Talk:Shutter (photography)

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Contents 1 Early discussion 2 Discussion at diaphragm (optics) 3 Some interesting examples of shutters 4 Intermittent mechanism 5 Shutter Lag 6 Merge?

[edit] Early discussion

Can a subject matter expert please add to this entry? I'd like to understand why central shutters do not expose the center of the frame longer than the edges.

The article does say, "[i]deally the opening and closing are instantaneous..." The current article correctly explains the reasons this is true, and also correctly does not mention anything about exposing the central parts of the image more than the periphery. I would like to understand, though, the reasons behind why central shutters do not overexpose the central portion of an image. Severoon 22:36, 21 February 2006 (UTC)

I'm not an expert, but I do work on cameras, so I know something about them. First of all, a terminology problem: nobody calls them "central shutters". These shutters are almost always referred to as leaf shutters, so that's the term I'll use.

It's true that, ideally, the shutter opens and closes "instantaneously". Obviously, this cannot happen in the real world. But it turns out that, for all practical purposes, they really do work nearly instantaneously; hence, the edges are not underexposed as you might expect.

Leaf shutters are nearly identical in their basic design and operation. The shutter blades are operated by small pins attached to the blades, which run in holes or grooves in a ring around the outside of the shutter opening. When the ring is turned a very small amount, the blades open. Since the distance between the blade pivot and the operating pin is so short, this works as a lever, so the working part of the blade, which is much longer, is really whipped open (and closed) quite fast. They seem to open and close instantaneously, with no perceptible "irising". Pretty fascinating stuff, actually.

In fact, leaf shutters are famously much less prone to uneven exposure problems than focal-plane shutters. In a FP shutter, if the curtains don't travel at pretty much identical speeds, you get problems with "fade", where one edge of the frame is significantly more exposed than the other edge (in the direction of curtain travel). I've seen, and had to fix, this problem with several of my own cameras. ==ILike2BeAnonymous 07:35, 22 April 2006 (UTC)

Hmm...I think you've presented the misunderstanding I was asking someone to address in the article. Diaphragm shutters (the iris type comprised of several curved blades) do not open or close, for all intents and purposes, instantaneously. The time it takes this kind of shutter to open and close is not at all instantaneous compared to the fastest shutter speed available on a given camera. In fact, the limiting factor on shutter speed is indeed the travel speed of the leaf shutter itself...you can bet that at the fastest available shutter speed, the relative amount of time the shutter spends in transit is not negligible at all.

I'm asking for someone to address this very topic in the article because of the misconception you express. Even a very slowly travellng diaphragm shutter would not, as you seem to indicate, underexpose the edges. If this were true, then setting small apertures would only expose the central region of the frame, right? Think about it, and you'll understand...you take a shot with an aperture of f/2 and the entire frame is evenly exposed, you take the same shot at f/64 and the entire frame is still evenly exposed despite the iris being only a tiny fraction of its size at f/2. This means when you take the shot at f/2, as the shutter opens and travels through f/64, f/32, etc, at every position along the way light is transmitting to every part of the image frame evenly.

Incidentally, a leaf shutter is indeed a type of central shutter, but it's not the iris type you're talking about—that's a diaphragm shutter. Click the links to learn more. Severoon 10:22, 28 April 2006 (UTC)

Let me respond to your comments. First of all, to get the easy subject out of the way: the last thing you wrote deals with semantics. Yes, all these shutters are indeed types of central shutters. But I stand by my assertion that almost all central shutters are what are commonly referred to as leaf shutters (more properly "diaphragm shutters" as you point out). By this, I mean bladed shutters with at least 3 blades, which form an iris in opening and closing. This covers the vast majority of in-lens shutters (Compur, Pronto, Prontor, Copal, Kodak, Vario, etc.). A very few earlier shutters, like the Derval, used only two blades, so they were not diaphragm shutters, but these were only used on cheaper shutters with three speeds (generally 1/25, 1/50 and 1/100), or what someone once told me are "shutters where you can pretend there are three different speeds", as they're notoriously inexact. And of course some really cheap cameras (like the 120 and 620 fixed-focus one-speed jobs) used one single shutter plate.

With that out of the way; so you're saying, basically, that leaf (diaphragm) shutters are inherently self-correcting so far as evenness of exposure over the field goes, correct? I'm not disputing that, just checking.

