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

[holmburgers]

Hi everyone,

So I'm looking for a practical way to determine the effect & degree of shutter efficiency at high speeds and small apertures.

Or, rather than determine it myself, are there any steadfast guidelines that one can go by?

I read the Leslie Stroebel book and she (he?) has an elaborate method to test this using neutral density filters. I don't have any and I'm not gonna go buy any just to test this, nor do I wanna go thru a lot of film to figure it out (I know, I'm lazy and cheap! )

I have electronic readouts of my shutter speeds, so that variable can be eliminated, but if anyone has done some tests themselves & would like to share, I'd love to know.

For what it's worth I have a Synchro-Compur in a Schenider 180mm/315 Symmar (convertible type, the golden oldy)

 

[RalphLambrecht]

How do you have electronic readouts for large-format shutter speeds, and what else do you need to determine shutter efficiency? I'm failing to understand the problem.

 

[Ian Grant]

High shutter speeds and small apertures don't really go together in practice.

I live in a region where once the sun comes up it's almost maximum readings in my light meters all day, and even a 400 ISO film at 400 EI doesn't allow maximum speed and smallest aperture, and that's why Strebel has to use ND filters.

It might surprise you that I do use 400 ISO films , actually HP5 @ 200 EI because I need to work hand held and stop down well, but the fast shutter speed/small apereture is never an issue.

Ian

 

[holmburgers]

Well, I sent it to Paul Ebel and he told me the actual shutter speeds (from an electronic tester). I don't own one.

And by shutter efficiency I'm talking about the phenomenon that a small aperture get's a more "perfect" shutter cycle than a large aperture, which is particularly a problem at high speeds where the time it takes to open & close is a higher % of the total shutter time.

 

[holmburgers]

Ian,

Stroebel doesn't use ND filters for the purpose of exposure, but for the purpose of testing this phenomenon.

And regardless of the fact that yes, I'll probably never need to use f/22 and 1/200th, I'd like to know at what point this becomes an issue.

But you're probably right that I won't run into any problems.

However, at what shutter speed would one theoretically need to start thinking about shutter efficiency?

 

[Ian Grant]

And by shutter efficiency I'm talking about the phenomenon that a small aperture get's a more "perfect" shutter cycle than a large aperture, which is particularly a problem at high speeds where the time it takes to open & close is a higher % of the total shutter time.

It's theory rather than reality, when you've been using a wide variety of camera's and lenses for years you'll realise eventually

Ian

 

[holmburgers]

Alright, I'll take your word for it.

But when my million dollar picture is ruined because of shutter efficiency, I'M COMING AFTER YOU! just kiddin'

 

[RalphLambrecht]

Well, I sent it to Paul Ebel and he told me the actual shutter speeds (from an electronic tester). I don't own one.

And by shutter efficiency I'm talking about the phenomenon that a small aperture get's a more "perfect" shutter cycle than a large aperture, which is particularly a problem at high speeds where the time it takes to open & close is a higher % of the total shutter time.

The issue is simply due to geometry. 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. Opening and closing the shutter usually takes 2-3 ms each. However, in practise it is rarely a problem, because large apertures and fast shutter speeds are not the norm with large-format photography, and some of the delay is taking into account by the maker of the shutter by adjusting the timing and assuming medium apertures.

If you still want to test, use your friend's shutter tester at max shutter speed and different aperture settings.

 

[ic-racer]

However, at what shutter speed would one theoretically need to start thinking about shutter efficiency?

I'd just ignore it and worry about something else

 

[holmburgers]

Thanks for the reply.

I'm familiar with the mechanics of it, but I've heard that manufacturers calibrate for large apertures, so that at small apertures and high speeds you actually overexpose.

Either way, Paul Ebel is a repair guy & I don't think that a shutter tester would tell me what I need to know (but it seems like I don't actually need to know this)

Though!.... I'd still like to.

Knowing that it takes 2-3 milliseconds might help me in calculating the degree to which it might be a problem.

 

[holmburgers]

I'd just ignore it and worry about something else

I'm not trying to be pedantic, I just want to know.

 

[RalphLambrecht]

... I don't think that a shutter tester would tell me what I need to know (but it seems like I don't actually need to know this)

Though!.... I'd still like to.

Knowing that it takes 2-3 milliseconds might help me in calculating the degree to which it might be a problem.

A shutter tester will tell you exactly what you want to know.

 

[Q.G.]

The effect is indeed rather the opposite as what has been said before. Shutter efficiency issues at small apertures lead to too long speeds and overexposure. Not to too short speeds and underexposure.

The effect is real, and you should allow for it at (usually) the top speed of the shutter, 1/500.
It is, by the way, why the big Mamiyas have a 1/400 top speed marking instead of 1/500.
And that is about the size of the effect too. A bit more perhaps: upto just under 1/2 stop overexposure at 1/500, depending on the aperture used, of course.


