for me (excuse pun) because I was just contemplating building a tester myself. I found several electronic designs (and code even) 'out there', and actually those aspects are not terribly difficult. But rather than addressing the puzzling issues identified here, they all seemed to hope they wouldn't be a problem.

 

[reddesert]

I don't understand this description, even after viewing the other links. How does one see any pattern if the shutter is open for only 1/1000 sec? Can the eye recognise the pattern in so short a time? Please can someone explain?

A correctly operating focal plane shutter at 1/1000 uses a traveling slit to expose any given part of the film for only 1/1000 sec, but it takes the sync speed (often 1/60 or even 1/30 sec) for the slit to travel across the entire width of the film gate. The Leica shutter tester for a horizontally traveling shutter illuminates it with a vertically traveling slit light source, so you see the combination of the two slits; it's very clever. (To use it with a vertical FP shutter one would have to turn the camera sideways).

The human eye will see this as a single pattern due to the limited time resolution (persistence) of vision. You can see that by looking through a shutter fired at 1/1000: you see the full scene rather than perceiving the motion of the slit.

BTW, this is a fantastic thread, and very timely for me (excuse pun) because I was just contemplating building a tester myself. I found several electronic designs (and code even) 'out there', and actually those aspects are not terribly difficult. But rather than addressing the puzzling issues identified here, they all seemed to hope they wouldn't be a problem.

Basic shutter tester designs just test how long the shutter is open for (the Photoplug, like the homemade version I made, plus the Shutterspeed phone app is a simple way of making one with minimal electronics). This is generally fine for leaf shutters, where the mechanism is fairly uniform and any non-uniformity is not in focus at the film plane.

For focal plane shutters, a true professional setup has to also detect non-uniformity or premature opening/closing caused by timing or speed differences between the curtains.

 

[ic-racer]

I don't understand this description, even after viewing the other links. How does one see any pattern if the shutter is open for only 1/1000 sec? Can the eye recognise the pattern in so short a time? Please can someone explain?

BTW, this is a fantastic thread, and very timely for me (excuse pun) because I was just contemplating building a tester myself. I found several electronic designs (and code even) 'out there', and actually those aspects are not terribly difficult. But rather than addressing the puzzling issues identified here, they all seemed to hope they wouldn't be a problem.

Keep us posted. There are a number of designs that will measure light, but interpreting the results in waveforms challenging. "Black Box" systems are not without their own problems. For example the Calument tester, which is a "Black Box" design, not showing any waveform of the sampled light, needs to be setup just perfect to get the same response they used to calibrate the thing.

 

[ic-racer]

Here are links to resources on focal plane shutter testing.

This one is good, but is a little out dated in that modern devices like AD converters for computers and high speed digital cameras are not mentioned. The trick with a CRT TV is good, but...those are all but extinct. Harder to find than a proper oscilloscope

https://pentax-manuals.com/manuals/service/focal%20plane%20shutters.pdf

Another one here:

https://learncamerarepair.com/downloads/pdf/NatCam-SingleLensReflex.pdf

Of course try to find the manual for the camera of interest, but sometimes these are very sparse. Like most Rollei manuals.

I found the Rollei SL35 is a copy of an early Pentax, and the Pentax manual has more explanation of what things do.

 

[snusmumriken]

Thanks @reddesert and @ic-racer, wonderfully helpful.

 

[snusmumriken]

Is the green screen on the Leica device likely to be phosphorescent, to reduce the dark phases of the strobe?
I am pondering whether one could use PWM in the light source to achieve a similar effect. Electronics is a lot easier for me than metal-working!

 

[Light Capture]

Is the green screen on the Leica device likely to be phosphorescent, to reduce the dark phases of the strobe?
I am pondering whether one could use PWM in the light source to achieve a similar effect. Electronics is a lot easier for me than metal-working!

