Easy to build open source shutter tester

[koraks]

Sorry, did I rub you up the wrong way or something?

It's not for ME to do any analysis of anything. It's the guy who designed it and is trying to sell it to prove it works.

Nobody's selling anything; at most, @bjpirt is 'selling' an idea, for free, and it's up to anyone to take it or leave it as they desire. I think we should be thankful for his willingness to share his work with all of us. I certainly am.

I was just hoping to engage the community here in creating something useful for everyone to use.

Please understand that those who find your idea the most useful and actually want to work with it, may remain silent and will certainly only respond by the time they've actually tried things out, looked at it thoroughly etc. We'll have to take the skeptical critics as part and parcel of an online community, although we strive on Photrio to keep exchanges as constructive as possible (and will take measures if people appear to work actively against this.)

 

[bjpirt]

Thanks @koraks - appreciate the support.

I'm well aware that having produced this first version it needs calibration and testing. I don't have the means to do this as I don't have an accurate reference shutter tester to verify against (it's why I'm building this one!) so I'm doing the best I can with what I have. I'd hoped that someone that does have such a tester might be able to compare the two so I can continue to improve it. But I'll persevere despite negativity

There are a few things I had in mind to improve the accuracy of the tester:
- measure the difference between the actual slit width and the measured slit width (just tried this using a quick and dirty bench setup - will add more details later) so that I can compensate for this in software
- use lasers to validate this on a real camera (lasers are a pain to get set up and aligned so I'd hoped to use a broad bright light like other shutter testers I've seen) and see what the difference is.
- use an LED strobe and a digital camera to do some comparison measurements
- compare my results to a known accurate shutter tester

So all of this is planned - and constructive feedback is very welcome to try to make it better.

 

[koraks]

- use lasers to validate this on a real camera (lasers are a pain to get set up and aligned so I'd hoped to use a broad bright light like other shutter testers I've seen) and see what the difference is.

You may have noticed that there's a project a bit like yours, but underway a bit longer, that uses this approach: https://www.photrio.com/forum/threa...cal-plane-shutters-cheap-easy-it-works.197756
The funny coincidence is that it also originated in the UK! Otherwise, there are mostly a lot of (fundamental) differences, which makes your project all the more interesting since it offers a true alternative for those with other requirements/needs.

As to laser vs. diffuse light - I'd expect that the influence of a diffuse light source would be minimized by (1) placing the sensors as close to the actual shutter as possible, (2) use some kind of collimator, and (3) use a narrow-angle sensor to begin with. W.r.t. 1 & 2, your design already does this to an extent, by placing the sensor PCB on the film gate and having small apertures in the PCB through which the sensor 'sees'.

 

[Andreas Thaler]

I find it sad how commitment and initiative are being dampened, for whatever reason. Instead of being happy that there are people with competence and perseverance who are also willing to make their work available for free.

I am happy to support this project and would like to use the tester in one of my next repair projects including a report here if possible?

 

[koraks]

I am happy to support this project and would like to use the tester in one of my next repair projects including a report here of possible?

By all means, go ahead!

 

[Andreas Thaler]

@bjpirt I‘ll contact you via PM

 

[bjpirt]

I am happy to support this project and would like to use the tester in one of my next repair projects including a report here if possible?

Thanks for the support Andreas - would be great to get some more feedback from someone else using it.

After measuring the error in a very rough and ready way with a hole in cardboard and some calipers (see photos - very rough and ready but I'll set up a proper rig soon!) I think the wide light source is causing a fair amount of error that throws off the faster shutter speed measurements. I'd hoped to avoid using lasers because they're a pain to get aligned each time and you need to build a rig to make it all work, and I'd seen that professional shutter testers just used a diffuse light source with holes for the sensors so I thought a thin hole in a 1.6mm PCB would be enough to reduce the error.

I'm going to try and characterise the error with diffuse light compared to laser light and see if I can compensate in software. I figure the same tester could support both diffuse light sources for slower speeds and lasers for faster speeds.

