Testing and calibrating shutters

Hello,

I'd like to share a method I'm using to check the shutter operation of film cameras without wasting film. The accuracy of the exposure time can be estimated together with the exposure uniformity across the frame. This method also remove uncertainties due to film processing. I thought I'd share it here in case other may find it useful.

I've recently started a new hobby of fixing old cameras. My first patient was a Canon IIc rangefinder found on ebay and advertised as non-working.
After replacing the shutter curtains that were rather old and with lots of pinholes, I had to recalibrate the shutter mechanism. Without a dedicated tool, I figured out another way.

The method I used requires a digital camera and a monitor or another uniformly lit subject. It consists in shooting a long exposure (1 or 2 seconds) with my digital camera through the analog-camera shutter while this is activated. The results is compared to another shot from the digital camera at the same subject and the same shutter speed used on the analog camera. If the shutter on the analog camera is accurate, the exposures of the two pictures should match.

The procedure is as follows, and it's easier done than explained:

- Mount the digital camera on a tripod in front of your monitor displaying a white background (the subject). A macro lens is preferable, but I think this will work with non-macro lenses too. A darkened room works best.

- Say you want to test 1/100 s on the analog camera, set the exposure time on the digital camera to 1/100 s and choose an aperture and ISO so that the monitor white background is rendered as a middle grey (histogram with a peak in the middle). At this point take a shot as a reference.

- Now put the analogue camera with the film door open and without lens between your monitor and the digital camera and set its exposure time to the target speed, e.g. 1/100 s.

- Focus the digital camera on the shutter of the analog camera.

- Set the exposure time of the digital camera to 1 or 2 s and enable the self-timer.

- Press the digital camera shutter button and wait till you hear the shutter opening. While it is still open, fire the analogue camera shutter.

If the shutter mechanism is calibrated correctly, the monitor will be rendered with the same shade of grey as the reference shot. A quick comparison between the histograms of the two shots is all that is needed.

I hope this is useful to someone. Comments and suggestions for improvement are welcome.






Some examples. First row, test shot and histogram of my monitor at 1/100 s with my digital camera. Second row, shot through the analog camera set at 1/100 s. The exposure on the right looks correct, but the left of the frame is darker. This leads to a broader histogram and it is due to the second curtain catching up with the first. Either the second curtain is tensioned too much, or the first too little. Since the exposure on the right seems find, I think it's the former option. Third row: after adjusting, the exposure is uniform and matches that of the digital camera.

Oh, very cool idea, thanks a lot for sharing!

I've been trying to make a device to calibrate in-lens shutters (I have several ones), and all my ideas were way more complicated.

Thanks again!

Yes excellent, good sample pictures also!

I have used this method too in tandem with others. Difference is, that I zoomed in with the digital camera so that there were no dark corners visible.

I photographed the moving curtain with video to see how the curtain slit worked, and used it to adjust curtain speeds - and then photographing through the mount to see if the overall exposure was similar to digital camera.

Other things you can try, is putting camera to bulb mode and recording the sound close up. With bulb you can more easily see from the sound waveform, and figure out what click is the shutter opening and what is closing "click". If you record, say at 1/125, the waveform will be impossible to interpret

jaeae said:

Other things you can try, is putting camera to bulb mode and recording the sound close up. With bulb you can more easily see from the sound waveform, and figure out what click is the shutter opening and what is closing "click". If you record, say at 1/125, the waveform will be impossible to interpret

Click to expand...

That sounds interesting! I've used audio recording to check the shutter times at long exposure times, e.g. above 1/4s, but I've never actually thought that the sound itself of the opening or closing curtains could be useful.

How do you interpret and use the recorded sound?

Vinc1973 said:

How do you interpret and use the recorded sound?

Click to expand...

I've used Audacity program to look at the waveform of the recording. Using bulb, you can record sound with some seconds between opening and closing. That way, you can just look at the waveforms and see what kind of sound the closing and opening make. Then you can look for similar forms in shorter exposure times also. Works well with slower shutters like Zenits with 1/30 flash sync. Why not with 1/60 speed shutters too. Then you know the timing is correct with sync speed. Of course faster speeds with only a slit in the curtain, other method are better

I am a satisfied customer of user "vfmoto" on e Bay, from Romania (I'm in Canada). He sells a range of LED-based shutter testers, including a very inexpensive one that you plug into your computer's audio jack and then use something like Audacity to determine the shutter speed - though I prefer the slightly more expensive ones that have a built-in display. I don't even need to adjust the shutters if it's just for my own use; all I need to know is something like, "when this shutter is set to 1/100th it's really shooting at 1/75th", and adjust exposure accordingly.

Best wishes,
Sterling
--
Lens Grit

SterlingBjorndahl said:

I am a satisfied customer of user "vfmoto" on e Bay, from Romania (I'm in Canada). He sells a range of LED-based shutter testers, including a very inexpensive one that you plug into your computer's audio jack and then use something like Audacity to determine the shutter speed - though I prefer the slightly more expensive ones that have a built-in display. I don't even need to adjust the shutters if it's just for my own use; all I need to know is something like, "when this shutter is set to 1/100th it's really shooting at 1/75th", and adjust exposure accordingly.

Click to expand...

+1 for vfmoto, +1 for the built in display models (I’ve had both). If you need to do this reasonably frequently it’s worth it for the time saved

Ok, this seems useful in some cases.

But for simple checking of longer exposures, wouldn't it make more sense to film the shutter and count how many frames it's open? This works especially well if you have a camera that can shoot 120 or 240 frames per second or the like.