If so, you may be correct. But it seems to me that this would depend on the proportion of time the shutter spends fully open versus the time it takes to open; correct? In other words, if the shutter takes a relatively longer time to open than it does staying open, wouldn't the center tend to be overexposed?

But since in the real world photographs taken with leaf shutters are, from my experience, always evenly exposed for all practical purposes, maybe we should just leave things as you have put them. Which, unfortunately, means your original question is still unanswered.

In my search for material on the web, the best I've been able to come up with is this page on Compur shutter operation, from Rick Oleson's inestimable camera site (worth digging around in if you haven't seen it before). But he doesn't talk about the matter of blade speed, exposure evenness, etc.

I'm not saying that diaphragm shutters are self-correcting—I'm saying they need no correcting because light that passes through the iris, regardless of the diameter, is spread evenly over the entire frame. The size of the iris affects depth of field, not coverage over the frame. As I said, just think about the effect of changing f-stops on the resulting image...no matter how small the aperture, the light falls evenly on the frame. Only dof is affected. Severoon 09:15, 1 May 2006 (UTC)

Bingo! Epiphany time: now I see what you mean. Of course; since it's not at the focal plane, it acts as an iris. So this ought to go into the appropriate articles, no? ==ILike2BeAnonymous 19:05, 1 May 2006 (UTC)

[edit] Discussion at diaphragm (optics)

There is a discussion at Talk:diaphragm (optics) about various similar terms with separate articles on Wikipedia, and trying to clarify what these terms all mean (from a confused amateur photographer!)... Carcharoth 23:25, 18 May 2006 (UTC)

[edit] Some interesting examples of shutters

While disambiguating links to shutter, I came across some interesting uses of the word shutter, uses that might be related to photographic shutters:

• Movie projector#Shutter - are these similar but different to shutters on a camera? One lets light in, and the other lets light out!
• Tachistoscope - the shutter on this device works a lot like the shutter on a camera in the sense that it is a one-use opening and closing of the shutter (as opposed to a continuous opening and shutting in a projector. But the light is still being emitted, rather than admitted. So should this article link to Movie projector#Shutter or shutter (photography)?

So are these projector shutters different from photographic shutters? And in what way? And should this be mentioned in the relevant articles? Carcharoth 00:28, 20 May 2006 (UTC)

Movie projector shutters are the same as camera shutters: they open an aperture for a certain time (and, in the case of the movie projector, at a certain time). Almost all movie shutters (cameras and projectors) are rotary (as are some peculiar still-camera shutters, notably the Univex Mercury and Olympus Pen F half-frame 35mm cameras).

By the way, you have it wrong: the purpose of a shutter on a camera (as well as the purpose of a door to a darkroom) is to keep the dark from leaking out. ==ILike2BeAnonymous 00:47, 20 May 2006 (UTC)

"Keep the dark from leaking out" - classic!! Next thing you'll be telling me the world turned colour in the 1930s... :-) Carcharoth 01:05, 20 May 2006 (UTC)

Another example of a shutter is at Signal lamp. Does this sort of shutter count as a photographic shutter? I think this is now broadening to have a general shutter (optical) terminology, with different sorts of optical shutters being used in projectors (with a signal lamp being a sort of projector) and cameras. Carcharoth 01:24, 20 May 2006 (UTC)

Since we're on the subject of oddball shutters, here are some more:

• Of all the cameras I own, the one with the weirdest shutter has to be my Exa, one of the original 35mm SLRs. Hard to describe what type of shutter it is, actually. Like a lot of early SLRs, this camera is "dark" (can't view through the lens) until the shutter is cocked. The shutter consists of the mirror board plus another part that swings horizontally below the mirror. Not a focal-plane shutter, not a leaf shutter. (Speeds up to 1/150 sec.)
• Another notable strange shutter, sort of, is the Packard shutter. While this is really just a simple 2-leaf shutter, what's interesting about these is how they're used. Their purpose in life is to give shutter-ness to lenses with no shutters, like the lenses formerly used in copy cameras and other graphic-arts uses, for large-format cameras. They're extremely simple: they're pneumatically operated with a squeeze bulb, and some only have a "bulb" setting (stays open as long as the bulb is squeezed), while others have an optional "instantaneous" setting which gives a (very approximate) 1/25 sec. or so exposure. They can be placed either behind the lens or even in front of it, depending on the camera architecture. See here and here for more info (the second has contributions by the inestimable Richard Knoppow, photography guru who also posts to several Usenet newsgroups on photographic subjects).

