Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,913   Posts: 1,556,257   Online: 855
      
Page 1 of 3 123 LastLast
Results 1 to 10 of 28
  1. #1

    Join Date
    Apr 2008
    Location
    Jacksonville, Fl
    Shooter
    Multi Format
    Posts
    528
    Images
    15

    Shutter times in relation to what the eye can see

    I was not particularly sure where to post this thread so hopefully the people interested will find it here.

    Recently I have been trying to sell a couple of Minolta x-570 camera bodies here on APUG. Obviously the question came up as to their condition so I put them to the test of the shutter tester. Which, I had not had the chance to really sit down and figure out how to use. Now I have and have some question as to what is expectable when shutter speeds are not right on the money. Funny enough, these two camera bodies are almost dead on. I thought this was just about impossible, so I got out my old standby camera I have been using for years and never had a problem with. Canon F-1. This camera's times seem way off and I have never had a bad exposure due to shutter malfunction. I assume the big difference here is, the Minolta's are electronically fired and The Canon is mechanically fired, being that the Minolta needs the battery to trip shutter and the Canon does not.

    The up hill battle begins down the mathematical road in trying to figure out exactly what the time differences mean in an F-stop scenario.

    This is the chart I am using as a reference for correct shutter speeds. These times and tests are based on the camera mounted without a lens so there is no iris to calculate for, just straight speed of curtain travel.


    Next is the test I ran on the Canon F-1. Four (4) consecutive shutter trips, then averaged. The percentage you see to the far right is the percentage of difference from the correct speed the shutter should be traveling.


    In my previous job, I dealt with digital capturing of art work for reproduction. Correct color is a must as to match the original piece. Through this, I learned quite a bit about color and how it is translated to "computer talk". This, including "Delta E". Not to get too into this subject, but simply for where I am going with this. One (1) measurement of Delta E is said to be the equivalent of one (1) shade difference in color that the human eye can differentiate between.

    So in relevance to this subject, does it apply to density?

    What percentage of correct shutter speed can the human eye detect?
    What does that translate into as fraction of F-stops?

    Can you actually see the difference in a shutter that is 25% (from perfect) or a 1/4 stop (either way) different? Is it 20%/ 1/5 stop? 10%/ 1/10 stop?

    I have searched high and low to find the answer over the past few days. Maybe I am not posing the question correctly in my searches. I have re-familiarized myself with LUX, Lumens, Footcandles and still can not really come up with a definitive answer.

    Any help/discussion is greatly appreciated.

    Jody

  2. #2
    nick mulder's Avatar
    Join Date
    May 2005
    Shooter
    8x10 Format
    Posts
    1,204
    Images
    14
    We learned about this stuff as 'JND's':

    http://en.wikipedia.org/wiki/Just-noticeable_difference (as dull as the article may be it's fascinating stuff huh)

    stops don't work like that by the way - log base2 calculators:
    http://www.tutorvista.com/math/logar...e-2-calculator

    Are you talking about seeing the result of a shutter difference in a print/neg or by looking/hearing the shutter itself ? Assuming the neg and everything else equal (i.e. a mental exercise) then, um, yeh no idea on the number - but yes, there is a number... Opinions will vary on its value, regardless of the fact that the number is best calculated as an average of actual empirical testing
    Cleared the bowel problem, working on the consonants...

  3. #3

    Join Date
    Mar 2007
    Location
    Shropshire, UK
    Shooter
    Multi Format
    Posts
    829
    Images
    7
    Hi,

    I've recently built my own shutter tester, so have got quite involved with this.

    (When I say involved - I was measuring the width of slots in aluminium discs being rotated at carefully measured revolutions to calibrate my tester, type involved!)

    There are two issues to consider here - the accuracy of your shutter - and the accuracy of the test.

    With a focal plane shutter there will always be an error in the tester.

    What type of shutter tester are you using?

