focal plane v diaphragm

[erikg]

They don't seem to constrain lens design options for Hasselblad.

Well they do. What is the fastest lens in the Hasselblad line? f/2.8 for the leaf shutter lenses (500 series), f/2 for focal plane shutter cameras (200 series). That 100 f/2 is spectacular by the way.

 

[Alan Gales]

Interesting. View camera users insist that some leaf shutters cause severe vibration..

I've heard that complaint about the large Copal 3's and also the Sinar shutters.

 

[film_man]

If FP shutters are that good, why does my Hassy have a facility to lock the mirror up and use the leaf shutter for exposure? To presumably cut down on vibration.

Obvious question number 3: if you lock up the mirror, which component's vibration do you eliminate?

 

[benjiboy]

I've never understood this because in an SLR by the time the mirror hits the bumper the picture has been taken.

 

[film_man]

I've never understood this because in an SLR by the time the mirror hits the bumper the picture has been taken.

Are you sure about that? I thought it needs to move out completely first, I guess it depends on the camera design and space in the mirror box. Besides, yt is not just hitting the bumper, the torque from rotating it is also causing shake.

 

[lxdude]

I've never understood this because in an SLR by the time the mirror hits the bumper the picture has been taken.

Where'd you get that idea? The shutter starts moving after the mirror reaches the bumper at the top of the miror box. Otherwise, the mirror would cut off part of the image from most lenses, and light from the eyepiece could enter the mirror box and reach the film.

 

[Steve Smith]

Where'd you get that idea? The shutter starts moving after the mirror reaches the bumper at the top of the miror box. Otherwise, the mirror would cut off part of the image from most lenses, and light from the eyepiece could enter the mirror box and reach the film.

On a lot of cameras, the operation is sequential with each part triggering the next.

e.g. the shutter button starts the mirror moving, the mirror reaching the top of its travel triggers the shutter, etc.


Steve.

 

[flavio81]

They don't seem to constrain lens design options for Hasselblad.

They do, because shutters cannot be "grown" to bigger sizes so easily. So the shutter throat diameter limits the max speed of the lenses.

The same happens in the RB67, and for example you see the normal lens (90mm) being f3.8 (3.5 in a later model), and the 180mm lens being f4.5. However, if you would want a theoretical 180mm f2.8 lens for 6x7 format, it would be so big and heavy that it would render the lens impractical.

The Pentax 6x7 machine has a focal plane shutter and it has a much faster normal lens available. However, if forums are to believed, the 6x7 has some residual vibration that limits its use on slower shutter speeds, while the Mamiya RB is steady as a rock and can be used down to 1/30 and 1/15 handheld (if you have good technique.)

Now, i'm perfectly happy with the RB lenses, to be honest, and I haven't heard any Hasselblad or Mamiya user complain of having a slow 1/500 (or 1/400) speed, or complaining about the lenses' speed. Depth of field in Medium Format is extremely narrow at those apertures!

Overall, i prefer central shutters due to less vibration compared to a normal focal plane shutter. And, in the case of the RBs, Hasselblad and similar shutter-in-lens camera, there is a big reliability advantage: one of the fragilest camera parts (the shutter) is removed from the camera. Thus, if you have shutter failure you just change the lens and keep going.

Another advantage of central shutters, often unnoticed, is ergonomics: Most cameras with in-lens shutters have the shutter speed ring and the aperture ring next to each other. In the case of the Mamiya RB and C, it allows you easily to see the available speed+aperture combinations for a given EV value at a glance (i.e. 250+f5.6, 125+f8, 60+f11, 30+f16...)

 

[RalphLambrecht]

I don't know but diaphragm shutters are quieter and will synchronise for flash at any speed.

However,they(diaphragm)tend to overexpose at small apertures.Focal plane shutters areeaposing independent of apertures,and therefore aremore efficient.

 

[RalphLambrecht]

But why?

my assumption: focal plane shutters are easier to make and adjustwhile the flash benefit of leaf shutters is not a big deal in practisewith inproved focal plane synchronization.whistling:

 

[RalphLambrecht]

Please explain.

because they don't overexpose at small apertures.a detailed explanation is illustrated in Way Beyond Monochrome.I guess, I could post a pdf on requestbut in short, leaf shutters expose small apertures more quickly and close them more slowly than the curtains of a focal plane shutter.

 

[Steve Smith]

Leaf shutter uncovers a small f No. aperture (large diameter) slower than a large f No. aperture (small diameter) as it has further to travel to reach its extents. The shutter has to open fully but if the aperture blades are closed down, most of the travel is wasted.


Steve.

 

[cliveh]

Thank you Ralph and Steve, as I never thought about that aspect. I suppose in theory a leaf shutter could be engineered to only open and close at a diameter to match the working aperture?

 

[Steve Smith]

Thank you Ralph and Steve, as I never thought about that aspect. I suppose in theory a leaf shutter could be engineered to only open and close at a diameter to match the working aperture?

I think there have been shutters without separate aperture blades where the shutter blades only opened to the required aperture size then closed again but I suspect that they were difficult to keep accurate and would still suffer from the difference in time between opening a small amount and opening fully.

Something else to consider is that if you are using a very fast shutter speed, i.e. one which requires the shutter to open then immediately close again without delay, then with the aperture blades wide open, the actual exposure is made at all apertures from wide open to pinhole. The longer the shutter speed, the less this will have any effect.


Steve.