In addition, it might be intereresting to point out the various mechanisms used internally by shutters. There are basically two types: mechanical and pneumatic. Mechanical shutters use levers, pawls, etc., to give certain timings, and clockwork delay mechanisms with buzzing pallets for "slow" speeds (anything slower than about 1/25 sec.). Pneumatic shutters (which are obsolete) use a piston and cylinder arrangement for slow speeds, like in the old Compound shutters. And of course, there are those newfangled electronic critters. ==ILike2BeAnonymous 03:10, 20 May 2006 (UTC)

[edit] Intermittent mechanism

I added a link to intermittent mechanism (or motion) from the movie projector bit at the bottom of the article. It sounds like the shutter and film bits of the projector both use intermittent mechanisms, but I'd be grateful if someone could check. Carcharoth 01:16, 20 May 2006 (UTC)

The film-moving mechanism (claw) is intermittent, but the shutter rotates continuously. The claw moves the next frame into place, and while it is stationary, the shutter opens and closes, 2 or 3 times. ==ILike2BeAnonymous 02:49, 20 May 2006 (UTC)

[edit] Shutter Lag

Would this be an appropriate place for a discussion of shutter lag - the delay between pressing the shutter release and the damn thing actually going off? This seems to be more relevant than ever in this brave new world of digital imaging! 88.110.45.118 22:50, 25 May 2006 (UTC)

I would be say no, but then, I'm a Luddite who still uses real cameras (ones which use film). I'm curious: just how long a delay are we talking about here? Half a second? More? I guess it could be relevant to digicams. ==ILike2BeAnonymous 23:11, 25 May 2006 (UTC)

It is hard to find figures, one would think that users would be more concerned. Compact digital cameras are said to be anything up to 1.5 seconds! Digital SLR's stated of the order of 100 - 150 milliseconds but my subjective feeling is that they are always slower than proper SLR's, whether electronically controlled [F4], or mechanical [FM2 or OM-1]. To my great surprise I have just found a figure of 200ms for the MD-12 drive on the FM-2. Subjectivity again, but over thousands of images taken with a Nikon D70, my wastage rate in demanding situations is far higher than it would be with a film camera. Moel Faban 23:53, 25 May 2006 (UTC)

Added the section. Go ahead and flesh it out. ==ILike2BeAnonymous 00:03, 26 May 2006 (UTC)

I see no reason whatsoever why a dSLR would by nature have more shutter lag than a film SLR. If you have any compelling evidence or reasoning behind this statement, let me know because I'd be interested to see what I'm missing. I shoot a Canon 30D right now, and from what I understand, what little (unnoticable to me) lag there is is due to the mirror flipping up and out of the way, which is exactly the same in a 35mm film camera. Well, not exactly, actually...since the 30D has an APS-C sized sensor, the mirror required to block it is smaller and therefore likely lighter than the one required in a 35mm film camera. Therefore, if anything, I'd expect it to lag less. Severoon 23:31, 27 June 2006 (UTC)

"....on the order of hundreds of milliseconds..." That's rather opaque! DMCer 05:43, 1 February 2007 (UTC)

[edit] Merge?

Since diaphragm shutter got merged into leaf shutter, perhaps it would make more sense to merge the combined article into this article and deal with it all in one place.--Srleffler 03:52, 12 December 2006 (UTC)

Support. Yes, they're too narrow to be separate. Dicklyon 05:10, 12 December 2006 (UTC)

Support, indeed. Scoo 07:18, 13 December 2006 (UTC)

Disagree. On the contrary, the Shutter article should explain what a shutter does and where it goes, with details on the various mechanisms in separate articles. Pol098 22:45, 2 April 2007 (UTC)

Thanks for your alternate view. However, since the articles are all so short, does this really make sense? Wouldn't subsections be the more conventional way to organize it? We pretty much decided to do the merge, hearing no dissent, but nobody has gotten around to it. Dicklyon 23:50, 2 April 2007 (UTC)

In which case you'll need to undo stuff I deleted from shutter which was duplicated in leaf shutter (as far as I remember). I've made a number of changes to shutter, leaf s, and central s. I maintain my preference for separate articles, but appear to be in the minority. Pol098 20:13, 5 April 2007 (UTC)

So who's going to do this? Dicklyon 21:13, 28 January 2007 (UTC)