Shutter Efficiency w/ Leaf Shutters & Higher Speeds...

lxdude said:

Here's a question-leaf shutters have a "twisted star shape" when less than fully open. At higher speeds and small apertures is there any noticeable effect on bokeh, maybe in say, out of focus highlights?

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How can there be, the restricted aperture negates any effects of the shutter, other way around, fast speed & wider open then just a tad more DOF, less that sick US word

Ian

RalphLambrecht said:

Correct, who said something different?

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RalphLambrecht said:

As the shutter opens, a small aperture is quickly revealed, while a larger aperture needs to wait until the shutter has fully opened. This can lead to underexposure with large apertures and fast shutter speeds, because the shutter delay becomes a significant portion of the the entire exposure time.

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It never leads to underexposure. Always to overexposure.

I know, i know: you were explaining things.
But only mentioning underexposure was enough for the OP to come back with "[...] but [...] at small apertures and high speeds you actually overexpose."
I confirmed that.

Q.G. said:

It never leads to underexposure. Always to overexposure...

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Incorrect!

I repeat your quote of my statement:

This can lead to underexposure with large apertures and fast shutter speeds, because the shutter delay becomes a significant portion of the the entire exposure time.

I stand by that statement, because during the shutter's operation, a small aperture is fully revealed for most of the time, where a large aperture is only fully revealed for a small fraction of that time.

RalphLambrecht said:

Incorrect!

I repeat your quote of my statement:

This can lead to underexposure with large apertures and fast shutter speeds, because the shutter delay becomes a significant portion of the the entire exposure time.

I stand by that statement, because during the shutter's operation, a small aperture is fully revealed for most of the time, where a large aperture is only fully revealed for a small fraction of that time.

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Yes.

And because people building shutters aren't stupid, they allow for that. The shutterspeed isn't measured form the time the shutter is fully open until it is not.
They can't allow for small apertures (they could, but neither you nor i would want to pay for such a shutter), and thats why - like i said - you always (!) get overexposure, never underexposure.
So even in textbooks explanations of why you get overexposure, that is correct.

holmburgers said:

ic-racer, thank you for the clarification. I didn't mean to snap.

and John Koehrer, I apologize if I used confusing wordage. By "small aperture" I'm referring to the actual aperture size or iris diamater; that is, f/16 and up. Large aperture meaning f/5.6 (in the case of my lens).

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Aperture is the size of the opening in the diaphragm. F/stop is the number assigned to it. Smaller apertures = greater f numbers. "Nobody" ever casually uses the actual size of the opening in conversation, hence the confusion comes from the incorrect use of the word aperture, which is rarely going to be used in a casual conversation about photography. The word aperture is, often and everywhere, erroneously used to mean diaphragm (e.g. "aperture blades"), and to mean f stop (e.g. "stop down to a higher aperture").

My solution: I don't use the word aperture unless I am talking about the actual physical size of the opening in the diaphragm. Any time I am talking f numbers, I use the term f stops. People often say, "I know all my apertures and shutter speeds", and I correct them to saying, "I know all my f stops and shutter speeds". I am now also making a concerted effort to avoid the terms "stop down" and "stop up" when speaking with students. I will instead say "close down" or "open up".

But the word aperture is indeed heard often. And almost always used correctly too. Just like the OP did.
I don't know why we should avoid the word.

Q.G. said:

But the word aperture is indeed heard often. And almost always used correctly too. Just like the OP did.
I don't know why we should avoid the word.

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We should not avoid the word. We should avoid using the word to mean anything other than aperture, or in a way that might be confusing to those who do not yet know better.

The phrases "stop up" and "stop down" seem to be the most confusing to beginners, as they are a hybrid of "open up or close down your aperture", and "select a lesser or greater f number". They are second nature to me, but I am trying to avoid them.

Another doozy that throws anyone for a loop is "smaller/larger f stop". When someone says that, you don't have much of an idea which way they are saying to go. Are they using the term f stop incorrectly to mean aperture? Are they using it to mean a smaller/larger denominator in the f stop? In short, you don't know if they are talking about the quotient, or just the denominator.

I try to avoid "smaller/larger" for anything but references to the aperture. I use greater and lesser, and I also use f number instead of f stop, to make it clear that I am talking about the denominator only.

The use by the original poster was correct in the original post, though vague ("...small apertures..."). I will have to look for the one that was not.

