Shutter-Speed-Tester for your iPhone

[polyglot]

I actually don't think the X-sync thing is a problem, depending on what impulses you're lining up the time measurements with. There are four events:
1) first curtain travel starts
2) second curtain travel starts
3) first curtain travel completes
4) second curtain travel completes

Slower than X-sync, the ordering is 1, 3, 2, 4 and faster than X-sync, it's 1, 2, 3, 4. As long as you measure the timing offset between 1 and 2 or between 3 and 4, that's the shutter time. The travel time (1-3 and 2-4) is irrelevant to the exposure.

The above assumes that it's possible to make out these four distinct events of course, and that may not be possible depending on the shutter design. And it assumes that the user knows enough to select the correct pair of events, the ordering of which depends on the relationship between shutter speed and x-sync.

 

[declark]

Great idea Lukas. Was about to download the app, but then remembered that my 3rd Gen iPod Touch doesn't have a microphone that I am aware of, so wonder if the compatible devices listed on iTunes might need to be updated?

 

[Filmomat]

Actually you can use this app on your iPod, if you have earphones with a built-in mic ! Just plug them in and voila, you have a microphone on your iPod . Maybe I should mention this in the description.

 

[RalphLambrecht]

yes!

 

[Chan Tran]

I will try the circuit Ralph but I would use the oscilloscope for the measurement rather the sound card. My set up currently works quite well for manual camera but I can't test a camera on automatic. I am thinking that I can make a variable standard light source out of a dichroic enlarger head to simulate the light level than measure the shutter time to test an aperture priority camera.

 

[Filmomat]

I made a short video about the App:

[video=youtube;tOcGn07YUpc]http://www.youtube.com/watch?v=tOcGn07YUpc[/video]

In the video I exemplary measure the 1/60, 1/125 and 1/250 of my Rolleiflex 2,8f. Afterwards I compare the results of the app with an exact optical measurement.

Maybe it is more comprehensible now for some of you how to use this app.

 

[Chan Tran]

Wow I noticed that your Rolleiflex has the exact shutter speed of 1/64 and 1/127. The perfect shutter speed should be 1/64 and 1/128. I am amazed at how accurate your camera shutter speeds are.

 

[Diapositivo]

Measured (without the IPhing) is taken the first time from peak to peak, the second time from baseline to peak, the third time from an arbitrary point to peak. In the third case a "peak to peak" stretch is not easy to identify.

You seem to always measure "Actual" from baseline to peak.

From what I see, "actual" can be reliable, "measured" (with iPhone) can give any result you want, depending on where you place the beginning of the exposure, which judging from the video seems quite arbitrary.

 

[Filmomat]

You have to distinguish between the measurement with the iPhone-App and the optical measurement on the computer. Those are two different types of measuring and therefore you have to set the points from where you measure differently (thats why I measure the actual value from baseline to peak).

In the second measurement, there were two peaks close together. In this case, I just took a point between those two peaks. Of course, this is a measurement error, but this error is quite small, just test it out yourself !

In the third measurement the peaks aren't that distinct, but you can still see them. Just search for the peaks that have the greatest amplitude. That's not arbitrary.

 

[Diapositivo]

In the second measurement, there were two peaks close together. In this case, I just took a point between those two peaks. Of course, this is a measurement error, but this error is quite small, just test it out yourself !

Why taking a point between two peaks? Isn't that arbitrary? Can exposure begin between two peaks? Logic would dictate, IMO, that exposure begins either at the first peak, or at the second, if we have to infer from noise.
Besides, considering that both methods (your app and the Audacity method) use the noise produced by the shutter, why is the method of calculation different*?

With audacity you seem to always use "baseline to last peak". With you app you use "peak to peak" first, then "point between peaks to peak" second, then I don't remember the third, but it is not coherent with the other two.

A clear algorithm should be given, such as "baseline to last peak" every time.

