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Focal plane vs. leaf shutters in MF SLRs



 
 
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  #1  
Old April 2nd 04, 03:07 AM
KM
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Default Focal plane vs. leaf shutters in MF SLRs

I was cleaning my RZ and began wondering why each lens must incorporate its
own leaf shutter, then began wondering why we find leaf shutters only in
lenses. I understand why the shutter has to be in the lens for rangefinder
systems (proxmity of wide-angle rear elements to focal plane = insufficient
space), but why couldn't they be incorporated into SLR bodies?

In current leaf-shutter systems like the Bronica ETR and Mamiya RB/RZ, doing
so would make the lenses smaller and lighter. In focal-plane systems like
the Pentax 645N, you'd get flash synch at any speed.

I'm sure there's a perfectly good explanation I'm overlooking.What is it?

  #2  
Old April 2nd 04, 03:29 AM
Wilt W
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Default Focal plane vs. leaf shutters in MF SLRs

I used to use a 35mm SLR (Topcon Auto 100) with the leaf shutter in the body 40
years ago! The problem is that the shutter can only be a certain size by
default, and putting it at the focal plane is problematic for that reason. In
my camera, the leaf shutter was where the lens mounted to the body, keeping it
somewhat smaller than at the focal plane, but that limits the rear element
size, and therefor the ultimate speed of the lens.

--Wilt
  #3  
Old April 2nd 04, 06:24 AM
Roland
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Default Focal plane vs. leaf shutters in MF SLRs

If the leaf shutter were not in a lens in an SLR then it would have to go
somewhere and inside the camera. The rear of the lens is near where the
mirror will flip up in any case so no room there. So you are stuck with
having to put it back near the focal plane. That's a very big "hole" for the
leaf shuuter to cover. It's housing would be outside this so you are looking
at changing camera design to fit it in. Also it would have to be a very
strong spring to get the blades to open and shut at something like 1/500th
sec over such a large diameter and you can forget about 1/1000th second. And
I doubt it would last more than about 500 firings before breaking. And it
would take some strength to cock the shutter.


"KM" wrote in message
...
I was cleaning my RZ and began wondering why each lens must incorporate

its
own leaf shutter, then began wondering why we find leaf shutters only in
lenses. I understand why the shutter has to be in the lens for rangefinder
systems (proxmity of wide-angle rear elements to focal plane =

insufficient
space), but why couldn't they be incorporated into SLR bodies?

In current leaf-shutter systems like the Bronica ETR and Mamiya RB/RZ,

doing
so would make the lenses smaller and lighter. In focal-plane systems like
the Pentax 645N, you'd get flash synch at any speed.

I'm sure there's a perfectly good explanation I'm overlooking.What is it?



  #4  
Old April 2nd 04, 08:38 AM
Lassi Hippeläinen
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Default Focal plane vs. leaf shutters in MF SLRs

KM wrote:

I was cleaning my RZ and began wondering why each lens must incorporate its
own leaf shutter, then began wondering why we find leaf shutters only in
lenses. I understand why the shutter has to be in the lens for rangefinder
systems (proxmity of wide-angle rear elements to focal plane = insufficient
space), but why couldn't they be incorporated into SLR bodies?


That isn't the reason. The shutter leafs move at finite speed. While the
shutter is only partially open, it will shadow the corners of the image
gate, unles it is at the optical center of the lens. The diaphraghm is
about exactly there, and the shutter is as close as mechanically
possible.

In current leaf-shutter systems like the Bronica ETR and Mamiya RB/RZ, doing
so would make the lenses smaller and lighter. In focal-plane systems like
the Pentax 645N, you'd get flash synch at any speed.

I'm sure there's a perfectly good explanation I'm overlooking.What is it?


All focal plane shutters are curtains, because they can expose all parts
of the image gate the same amount of time.

-- Lassi
  #5  
Old April 2nd 04, 11:17 AM
Bob Salomon
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Default Focal plane vs. leaf shutters in MF SLRs

In article ,
Lassi Hippelainen wrote:

because they can expose all parts
of the image gate the same amount of time.