I believe that you need moving slit effect. CRT TV's form picture line by line by shooting the beam. Leica device will move slits across the frame.
Green screen appears to be only to make the light green and possibly more visible and I don't think it affects usability.
Metal strips could be spaced on a wheel and it could also be 3d printed. Rotating drum can be driven by a stepper and speed can be quite easily controlled to desired rpm.
I'm planning to make one myself since my CRT is gone.

Camera with high fps will help measure curtain travel precisely and observe if there's any bounce or other undesirable effects.
Camera and the testers isn't really a must but if there are issues, it helps establish correct speed and compare speeds and accelerations of both curtains.

If there is an intermittent issue where there is an artefact every 10-20 or 100 shots, Leica rotating drum is the best to evaluate.

 

[snusmumriken]

Camera with high fps will help measure curtain travel precisely and observe if there's any bounce or other undesirable effects.

I looked into ultra slo-mo apps available for iPhone. I could only find one, which achieved nine hundred and something fps by a process called ‘optical flow’. That sounds to me like interpolation, which could be unhelpful in our context? I wouldn’t be surprised if fast frame rates always involve such a process unless one uses highly specialised kit.
A couple of years ago I needed to record the action of some mechanical kit for my work, and was advised by a genuine slo-mo physicist that among consumer devices a GoPro achieved the fastest genuine fps, when set at its lowest resolution.

 

[Light Capture]

I looked into ultra slo-mo apps available for iPhone. I could only find one, which achieved nine hundred and something fps by a process called ‘optical flow’. That sounds to me like interpolation, which could be unhelpful in our context? I wouldn’t be surprised if fast frame rates always involve such a process unless one uses highly specialised kit.
A couple of years ago I needed to record the action of some mechanical kit for my work, and was advised by a genuine slo-mo physicist that among consumer devices a GoPro achieved the fastest genuine fps, when set at its lowest resolution.

Nikon V1 I have achieves real 1200fps but resolution is very low at 320x120. It's still plenty to evaluate shutters. I got the whole kit in local classifieds for less than $200 few years back. They do appear for sale relatively often. It needs a lot of light at 1200fps to produce bit cleaner video. It will still be grainy.
There should be other cheap cameras with high fps.

 

[ic-racer]

Working presently on a modification of my tester to get a better indication of curtain speed.

I'll be using two lasers and a single receptor. Keep It Simple technique; all I have to add to the system is a second laser pointed at the sensor.

As the slit passes each laser if forms a waveform evident with the computer recording software. The distance between waveforms is the travel time and the distance between the two red laser dots on the shutter curtain is the distance traveled. An easy calculation of speed.

 

[ic-racer]

I can't update the original post, but I wanted to point out the speeds indicated are 'nominal' speeds.
For example a 2.25mm slit width produces a shutter speed of 1/960th second rather than 1/1000. The error is 4% only. This is less than 1/16 of a stop. The acceptable error for a 1/1000 shutter speed is +/- 30%.

 

[Alan Edward Klein]

Curious. Cameras have sync modes for strobe that flash off the front and rear curtains. Can you attach probes to a scope to measure using these?

Second, my Nikomat FT3 can sync up to 1/125th second for flash meaning both curtains are open for quicker shutter speeds than many other cameras that only sync to 1/60th at the most. How this effects measurements I'm not sure but I wanted to pass this on.

 

[ic-racer]

Watching the frame when firing a flash is usually not useful for setting a speed, but it is very helpful for serious problems.

At 1/60 (or whatever synch speed) if the whole frame is not visible you can get clues to what is messed up.
Then as you go up the speeds to 1/1000 you should see a nice progression of 1/2, 1/4, 1/8th of the frame closed off.
Measuring the 2.25mm width is not really possible because, usually the synch is set to fire the flash just AFTER the opening curtain hides behind the film gate, just to ensure it is totally out of the picture when the flash fires. So, sometimes at 1/1000 you may only see a tiny slit or no light at all.