    If the shutter tester has a single sensor (photodiode or phototransistor) then this has a size, a width. As the slot in the shutter passes this sensor, after a certain portion has been uncovered the output will rise until the circuitry registers this as 'on'. As the trailing edge covers the sensor at some point it will register as 'off'. There is likely to be a difference between these two points - and it could be a fair chunk of a millimetre or so. Obviously the calibration of the tester will allow for this - but the problem is that different shutters have different curtain speed and slot sizes. So... if the sensor is effectively 0.5mm, say, and a particular shutter uses a 2mm slot at a certain curtain speed for, say 1/250s, then the sensor is 25% the size of the shutter slot. If a different camera uses a faster curtain speed to get the same exposure (say a vertically moving titanium film rather than a horizontal cloth curtain) with a bigger slot, say 3mm, then the sensor is more like 15% of the shutter gap. The correction factor applied would need to be quite different.

    So - unless the shutter tester is calibrated differently for different shutters, the accuracy will vary.

    Of course, with a film it is individual photosensitive grains in the emulsion that 'see' the patch of light passed by the shutter - and these are more or less a dimensionless point, compared to the shutter testers sensor.

    A different approach is to measure the curtain speed using two sensors (both detect the leading edge of the curtain - and do so in the same way with the same sensor - so the errors cancel out). This is more accurate and can give an accurate measure of curtain speed. You then calculate the exposure knowing the slot size.

    BUT! There is also an inherent error here, too. The patch of light on the film is not exactly the same size as the shutter slot, with nice sharp edges. Because the shutter must sit at least a short distance clear of the film, the light patch will tend to be a little larger, with fuzzy edges. Again, this will vary with different cameras. My tester was built for use with a Speed Graphic. Here the shutter is so far forward of the film (to clear the sides of the dark slide) that the patch of light seen on the film (or ground glass) is MUCH bigger than the shutter slot!

    I hope that makes some sort of sense :-)

    In the end I calibrated my shutter photographically using 'traditional' methods (Photographing a grey card and measuring the resulting densities) and the used the shutter speeds I determined to calibrate my shutter tester!
    Last edited by steven_e007; 08-26-2010 at 02:54 AM. Click to view previous post history. Reason: typos
    Steve

  4. #4
    nick mulder's Avatar
    Join Date
    May 2005
    Shooter
    8x10 Format
    Posts
    1,204
    Images
    14
    Quote Originally Posted by steven_e007 View Post
    If the shutter tester has a single sensor (photodiode or phototransistor) then this has a size, a width. As the slot in the shutter passes this senor, after a certain portion has been uncovered the output will rise until the circuitry registers this as 'on'. As the trailing edge covers the sensor at some point it will register as 'off'. There is likely to be a difference between these two points
    There's also hysteresis to account for...

    From wikipedia again: (I know, yes I'm lazy)



    "Hysteresis can be used to filter signals so that the output reacts slowly by taking recent history into account. For example, a thermostat controlling a heater may turn the heater on when the temperature drops below A degrees, but not turn it off until the temperature rises above B degrees. Thus the on/off output of the thermostat to the heater when the temperature is between A and B depends on the history of the temperature. This prevents rapid switching on and off as the temperature drifts around the set point."



    Hysteresis is additive in the math, it wont scale with the period changes so it will cause more and more relative error the shorter the period it is you are testing...

    I haven't thought about it enough yet to be %100 its a concern - need to draw some pictures, but its a hunch - I'm trying out the new tactic that my hunches are enough for me to go on nowadays
    Last edited by nick mulder; 08-26-2010 at 03:05 AM. Click to view previous post history.
    Cleared the bowel problem, working on the consonants...

  5. #5

    Join Date
    Mar 2007
    Location
    Shropshire, UK
    Shooter
    Multi Format
    Posts
    829
    Images
    7
    Quote Originally Posted by nick mulder View Post
    There's also hysteresis to account for...
    Yep!
    There the rise and fall times of the sensor, too. Photodiodes are very fast - but phototransistors are usually quite a bit slower to react. Unfortunately, steps taken to reduce the sensor size error (e.g sticking a pinhole over them) is likely to reduce the current, slowing them down. It will still be fast - a lot less than a millisecond probably, so as a percentage of the time measured at slow speed it will be quite negligible - but as the shutter speed gets faster - approaching 1/1000s or more - it can start to become a significant error.

