645 Pro: Intake Testing of Shutter Speeds
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
When a camera comes into the shop I like to do a function test on intake to get an idea of its health. This 645 Pro is shown having shutter speeds checked.
As you can see in the first photo, 1/2 second shutter speed is perfect at 500 milliseconds. The display shows A for the beginning of the exposure, B for the middle and C for the ending of the exposure. In a perfect shutter, these numbers will all be the same or very close.
Photo two shows the beginning of an issue: this is 1/60 of a second and the display shows A at 20.1 milliseconds and C at 20.2 milliseconds. While this is within specs (barely), it is beginning to show a pattern.
By 1/1000 of a second, photo three shows A at 1.37 milliseconds and by the time the shutter is closing at C, it is 1.95 milliseconds. The speed at A is right at the edge of specs and C is quite a bit out and is actually closer to 1/500 second.
All of these issues will be resolved by cleaning/lubricating shutter bearings and adjusting curtain travel times. Finally, the actual speed will be adjusted. In reality, a user of this camera might not notice this discrepancy if they were shooting at shutter speeds from one second to around 1/250. At 1/500 and 1/1000 they might notice some tapering of the image.
Photo three shows the dedicated sensor that I use on my tester for the 645 Super/Pro/Pro TL. It was made by putting the sensor electronics in a shell of a 645 film back. Makes it much easier to test these particular models of camera.