If I don't see this progression, then it is not even worthwhile to setup the shutter tester as the camera still needs work or was put back together wrong.

If you have access to the synch mechanism, and set it so it flashed just BEFORE the first curtain reached the end, it seems one could then observe the 1/1000 slit in its entirety and probably measure it's width as you see the flash. I have not done this but I bet it would work.

 

[Bill Burk]

I guess I could glue a tag to the opening curtain to measure that

 

[henryvk]

Here are links to resources on focal plane shutter testing.

This one is good, but is a little out dated in that modern devices like AD converters for computers and high speed digital cameras are not mentioned. The trick with a CRT TV is good, but...those are all but extinct. Harder to find than a proper oscilloscope

Interesting. I'm a bit into vintage computers so I have an old EIZO 14" CRT monitor. The premium brand older CRTs are getting hard to find but where live you can still find any number consumer grade 17" monitor in the classifieds either for free or very cheap.

Anyway, I use the 14" CRT monitor for focal plane shutter testing. I plug it into an old netbook, set it to 60 Hz, pull up MS Paint for a white background and fire away with the camera. Checking that the curtains run parallel works very well with this method, as for speed, I'm not sure. I *think* I can tell the size of the slit accurate enough to know when something's off. My cameras only go up to 1/500th, so maybe that makes it less of an issue.

 

[ic-racer]

Checking that the curtains run parallel works very well with this method

Yes, that is the important part. It is easy to compensate with the aperture if the speed is a little off, but burning or dodging a negative that is too dark or light on one side is very challenging. In fact, that is how I got into shutter repair; trying to figure out why some negatives taken at a beach were too thin on one side and the challenges of printing them.

 

[henryvk]

Yeah, I had the same issue with my FED 5C. At 1/500th there was some shutter bounce, a narrow overexposed strip at the far edge of the negative. Not in every frame, though, since the orientation of the camera actually also plays a role, i.e. whether the curtains have to work "uphill" or not. You could actually see the shutter bounce back slightly with the naked eye if you held the camera up to a bright window.

Anyway, I reduced the tension on the 2nd curtain, I think, to cure this issue.. which produced a different problem where at 1/30th the shutter would behave like bulb. Not all the time either but again depending on the orientation of the camera. I had to tension the rollers back and forth, by quarter turns of the screws, to adjust it just so that there'd be no bounce on 1/500 and the shutter wouldn't get stuck open on 1/30.

I don't want to veer OT to much; suffice to say that each camera is a little different (the Soviet ones even more so) and I'd love to try out an electronic shutter tester some time.

Actually, this thread gave me an idea. I recently discovered that even my iPhone 6s has a high speed mode with 240 fps so maybe I'll try recording some shutter movement with it.

 

[Alan Edward Klein]

I've checked shutter speeds in large format lenses, medium format lenses, and 35mm camera electronic shutters. The 35mm were right on. The rest varied up to about 1/3 of a stop off up or down. The lens manufacturers state that their lenses are accurate to 1/3 of a stop.

I think once you check your shutter speeds and find that most are off a little, you'll drive yourself crazy trying to correct for each lens, each shutter, at each speed when you start shooting.

 

[ic-racer]

Yeah, I had the same issue with my FED 5C. At 1/500th there was some shutter bounce, a narrow overexposed strip at the far edge of the negative. Not in every frame, though, since the orientation of the camera actually also plays a role, i.e. whether the curtains have to work "uphill" or not. You could actually see the shutter bounce back slightly with the naked eye if you held the camera up to a bright window.

Anyway, I reduced the tension on the 2nd curtain, I think, to cure this issue.. which produced a different problem where at 1/30th the shutter would behave like bulb. Not all the time either but again depending on the orientation of the camera. I had to tension the rollers back and forth, by quarter turns of the screws, to adjust it just so that there'd be no bounce on 1/500 and the shutter wouldn't get stuck open on 1/30.