 

[E. von Hoegh]

But why?

http://collectiblend.com/Library/Photographic_Shutters_Neblette.php
Physics.

 

[E. von Hoegh]

I think there have been shutters without separate aperture blades where the shutter blades only opened to the required aperture size then closed again but I suspect that they were difficult to keep accurate and would still suffer from the difference in time between opening a small amount and opening fully.

Something else to consider is that if you are using a very fast shutter speed, i.e. one which requires the shutter to open then immediately close again without delay, then with the aperture blades wide open, the actual exposure is made at all apertures from wide open to pinhole. The longer the shutter speed, the less this will have any effect.


Steve.

The Goerz Sector, for one. Early Bausch & Lomb as well. Accurate enough at slower speeds.

 

[cliveh]

I wonder if it would be possible to engineer a double leaf shutter, where one is closing as the other opens, with the time for each computer controlled to give an overall accurate exposure time?

 

[E. von Hoegh]

It's an explanation with graphic representation of the efficiencies of shutters, as you asked.

So my opinion, in a 35mm camera, a focal plane shutter is about the best kind. I like when they are mechanical and of fine construction quality, but have to admit an electronic focal-plane shutter is probably the most precise.

I don't know any electric leaf shutters, so the only fair thing would be to compare mechanical to mechanical.

With a focal plane shutter, mechanically you need to get the base speed precise. Then the curtain openings are the only changes to make. So long as both curtains travel the same speed, and the first curtain starts rapidly, you will get an accurate exposure.

A leaf shutter needs to get its higher speeds through faster and faster action against resistance. Some achieve their high speed by an extra spring, whose tension might vary over its lifetime.

So I think focal plane shutters are more easily kept accurate at the higher speeds.

Slower speeds, I think both kinds would be the same, since it's the time for escapement to pass its course.

Compur electronic. http://www.skgrimes.com/library/used-obsolete-discontinued-shutters/compur

 

[Sirius Glass]

Where'd you get that idea? The shutter starts moving after the mirror reaches the bumper at the top of the miror box. Otherwise, the mirror would cut off part of the image from most lenses, and light from the eyepiece could enter the mirror box and reach the film.

The vibrations are damped out before the shutter opens. The war on reflex cameras is based on bunk to push an agenda for rangefinder cameras.

https://www.youtube.com/watch?v=CkKcbyh2CrA

 

[E. von Hoegh]

I wonder if it would be possible to engineer a double leaf shutter, where one is closing as the other opens, with the time for each computer controlled to give an overall accurate exposure time?

No. As has been pointed out, leaf shutters have inherent 'flaws', that is they are part of the design and inseparable from it, regardless of what does the timing, computer or mechanical. A good Compur or Copal does an excellent job even though it's inefficient at higher speeds.
The old Kodak professional dataguides had tables of shutter efficiencies.

 

[Ian Grant]

Interesting. View camera users insist that some leaf shutters cause severe vibration.

Some definitely do, particularly the self cocking ones, but a lot also depends on the rest of the camera stability.

Ian

 

[Arklatexian]

focal plane v diaphragm

But why?

The way it was explained to me is the light coming to the film on a focal plane shutter is the same anywhere on the film plane while on the other hand the blade shutter allows slightly more light in the center than to the edges of the film plane because the blades must travel to the edges and back at whatever shutter speed was selected. My eyes have never been good enough to see the difference on my negatives.....Regards

 

[Steve Smith]

The way it was explained to me is the light coming to the film on a focal plane shutter is the same anywhere on the film plane while on the other hand the blade shutter allows slightly more light in the center than to the edges of the film plane because the blades must travel to the edges and back at whatever shutter speed was selected. My eyes have never been good enough to see the difference on my negatives.....Regards

That's nonsense though. All parts of the lens transmit light to all parts of the film.

As an inquisitive child, I once covered up half of the projector lens during one of my father's slide shows expecting half of the image on the screen to disappear. That doesn't happen though. All you do is reduce the intensity of the whole image.


Steve.

 

[flavio81]

However,they(diaphragm)tend to overexpose at small apertures.Focal plane shutters areeaposing independent of apertures,and therefore aremore efficient.

I have not noticed that overexposure error yet.

On the other hand, focal plane shutters can distort the image because, at top speeds (say, 1/1000), instead of having a full shutter that opens and closes, what we have is a narrow slit that "sweeps" the film area in a speed slower than 1/1000...

And in certain cases this can give a slant distortion to the image.

This does not happen with central shutters.

So I could argue that a camera with a FP shutter that tops at 1/2000 and synchs with flash at 1/90, is honestly a 1/90 speed camera, for moment-freezing purposes. While a camera with a leaf shutter that tops at 1/500 is really a honest near-1/500 speed camera.

 

[cliveh]

I have not noticed that overexposure error yet.

On the other hand, focal plane shutters can distort the image because, at top speeds (say, 1/1000), instead of having a full shutter that opens and closes, what we have is a narrow slit that "sweeps" the film area in a speed slower than 1/1000...

And in certain cases this can give a slant distortion to the image.

This does not happen with central shutters.

So I could argue that a camera with a FP shutter that tops at 1/2000 and synchs with flash at 1/90, is honestly a 1/90 speed camera, for moment-freezing purposes. While a camera with a leaf shutter that tops at 1/500 is really a honest near-1/500 speed camera.

Yes, this is what I find disturbing about a FP, as it does not expose all of the image at the same time. This is not very zen.