ACST-35 Shutter tester



The built-in sensors are identified as follow :  
1> upper left corner  
2> centre  
3> lower right corner  

During the first test (TEST01), a reference speed is defined from the measure of the central sensor n°2 in order to compute the IL deviations of the three points compared to the speed scale selected (typically 1s, 1/2s, 1/4s, 1/8s, 1/15s, 1/30s, 1/60s, 1/125s, ...)

  • Exposure
Display of the shutter speed for the three sensors together with the IL deviations compared to the reference speed defined by the central sensor n°2 during the first test triggering (TEST01). 

At any time the test sequence, with a fixed reference speed, can be interrupted to define a new reference speed. 

R> reference speed 
1> speed sensor n°1 / IL deviation 
2> speed sensor n°2 / IL deviation 
3> speed sensor n°3 / IL deviation 

Exposure function example (picture) :
    • TEST01 measure on the central sensor: 1/50s
    • reference speed: 1/60s
    • exposure deviation central sensor (1/50s compared to 1/60s): +0.25IL
    • flash triggering: 7ms after the central sensor detection
    • flash activation covers 65% of the central sensor exposure

  • Curtains 
Display of the elapsed time (milliseconds) of ‘first curtain’ opening and the milliseconds deviation of the ‘second curtain’ closure. 

13> path from sensor n°1 to sensor n°3
(complete path of the curtains) 
12> path from sensor n°1 to sensor n°2 
23> path from sensor n°2 to sensor n°3 

Curtains function example (picture) :
    • reference speed: 1/60s
    • curtain opening path 1 to 3: 12.42ms (complete path of the curtains)
    • curtain closure path 1 to 3: 12.42ms + 3.28ms
    • curtain opening half path 1 to 2: 5.79ms
    • curtain closure half path 1 to 2: 5.79ms + 1.43ms

  • Flash 
Display of the elapsed time (milliseconds) between the flash triggering and the beginning of the central sensor n°2 exposure together with the ratio (%) of the flash activation during the central sensor n°2 exposure.
F> (flash triggering time - central sensor n°2 triggering) in milliseconds  
/ (flash activation with central sensor n°2 triggered / exposure time of central sensor n°2) in % 


A calibration menu allows adjusting, on a 2.25IL range, the threshold of the sensors triggering. This adjustment can be manual or automatic.
Three circles full or empty allow to vizualise the statuts of the three sensors during the calibration. 
An horizontal scale also gives the triggering threshold value.

  • Manual calibration 
Manual modification and simultaneous of the thresholds of the three sensors according to the ‘step’ selected in the configuration menu.
  • Automatic calibration
Automatic modification and independent of the thresholds of the three sensors. When the calibration is finished the triggering threshold is lower of the value selected in the configuration menu.
The setting defined by this calibration is maintained as long as the tester is powered but can be modified between two tests.


Note : The automatic calibration mode associated to a lowering of the sensitivity threshold is particularly interesting for the tests of leaf shutters for speed greater than 1/125s (the time when the shutter is fully ‘open’ is then negligible compared to the time needed to open and to close the blades).


When powering up the tester one can access the setup menu to configure the custom parameters. 
The selected setup is then stored for the future tests after the power cutoff. 

  • Language
Selection of the display language (except setup menu which is displayed in the language selected at the purchase)
    • English 
    • French 
    • German 
    • Spanish 
    • Italian 
    • Portuguese

  • Function
Selection of the tester function 
    • Exposure 
    • Curtains 

  • Reference  
Selection of the type of the reference speed scale during the first test
    • 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000, ... 
    • 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, ... 
    • 1, 2, 5,10, 25, 50,100, 200, 400, 800, ... 
    • ... (additonal scales suggestions)
  • Manual calibration 
Activation/deactivation and ‘step’ of the manual calibration  
    • o Deactivated 
    • -0.25 IL 
    • -0.5 IL 
    • -0.75 IL 
  • Automatic calibration
Activation/deactivation et IL correction after automatic calibration  
    • o Deactivated 
    • 0.00 IL 
    • -0.50 IL 
    • -1.00 IL 
    • -1.50 IL 


I want to thank Léon MARI and Corentin VAN PRAET for their advices and support during the development of this device. 
I want to thank also the members of the French forum 'Galerie-Photo' for the exchanges which made me define the best trade-off for the device features. 


For any question or suggestion please contact me through the 'Contact' page including 'ACST-35' in the email title.

ACST-35 is a compact and versatile shutter tester for analog camera.

The tester compute and display the shutter speed in three points or the opening and closing speeds of the curtains together with the flash triggering instant. 
The tester uses three built-in sensors (35mm format) but can be plugged to one, two or three external sensors.
When plugging the Dupont connector 7 pins the tester switch automatically to the plugged external sensors. 

This functionality make possible the measure of the curtain speeds for all the 120 formats.

The device is powered by a micro-USB Type-B plug (mobile phone charger) or by an external power source (up to 12V).  
Dimensions : 55.5x32.0x16.5mm
(compatible with 24x36 camera including Leica M) 
Mass : 35g