Here's the shonky setup I used:

I attached the PCB to one jaw, a card with a slit to the other. Measured the slit with the calipers (before attaching!) and then moved the slit until it triggered a sensor and measured again until the sensor wasn't triggered. The measured width was approximately 1mm wider than the actual width.

Compensating for this extra 1mm at faster speeds brought the shutter measurements much closer to what they were meant to be.

 

[Andreas Thaler]

Thanks for the support Andreas - would be great to get some more feedback from someone else using it.

After measuring the error in a very rough and ready way with a hole in cardboard and some calipers (see photos - very rough and ready but I'll set up a proper rig soon!) I think the wide light source is causing a fair amount of error that throws off the faster shutter speed measurements. I'd hoped to avoid using lasers because they're a pain to get aligned each time and you need to build a rig to make it all work, and I'd seen that professional shutter testers just used a diffuse light source with holes for the sensors so I thought a thin hole in a 1.6mm PCB would be enough to reduce the error.

I'm going to try and characterise the error with diffuse light compared to laser light and see if I can compensate in software. I figure the same tester could support both diffuse light sources for slower speeds and lasers for faster speeds.

Here's the shonky setup I used:

View attachment 392205 View attachment 392206

I attached the PCB to one jaw, a card with a slit to the other. Measured the slit with the calipers (before attaching!) and then moved the slit until it triggered a sensor and measured again until the sensor wasn't triggered. The measured width was approximately 1mm wider than the actual width.

Compensating for this extra 1mm at faster speeds brought the shutter measurements much closer to what they were meant to be.

Excellent!

For me, practical usability is important, less theoretical considerations, for which I am not competent here anyway.

Perhaps there will be an opportunity to use the tester to repair a Minolta (Maxxum, Alpha) 7000 AF, that is my main focus at the moment:

The Minolta 7000 AF repair marathon

I was recently able to purchase a bundle of eight Minolta 7000 AF cameras that were advertised as defective at an extremely reasonable price. The cameras arrived today and have all been through a lot. From a cracked top cover and broken light inlet cover, a shredded shutter curtain or...

www.photrio.com

Regarding the report, could we do it like this?

Reveni Labs Camera Tester: New perspectives for professional and private camera repairers

Professional test devices for analog cameras are usually only available from old stock. Their heyday is over with the switch to digital photography, their technology is clearly no longer state-of-the-art, but they are still used in repair shops. The devices were large and heavy and were...

www.photrio.com

---

My repair projects:

Photo equipment from the 1980s: Repair projects and recommendations

I would like to bring together a selection of my previous contributions here in the hope that they will help readers with their work or inspire them to get involved in repairs. It is always worth trying to repair something, because if you do nothing, a camera or lens will definitely remain...

www.photrio.com

 

[bjpirt]

Regarding the report, could we do it like this?

However you like Although bear in mind it's still in development so don't expect quite as finished a tester as the nice Reveni one!

Would be great to compare readings with that though

 

[Andreas Thaler]

However you like Although bear in mind it's still in development so don't expect quite as finished a tester as the nice Reveni one!

Would be great to compare readings with that though

Great, please let me know how we can do it technically. Could you provide me with a test device? I am located in Vienna.

I'm ready, but first I have to find out how to set the shutter speed on the 7000 AF. To set the speed of the two shutter curtains, the shutter has to be removed, as it seems to be the case with many vertically running models.

I'm looking forward to it

 

[bjpirt]

Could you provide me with a test device? I am located in Vienna

I'll DM you to work something out

Edit: I'm not allowed to yet - @koraks any chance you'd be able to let me DM please?

 

[koraks]

Edit: I'm not allowed to yet - @koraks any chance you'd be able to let me DM please?

Sorry about that; I intended to fix it earlier, but just did now anyway. You should now be able to reach out to @Andreas Thaler !

 

[bjpirt]

Sorry about that; I intended to fix it earlier, but just did now anyway

Thank you!

 

[Andreas Thaler]

Sorry about that; I intended to fix it earlier, but just did now anyway. You should now be able to reach out to @Andreas Thaler !

Thanks we are connected.

