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Focal plane vs. leaf shutters in MF SLRs



 
 
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  #31  
Old May 11th 04, 01:01 AM
Bob Monaghan
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Default convertible lens RF? Focal plane vs. leaf shutters in MF SLRs


yes, ditto my topcon 35mm SLR, with great lenses but a hard to maintain
leaf shutter in body ;-( However, a very large number of 35mm rangefinders
from the 1950s and 1960s had fixed lenses and leaf shutters, provided
flash synch at any speed, but without danger of getting dirt or damaging
shutter during lens changes (as just one fixed lens was used).

a number of leaf shutter oriented MF SLRs feature an adapter which can be
machined to take other non-leaf shutter lenses. In effect, this
combination is a MF SLR body with a leaf shutter mounting into which you
can adapt other lenses. A similar setup is used with microscopes and
telescopes. I have described how to adapt an existing low cost leaf
shutter lens by removing the glass etc., largely because the kowa shutter
adapter is rare and costly and busted lenses are lots cheaper ;-) (see
http://medfmt.8k.com/mf/kowafaq.html).

the trend seems to be the other way in many cases. For example, the 4x5"
and miniview graphic cameras usually used leaf shutters in the lenses, but
then added models with focal plane shutters in the camera body which could
be used instead of the leaf shutters with barrel lenses (i.e., lenses
which do not come with leaf shutters for view camera use etc.).

the hasselblad 200/x series provide focal plane shutters in the camera
body, but allow you to use leaf shutters in the lenses as well.

=====

Personally, I have wondered why nobody has created a MF RF with leaf
shutter and convertible lenses, as with the old contaflex and kodak retina
examples, see http://www.photo.net/bboard/q-and-a-...?msg_id=003HSZ

I would think that with modern glasses and precision mounts, such a system
could provide very good performance, while minimizing cost and weight.
Instead of paying for 3 lenses, complete with three shutters and three
lens mounts, you had one lens and three lens front elements. Swap these
out, and you get a wide angle, normal, or telephoto lens effects.

The cost for a three lens kit would be minimal over a similar 3 lens kit
model which required three separate lenses, complete with three machined
mounts and integral leaf shutters in each lens, yes? ;-)

but I think the mfgers would rather sell us two additional lenses at full
markup than provide us with a few extra front lens elements as part of the
kit, yes? ;-)

grins bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************
  #32  
Old May 11th 04, 01:55 AM
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Default convertible lens RF? Focal plane vs. leaf shutters in MF SLRs

Bob Monaghan wrote:

yes, ditto my topcon 35mm SLR, with great lenses but a hard to maintain
leaf shutter in body ;-( However, a very large number of 35mm rangefinders
from the 1950s and 1960s had fixed lenses and leaf shutters, provided
flash synch at any speed, but without danger of getting dirt or damaging
shutter during lens changes (as just one fixed lens was used).


But none of these ever reached the image quality levels of Leica, which makes
me wonder if my earlier proposition that focal plane shutters yield sharper
results isn't true.

Personally, I have wondered why nobody has created a MF RF with leaf
shutter and convertible lenses, as with the old contaflex and kodak retina


Why hasn't this approach been used more frequently in 35mm as well? I would
think there would be lens design limitations with this approach. I just saw a
camera on eBay (I forget the brand) that had an integral rangefinder/lens
combination which was interchangeable. That is you pulled off the lens *and*
the rangefinder assembly off of the camera body simultanaously and then
swapped it wiht another lens/rangefinder assembly. Neat idea.
I've always wondered why advanced flash features found on say the Konica Auto
S3 haven't found their way onto MF cameras. Or even Minolta's new "D" lens
range where focusing distance enters into the flash formula? Obviously MF
cameras are used to shoot weddings and parties all of the time. I scratch my
head as to why they don't have the latest and greatest automatic flash
features.

  #33  
Old May 11th 04, 10:41 AM
Lassi Hippeläinen
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Default convertible lens RF? Focal plane vs. leaf shutters in MF SLRs

Bob Monaghan wrote:
...
Personally, I have wondered why nobody has created a MF RF with leaf
shutter and convertible lenses, as with the old contaflex and kodak retina
examples, see http://www.photo.net/bboard/q-and-a-...?msg_id=003HSZ

I would think that with modern glasses and precision mounts, such a system
could provide very good performance, while minimizing cost and weight.
Instead of paying for 3 lenses, complete with three shutters and three
lens mounts, you had one lens and three lens front elements. Swap these
out, and you get a wide angle, normal, or telephoto lens effects.


I've been thinking about it as well, except that I'd like to see a TLR
with such lenses. The savings would be even more obvious.