If it is understood that "aperture" means nothing more nothing less than "opening", that when you stop something you fill in an opening, there should not be much confusion, yes.

Talk about aperture does not have to be talk about the actual, i.e. 'non-optical', size of the opening. No such restrictions exist.

I would avoid saying things like "stopping up" (must say i haven't heard that one before). "Opening up" and "stopping down" it is.

A smaller f stop indeed is a smaller opening, is a smaller aperture. That is correct.
You're confusing f stops with f-numbers yourself, i think.

Q.G. said:

You're confusing f stops with f-numbers yourself, i think.

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I am not. I am speaking of knowing whether or not to trust a fellow shooter; speaking of the fact that, not knowing the proclivity for accurate use of terminology by this person, and knowing the easy possibility for confusion in the matter, it can be bad to assume that they are always using the right terminology, and not a common misnomer for something.

So, when someone says "smaller/larger f stop", I always ask them to clarify. That was all I meant. I also stated that I personally use "greater/lesser f number". A lesser f number describes a larger aperture, and vice versa. The use of the word "number" clarifies that you are talking about the numbers on the lens, and not the size of the aperture.

I have always heard "stop up" and "stop down", and "open up" and "close down"...for...well, forever!

Yes. A smaller f stop is indeed a smaller aperture...but how do you know that the person to whom you are talking knows this?

In short, your "If it is understood..." is a rather huge IF. You can trust yourself, but not just anyone.

Maybe I have more faith in the general amount of extreme technical ignorance of most people than you do, so I try to be extra clear when talking with students and other shooters.

2F/2F said:

I am not.

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Not after you have edited your post, perhaps. No.

I agree that wrong use of words can be confusing. But we mustn't assume that people use terms incorrectly. If we don't know, we can ask indeed.

I see again that i should quote the entire post i'm replying to.
"In short", they get longer while i'm writing a reply.

Q.G. said:

I see again that i should quote the entire post i'm replying to.
"In short", they get longer while i'm writing a reply.

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Yes, I tend to write fast to get the vomit onto the page, and then rewrite constantly...as do most trained writers.

In this paragraph:

"The phrases "stop up" and "stop down" seem to be the most confusing to beginners, as they are a hybrid of "open up or close down your aperture", and "select a lesser or greater f number". They are second nature to me, but I am trying to avoid them."

I originally had the word stop where number is in this paragraph. I did not, however, change anything in response to anything you wrote, to make myself more correct, as you have stated.

In this case, the change does not make me any more or less correct. The edit came from my realization that I had myself used the word stop where by my own standard I should have used the word number. The correctness remains the same with either word in this particular sentence, but I wanted to meet my own standard once I explained it in a later added paragraph. Additionally, note the quotations. They indicate that these are common phrases, not necessarily how I would state them.

2F/2F said:

Yes, I tend to write and rewrite constantly.

I did not, however, change anything in response to anything you wrote.

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Perhaps not. But you added stuff, turning the thing around a bit.
How does that not qualify as changing anything?

I've inserted a longish pause here...
And lo and behold:

2F/2F said:

Yes, I tend to write fast to get the vomit onto the page, and then rewrite constantly...as do most trained writers.

In this paragraph:

"The phrases "stop up" and "stop down" seem to be the most confusing to beginners, as they are a hybrid of "open up or close down your aperture", and "select a lesser or greater f number". They are second nature to me, but I am trying to avoid them."

I originally had the word stop where number is in this paragraph. I did not, however, change anything in response to anything you wrote, to make myself more correct, as you have stated.

In this case, the change does not make me any more or less correct. The edit came from my realization that I had myself used the word stop where by my own standard I should have used the word number. The correctness remains the same with either word in this particular sentence, but I wanted to meet my own standard once I explained it in a later added paragraph.

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This doesn't work, 2F.

1. Assuming that people are wrong put you in this strange mess.
2. Do you indeed first ask? Considering 1. why?


Yes indeed you did change the meaning of your statement!
Hoping to make it sound more correct, i presume. (I only presume, not assume, that people are incorrect )

2F/2F said:

The phrase I used was, "I did, however, change everything in response to anything you wrote."

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You'll do it anyway (thus making a conversation nigh impossible), so i might as well not wait and do it myself.

Q.G. said:

Not after you have edited your post, perhaps. No.

I agree that wrong use of words can be confusing. But we mustn't assume that people use terms incorrectly. If we don't know, we can ask indeed.

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1. I do assume this. I must. I consider it a good survival skill that has been honed based on experience.

2. I do ask...often...because of number one!

Q.G. said:

Perhaps not. But you added stuff, turning the thing around a bit.
How does that not qualify as chancing anything?

I've inserted a longish pause here...
And lo and behold:

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I added stuff. I did not change meaning or "[turn] the thing around a bit".

The phrase I used was, "I did not, however, change anything in response to anything you wrote."

If I intended to not change anything, I would not edit. Thus, of course I never stated that I did not change anything.

So, your question, "How does that not qualify as chancing anything?" cannot really be answered, because it refers to a statement that was not made.

"This doesn't work, 2F.

"1. Assuming that people are wrong put you in this strange mess.
2. Do you indeed first ask? Considering 1. why?


"Yes indeed you did change the meaning of your statement!
Hoping to make it sound more correct, i presume. (I only presume, not assume, that people are incorrect )"

1. There is no strange mess...except the one that follows you around these forums. You are a knowledgeable and helpful person, and I appreciate you being here...really! A lot! ...but things tend to get really useless really fast when you start going back and forth with someone.

FWIW, my assumption that I stated is, "I do assume this." It was in response to your statement, "But we mustn't assume that people use terms incorrectly." Therefore, I stated nothing but I assume that people use terms incorrectly. I did not say EVERYBODY or ALL THE TIME.

Would it not make sense to ask what people mean, knowing that people use terms incorrectly?

...and yes, it is to assume: to suppose to be the case, without proof. I have not polled the world scientifically...just collected experience and used it to make assumptions about future experiences.

People, especially students, but all sorts of people, really, tend to be unclear on technical terminology. I know this, and I do not assume that they are correct when they use a term. That can be a shoot-ruining disservice in some cases. I assume that most of them use terms incorrectly, at first. An assumption is simply an assumption. It is not a be all and end all, to be taken with great weight. It just prepares one to deal with certain situations and approach them a certain way. It does not mean that things will always go the way of your assumption...not at all!! Being wrong in an assumption does not bother me. The point of having an assumption is not to be "right" all the time. The assumption is there for good reason, whether it is strengthened or not in a particular situation. As you get to know certain folks, you know when to be more wary that they don't really know what they are saying, and when when to be more confident that they mean what they say. Until proven otherwise by experience with an individual, I will assume that he/she needs to be asked for clarity in a situation like the following:

2. I ask upon being asked something like, "I am supposed to use a smaller f stop, right?" This could mean one of two things. I ask things like, do you mean a smaller aperture, or a larger aperture? More light or less light? More depth of field of less depth of field?

I do not ask before, because where does it end? Do you have to quiz someone on his/her use of terminology before they may ask you a question in the studio or the darkroom? What about 20 or 30 someones? That is what lecture period is for. To learn that stuff. Lab is to reinforce it through practice...which I help to do...but not by repeating an entire lecture when a student has limited tie in studio or with an enlarger.

As for why I ask, it is to find out what they meant by their statement...so I know what they meant. Just because I assume that people use incorrect terminology does not mean that everyone does...it just means that they can.

My points in this all: Lots of people use incorrect terminology. 1. We should be aware that this is the case, and 2. We should strive to be extra clear with terminology in accident-prone situation (operating a camera), especially with those whose level of accurate terminology use is unknown or little known.

That is all...and it got blown into picking nits...because we both have time and are stubborn, I guess.

I really do not appreciate the misquote, even in jest. It's point is also incorrect, IMO. I rarely change everything in an edit, and I certainly did not in this thread.

So, good evening.

2F/2F said:

1. There is no strange mess...

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The strange mess, 2F, is the one in which a post, after it has received a reply, doesn't say what it did before anymore.

The thing to do, 2F, is to deal with replies to posts by posting a further post.

The thing not to do, 2F, is to deal with a reply by altering the original post.

Q.G. said:

Yes.

And because people building shutters aren't stupid, they allow for that. The shutterspeed isn't measured form the time the shutter is fully open until it is not.
They can't allow for small apertures (they could, but neither you nor i would want to pay for such a shutter), and thats why - like i said - you always (!) get overexposure, never underexposure.
So even in textbooks explanations of why you get overexposure, that is correct.

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Overexposure with small apertures, and underexposure wide open. It's all relative and depends on the aperture chosen to set the nominal shutter speed.

Wait a tick

This discussion has devolved....... but it's been mighty interesting!