I am really looking forward

 

[Niglyn]

Hi Bjpirt,
Welcome to the world of shutter tester design )
Neat idea to build everything into the film back. Although this does limit future options.

Sending everything to an app is the modern way, some people have asked me for this feature, but I prefer stand-alone test kit.
I use a TFT screen and/or dump the results to the PC screen & SD card.

As for (in)accuracy, you will suffer the same problem as (almost) every other home-brew or garden-shed design.
The higher the shutter speed, the greater the error will be.
Some people use an oscilloscope & get the same readings (they will, assuming the coding is correct) but the scope is measuring the same error.

You are trying to measure a photon which has zero (debatable) width, with a sensor that has width.
So you are not only measuring the exposure, but also the width of the sensor..

As the 'shutter speed' (which of course remains constant) increases, the inaccuracy will exponentially increase.
For an actual 1/500s correct 'shutter speed' one can expect a reading of between 1/300 and 1/400s using a sensor & oscilloscope or microcontroller just measuring pulse length. This of course will vary on sensor type, light intensity etc.

Putting a mask to make the sensor smaller may help a bit, but now you have the inverse square law working against you, the sensor sees less light, so will trigger later.

Using photo-resisters will also suffer the same fate and as they are larger and circular can be even more problematic than a modern fast switching photo-transistor.

Next we have the light source. The last thing you want is a diffused light. Light will be hitting the sensor from random angles, creating inaccuracy.
Ideally one wants a collimated light source.

Again the problem of inverse square law arises, start putting masks in front of sensors or varying the light intensity and the sensor trigger point will change. IC Racer posted a nice graph showing this, in another thread.

If using PWM to vary LED output, the sensor will see the pulses as shutter actuations & go nuts. I have written code to reject all pulses above 5khz, it works but I do not like it as it is introducing error. Ok only 2Ms but still an error. You also have the inverse square law again.

1970's professional testers would have a bespoke long, thin photo-resister. This was then hidden behind a thin slot. So it still retained a large, but narrow surface to see the light.

Whether they do anything else as well, I do not know, they are full of 1970s logic chips rather than microprocessors.

As for the open-source,'insructables' youtubes etc, that I have looked at, none of these account for the errors described above.

I'm sure if side-by side comparisons were made with 'professional' testers and the likes of mine & Matts, they would all vary as no doubt we all have differing ideas of how to calibrate for the issues described above.

As you can see, one thinks making a shutter tester is easy, until one starts to do so.
Ask me how I know )

Good luck with your design )

 

[bjpirt]

Welcome to the world of shutter tester design

Thanks @Niglyn - and thanks for your pinned post in this forum - that and a few other posts on the accuracy were a big inspiration for me

The last thing you want is a diffused light.

That makes sense, but what I don't get is that when you look at a lot of the professional kit they seem to be using a diffuse light. Would love to see a teardown of one of these machines to see how they're reducing errors.

If using PWM to vary LED output, the sensor will see the pulses as shutter actuations & go nuts

I hadn't considered this - thanks for the heads up!

1970's professional testers would have a bespoke long, thin photo-resister. This was then hidden behind a thin slot. So it still retained a large, but narrow surface to see the light.

I'd wondered about something similar - stacking some PCBs to make a deeper hole, though I'm also trying to keep the build quite simple and this would complicate things. Might give it a shot though.

For me, this is a fun project that I'm hoping can be useful to others and I'm learning lots. I'm going to spend the next period of development benchmarking the errors and trying to identify ways of either reducing them or of compensating for them reliably. I've had an offer of help from someone with access to a few different professional testers so I'm very interested to see how far off I am and how close I can get the results with some compensation.

I'm also building an LED strobe tester that I should be able to use to get a more accurate measurement of the actual speed of some of my own cameras so I can compare results. That should help me be able to benchmark the actual accuracy of the tester too.

Thanks for all of the useful input - I appreciate all advice you can give as you've been sucked into this wormhole a lot longer than I have

 

[4season]

I like how you designed it using just two values of resistors and a single capacitor value.