    You can correct for some of these errors using a 'fudge factor' - but the big problem is when the conditions change with a different shutter... you really need to change the fudge factor.
    Steve

  6. #6

    Join Date
    Aug 2009
    Shooter
    Plastic Cameras
    Posts
    37
    Well.
    Your shutter seems to work really good...
    Most high end companies standards were 20% on slow speeds and 35% on high speeds.

    For the test conditions, there are a lot of variations in a non controlled environment (back torsion due to the opening of the door, air moisture and temperature...) plus the fact that the first fire on a camera in the day is generally slower than the others, the phenomenon is worst when the camera was kept cocked...

    For a true answer to your question: camera makers know that a spring can not behave linearly, so most of them tricked the cells to match their speeds.
    But the reason why your films seems good is just because film have a huge overexposure tolerance.
    You can for example give an HP5 a difference of 2.5 fstops to really see a difference. And this tolerance is the reason why most fineprint shops keep telling us to overexpose and under develop. I'ts a rule since the begining of photography and wih a good developper it's quite and hard game to give too much exposure.
    Réparation, Restauration d'appareils et équipements anciens, exotiques et modernes: http://www.atelierdeblanc.fr

  7. #7

    Join Date
    Apr 2008
    Location
    Jacksonville, Fl
    Shooter
    Multi Format
    Posts
    528
    Images
    15
    Quote Originally Posted by nick mulder View Post
    We learned about this stuff as 'JND's':

    http://en.wikipedia.org/wiki/Just-noticeable_difference (as dull as the article may be it's fascinating stuff huh)

    Are you talking about seeing the result of a shutter difference in a print/neg or by looking/hearing the shutter itself ? Assuming the neg and everything else equal (i.e. a mental exercise) then, um, yeh no idea on the number - but yes, there is a number... Opinions will vary on its value, regardless of the fact that the number is best calculated as an average of actual empirical testing
    Nick,
    1st, I'm omitting the log base2 thing, because I am just not on that level.lol

    Ultimately I am looking for the expectable value of change in exposure that any one individual can visually detect a difference and relate it to a fraction of "Stops". Quick, short story. Many years ago when I purchased my first shutter, lens combination (which I thought was for LF and turned out not, different story), I took it to the local camera repair shop. He took it back to a piece of equipment out of my view, click, click, click and brought it back and said "it's about a 1/3 stop of, just adjust your exposure at the time of imaging". I understood this in a relation as to how it effected my photography. Had he handed me a sheet of paper with a bunch of numbers on it shows me actual shutter speeds and percentages, I believe I would have dropped it in the nearest trash. It would have meant nothing to me at the time and now I want to relate the two.

    Further links from the link you provided did give me this:

    "It was found that the emission of only 90 photons was required in order to elicit visual experience. However, only 45 of these actually entered the retina, due to absorption by the optic media. Furthermore, 80% of these did not reach the fovea. Therefore, it only takes nine photons to be detected by the human eye."

    Not that I have any perception how to use the measurement of 9 photons to determine an answer for myself. I'm also not sure it would really help to break it all down to the wave length of light in nm, but, do understand that out visual region is between 400nm - 700nm.


    Steven,

    What type of shutter tester are you using?
    Here it is

    Bottom Lt is the sensor I used. Sorry for the camera phone pics, it's the only digi I have. Basically I ran through this quickly and found what was working for my needs at the time. I don't completely understand all the workings of this thing yet. I used the one with the diffuser in it first w/ a 50mm lens and got results, but decided I would rather test w/o a lens.

    If I understand the rest of your statement here correctly, I'm not sure these variables have a bearing on the outcome of the test I am performing. Though the differences from camera to camera and how they have determined their ratio of slot sizes and curtain travel is camera specific, the overall result should be the same when measuring the amount of time it takes for light to pass through that ratio and onto the tester sensor and/or film in milliseconds. In the end, a 1/4 of a second is a 1/4 of a second regardless of how the camera is set up, right?

    Blanc,

    Your shutter seems to work really good...
    Most high end companies standards were 20% on slow speeds and 35% on high speeds.
    So that would be approx 1/5 stop in slow speeds (either direction) and approx. 1/3 stop in fast. I was scared that I might be in need of a new Canon F-1 (not F-1n). I am going to need to sit down and really learn the functionality of this shutter tester. Hopefully in the long run it will work for older leaf shutters as I like to repair TLRs' and LF shutters for a hobby.

