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Thread: Copal 0 shutter accuracy

  1. #11

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    Re: Copal 0 shutter accuracy

    What is the actual "speed" of the film being used? B&W film's actual "speed" or sensitivity to light will vary depending on a give batch-lot of film, developer used, needs of the print making process and more. Color transparency film is often very close to the speed noted on the box.

    If you're just beginning LF, there are many other things and needs to be concerned about like loading film, setting up the camera, making sure the lens is stopped down to the needed aperture before exposure, setting the shutter speed, metering the scene to be imaged and ....

    It takes LOTs of experience and wasted sheets of film before gaining the ability to get the image in mind in one sheet of film.

    ~Use the same techniques learned-gained from roll film and apply them in a more controlled fashion (avoid bracketing exposures) for LF and you should be OK.~

    ~Expect to waste LOTs of film initially. This IS part of the learning curve that is difficult to escape in the beginning.~

    Being overly concerned about shutter speed accuracy (IMO, this Copal shutter is not a problem at all), lens performance and all that is not going to help one to progress up the learning curve. As with most learning, errors will be made, most important learning from the errors made is what matters most.


    Bernice


    Quote Originally Posted by Alan Klein View Post
    Thanks Bernice, I understand. But I have to start somewhere. Large format photography is all knew to me I'm planning on shooting Tmax 100 BW and Velvia 50 chromes. When I shoot these in medium format, I meter for box speed and bracket +1 and -1 on my landscapes. (A pro lab processes). Now with LF 4x5, I'm not going to bracket like that, at least I didn't plan on it.

    So what do you and others feel I should start with for these film and lens "in-accuracy" situation? SHould I just dial in 1/3 more on the meter's ISO setting from box speed? Ignore the errors?

  2. #12

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    Re: Copal 0 shutter accuracy

    So you tested the shutter by sound? That's probably the problem...

    A leaf shutter is like an opening and closing iris... It takes some time to the point where it is fully open, then the dwell time opened and some fraction of the time to close... This is called shutter efficiency... Shutters are calibrated for the time fully open, but some extra time happens between that open and shut...

    For color professional work on chrome film, speeds can be critical but for color or B/W neg, not as critical, as these films have more latitude... (A 1/3 stop is not too much for general subjects...)

    Film tests are in order, and hopefully your next shutter is in the same ballpark... A professional test is more precise...

    Steve K

  3. #13

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    Re: Copal 0 shutter accuracy

    Quote Originally Posted by LabRat View Post
    So you tested the shutter by sound? That's probably the problem...

    A leaf shutter is like an opening and closing iris... It takes some time to the point where it is fully open, then the dwell time opened and some fraction of the time to close... This is called shutter efficiency... Shutters are calibrated for the time fully open, but some extra time happens between that open and shut...

    For color professional work on chrome film, speeds can be critical but for color or B/W neg, not as critical, as these films have more latitude... (A 1/3 stop is not too much for general subjects...)

    Film tests are in order, and hopefully your next shutter is in the same ballpark... A professional test is more precise...

    Steve K
    +1

    sound is not a measure of light entering the camera.

    if you are using a diy gizmo that uses a microphone, just substitute a photo transistor in its place.

    best is get a shutter tester. calumet had a nice one you can still find on ebay cheap.

  4. #14

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    Re: Copal 0 shutter accuracy

    Quote Originally Posted by Bob Salomon View Post
    Industry speck is +- 30% of the marked speed except for the highest speed which was an engineers dream
    ... marketing persons dream.

    ... engineers requirement and design goal.


  5. #15
    Alan Klein's Avatar
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    Re: Copal 0 shutter accuracy

    Quote Originally Posted by dfort View Post
    With those emulsions youíll need stopwatch to time your exposures unless youíre shooting at wide apertures in full sunlight. Donít worry about a slightly slow top speed.

    I used to shoot Polaroids to check my exposure but I take it we donít have that technology these days.


    Sent from my iPhone using Tapatalk
    With my medium format equipment, I often shot at 1/2 or 1 second. But I shoot mirror up on a heavy tripod and haven't noticed any shake. Hopefully, I'll have the same experience with 4x5.

  6. #16
    Alan Klein's Avatar
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    Re: Copal 0 shutter accuracy

    Quote Originally Posted by BrianShaw View Post
    Ignore the errors... first make a picture and see if it matters.
    Still waiting for the camera. FedEx has in in Tennessee. I'll probably bracket at first at least to get a feel with what's going on.

  7. #17

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    Re: Copal 0 shutter accuracy

    Quote Originally Posted by Alan Klein View Post
    I'll probably bracket at first at least to get a feel with what's going on.
    Bracketing is an advanced technique used by professional photographers working on assignments where it is critical to deliver a properly exposed shot and the client is paying the expenses.

    Believe me--in school I had to learn the zone system, got my shutters and light meter checked for accuracy and ran countless tests with fellow students holding grey cards. I learned how to nail the exposure but once I was in the position where my reputation depended on it, I bracketed.

    When shooting chromes (slide film, transparencies, etc.) and for whatever reason I couldn't bracket (fashion, portraits, action) I would have the lab develop a "test shot" and then push or pull the rest of the film. By the way, we also did this with 35mm and medium format by running a clip test, that's basically snipping off a piece of the roll and running it through the processor.

    Back on topic, I had my shutter speeds checked by the legendary Marty Forscher of Professional Camera Repair and he gave me a list of the marked and actual shutter speeds. There was no way to get these mechanical devices running 100% accurate. So I had a friend who was handy with electronics build me a shutter speed checker and I made lists with the marked and actual shutter speeds for each lens. Now that we're in the age of the smartphone -- someone made an app for that. Check out THE PHOTOPLUG.