 

[vandergus]

That makes sense, but what I don't get is that when you look at a lot of the professional kit they seem to be using a diffuse light. Would love to see a teardown of one of these machines to see how they're reducing errors.

Diffused light or collimated light can be used, they just measure slightly different things when you get to really fast speeds. In a nutshell, diffused light better mimics image forming light as it comes through a lens and does a better job measuring effective exposure. Collimated light is better at accurately measuring slit width. Here's a reddit post that goes into more detail.

 

[bjpirt]

@vandergus that's a good article - I used Serhiy Rozum's tester as some inspiration for mine

 

[snusmumriken]

Here's a reddit post that goes into more detail.

@vandergus that's a good article

Evidently this worked for some, but I don't see a link. Please could you try posting it again?

 

[vandergus]

Evidently this worked for some, but I don't see a link. Please could you try posting it again?

I'll try changing the link format a little...

 

[snusmumriken]

I'll try changing the link format a little...

Thanks, that's done the trick!

 

[ic-racer]

There are various ways to test a shutter tester. There are some projects on GitHub. Also, I made a calibrated focal plane shutter of known speed when I was calibrating my home-made shutter tester.

BTW, currently I'm using a Serhiy Rozum tester.

 

[ic-racer]

I verified calibration of my Serhie Rozum tester, kind of like the way one might verify autofocus function per Nikon manual below.

What I did was to test 15 late-model Nikon cameras with vertical electronic shutters at different distances from the light source. In the case of my individual tester, the camera positioned about 25cm from the light source gave the best results.

 

[bjpirt]

Thought I'd give a quick update on some progress I've made on this - I've been quite busy recently so haven't been able to do as much on this as I'd hoped.

I've set up an oscilloscope and used a phototransistor to try to measure the actual shutter speed of a camera more accurately so that I can characterise the behaviour of the sensor I've used in this version. Here's what I set up:

• Used a Nikon FM2n because it's got 1/4000 shutter speed which will cause more inaccuracy in measurement
• Replaced the digital sensor with a phototransistor behind the same hole in the PCB
• Hooked this up to an oscilloscope
• Measured the time from the waveform first starting to rise to first starting to fall

(Tried to embed some photos here, but kept getting an error from the forum for some reason - they're attached for those who are interested)

At 1/4000 speed it should have been 250us, though I had a suspicion this camera was a little slow at this speed. The phototransistor measured 350us and the IS485 measured 470us which is as expected because of the sensor width (somewhere between 0.7mm and 1.0mm)

I compared measurements between the sensors for 1/500, 1/1000, 1/2000 and 1/4000 as well as with the digital sensor with a sensor width compensation algorithm I've written.

This table shows four measurements for comparison:

• The phototransistor
• The IS485
• The measured time as measured by the ESP32
• The compensated time

It shows the time in microseconds and in 1/x seconds as well as how many stops away from the phototransistor (which I'm taking to be the most accurate measurement).

Although the Nikon seems quite reliable and consistent in its timing, one of the issues with this is that I'm having to time and compare separate shots. I'm going to make another test PCB that lets me compare side by side the two sensors with the oscilloscope and the ESP32 measurements so that I can eliminate any errors caused by variation between shots.

So the summary from this is that, uncompensated, the IS485 sensor is around 1/3 stop away from the actual measurement at higher speeds, but that when I apply the compensation algorithm this reduces to under 1/5 stop. Again, some of this variation might be caused by two separate shots having slightly different actual times since there will always be some variation in a mechanical camera.

Next steps:

• I'm going to investigate using a photodiode with an op-amp because this should be the highest bandwidth sensor
• I'm going to build another PCB to use for testing with three sensors side by side so I can get a consistent set of measurements for each sensor and be able to compare this to what the ESP32 actually measured.
• I'm going to investigate using ADC on the ESP32 rather than digital inputs. This way I could potentially sense the start of the slope as the sensor first gets exposed to the point where it begins to sink. It's more complex but should be more accurate with no compensation required. Apparently it's possible to use DMA and I2S to read the ADC at high frequency in the background, but whether this is actually possible to process in time remains to be seen. It's certainly pushing the chip to its limits.