    Thanks for the replies guys,
    Jody

  8. #8
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,618
    Images
    1
    Quote Originally Posted by jerk151 View Post
    ... What does that translate into as fraction of F-stops? ...
    f/stop difference =LOG(actual time / target time )/LOG(2)

    Let's take your first average measurement example for 1 s.

    f/stop difference =LOG(0.738/1.0)/LOG(2)
    f/stop difference =LOG(0.738/1.0)/LOG(2)
    f/stop difference =0.13194/0.30102
    f/stop difference =0.44 stops

    The standard for shutter speeds is quite liberal and allows different deviations for different temperatures. For B&W work I consider red, yellow, green approach (see attached) with a tighter tolerance towards underexposure.

    Also, please note how I chart the ranges plus the average. A shutter set to 1 s and exposing for 1/2 s one time and 1 1/2 s the next has a perfect average of 1 s but a terrible performance.
    Attached Thumbnails Attached Thumbnails ShutterSpeeds2.jpg  
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  9. #9

    Join Date
    Mar 2007
    Location
    Shropshire, UK
    Shooter
    Multi Format
    Posts
    829
    Images
    7
    Quote Originally Posted by jerk151 View Post
    Nick,

    Steven,

    If I understand the rest of your statement here correctly, I'm not sure these variables have a bearing on the outcome of the test I am performing. Though the differences from camera to camera and how they have determined their ratio of slot sizes and curtain travel is camera specific, the overall result should be the same when measuring the amount of time it takes for light to pass through that ratio and onto the tester sensor and/or film in milliseconds. In the end, a 1/4 of a second is a 1/4 of a second regardless of how the camera is set up, right?

    Blanc,
    No, it is not the same. The reason is that the way the film behaves and the way a sensor behaves are completely different.

    I don't know what type of sensor you are using - I can't tell from that photo - but whatever it is it will be a photoelectric device of some sort with a particular size, probably a few millimetres across. Your shutter consists of a slot moving across this sensor. As soon as light illuminates the edge of the device - it will start to produce a voltage (or allow current to flow or whatever... depending on the device type. Let's say it produces a signal). As the slot exposes more of the sensor's surface to light, the signal gets bigger. At some point, decided by the designer, the electronics must be triggered to register this as 'on' or 'being exposed'. After the electronics have been triggered to record the signal as 'on' - it will stay in this state as the shutter continues to move - until the sensor starts to be covered again. In the same way - at some threshold the falling signal level will be regarded as 'off' or 'shutter closed'.

    The important thing is that the distance between the point at which the tester decides is 'open' and the point at which it decides it is 'closed' will be of the order of something like 1/2 a millimetre or more, maybe. This could be 25% of the width of the slot you are measuring. But - on a different shutter making the same exposure - it might be 10% or 30%. So - the error changes with the slot size.

    Now consider a photographic film. This consists of millions of microscopic of photosensitive grains. The size of each grain is totally negligible compared to the size of the slot - any slot.

    Consequently the way the sensor sees the slot and the way the film grains see the slot are totally different.

    That is just one scenario - with a single sensor. With a diffused sensor the situation is different - and with multiple sensors different again (here you are measuring the curtain speed, which is better for small focal plane shutters) but in every case the way you detect the moving shutter slot has characteristics which are quite different to the way film works. You have to take these factors into consideration if you want to get accurate readings.

    I suspect that most manufacturers know what curtain speed relates to what effective shutter speed they require for a given slot size - and measure for that.
    Steve

  10. #10

    Join Date
    Apr 2004
    Location
    Montgomery, Il/USA
    Shooter
    Multi Format
    Posts
    5,159
    All the speeds are close enough for government work except 1/2000 which is a stop off. That's not at all unusual.
    Your slow speeds are fast, not slow until you get to 1/8 which should be 125ms and you're at 113ms that's mighty fine.
    Heavily sedated for your protection.

Page 1 of 3 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin