How is shutter speed defined really?

E

emjo

Established
Local time
10:52 PM
Joined
Jul 19, 2011
Messages
66
Ok I know what shutter speed is in general terms but when it comes to timing a shutter then how do you measure it? Is it from when the first ray of light comes through the shutter? Or from when the shutter is half open? Or full open? Or 90 % open (as rise and fall times in electronics)? Same goes for when it closes.

I have a number of folders with mostly Compur shutters that are off in their speeds and I want to whack them back into shape:)
 
Focal plane shutters work via a variable width slit (determined by the speed which you set) which travels across the focal plane therefore exposing the entire frame the same amount of time which is measured in miliseconds.

Leaf shutters work slightly different in that they open in a circular fashion giving equal exposure.

You'll need to have the shutters CLA'd if they are out..
 
Gabriel M.A. said:
I'm sure it has something to do with the time that light is allowed to pass through, from start to finish.
Click to expand...

With leaf shutters, it is bound to be a bit more complex, as they have a bidirectional pattern, so that different parts of the shutter area are open for different times - that causes the timing accuracy (especially for short times) to be aperture dependent.

There must be some definition for the measurement beam pattern and aperture. However the shutter service manuals I own contain nothing like that.

Perhaps there was a de facto standard set by the then common makes of shutter testers - unfortunately these (which would have been made in Germany) seem to have perished to the degree that nobody even seems to know the makers and models any more. Even the more recent (Japanese) Kyoritsu SLR focal plane shutter testers are as rare as hen's teeth. Or there was some former DIN that defined leaf shutter tests - unfortunately researches there cost a arm and a leg, as the standards body wants to be paid for each search request...
 
Ansel Adam's book "The Camera" has a very informative discussion about the characteristics of focal plane versus lens shutters and their actual efficiency, strengths and weaknesses in use. Chapter 6 has a paragraph entitled "Shutter Efficiency" and he suggests that usually lens shutter speeds are calculated on basis of full aperture. It also discusses changes in effective speed at other apertures; in general leaf shutter efficiency decreases at higher speeds as it deviates from theoretical ideals more than at slower speeds.

I acquired a factory service manual for dozens of different Compur shutter ex ebay a few years ago which provides detailed information about adjustment and lubrication etc. They were built to tight tolerances so a fairly notorious for running slower than their stated maximum speeds and Deckel themselves stated a generous 20% acceptable tolerance for accuracy. As long as the shutter adjustment is correct and the mainspring and booster spring (if applicable) is in good condition I am not sure how much more accurate you are likely to make one that is clean, lubricated and in good working order. Please let us know how you fare though, as it would be interesting to hear some real-world experience of investigations into this.
Regards,
Brett
 
sevo said:
With leaf shutters, it is bound to be a bit more complex, as they have a bidirectional pattern, so that different parts of the shutter area are open for different times - that causes the timing accuracy (especially for short times) to be aperture dependent.

There must be some definition for the measurement beam pattern and aperture. However the shutter service manuals I own contain nothing like that.

Perhaps there was a de facto standard set by the then common makes of shutter testers - unfortunately these (which would have been made in Germany) seem to have perished to the degree that nobody even seems to know the makers and models any more. Even the more recent (Japanese) Kyoritsu SLR focal plane shutter testers are as rare as hen's teeth. Or there was some former DIN that defined leaf shutter tests - unfortunately researches there cost a arm and a leg, as the standards body wants to be paid for each search request...
Click to expand...

good question (related to the leaf shutters). :)
I don't know the official definition, and indeed something like in electronics "90% open) would make sense but, i strongly suspect that that would have been too complicated.
Does it matter, in fact? is the total exposure influenced if you just shift the exposure window in time? have to think about this...
 
By the way, for a good working leaf shutter i can imagine this only matters -if it does -for the highest shutter speed settings. The opening/closing times are considerably shorter than the time of being open...
 
Read books?

Read books?

Sarcophilus Harrisii said:
Ansel Adam's book "The Camera" has a very informative discussion about the characteristics of focal plane versus lens shutters and their actual efficiency, strengths and weaknesses in use. Chapter 6 has a paragraph entitled "Shutter Efficiency" and he suggests that usually lens shutter speeds are calculated on basis of full aperture. It also discusses changes in effective speed at other apertures; in general leaf shutter efficiency decreases at higher speeds as it deviates from theoretical ideals more than at slower speeds.

I acquired a factory service manual for dozens of different Compur shutter ex ebay a few years ago which provides detailed information about adjustment and lubrication etc. They were built to tight tolerances so a fairly notorious for running slower than their stated maximum speeds and Deckel themselves stated a generous 20% acceptable tolerance for accuracy. As long as the shutter adjustment is correct and the mainspring and booster spring (if applicable) is in good condition I am not sure how much more accurate you are likely to make one that is clean, lubricated and in good working order. Please let us know how you fare though, as it would be interesting to hear some real-world experience of investigations into this.
Regards,
Brett
Click to expand...

You're asking modern photographers to read books? Bizarre concept!
 
Pherdinand said:
By the way, for a good working leaf shutter i can imagine this only matters -if it does -for the highest shutter speed settings. The opening/closing times are considerably shorter than the time of being open...
Click to expand...
Yes, it does matter, and yes, it becomes more important as speeds increase and vice-versa.
Regards,
Brett
 
Sarcophilus Harrisii said:
Yes, it does matter, and yes, it becomes more important as speeds increase and vice-versa.
Regards,
Brett
Click to expand...

have any numbers available? I 've never seen a number on the order of magnitude of a leaf shutter opening/closing time.
A \___/ type graph would be even better of course (eventually, upside down) :D
 
Indeed now that i htink of it, even the aperture setting should matter i.e. a smaller aperture means longer "open" time for the shutter, with the same speed settign, than a big aperture...
 
Pherdinand said:
have any numbers available? I 've never seen a number on the order of magnitude of a leaf shutter opening/closing time.
A \___/ type graph would be even better of course (eventually, upside down) :D
Click to expand...

Page 89 of the Adams book I mentioned previously has exactly the information in the form you request. He suggests that:
"The efficiency of a typical leaf shutter is usually in the range of about 60 to 90 percent.
The actual efficiency will vary depending on several circumstances. First, note that as exposure times become longer efficiency increases, since the difference between the actual and the ideal is proportionally smaller. Leaf shutters are obviously more efficient at slower speeds; at one or 1/2 second, the efficiency should be over 95 percent.
In addition, the aperture selected alters the actual exposure time for a given leaf shutter setting, since the blades uncover a small aperture more quickly than a large one. Thus the shutter's efficiency increases at small apertures. It's accuracy, however, may be greatest at large apertures if the shutter, as is usually the case, has been calibrated for full aperture."

​
Again, I recommend consulting Adams's book for a worthwhile discussion of the characteristics of both focal plane and lens shutters.
Regards,
Brett
 
Last edited:
sevo said:
With leaf shutters, it is bound to be a bit more complex, as they have a bidirectional pattern, so that different parts of the shutter area are open for different times - that causes the timing accuracy (especially for short times) to be aperture dependent.

There must be some definition for the measurement beam pattern and aperture. However the shutter service manuals I own contain nothing like that.

Perhaps there was a de facto standard set by the then common makes of shutter testers - unfortunately these (which would have been made in Germany) seem to have perished to the degree that nobody even seems to know the makers and models any more. Even the more recent (Japanese) Kyoritsu SLR focal plane shutter testers are as rare as hen's teeth. Or there was some former DIN that defined leaf shutter tests - unfortunately researches there cost a arm and a leg, as the standards body wants to be paid for each search request...
Click to expand...

I remember reading about the leaf shutter some 30 years ago. There was mention of how the shutter blades opening from the middle, but almost at the same time, out to the edges, aided in accurate exposure. Unfortunately I don't recall the specifics, and I seem to recall I had trouble conceptualizing it since the middle of the shutter opened first and stayed open longest. I guess it must give some acceptable amount in an acceptable intensity to be called a certain 'speed.'
 
Jockos: Yes exactly like that. (fast jag uppfann det själv:)

oftheherd: The shape of the individual leaves help too. Aperture leaves aim at circular openings while shutter leaves try to open as quickly as possible. See picture below:

Pherdinand: The 'V'-shape is quite pronounced with a sloping flank for a few milliseconds before the actual full opening. I'll remember taking some photos of it next time.

Thanks all for the tips. I am learning to do my own CLA properly now, with Moebius synthetic oil and so on. Disassembling/reassembling shutter of various kinds is a part of the hobby:)

attachment.php
 
You must log in or register to reply here.
Back
Top Bottom