Only at the synch speed or slower. At faster speeds only part of the
image is exposed at any one time as the shutter becomes a moving slit.
The higher the speed the narrower the slit.

This is why you have limited flash synch with a focal plane shutter vs a
leaf shutter.

--
To reply no_ HPMarketing Corp.
  #6  
Old April 2nd 04, 12:29 PM
Roland
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Default Focal plane vs. leaf shutters in MF SLRs

"Bob Salomon" wrote in message
...
In article ,
Lassi Hippelainen wrote:

because they can expose all parts
of the image gate the same amount of time.


Only at the synch speed or slower. At faster speeds only part of the
image is exposed at any one time as the shutter becomes a moving slit.
The higher the speed the narrower the slit.

This is why you have limited flash synch with a focal plane shutter vs a
leaf shutter.


You didn't get what he wrote which was "because they can expose all parts
of the image gate the same amount of time." He didn't write "at the same
time". He wrote "the same amount of time". What he was pointing out is
perhaps the most important feature of leaf shutters is that because they
exist near the lens aperture diaphram then they work in the same way at
reducing the light. If you reduce the aperture then the image doean't go
dark at the outside and towards the centre as you reduce it. It gets darker
the same amount all over the frame. So if the leaf shutter is there it does
not matter how long it is obscuring the edge of the image in relation to the
centre of the image. No matter how the blades are working, the effect is
spread over the whole image. So the centre does not get more exposure than
the edges, even though the centre of the blades is open for longer than the
edges. So if the leaf shutter were at the back near the film plane then the
centre of the image would get exposed more than the edges of the image due
to the way the blades have to open and close. You would need an extremely
fast-acting blade system to overcome this so that the time in transit for
the blades was negligible compared with the time the blades were fully open.
But a focal plane cloth shutter gives regular exposure over the whole of the
area. The film edges get as much light as the centre as the slit moves
across. Each part of the film gets exposed for the same amount of time (not
"at" the same time). This is probably the most important reason why a leaf
shutter can not be used in this way and why it has to exist in the lens near
where the diaphram is.


  #7  
Old April 2nd 04, 01:30 PM
Bob Salomon
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Default Focal plane vs. leaf shutters in MF SLRs

In article ,
"Roland" wrote:

This is probably the most important reason why a leaf
shutter can not be used in this way and why it has to exist in the lens near
where the diaphram is.


No the leaf shutter is placed where it is as small as necessary.

And the overriding benefit to the leaf shutter is optimal flash synch so
you can balance ambient and flash light to whatever ratio you want.

--
To reply no_ HPMarketing Corp.
  #8  
Old April 2nd 04, 03:40 PM
Bandicoot
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Default Focal plane vs. leaf shutters in MF SLRs

"Bob Salomon" wrote in message
...
In article ,
"Roland" wrote:

This is probably the most important reason why a leaf
shutter can not be used in this way and why it has to exist in the lens

near
where the diaphram is.


No the leaf shutter is placed where it is as small as necessary.


No. Roland is correct - logic should tell you that, rally, apart from
anything else. The only cameras that get away with leaf shutters in the
bodies (Pentax Auto110, for example) do so by having specially designed
lenses that effectively have a node where the shutter is.

I'm surprised, slightly, by this thread - I sort of thought everyone knew
this.


And the overriding benefit to the leaf shutter is optimal flash synch so
you can balance ambient and flash light to whatever ratio you want.


That is correct - though lightness is also a factor, and some see having a
shutter in each lens as a reliability issue: if one breaks at least you can
go on using the other lenses.


Peter


  #9  
Old April 2nd 04, 11:40 PM
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Default Focal plane vs. leaf shutters in MF SLRs

Enough with the design details - which one provides the sharpest image overall?

Thanks

  #10  
Old April 2nd 04, 11:50 PM
Bob Salomon
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Default Focal plane vs. leaf shutters in MF SLRs

In article ,
wrote:

Enough with the design details - which one provides the sharpest image
overall?

Thanks


That is impossible to answer if you are looking at an SLR. With what
lens?

--
To reply no_ HPMarketing Corp.
 




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