    And just for fun: Test Your Camera's Shutter Speed - Mr. Wizard's Challenge

  8. #18
    Exploring Large Format
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    Re: Copal 0 shutter accuracy

    Quote Originally Posted by Bernice Loui View Post
    Some thoughts on shutter speed accuracy.

    ~Back in the day when color transparencies were the most common means of producing color images for mass printing, high quality strobe lighting was absolutely preferred over shutter timed exposure. High quality studio strobe units can be held to 1/10 f-stop with ease and consistency and color temperature can be controlled and CC filtered as needed to achieve neutral color balance with color transparency film.

    ~Shutter speed is not a significant factor when strobe light is used in a controlled studio setting. Shutter speed accuracy and consistency comes into play if "synco-sun" or mixed outdoor lighting with strobe is used for images to be produced.

    ~This is NOT easy to do or even close to achievable with sun light which it's color temperature changes depending on the time of day, location and much more. Add to this, errors-tolerances in shutter speeds make absolute consistent exposures to 1/10 f-stop quite difficult to impossible.

    ~Fact is ALL mechanical shutters have variations in their shutter speed cycle to cycle, over time, over aging, over temperature, over condition of the shutter. This is how electronic shutters came to be as this was an effort to reduce shutter speed variations and improve shutter accuracy, consistency and related shutter requirements.

    ~Using a single reliable-accurate mechanical shutter can help reduce variations in accuracy, shutter speed, and all that by the fact a single shutter is used for each lens chosen to make a given image. This is one of the reasons why using a know good Sinar shutter with barrel or Sinar DB lenses can reduce shutter speed errors.

    ~The most accurate shutter ever used was the Sinar Digital, highest speed is 1/500 and it is accurate at 1/500 second, will time down to many seconds with equal accuracy and reliability. It is also HUGE, heavy, $$$$, not really portable at all.

    ~Fact is, for the majority of outdoor photography that 30% error is not that significant. There is sufficient differences in actual film speed, light at the moment of shutter release, light transmission of a given lens and a long list of many other variables that puts that 30% tolerance of shutter speed into perspective.

    ~While color transparency film is the least tolerant to exposure errors, B&W film is significantly more tolerant to exposure errors. Do consider variations in processing, developers and more to print making. This is why gaining control over the entire print making process often makes the greatest difference in the finished print.

    ~Focusing on a single parameter like shutter accuracy, camera, film and... can produce neglect of all the other factors that will affect the finished print.


    Suggest not worrying about this variation in shutter speed and focus far more on image making and image content.


    Berince
    Bernice, it is replies like this one that I just learn so much from. I too am just beginning ("wasting" sheets), and I have learned a great deal already from you experienced LF photographers. Really appreciate the patience with which so many of you explain, re-explain the basics. Also learning from fellow newbie questions. Thanks to all for such a generous community! Honestly can say that I'd not have taken the plunge into LF without this forum.

    Sent from my SM-G955U using Tapatalk

  9. #19

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    Re: Copal 0 shutter accuracy

    Every Copal shutter I have, from size 0 through 3, gets tested using a Calumet* shutter speed tester. This is repeated every few years to detect changes as the shutters age. Most of my lenses were purchased brand new, and all exhibited the kind of inaccuracies described by the OP. Newer ones are more precise (i.e. repeatable), but not more accurate.

    I attach a small printed table to the lensboard of each lens indicating how much exposure compensation is needed at every speed where that shutter is not within 1/6 stop of accurate. For example:

    1/500 -- close 2/3 stop
    1/250 -- close 1/2 stop
    1/125 -- close 1/4 stop
    1/60 -- close 1/3 stop
    1/2 -- open 1/3 stop

    This is generated using MS Word in 8-point Arial Narrow bold, printed on a laser printer, cut out and affixed to the lens board using Scotch 810 Magic Tape. That particular tape can be removed without damaging lensboards when subsequent shutter recalibration requires replacing the table with a new one. After metering a scene and establishing a combination of aperture and shutter speed, simply adjust aperture by whatever amount the table indicates.

    In my experience, this is the optimum way to deal with shutter speed inaccuracy. Attempting to adjust light meters every time a different shutter speed is used will inevitably lead to errors; it's too much to keep track of. With an extremely narrow latitude emulsion like Velvia 50, depending on subject brightness range, even 1/6-stop shutter speed errors might need exposure correction. If that proves to be the case, expanding the tables to include those speeds would be wise.




    * The Calumet tester is long out of production. If one were in the market for such a device today, this one


    might be worth investigating. I have no experience with it.

  10. #20

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    Re: Copal 0 shutter accuracy

    Alan,

    Test your shutter speeds again, firing the shutter multiple times on each setting. If they are consistent (i.e., really close to the same every time), your shutter is just fine mechanically. No clockwork shutter is going to be 100% precise. the 30% margin of error for new shutters should tell you this.

    Now, if the error for a given setting approaches a 1/3-stop difference, do what I do: Make a label with the actual speeds rounded to the nearest 1/3-stop and stick it to the lensboard. I mark my shutter speeds with a "+" and a "-" sign to indicate 1/3-stop faster and slower respectively, e.g., "1/15-" equals 1/3-stop slower than 1/15 (or 1/10 if you prefer). If you have a setting that's off by more, say your 1/125 is really just 1/3-stop faster than 1/60, then mark it "1/60+". Use these speeds to set your aperture against. Note that most meters and lenses have 1/3-stop increments marked; hence the use of 1/3-stop as a unit. Now you've got "accuracy" to 1/3 stop give or take a bit; well within exposure tolerances even for transparency films.

    Best,

    Doremus

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