This site uses "from baseline to beginning of peak excluded" that might be clearer and give more repeatable results.
http://www.mraggett.co.uk/shuttertester/shuttertester.htm

And I know that you do and I criticise, and criticizing is easier than doing , I just wanted to say that your video doesn't seem to demonstrate a lot regarding the application. Which doesn't mean your application isn't useful or precise, as it can still be both things.

* Mmmh maybe the audacity method generates an electric noise through light, which is recorded by the sound card of the computer? A proper comparison would better use a proper optical measurement.

 

[Filmomat]

Ok I think you misunderstood something
My iPhone App is a acoustic measurement. But the measurement via Audacity, seen in the video, is a "real" optical measurement !! I use a IR-LED and an IR-Fototransistor, which is connected to the audio-input of my computer. When light hits the transistor, I can see this on the audacity signal. This method of measuring is very exact, so it can be used as a reference to the acoustic measurement from my App.

I thought this was clear to see in the video, apparently it isn't...

 

[Diapositivo]

Well OK, let's take the Audacity measurement as "exact", I have a problem with what I would do, as a user of the App, to measure the shutter speeds if I don't have a clear method (such as: first peak to last peak, or base of first peak to base of last peak, etc.) and if I have to choose the measure extremes on the graph based on "circumstances".

Maybe, as the other site does, "base of first peak" to "base of last peak" should be easier to identify. It should always be the same method in any case or the user would end up just choosing the method that more easily matches the desired speed...

 

[Filmomat]

Ok now I understand your problem. Well, the problem with the acoustic measurement is, that there are no hard and fast rules how to do it (at least with the fast speeds). That's because every camera is different and therefore every signal is camera specific. You just have to experiment a bit. Look, which parts of the signal change when you compare different speeds, and which parts stay the same.

Maybe it wasn't the best idea of me to measure between those two peaks as it confuses people. But the point is, it doesn't matter that much whether you measure on the left peak, the right peak, or in between. This is the measurement error, that you have to deal with when using this app. But this error is small enough to still get usable results, and thats the point ! It may not be 100% exact, but it is not arbitrary, because the results you end up with always are in a certain range, which is about 1/3 of a f-stop.

 

[Richard S. (rich815)]

I could not see exactly how to use this at first but on seeing the video and the clarifications given here I can now see how this works. I tested out my Rolleiflex 3.5E Planar (recently back from a full CLA from Harry Fleenor) and the shutter speeds tested out very well. All within 1/3rd a stop.

 

[ambaker]

Ok,

I've tried the app on two cameras, so far. The first I did not expect to work, because the Mercury II has a rotary shutter, and the spacing between the blades determines the timing. Rotational speed is always the same.

The second is a Ricoh XR-S. I'm not sure how best to read the results. I've attached a screen capture to demonstrate. I am not sure where to read the pulse. The test was at 1/500 sec., so I have placed the cursors at what should be that width.

 

[Filmomat]

First, thanks for testing the app.
Well, your Ricoh XR-S is a SLR isn't it ? With SLRs you can't measure times faster than the x-synchro speed, because faster Speeds are generated by the distance between the two curtains which has no effect on the sound.
Have you tried testing longer times like 1/60 or 1/30 ?

 

[Filmomat]

Update !

Hello,

it's been a while since this thread started, but I have some news regarding the App

First, there will be an update very soon (it is still in review by Apple). It will fix a major problem regarding iOS 5 users (the content was displayed in wrong display orientation) and offer the possibility of measuring and saving old shutter speeds like 1/5, 1/10, 1/50 etc. as suggested in this thread.

Second, there is now a possibility of doing real light-measurements with this App !!
As discussed in the thread, the acoustic-measurement has its limits. Much better would be a light measurement via phototransistor. Unfortunately, the iPhone doesn't has such a sensor build inside. BUT, what most people don't know: The iPhone has a microphone-input inside the earphone-socket. This offers the possibility of attaching a phototransistor to the iPhone, and do light measurements.

I did some experiments, and found a very smart solution I think:



This small plug contains this very simple schematic:


It doesn't need batteries, it just uses the small voltage which the iPhone provides (for the electred microphone). The resistor is 4,7 kOhm and the fototransisitor I use is a BPX 38. The resistor is needed so that the iPhone recognizes the plug as a microphone.

Plug it into the headphone socket, and voilà, you have a mobile light-measureing shutter tester:


To use it, just take a camera, remove the back, light it with a light source from the back and position the plug to the lens:


Then you proceed as usual.
What you get is a very nice and clean signal with clear visible peaks:
Here with 1/60:


1/125:


It works very nice, even at 1/500:


It is very simple to build a plug like this, the only thing which is a bit hard to get is the 4-pin phone-connector.
Would be great if someone would try this out !

 

[Curt]

Very nicely thought out and presented. I like the app and the old shutter speed levels will be a welcome addition. The light measuring phototransistor would be excellent. If one could be placed in a bellows near the front of the camera, perhaps at or near the rear of the lens, it might be possible to see and record the actual exposure for timed shots, that would be an incredible advance. Especially in the the range from one second to a few minutes.

Thanks,
Curt

 

[Tenoates]

This sounds like a great app and sensor Idea. I'll check if I can find that fototransistor here and assemble one for your app. Thanks

 

[polyglot]

Excellent addition to the app; this is what it really needs.

Very nicely thought out and presented. I like the app and the old shutter speed levels will be a welcome addition. The light measuring phototransistor would be excellent. If one could be placed in a bellows near the front of the camera, perhaps at or near the rear of the lens, it might be possible to see and record the actual exposure for timed shots, that would be an incredible advance. Especially in the the range from one second to a few minutes.

This is a good idea except that the sensor will be outside of the image area of the lens, which means you're metering the wrong thing. However if you wanted to modify an LF camera for example, you could take the Minolta approach of metering off the film - google for "OTF meter". Requires a little sensor and very simple optics inside the camera body to average the intensity of the light diffusing off the film during exposure and when there's "enough", ends the exposure. Minolta used that for TTL flash metering with no preflash and I believe another 35mm manufacturer (Olympus?) used it for metering long exposures under varying light; both were in the 1980's.

 

[oldlincoln]

This is great stuff... I only hope that Echolot will extend his powers to an Android version so I wont have to borrow an iPhone! BTW, the BPX 38 is widely availible; Mouser, digikey and RS all have thousands in stock at 10 for 12 bucks or so.
Thanks Echolot, way to go!

 

[Chan Tran]

Excellent addition to the app; this is what it really needs.



This is a good idea except that the sensor will be outside of the image area of the lens, which means you're metering the wrong thing. However if you wanted to modify an LF camera for example, you could take the Minolta approach of metering off the film - google for "OTF meter". Requires a little sensor and very simple optics inside the camera body to average the intensity of the light diffusing off the film during exposure and when there's "enough", ends the exposure. Minolta used that for TTL flash metering with no preflash and I believe another 35mm manufacturer (Olympus?) used it for metering long exposures under varying light; both were in the 1980's.

Although I read somewhere that Minolta invented the technique for flash exposure but Olympus had it first in their OM-2 and it did long exposure as well like you said. Most cameras with TTL flash auto exposure used this technique until the introduction of the digital SLR then the cameras would rely only on preflash. In the 90's a number of cameras used both off the film plane and preflash.

 

[Filmomat]

Update released

The new Update, including old shutter-speed-values and a bug fix regarding iOS 5 users is now available for download

 

[Filmomat]

Fototransistor-Plugs for sale

Hello,
In my last posts I told you about the fototransistor-plug, which allows you to make real light-measurements with your iPhone.
I am know able to offer those plugs for sale, if you don't want (or don't know how) to built the plug yourself.



The price is $15,50 each. Shipping to USA is $4,50, so total $20 incl. shipping.

If you are interested, just send me a short email at: lukasfritz@gmx.net

 

[Filmomat]

Fototransistor Plugs for sale

The plugs are now available on eBay !

http://www.ebay.com/itm/Shutter-Speed-Tester-for-your-iPhone-Verschlusszeitentester-fur-das-iPhone-/251288249805?pt=DE_Foto_Camcorder_Analogkameras&hash=item3a81f265cd