I don't want to veer OT to much; suffice to say that each camera is a little different (the Soviet ones even more so) and I'd love to try out an electronic shutter tester some time.

Actually, this thread gave me an idea. I recently discovered that even my iPhone 6s has a high speed mode with 240 fps so maybe I'll try recording some shutter movement with it.

Is there a 'brake' for that curtain? As I mentioned before, it seems the focal plane shutter info is scattered in various documents on the "Learn Camera Repair" site. This good description of setting the brake is in the K1000 guide:

 

[ic-racer]

I've checked shutter speeds in large format lenses, medium format lenses, and 35mm camera electronic shutters. The 35mm were right on. The rest varied up to about 1/3 of a stop off up or down. The lens manufacturers state that their lenses are accurate to 1/3 of a stop.

I think once you check your shutter speeds and find that most are off a little, you'll drive yourself crazy trying to correct for each lens, each shutter, at each speed when you start shooting.

Turns out of the four SL35 Rolleiflex I bought, all of them came into spec by just cleaning.
I did go ahead and make all the adjustments on one of the "Parts" cameras, do see what turning the screws would do. But wound up having each screw back in its original spot after I build the shutter tester.

In fact, there was no correlation at all between "good" or "bad" camera based on the price I paid for the cameras. The three "Parts" cameras, after repair, were just as nice as the $200 black German camera. In fact I got ripped off on that because it was a Singapore camera with a replaced black "Made In Germany" top.

 

[henryvk]

Is there a 'brake' for that curtain? As I mentioned before, it seems the focal plane shutter info is scattered in various documents on the "Learn Camera Repair" site. This good description of setting the brake is in the K1000 guide:

Yes, good point, when I encountered issues with focal plane shutters I mostly researched forums and repair guides (there's an excellent one for the Zorki 4K floating around and much of it applies to other Soviet RFs too) in order to find the relevant information. With the FED 5 there is indeed a shutter break which invites further tinkering when trying to adjust the shutter.

Being a Soviet camera there is no fancy adjustment screw for the break, though, you simply bend the metal flange in or out and hope for the best. If the break is too tight it also results in the shutter being stuck open on slower speeds. There's actually a thread on a similar issue with some pictures: https://www.photrio.com/forum/threads/fed-3-shutter-issues.188881/

Other factors that could potentially introduce drag and throw speeds off are old grease either on the rollers or the big gear at the bottom end of the curtain "drum" as well as on the speed selector shaft. Imo cleaning the gears and lubing probably should come first (as I think you learned with your Edixa, if memory serves) before one starts re-tensioning the curtains.

 

[ic-racer]

Good point that each shutter is a little different and each camera has a different method to test and adjust. One take home point of this thread is the build or obtain a shutter tester suitable to the camera under scrutiny. Post #6 is an excellent example.

 

[ic-racer]

So, the Rollei SL35 shutter travels faster than 1/60, so, at 1/60 the release cam does hold it open slightly. How is this so? It is because the shutter is specified to travel across the shutter tester sensors* in in about 10.9 to 11.4 milliseconds. That is faster than 1/60. Indeed it is about 1/85 of a second. So it needs to be slowed down and the closing curtain has to wait a little.

Other cameras do specify 16 milliseconds for the curtain to travel across, in that case the second curtain is released immediately as the first curtain reaches the other side to make 1/60th.

So, I was able to test this with a single sensor. I merely aimed TWO lasers at the single sensor. The distance between the laser dots on the curtain was measured ( for example 27.5mm) and the shutter fired at 1/1000. The software recorded two open/close cycles as expected. The time between them (0.00916 seconds) was recorded. This gave a shutter travel speed of about 10.8 milliseconds to travel 32mm which is my guess of the distance on the Rollei Shutter tester the factory uses.

*The Pentax factory shutter tester has sensors 32mm apart, so, since the SL35 is somewhat a copy, perhaps they used the same type of shutter tester.

This is from the Pentax manual: