Build a shutter tester for Focal Plane shutters - Cheap, Easy & it Works

[Niglyn]

Hi, you need to select ESP32 Dev Module.

Your screenshot is showing it is not recognising the board. The latest update to Arduino IDE seems to have caused the issue.

 

[pierre69]

I have changed "NodeMCU-32S" to "ESP32 Dev Module" and now everything works fine ! Thank you very much !
In the PDF file "5_ESP32 Arduino IDE software load", page 3, it is recommanded to select "NodeMCU-32S". That's why I was wrong. I don't understand...

 

[Niglyn]

Hi, the first part of the document says to use Nano and baud rate 460800. Which works fine.

It is only for advanced users wishing to progress to programming their own boards that loading of the ESP32 definitions are required.

This worked fine until this week when the latest Arduino IDE build broke the use of NodeMcu-32s.

Sorry for the problems you encountered. Github and Instructables have been updated.

 

[pierre69]

It was a very small problem ! ;-)
Thank you for your help !

 

[Niglyn]

Latest version, 3_0_8_9 will be on github soon.
No changes to the measuring engine, but plenty of tweaks elsewhere.

Pressing Black button when the splash screen shows, will jump straight to the testing screen.

When in the alignment utility, one can return immediately by pressing the Black button, rather than having to wait 5 seconds for the LCD to change from button function display, to alignment display.

When returning from the averages screen, rather than a zeroed display, the last test reading is again shown on TFT & LCD.

LCD now shows averages from all three sensors.

When using the LED matrix shutter tester, pressing the Green button will jump straight to the next speed, rather than waiting for the display to scroll through.

Additional error checks & warnings displayed. These include shutter capping, exposure imbalance and detecting LED flicker, (which plays havoc with the sensors)

When a bad reading has been taken (LED flicker, or one sensor tripped by strong ambient light) rather than a zeroed display, the data is shown. Which can help if it is a genuine reading & the camera is that bad! (Pin-holes in the blinds, or big imbalance in the three exposure readings for example).

Flash testing improved with descriptive output.

TFT and PC screen now also show raw (uncalibrated) values from the sensors, This can help if you have a really worn and sticky/juddery shutter mech. Also demonstrates the issue of sensor width & how cheap (hell this is free!) or single sensor testers will cause huge measurement errors.

TFT & PC screen now show curtain travel speeds for full and half travel. This highlights slow to get started curtains or if the springs are running out of puff towards the end of travel.

That's all I can think of for now. )
Happy for any feedback, for other change suggestions or photo related project ideas.

 

[Niglyn]

Three photos below.
First shows camera under test, using rear-mounted sensors (masking tape holding it in position ) and a cheap Aliexpress LED light source.
Note LED light must be on full. If dimmed, it uses PWM which pulses the LEDs on & off thousands of times a second, which will give LED flicker warning on tester.
Note flash sync cable connected to side of the camera.

Next picture is of the TFT screen showing changes, removal of uS values to make space for uncalibrated senor reading (first reading on the screen)
and
curtain travel speed from right to middle then middle to Left (L-M M-R) for each curtain.
I hope that makes sense?

Third photo is a screen grab, showing output on the PC screen.

 

[simplex]

This thread actually made me sign up to the forum. Looks great to me, though a haven't read all the posts yet.
At the moment, I have around a dozen SLR cameras from the 1960's / 1970's in my drawer and would really love to test their shutter speeds.
When browsing other forums on this topic, what puzzled me most is the discussion of whether it's needed to have a dual sensor or a single sensor device for our measurement.
In my understanding, once we have a light source that's close enough to an ideal point source aiming at our receiver we should do fine with only one emitter & receiver and achieve valid results.
Am I missing the point? I'm here to learn and discuss, so please correct me if I'm wrong.

 

[Niglyn]

This thread actually made me sign up to the forum. Looks great to me, though a haven't read all the posts yet.
At the moment, I have around a dozen SLR cameras from the 1960's / 1970's in my drawer and would really love to test their shutter speeds.
When browsing other forums on this topic, what puzzled me most is the discussion of whether it's needed to have a dual sensor or a single sensor device for our measurement.
In my understanding, once we have a light source that's close enough to an ideal point source aiming at our receiver we should do fine with only one emitter & receiver and achieve valid results.
Am I missing the point? I'm here to learn and discuss, so please correct me if I'm wrong.

Hi Simplex,
I'm Sure icracer will also have some input, as he has studied this subject as well.

Simply put, no a single sensor will not work.

Most home-brew or DIY shutter testers found on t'interweb and quite possibly ones available for purchase, whether they have one or two sensors will also be inaccurate at higher speeds.

Visit youtube for slow motion shutter videos. You will then see how a focal plane shutter works.

The shutter actually always operates at the same speed. There are two curtains. The first opens, travelling right to left (viewed from behind) and then the second curtain closes, travelling right to left.

When cocking the shutter, the two curtains are wound back to the start position.

Now the magic. The second curtain is released at a different time, depending on 'shutter speed'. For example at flash sync speed, the first curtain will fully open before the second curtain starts to close. The entire negative is exposed to light.
At the next higher speed, the second curtain is released when the first curtain is half-way open. So only half of the negative is exposed to light. As both curtains continue their travel right to left, it exposes the rest of the negative.

At the next higher speed, the second curtain will start to close when the first has travelled 1/4 of the way. At the next higher speed 1/8 and so forth.

So what the shutter is actually doing, is making a narrower and narrower slit between the two curtains, as the 'speed' increases. The curtains always travel at the same speed. It is the different widths that change the exposure.
The slit width must be constant, to give even exposure across the frame. If it gets wider or narrower as it travels, it will give more or less exposure to that part of the film.

So, what does all of this mean?

Simply put, a single sensor will not be able to measure the exposure difference across the frame. It may be ok at one end of the travel, but not at the other. A shutter curtain mech gummed up with solid grease would cause a slow start, for example, causing over-exposure at the start, but be ok once it is moving, so exposure maybe ok at the other end. Worn springs may also cause a curtain to slow down towards the end of travel, again creating exposure imbalance.

Many service manuals specify the travel time each curtain should take. If this is correct, exposure will be correct. This cannot be measured with one sensor (imagine trying to time a 100 metre runner by starting the stopwatch at the start, but not at the end)

Now you would think this enough, but no....
We are trying to measure a photon's width. However, light sensors are far wider. Sensors may start timing when they see the first chink of light on one edge, but not stop seeing it until the light has passed over the sensor and is now at the far edge. So we have measured the time the slit in the curtain has passed the sensor AND the time it took to move over the whole measuring window of the sensor.

Why does this matter?
Well remember the slit width getting smaller with each increase in shutter 'speed'?
A camera with a flash sync of 1/30s will fully open the shutter at 1/30s. So a slit of 36mm wide.
at 1/60s the second curtain will start to close when the first curtain has only travelled half way, a slit of 18mm.
At 1/125s (actually it is 1/120s) second curtain will start to close when the first curtain has travelled a quarter of the way, 9mm.
At 1/250 (1/240s), it will be 4.5mm.
At 1/500s (1/480s) 2.25mm.

As both sensor width and slit width is measured, at 1/30s, the ratio (assuming a 1mm sensor window) is 1:30
at 1/500s the ratio is 1:2

So, the ratio is insignificant at low @speed' one gets 1/30th of the shutter 'speed' added, but
at 1/500s we see we get 1/2 added, or 50% inaccurate speed measurement.

Yikes -
So what do we do? (build my shutter tester it works )
We could use a mask in front of the sensor with a pin-hole and a very strong light. A mask does help, but we get diffraction at small values. It is also a right pain to align.

We could use multiple sensors to take readings during the shutter test & use some maths to sort it all out.

Or, use both )
The sensors I specify have a lens and a narrow light acceptance angle (assuming ambient light is not too strong) so that sorts the mask. A physical mask can be assed, with a hole diameter of 1mm. I use this in the film-gate mounted sensor box.

Next is the maths. My tester takes twelve separate measurements during the shutter test. It then uses these to compute the sensor-width:slit-width. From this, a computed shutter 'speed' can be given.

Even with my method, it is not fool-proof. It is assumed the curtain moves linearly. The curtain has to start from zero and accelerate up and then at the other end, it maybe slowing down due to worn or mal-adjusted springs, or still accelerating. The second curtain may do the same, or the exact opposite!

My code has numerous error-checks to look for sticky & slow curtains, shutter bounce etc, to warn the user. It is pretty obvious when looking at the readout, if the shutter mech is really out of alignment. Once the shutter mech is adjusted & starts coming into spec, the readings will give the correct results.

 

[simplex]

Simply put, no a single sensor will not work.

First of all: thank you so much for taking the time to answer my question in such detail. Very much appreciated! For the very first time, somebody gave me an explanation that at least brings me close to understanding the topic. From the quality of your answer I assume that you do not only design electronics, but also teach the subject?

So what do we do? (build my shutter tester it works )

That's exactly the plan. First I'll browse the rest of the thread in order not to miss more recent developments, and then I'll scan my smallish hobby department for required parts. Most should already in stock.

Regarding your Arduino code: since I'm a new member, I can't send you a PM yet to ask for a copy. But it's well possible that I will gain the required number of 20 posts until the stuff arrives. There's much interesting stuff in this forum to discuss.

 

[Niglyn]

First of all: thank you so much for taking the time to answer my question in such detail. Very much appreciated! For the very first time, somebody gave me an explanation that at least brings me close to understanding the topic. From the quality of your answer I assume that you do not only design electronics, but also teach the subject?


That's exactly the plan. First I'll browse the rest of the thread in order not to miss more recent developments, and then I'll scan my smallish hobby department for required parts. Most should already in stock.

Regarding your Arduino code: since I'm a new member, I can't send you a PM yet to ask for a copy. But it's well possible that I will gain the required number of 20 posts until the stuff arrives. There's much interesting stuff in this forum to discuss.

Hi, all the code and all the build materials, with links to aliexpress, and instructions can be found on my github.

GitHub - billbill100/Camera-Shutter-tester-Cheap-Easy-it-Works: Arduino / ESP32 based shutter tester using three lasers. This allows for correct focal plane curtain speed adjustment & even exposure across the frame.

Arduino / ESP32 based shutter tester using three lasers. This allows for correct focal plane curtain speed adjustment & even exposure across the frame. - billbill100/Camera-Shutter-tester-Cheap...

github.com

select:-
Camera-Shutter-tester-Cheap-Easy-it-Works

I would suggest building the ESP32 version, not (Arduino nano). Click on ESP32 and read all the documents. They are numbered in the order they should be followed.

Look at the file ESP32_Shutter_Tester minimum_3.1.8_schematic.pdf
As this is the simplest version to build (unless you are familiar with electronic tinkering) it omits the tft & LCD screens and other bits. All output is displayed to the computer screen. (Personally, I find looking at the PC screen easier than the tft)

You can add the extra parts on at a later date, if you wish. Or go for the full build straight off )

Please keep us updated on your build. As per the rules, a photo of the finished project is required )

 

[RMN]

Made an account to post in this thread as I recently decided to make a shutter speed tester. I have even bought a four pack of the laser emitters and detectors used by Niglyn. I was going to just use one sensor because I wasn't considering some of the things Niglyn posted about at higher shutter speeds.

What I need is to confirm the shutter speeds on a Nikon FE that I repaired. The camera is in perfect cosmetic condition but had a lazy light meter that hovered around the middle of the range in all light conditions. Not sure what I did to fix it but something must have connected/disconnected while I was probing the light detector diodes with a multimeter and the light meter is back to normal (yay!). My issue is that I also moved one of the pots that control shutter speed while doing this (boo!). The Nikon FE/FE2 repair manual clearly states how to adjust that pot based on shutter speed and EV value.

A few questions.

1. What the heck is EV(x)? Is EV14 the light level that causes the light meter to move to the 14th position (In my case 1/1000)? In the github, its mentioned the LED light box gives EV13. Is that specific to a particular camera or is that universal?
2. If my shutter moves vertically, can I just use the laser emitter/detector instead of the light box? And would I put the light sensors one on top of the other centered in the frame?

 

[MattKing]

What the heck is EV(x)?

Welcome to Photrio.
EV stands for Exposure Value, and with some wrinkles factored in, relates to a quantity of exposure required for a particular light level.
Assuming a sensor/film of a particular sensitivity, a particular EV represents all the shutter speed and aperture combinations that give the same amount of exposure.
Most commonly, EV numbers are quoted in relation to a sensitivity of ISO 100, but there is nothing that absolutely requires that choice - it is a convention.
Each change of EV number by one represents an increase or decrease by one stop of exposure.
This article isn't perfect, but it might help: https://en.wikipedia.org/wiki/Exposure_value

 

[Niglyn]

Made an account to post in this thread as I recently decided to make a shutter speed tester. I have even bought a four pack of the laser emitters and detectors used by Niglyn. I was going to just use one sensor because I wasn't considering some of the things Niglyn posted about at higher shutter speeds.

What I need is to confirm the shutter speeds on a Nikon FE that I repaired. The camera is in perfect cosmetic condition but had a lazy light meter that hovered around the middle of the range in all light conditions. Not sure what I did to fix it but something must have connected/disconnected while I was probing the light detector diodes with a multimeter and the light meter is back to normal (yay!). My issue is that I also moved one of the pots that control shutter speed while doing this (boo!). The Nikon FE/FE2 repair manual clearly states how to adjust that pot based on shutter speed and EV value.

A few questions.

1. What the heck is EV(x)? Is EV14 the light level that causes the light meter to move to the 14th position (In my case 1/1000)? In the github, its mentioned the LED light box gives EV13. Is that specific to a particular camera or is that universal?
2. If my shutter moves vertically, can I just use the laser emitter/detector instead of the light box? And would I put the light sensors one on top of the other centered in the frame?

Hi, thanks for joining the forum to let me know you are making the tester, Please post a photo of your finished design.

Yes, stack the sensors vertically, centred is fine & makes alignment easier than diagonal. Spacing should be 20mm between the top and bottom sensor.

The light box I randomly purchased on aliexpess, gives me a reading of EV13. A brighter light would give a higher EV.
A bright sunny day would be EV16.

The EV chart is printed in the instructions for the tester, for iso 100. It is also displayed on the tft.
The light sensor used has a stated uncalibrated accuracy of 20%,

To use the light sensor, a light is shone on it & note the EV value. shown on the tester, e.g EV13
Now set the camera iso to 100.

Shining the same light into the camera should also give a reading of EV 13. As cameras work in f/stop and shutter speed, one would see 1/1000s f/2.8 or any other equivalent e.g 1/500s f/4 or 1/60s f/11

 

[ic-racer]

This software has spawned the creation of some very nice shutter testers!

 

[Niglyn]

This software has spawned the creation of some very nice shutter testers!

Hi, yes some nice examples have been built, but nothing so-far beats the Lego )

I wonder how many have been built but the builder have not posted on here?
Maybe I should add an activation code, so it will not run until the builder has posted on here & I send them the code )

I'm happy for ideas for changes and/or additions. I'm thinking about adding an option to have the screen in portrait with large text.
It would only show basic details, but much easier to read.

 

[RMN]

Thanks for the info MattKing and Niglyn. The shutter tester gets me half way but I'm still unsure about producing EV light values and could use some tips.

Below is the Nikon repair manual on the adjustment of the potentiometer i messed with. The pot is correct once (a) and (b) result in the same shutter speed.

What's the most reasonable way to To get EV4 and EV14 at home? For example for EV4, do I use a known-good camera, set set ASA to 100, set shutter speed to 1/4sec and f=2.0 then increase the light until the meter matches that setting. Or do I get an external light meter?

 

[Niglyn]

Thanks for the info MattKing and Niglyn. The shutter tester gets me half way but I'm still unsure about producing EV light values and could use some tips.

Below is the Nikon repair manual on the adjustment of the potentiometer i messed with. The pot is correct once (a) and (b) result in the same shutter speed.

What's the most reasonable way to To get EV4 and EV14 at home? For example for EV4, do I use a known-good camera, set set ASA to 100, set shutter speed to 1/4sec and f=2.0 then increase the light until the meter matches that setting. Or do I get an external light meter?


View attachment 373062

Hi, A professional tester has a calibrated light source that you can adjust to different EV settings. This of course does require that he owner get the tester regularly calibrated, as light sources loose luminosity as they age.

What this nikon process is doing, is setting the light-meter calibration, so it is equal at both ends of the scale, rather than over-reading at one end and under-reading at the other.

An alternate diy method would be to get a light-meter. They are very cheap on aliexpress or ebay. But the display is in Lux. A simple calculation will give you EV and you only need to find EV 14 and 4.

Next, find an adjustable light source. A table lamp with a dimmer, for example. Adjust it so the light-meter shows the Lux equivalent of EV14. Set the camera as per a) and see what the shutter speed is.
Adjust the lamp to give a light output of 4EV and repeat the process for the b) settings.

 

[canaq]

Three photos below.
First shows camera under test, using rear-mounted sensors (masking tape holding it in position ) and a cheap Aliexpress LED light source.
Note LED light must be on full. If dimmed, it uses PWM which pulses the LEDs on & off thousands of times a second, which will give LED flicker warning on tester.
Note flash sync cable connected to side of the camera.

Next picture is of the TFT screen showing changes, removal of uS values to make space for uncalibrated senor reading (first reading on the screen)
and
curtain travel speed from right to middle then middle to Left (L-M M-R) for each curtain.
I hope that makes sense?

Third photo is a screen grab, showing output on the PC screen.


View attachment 372455

It's been a while since I visited this forum and unfortunately the build of my tester has been on hold for a while. Now I see your picture with the LED light source and the sensor box, I find this a very interesting option (I was messing around with the alignment of the lasers the whole time). Can I just follow the entire build guide and leave out the lasers (this will then be replaced by the LED)? And if I'm going to use the TFT screen, can I just leave out the LCD screen? Sorry if these are dumb questions, been out of the loop for a while

And as for the sensor box, it might be an idea to 'steal' the box from srozum's project and 3D print this:

 

[Niglyn]

Hi,


Yes you can leave out the Lasers and replace them with a light source and film gate sensor box.
Yes, the TFT and LCD are both optional, so you can leave out the LCD screen.

There is a post within this thread by someone saying hardware in srozum's project is open source, but I will not comment on the use of his parts for mine.

It would be nice if somebody with a 3d printer & skills were to make a film-gate box for use with my tester and share the files, maybe even a project box, in return & appreciation for the hours I have spent building & sharing my project, writing all the documentation etc.

The light source used must not be using PWM to dim it. The light source shown in my parts list is PWM, but at full brightness runs at 100% PWM so works fine if turned to full brightness and the colour wheel is also turned fully up.







..

 

[canaq]

Hi,


Yes you can leave out the Lasers and replace them with a light source and film gate sensor box.
Yes, the TFT and LCD are both optional, so you can leave out the LCD screen.

There is a post within this thread by someone saying hardware in srozum's project is open source, but I will not comment on the use of his parts for mine.

It would be nice if somebody with a 3d printer & skills were to make a film-gate box for use with my tester and share the files, maybe even a project box, in return & appreciation for the hours I have spent building & sharing my project, writing all the documentation etc.

The light source used must not be using PWM to dim it. The light source shown in my parts list is PWM, but at full brightness runs at 100% PWM so works fine if turned to full brightness and the colour wheel is also turned fully up.







..

Thanks Niglyn!

I guess there is no need in designing a new film-gate box for your tester, we can use the one from srozum's project, all the 3D printer files (STL) are on his Github. I understand that you don't want to be dependent on someone else's project, but there is also no need to reinvent the wheel
And all your work for this project is much appreciated!!

 

[alinCiortea]

I'm close to completing the build of the shutter tester and I have a couple of questions regarding the wiring before firing it up...

There are some differences between what's written on my extension board and the drawing from the PDF. For instance, in the schematic between Pin 12 and pin 13 there's a pin named VB. On my board there's a GND (and judging by what wires connect to that pin it makes sense to be a ground pin).
Other differences don't involve used pins (on my board, on the lower right side from bottom to top, I have CLK, SDO, SD1, P15 - instead of the 06, 07, 08, 15 on the schematic. On the left side, bottom to top, I have 5V, GND, SD3, SD2, P13, GND, P12 - instead of the IN, 11, 10, 09, 13, VB, 12 on the schematic and on the left top side I have SVP and SVN instead of 36 and 39)

If you could just confirm that I've wired correctly and VB = GND...

 

[Niglyn]

I'm close to completing the build of the shutter tester and I have a couple of questions regarding the wiring before firing it up...

There are some differences between what's written on my extension board and the drawing from the PDF. For instance, in the schematic between Pin 12 and pin 13 there's a pin named VB. On my board there's a GND (and judging by what wires connect to that pin it makes sense to be a ground pin).
Other differences don't involve used pins (on my board, on the lower right side from bottom to top, I have CLK, SDO, SD1, P15 - instead of the 06, 07, 08, 15 on the schematic. On the left side, bottom to top, I have 5V, GND, SD3, SD2, P13, GND, P12 - instead of the IN, 11, 10, 09, 13, VB, 12 on the schematic and on the left top side I have SVP and SVN instead of 36 and 39)

If you could just confirm that I've wired correctly and VB = GND...

HI, yes VB = GND

Unlike Arduino, there is no set standard for ESP32 development boards.
Sometimes they are marked with their function, rather than pin number, pin 36 is SVP and pin 39 is SVN, for example.

There are also an array of different boards, with different pin spacing and number of pins. I used the NodeMCU32 38 pin version simply because it was the only board that had a matching 38-screw-terminal breakout board.