A focal plane shutter, by the way, also suffers shutter efficiency problems, though not aperture dependent, but depending on speed and distance to film.

 

[Voyager13b]

I remember the subject being discussed in magazines and books back in the 70's, when there were quite a few leaf shutter lenses in use as a percentage of the market. It wasn't an issue with strobe light, for obvious reasons, but with ambient light, high shutter speeds caused an uneven exposure at the edges of the frame compared to the center. There was only so much tweaking that could be done to compensate, as pushing the exposure at the periphery of the frame tended to overexpose the center. The effect also caused some unique funky looks to stop motion shots that had no parallel in the focal plane shutter world.

I think this is the reason some companies limited top speed to 1/400 sec, as even with modern shutters having fast opening and closing times, the problem would begin to appear at 1/500 sec unless the lens was stopped down pretty far. It's been a long time since then, but I could swear that there were some charts from Hasselblad Paillard back in the 70's that mapped out problem shutter/aperture combinations. Then again, there was a soft-cover magazine sized book about a half inch thick titled "Medium Format Cameras" or something close that I recall tackled the subject. Maybe someone here still has that book, and can let us know if I'm thinking about the right book....

 

[RalphLambrecht]

The effect is indeed rather the opposite as what has been said before. Shutter efficiency issues at small apertures lead to too long speeds and overexposure. Not to too short speeds and underexposure...

Correct, who said something different?

 

[david_mizen]

isnt the optical aberrations going to be a greater issue than shutter efficiency at wide open apertures given that lens correction is optimised for f16/f22?

 

[cowanw]

Which makes me think of the mounting of packard shutters in camera.
If a 5 inch packard was mounted in camera and fired at 1/15 sec., would there be a difference in exposure if you used a lens with a 5 inch diameter glass or a lens with a 2 inch diameter glass at the same f stop? I suppose there has to be.

 

[holmburgers]

Finally, a resource...

Ok, I found an eBook that talks about it. Page 8 & 9, and it actually gives a table. Though I'm not sure what the left-most column means. It says "When the lens is closed down by (stops):......" Does that mean closed down from maximum aperture? Kind of a weird way to word it, eh?

Thanks to those who attempted to answer my question instead of just dismissing it as fretting over particulars.

http://books.google.com/books?id=pKFVX-KVU6EC&pg=PA6&lpg=PA6&dq=shutter+efficiency+leaf&source=bl&ots=f-vMgCPUdb&sig=v-v7oi7QAkTREUGots94uPEnB-0&hl=en&ei=Rt6XS5P0N5rIMuXZrHs&sa=X&oi=book_result&ct=result&resnum=9&ved=0CCIQ6AEwCDgK#v=onepage&q=shutter%20efficiency%20leaf&f=false

 

[John Koehrer]

#4 in this thread, "And by shutter efficiency I'm talking about the phenomenon that a small aperture get's a more "perfect" shutter cycle than a large aperture, which is particularly a problem at high speeds where the time it takes to open & close is a higher % of the total shutter time."
I think the convention is : a large stop is a lower number, not higher IE:2.8= a large stop & 16= a small stop. that's why it called "stopping down"
This depends on whether you're looking at the f number or into the lens

 

[ic-racer]

I'm not trying to be pedantic, I just want to know.

Seriously, I was just answering your question when I said 'ignore it' as that is the guideline many follow with negative film where a slight overexposure is inconsequential

are there any steadfast guidelines that one can go by?

I, like you, am also curious, and if I wanted to quantify the effects I'd break it down into two possible paths of discovery.
One path would be an emperic method. For example, you could plot exposure at the film plane vs aperture for a number of apertures and quantify the deviation from a straight line by using a curve fit and then making an equation that would solve your variable based on the curve.

The other way would be to do an a priori calculation. In which case you would need to know the size and shape and velocity of the shutter blades, and some complex math to associate bizzare aperture shapes with their light passing capacity etc.

Realize that in both cases results would apply only to the system tested or mathematically evaluated because shutter shape and velocity is not standardized.

 

[Saganich]

I have noticed exposures which were greater then anticipated when shooting 1/500@f16. Never thought much of it until now.

 

[RalphLambrecht]

I have noticed exposures which were greater then anticipated when shooting 1/500@f16. Never thought much of it until now.

This combination is a candidate for slight overexposure, but I would be surprised if one finds it to be obvious with B&W negative films.

 

[holmburgers]

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).

 

[kristopher_lawrence]

you main problem will be the shutter calibration, especially at high speed. 500th of seconds is rarely attained in reality for instance on a leaf shutter.

Same with leica: the 1000th is rather a 750th in reality.

This never been a problem for me in real world situation even when shooting slides.

Best,

K

 

[lxdude]

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?