Leaf shutter

[DCB]

I am searching for a good explanation of how a leaf shutter works with the f stop and speeds.

Is there a good video around?

Thanks

Peace

 

[Denverdad]

I'm not sure that I've ever seen a video explaining how leaf shutters work, at least not in any detail. There is a fair amount of information to be found online about leaf shutters, but it tends to be geared more towards servicing them as opposed to introducing one to how they function in a more general sense. Perhaps a good place to start would be this page which provides some some background explanation, but also includes a couple videos which show the operation of shutter leaves opening and closing. That is after all pretty much the heart of what is going on.

A key thing to get straight with leaf shutters is that the shutter blades are what actually snap open and closed for a specific duration, so as to control exposure time (speed). But there is also a separate mechanism to think about - the iris diaphragm - which is what you use to set the aperture or (f-stop). Sometimes the the two get confused, I suppose because they both have "blades" or "leaves" which can open or close to let light through.

Hope that helps!

Jeff

 

[Sarcophilus Harrisii]

I'm not sure that I've ever seen a video explaining how leaf shutters work, at least not in any detail. There is a fair amount of information to be found online about leaf shutters, but it tends to be geared more towards servicing them as opposed to introducing one to how they function in a more general sense. Perhaps a good place to start would be this page which provides some some background explanation, but also includes a couple videos which show the operation of shutter leaves opening and closing. That is after all pretty much the heart of what is going on.

A key thing to get straight with leaf shutters is that the shutter blades are what actually snap open and closed for a specific duration, so as to control exposure time (speed). But there is also a separate mechanism to think about - the iris diaphragm - which is what you use to set the aperture or (f-stop). Sometimes the the two get confused, I suppose because they both have "blades" or "leaves" which can open or close to let light through.

Hope that helps!

Jeff

Very true, however it's also worth noting that leaf shutters have been manufactured where the shutter blades combine the functions of both exposure duration, and effective f stop on the basis of how far they open up. Sometimes they feature maximum shutter speeds that are only obtainable at the smaller apertures, with the largest apertures being available at speeds less than their highest.

Ansel Adams's book The Camera has a good theoretical primer on the advantages and disadvantages of lens versus focal plane shutters. The topic has been discussed previously at RFF also.
Cheers,
Brett

 

[sevo]

Very true, however it's also worth noting that leaf shutters have been manufactured where the shutter blades combine the functions of both exposure duration, and effective f stop on the basis of how far they open up. Sometimes they feature maximum shutter speeds that are only obtainable at the smaller apertures, with the largest apertures being available at speeds less than their highest.

Once a leaf shutter spends all its time opening and closing it can never reach the fully open state, so that its leaves will obscure part of the aperture (it that is wider open than the shutter leaves). That effect has been tamed to build unified "program mode" shutters (as common on AF compacts) whose aperture is a function of its speed - the only widespread type of shutters without a separate aperture.

 

[Denverdad]

Very true, however it's also worth noting that leaf shutters have been manufactured where the shutter blades combine the functions of both exposure duration, and effective f stop on the basis of how far they open up. Sometimes they feature maximum shutter speeds that are only obtainable at the smaller apertures, with the largest apertures being available at speeds less than their highest.

Ansel Adams's book The Camera has a good theoretical primer on the advantages and disadvantages of lens versus focal plane shutters. The topic has been discussed previously at RFF also.
Cheers,
Brett

Yep! Actually I was being very careful at first to use the qualifier "most," but I seem to have lost that when paring down my response.

Anyway, as I look for online references to cite I can't help noticing how scare general information on the topic seems to be. I mean sure, there's all kinds of descriptions of how to repair this one or that, advantages/disadvantages compared to a focal plane shutter, details like how to accurately measure the speeds, whether they really reached advertised speed from the factory, and so forth and so on. But I have to think that for someone just trying to figure out the basic concepts , it must be hard to assimilate all of that into something resembling a basic "what is it and how does it work" level of understanding.

Jeff

 

[Rob-F]

Let's think about the special case where the iris is set wide open. As the leaf shutter begins to open, it initially behaves like an iris diaphragm that is stopped down to a small opening, producing good sharpness and good depth of field. At the next instant it is a little wider, slightly reducing DOF. Eventually it is completely open, with correspondingly limited DOF and probably some loss of sharpness. In between the fully open and fully closed extremes, it must produce every possible nuance of sharpness and DOF. Presumably, this results in the picture being a composite of an infinite number of gradations of sharpness and DOF. I should think that ought to produce a picture with a different character (not necessarily better or worse, but different) that you get with a focal plane shutter.

How different? I don't know, buy maybe a very gradual transition from sharp to unsharp; or maybe a three-dimensional "roundedness" or "3-D Pop."

Anyone ever noticed anything like that with a leaf shutter?

 

[Filzkoeter]

I believe the opening/closing of the blades is so fast that effectively nothing of it is recorded (at least at closed apertures or slower speeds, as the time the shutter takes to open and to close is very short compared to the exposure time itself).
It is often stated that leaf shutters run a little bit slow at the higher speeds (like 1/500 actually being often ~1/300)... I think that's a misconception based on disregarding how a leaf shutter works. I believe that as you stop down the aperture, the shutter effectively "runs faster" as the blades only have to cover a small opening and so the time of their travel is shortened.
So wide open you'll get something like 1/300 and stopped down the real 1/500.

 

[sevo]

I believe the opening/closing of the blades is so fast that effectively nothing of it is recorded (at least at closed apertures or slower speeds, as the time the shutter takes to open and to close is very short compared to the exposure time itself).

The opening is not quite that fast. Usually, the fastest times of a leaf shutter have no escapement (often that applies to both top speeds, the faster being formed by an increase in spring load). At that time (or these times), the shutter will constantly move throughout its action, closing immediately after it has fully opened. In that state, a shutter with linear action would lose about 2/3 of a stop given a lens that utilizes the full aperture circle. Most lenses however are not mounted in the smallest shutter that can fit, and for them that translates to less. And even in the said worst case, stopping down by only one stop will already eliminate that speed dependency completely (and view camera lenses are generally stopped down by three or four stops to match the sweet spot of the lens IQ).

 

[Dwig]

... I believe that as you stop down the aperture, the shutter effectively "runs faster" as the blades only have to cover a small opening and so the time of their travel is shortened.

That is not how the common leaf shutters work. They open all the way regardless of what aperture is selected ...

So wide open you'll get something like 1/300 and stopped down the real 1/500.

... thus, this is backwards with common leaf shutters.

The shutter opens at the center first and some time later reaches a fully open state. It then waits a while if the shutter speed is set below maximum and then closes, starting at the outside and finally, sometime later, finishes closing at the very center. As a result, when you set a small aperture, the shutter is open over that aperture longer than the mean effective open time would be if you had set the largest aperture. A shutter with a max speed of 1/500th and set to that speed will generally yield a exposure time of around 1/250 when set to an aperture some 4-5 stops below the maximum.

There were a few trick shutters that didn't exhibit this behavior or exhibited it to a significantly lesser degree. The in-lens shutter made for the last Super Speed Graphic comes to mind. This shutter had double-ended blades that spun on a central pivot and did not have to stop and reverse direction. This allowed it to achieve a 1/1000 top speed and its aperture shape while closing was not a continually reducing circle. Also, the many integrated shutter/iris shutters found in many program only P&S cameras where the shutter blades also act as the iris are programmed to compensate.