For what it's worth, I originally said "small aperture". I never mentioned f-stops, and therefore I'm not sure where any confusion could arise. The word aperture means "opening, slit, gap....", and therefore by saying small aperture, I meant just that.

What seems funny to me is the obvious fact that even f16 isn't a LARGER number; it's a fraction! 16 is the denominator, therefore it's a smaller number than f1!

No one goes around saying that a McDonald's quarter-pounder is bigger than a two-thirds pound thickburger from Hardee's (or Carl's Jr, depending on where you're from ) because the denominator is bigger!

Have we forgotten the fundamentals here??

Oh, and by the way, why don't we keep personal tiffs between members hidden away in private messages. It looks bad for APUG & it's annoying to everyone else who isn't involved.

In other words, take it outside.

holmburgers said:

...No one goes around saying that a McDonald's quarter-pounder is bigger than a two-thirds pound thickburger from Hardee's (or Carl's Jr, depending on where you're from ) because the denominator is bigger!

Have we forgotten the fundamentals here??

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Perfect example! I must remember that one. The other one I heard was, Should I hit you over the head with a 1/2-inch or a 1/4-inch pipe?

It's indeed the denominator. That's why I prefer writing it f/stop and f/16, for example, to show that the aperture is the focal length divided by 16.

Oh poo!
Stopping up is what happens to a drain.
You don't commit vomit to a page, it's verbal diarrhea.
You can test a leaf shutter with no optics inserted & get an accurate result. Keep in mind though that ANSI/ISO tolerance is 25% at moderate to long speeds and 50% at high speeds 500 & greater.

Interesting thread so far. I just acquired a couple of Hasselblad lenses and am new to the system. I figured I'd try a lame attempt to test the shutter speeds, well at least the slow ones using a p&s digicam in video mode which records at 30 fps. I hold the camera to the back and fire the shutter while recording at 1s.... thru 1/30 figuring the slow shutter speeds are most likely to be off due to being gummy or worn springs etc. I review the video on the digicam and count frames in slow motion playback to see how close the speeds are. Not that this pertains a whole lot to this thread.... but during my search for info on the subject I found an article where a person used a DSLR and it's histogram function to check accuracy, which is much more sophisticated than my approach and might answer the OP's original question rather easily - see link:http://photo.net/large-format-photography-forum/00Uajj

If shutter opening/closing time is 2-3 milliseconds as mentioned above, the maximum error, when converted to shutter speeds, is somewhere between 1/500th and 1/320th of a second. This could be converted to a fraction of the exposure you are using and then added to the exposure. Example: my taking aperture is f8 and I'm using 1/125 sec. 1/125 + 1/500 (2ms) = 4/500 + 1/500 = 5/500 =1/100 or, about a third stop more exposure. Using max error, the difference would still be less than 1/2 stop.

If you really want to get picky, you could simply open 1/3-1/2 stop when using your widest apertures to compensate. However, your tested shutter speeds are likely made at full aperture and, therefore, you are more likely to be overexposing things taken at your fastest speeds, assuming you are calculating for the actual shutter speed when using faster than 1/60 (higher speeds on clockwork shutters are rarely as fast as indicated and have a tendency to overexpose anyway if you don't compensate...). In that case, you might want to close down a third of a stop at your fastest speeds, that is, if you use 1/125-1/500 regularly (I sure don't).

Or, assuming your shutter is consistently withing 10% or so (likely not), you can just have your shutter testing done at the aperture you use most (for most of us, somewhere around f22-32) and then calculate exposure using the actual shutter speeds rounded to the nearest 1/3 stop (way accurate enough).

Or, you can use neutral density filters to get your shutter speed longer, where there is much less error.

Or... you can just ignore the relatively small error, especially if you are shooting B&W, since it is well within "normal operating parameters" and won't have a practical effect on your final product. When in doubt, err on the side of overexposure a bit. Your metering, shutter inconsistencies, changing light, different film batches, how long you wait before you develop, etc., etc. will all have more effect than adjusting exposure for the difference in illumination due to shutter opening time at different apertures...

Best,

Doremus Scudder
www.DoremusScudder.com

Stumbled upon an interesting article slightly relevant to the topic...

Might need new graph due to different scan rates

Dead Link Removed

Dec 1967 pg 106 Smart way to check your camera shutter: Use your TV
...Shutter-calibration table...TV Lines - Exposure Time