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Mike in NY
10-Oct-2012, 07:39
I'm curious to know why most modern shutters are mounted between lens elements. Why are they not more frequently mounted behind the entire lens; i.e, why isn't the entire lens usually screwed into the front of the shutter (functioning sort of like a Packard shutter does, mounted inside the camera)? Are there technological advantages of having the front element mounted on the front of the shutter, and the rear element mounted on the rear of the shutter?

Thanks in advance for educating me!

E. von Hoegh
10-Oct-2012, 09:01
I'm curious to know why most modern shutters are mounted between lens elements. Why are they not more frequently mounted behind the entire lens; i.e, why isn't the entire lens usually screwed into the front of the shutter (functioning sort of like a Packard shutter does, mounted inside the camera)? Are there technological advantages of having the front element mounted on the front of the shutter, and the rear element mounted on the rear of the shutter?
Thanks in advance for educating me!

Yes. It makes for a more compact assembly. Also, quite a few early shutters used the same leaves for shutter and diaphragm - when the aperture was stopped down, the leaves didn't open any farther than neccesary to provide that aperture.For optical reasons, the aperture requires a specific location within the lens.

rdenney
10-Oct-2012, 10:58
I'm curious to know why most modern shutters are mounted between lens elements. Why are they not more frequently mounted behind the entire lens; i.e, why isn't the entire lens usually screwed into the front of the shutter (functioning sort of like a Packard shutter does, mounted inside the camera)? Are there technological advantages of having the front element mounted on the front of the shutter, and the rear element mounted on the rear of the shutter?

Thanks in advance for educating me!

There are several reasons:

1. The centered location is where the aperture is smallest, and thus allows the smallest shutter possible. Consider the size shutter that would be required for, say, the Schneider 72mm Super Angulon XL, for which the rear element might be three inches in diameter (I'm guessing, but I doubt I'm far off). It is mounted in a No. 0 shutter, which has an opening only a small fraction of that.

2. When mounted between the lens cells, the lens cells prevent dust from reaching the internals of the shutter or the shutter blades. Users of Sinar shutters are extremely careful with them--an errant finger or corner of the camera can unfold and ruin those shutter blades in a snap. I keep mine in the focus position (blades open and therefore protected) and in a plastic bag to protect it from dust.

3. There are only three sizes of currently available shutters, but it's unlikely that only three sizes of shutters in front of the lens could accommodate all lenses, unless they are grossly oversized for the smaller lenses that are still too large for the next smaller shutter size.

4. The bigger the shutter, the greater the mass of the internal parts, and the greater the force required to accelerate that mass. That's why larger shutters have slower top speeds, or limited ranges of speeds.

5. Large, short lenses have rear elements that approach the film quite closely, and don't provide sufficient room for a shutter behind them, unless it's a real focal-plane shutter like what is found in a Speed Graphic. Playing with a Speed Graphic will explain why that did not become a prevailing design.

6. It's mechanically convenient to include the diaphragm with the shutter so that the lens cells don't require any mechanical parts, and as was E. v. H. mentioned, the diaphragm needs to be near the optical center so that it won't cause a shift in focus as it is stopped down.

Rick "suspecting that minimizing product diversity is a prime directive for Copal, and was for Compur" Denney

ImSoNegative
10-Oct-2012, 11:02
hey rick i always enjoy reading all your middle names, any time i see a post with your name in it, i always have to read it. very creative. lol

Mark J
10-Oct-2012, 11:15
and .....
7. It would be desperately difficult to correct lenses ( especially wide-angle lenses ) where the stop was at the back and you couldn't use pseudo-symmetry of the lens elements before and after the stop to help reduce or eliminate certain aberrations. Lenses would get a lot heavier and more complicated as a result .

Dan Fromm
10-Oct-2012, 12:01
Mike, I use a number of lenses in barrel (diaphragms in the barrels) mounted in front of shutters, one mounted behind a shutter.

The advantages are simple. Cost, cost and cost. One shutter, fewer than one adapter/lens because some of my lenses have the same mounting threads, no expensive adapters to make the lenses' cells fit properly in shutters. In general, a lens mounted in front of a shutter will cost more than the same lens mounted properly in shutter.

The savings come from using a single shutter for a number of lenses. This is what the Polaroid MP-4 did (all of the lenses for it screw into the front of a #1) and what the Sinar shutter and DB mount system do.

The disadvantages don't hurt me much, can be severe for photographers shooting the same lenses on formats larger than my 2x3. There are two: Mechanical vignetting, reduces coverage. If the shutter's maximum opening is smaller than the lens' exit pupil wide open, then the shutter will prevent the lens' diaphragm from having any effect on exposure until the lens is stopped down far enough that the exit pupil is smaller than the shutter's maximum opening.

Neither is a problem with the MP-4 or the Sinar system.

Which is best for a photographer depends on its situation.

Mike in NY
11-Oct-2012, 08:32
Thanks you guys, this was very helpful and informative. I appreciate the explanations of both the technology and your personal experience.

Mike

John Fink Jr.
11-Oct-2012, 08:49
Indeed it was.

Emmanuel BIGLER
11-Oct-2012, 09:04
Dan mentioned mechanical vignetting, but he forgot to speak about dynamical mechanical vignetting.
This is a very subtle effect.
When the shutter is not located close to the iris, or conversely exactly located in the image plane, there is an additional source of vignetting at high speeds.
The origin of the phenomenon is as follows: when the shutter starts to open, points of the image located in the corners will see the exit pupil of the lens (the image of the iris seen through the rear lens elements) at a later time than points located at the centre or the field. Hence, during the short time when the shutter opens, the edges of the image are affected by an additional vignetting effect.
Fortunately, front- or rear-mounted large-size shutters cannot reach high speeds, hence the phenomenon is hardly ever visible, as long as the opening time will be kept negligible with respect to the total exposure time; if this is true, the partial exposure of the image affected by dynamical vignetting during the opening sequence contributes to a very small amout of the total number of recorded photons. Hence the effect will be invisible
However, dynamical vignetting is documented in Sinar brochures for use with the SINAR DB system, but in most practical cases with the SINAR DB shutter one can actually neglect this effect.

Emmanuel BIGLER
11-Oct-2012, 09:16
And now it is time for reading Dan's article !!

Unlikely lenses on 2 x 3 Graphics (http://www.galerie-photo.com/1-lens-6x9-dan-fromm.html)

selected sections relevant to this discussion:
Mounting barrel lenses on boards (http://www.galerie-photo.com/1-lens-6x9-dan-fromm.html#htoc4)
Oscilloscope cameras as a source of shutters - Some see lenses, others see shutters (http://www.galerie-photo.com/3-lens-6x9-dan-fromm.html#htoc6)