Note where you say "On the left side, bottom to top, I have 5V, GND, SD3, SD2, P13, GND, P12 - instead of the IN, 11, 10, 09, 13, VB, 12"
11 is NOT GND it is CMD. Do not use it as a Ground connection. Same is true on the right side, where a pin is incorrectly labelled as GND.

 

[alinCiortea]

The GND pins were easy to find and confirm. I'm done wiring the tester (the TFT, film gate only version) but something is not working. The TFT lights up but shows nothing. I've rechecked all connections and everything seems fine (I've used your wiring chart as reference). Obviously I have no idea where to look next... (firmware was flashed without incidents, all parts were ordered from aliexpress through the links you provided, so the board should be the same as yours)

 

[VirtualFeature]

Even with my method, it is not fool-proof. It is assumed the curtain moves linearly. The curtain has to start from zero and accelerate up and then at the other end, it maybe slowing down due to worn or mal-adjusted springs, or still accelerating. The second curtain may do the same, or the exact opposite!

I was just thinking about this from a software point of view, and thought I'd make a suggestion for "linearity testing" that could be used for a readout of some kind.

Having a simple readout of the deviation between sensor points would be very useful. Using the data you've already acquired would make this easy. A, B and C points when light has been detected, as well as A, B, and C points when light has stopped being detected. This will tell you at what ms the opening shutter reached the pionts, and at what ms the closing shutter reached the points. You can just check the delta between the points to determine in ms (or any other metric you like, really) how much faster the shutter is moving on one side than the other.

If you have a known working, fully accurate camera, you could even make a simple lookup table for "acceptable acceleration boundaries" to give a readout if the curtain trajectories are out of spec. eg, according to the table, an acceleration of 0.20ms between points is acceptable, as the curtain races to the end - but the actual reading states that the A to B points were 0.20ms, but the B to C points were 0.35ms, indicating that the shutter was slowing down as it approached the end of its travel. This would indicate a non-linear acceleration and something amiss. More sensors (5 instead of 3 for instance) would improve accuracy.

But, I might not know what I'm talking about

Edit: I realised some of this information is, in fact, already displayed on the larger LCD versions, but my idea still stands for interpreting the acceleration and displaying the linearity!

 

[Niglyn]

I was just thinking about this from a software point of view, and thought I'd make a suggestion for "linearity testing" that could be used for a readout of some kind.

Having a simple readout of the deviation between sensor points would be very useful. Using the data you've already acquired would make this easy. A, B and C points when light has been detected, as well as A, B, and C points when light has stopped being detected. This will tell you at what ms the opening shutter reached the pionts, and at what ms the closing shutter reached the points. You can just check the delta between the points to determine in ms (or any other metric you like, really) how much faster the shutter is moving on one side than the other.

If you have a known working, fully accurate camera, you could even make a simple lookup table for "acceptable acceleration boundaries" to give a readout if the curtain trajectories are out of spec. eg, according to the table, an acceleration of 0.20ms between points is acceptable, as the curtain races to the end - but the actual reading states that the A to B points were 0.20ms, but the B to C points were 0.35ms, indicating that the shutter was slowing down as it approached the end of its travel. This would indicate a non-linear acceleration and something amiss. More sensors (5 instead of 3 for instance) would improve accuracy.

But, I might not know what I'm talking about

Edit: I realised some of this information is, in fact, already displayed on the larger LCD versions, but my idea still stands for interpreting the acceleration and displaying the linearity!

Hi Virtual,
Thanks for adding your comments & thoughts to the thread. All are most welcome.
Taking A, B & C as Right, Middle & Left sensors,

Point A would always be 0ms, as that is when the tester sees the first change and starts measuring.
Time between A and B is shown as first curtain travel first half.
Time between B and C is shown as first curtain second half.

This is then repeated for second curtain.
The total travel time A to C is shown as curtain travel speed.

Exposure at A, B and C is shown, as well as deviation from centre (as a 'professional' tester would)
and also the tester guess what speed the camera has been set at and shows deviation from this nominal speed.
Currently it guesses separately at A B and C, so could guess different exposures, but I may change this, so it only guesses for B.

I don't know if people find all of the data shown on the tft, useful or if they just look at the larger summery at the bottom?
The details could be removed and replaced with something different.

So all the data is there, if you have an idea for displaying it differently, draw a sketch & I can implement it
Something like the below?


A-----12mS------B--------8mS-------C

1/30 1/26 1/38

A-----18mS-----B---------14mS------C