-- Lassi
  #35  
Old May 11th 04, 01:32 PM
Georg N.Nyman
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Default Focal plane vs. leaf shutters in MF SLRs

Hi,
I would like to try to answer the original question -
shutters need to be designed such that the exposure time of each part of the
image is more or less the same to get an evenly exposed image. The location
of the leaf shutter needs therefore determined in such a way that its
opening and shutting mechanism produces an evenly exposed image on the film
plane. It therefore can only be positioned in one certain place within the
lens, where its mechanism works with the light flow in the mentioned proper
way. On top of it, by definition, it is circular and therefore would
require more space if positioned close to the film plane than if it is
placed between the lens elements. Usually it also is located very closely
to the diaphragms of the aperture and they can only be located where the
have to be optically - again same reason - uniform image exposure. And by
definition the diaphram need to sit in or very close to the aperture plane
or one of the conjugated planes of it. If you place the aperture not in the
correct plane, you get not only uneven exposure in the film plane but also
vignetting etc.
If you like to know more about it and in detail, email me directly. I
presume that the full explanation would be not really of interest for most
readers as it would involve more details about lens design and I am not
sure if readers would like to read a lot of theory....
Regards George Nyman



Dean Hoffman wrote:

There have been SLRs with a leaf shutter incorporated into the body. The
Kowa 35mm slrs come to mind. Unfortunately these involved complex linkages
that were prone to failure.

"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?


  #37  
Old May 11th 04, 11:16 PM
jjs
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Default convertible lens RF? Focal plane vs. leaf shutters in MF SLRs


wrote in message
...

Why hasn't this approach been used more frequently in 35mm as well? [...]


Funny this should come up. One of my student workers just now returned my
Contaflex, which as you know is an SLR that with a Prontor leaf shutuer and
X,M synchro, and of course it has interchangable lenses. It remains one of
my favorite miniature cameras with the 30mm lens.

Why wasn't it used more? For one, it's expensive and entails rather strident
limitations. To make this Contax system work there is one common lens behind
the shutter and all the lenses use it as the rear element. I can post some
pictures of the lens system if you like.


  #38  
Old May 11th 04, 11:18 PM
jjs
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Default Focal plane vs. leaf shutters in MF SLRs


"Georg N.Nyman" wrote in message
...
Hi,
I would like to try to answer the original question -
shutters need to be designed such that the exposure time of each part of

the
image is more or less the same to get an evenly exposed image. [...]


And obviously, the larger the leaf shutter, the more limited the top shutter
speed. Look at the Copal #0 with 1/500th compared to the *gasp* Ilex #5
which has a (nominal) 1/50th top speed (which I find is actually closer to
1/30th).


  #39  
Old May 12th 04, 02:01 AM
Bob Monaghan
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Default convertible lens RF? Focal plane vs. leaf shutters in MF SLRs


yes, I should clarify that I am NOT saying that my proposed convertible
lens Med Fmt camera would require the highest performance levels possible
requiring equaling leitz or contaflex or mamiya 7II optics. ;-)

Rather, I would like a decent MF camera where you have low cost (as three
lenses for little more than cost of one leaf shutter with swappable front
elements) and light weight (three lenses weighing little more than one), a
RF for low weight and ruggedness with lower costs than a mirror and prism
SLR, perhaps even a folding RF (cf. old folders, fuji..) design for
compactness for travel.

There have been convertible lenses in LF for ages, and there have been
examples of this design approach (as with the cited Contaflex, Kodak
Retina..) which worked quite well. Given that most of the lens cost is in
the shutter, iris, and mounting mechanics, a design which eliminates these
costs by substituting interchangeable lens fronts for different focal
lengths seems pretty direct design for a low cost low weight camera
option. I understand exotic lenses would be problematic, but I am just
looking for the relatively modest standard lens trio (50/80/150mm) in MF.

If some of the MF fuji zoom lenses had a longer zoom range, this might not
be such an issue. But it looks like fuji is getting out of that business
;-(

regards bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************
  #40  
Old May 12th 04, 02:12 AM
Bob Monaghan
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Default convertible lens RF? Focal plane vs. leaf shutters in MF SLRs


yes, quite true, but I wasn't thinking in historical terms but in terms of
operationally useful examples like the speed and crown graphics rather
than the old hood viewing models (http://medfmt.8k.com/mf/graflexb.html)

in most cases, you pay quite a bit extra for a camera with a built-in
focal plane shutter over a similar model limited to leaf shutter lenses;
there are also issues of repairability and shutter speed variations (esp.
at maximum speed end and so on). So I think most users today tend to opt
for leaf shutter lenses and a simple body, and mainly those who expect to
adapt or use barrel lenses will seek out the more complex and costly and
often heavier bodies with the focal plane shutters built-in.

I have seen a few bodies offered for sale where the individual stripped
out the focal plane mechanics (and RF) in order to save weight, but can't
recall anyone adding a focal plane shutter to a non-f.p. body ;-) ;-)

grins bobm

--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************
 




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