zone system test with filter on lens?

Michael Scarpitti wrote:
: Frank Pittel wrote in message ...
: Michael Scarpitti wrote:
: : Frank Pittel wrote in message ...
: : there is compensation built into the time for the time required to open and close
: : : the shutter completely.
:
: : : I don't see how that can be done, as the amount of compensation
: : : necessary depends on the aperture being used.
: :
: : It does work though. After all leaf shutters have been in use for a long time and
: : are still in virtually exclusive use in LF cameras and are prized by studio
: : photographers with MF cameras. I know for a fact that the Mamiya cameras have lenses
: : with leaf shutters that can be used with cameras with focal plane shutters ( the focal
: : plane shutter is simply opened and the exposure is made with the leaf shutter ).
: :
: : Although Mamiya and conventional lenses are common and going cheap on Ebay as studios
: : are dumping their MF cameras and going digital. The lenses with leaf shutters are rare
: : and go for a lot of money. It simply isn't the issue you're trying to make it out to
: : be.
:
: : If you're 'calibrating' it may very well be.
:
: It may be an issue but it's not. I understand that you don't have any significant experience
: with leaf shutters. They do work and they work well.

: How would you 'know' this? I have lots of experience with all kinds of
: cameras and shutters, dating back 40 years.

I know a lot of things. One of the things I do know for a fact from personal experience
is that leaf shutters work well at their full range of speeds (I have yet to see one
that will go faster then 1/500) even with the aperature wide open.
--




Keep working millions on welfare depend on you
-------------------

Frank Pittel wrote in message ...


I know a lot of things. One of the things I do know for a fact from personal experience
is that leaf shutters work well at their full range of speeds (I have yet to see one
that will go faster then 1/500) even with the aperature wide open.

In addition to being unable to spell, here's the point you missed: The
shutter works just fine, but at high speeds (intervals shorter than
1/50 sec) and large apertures the efficiency of a leaf shutter is
lower than at lower speeds (longer than 1/50 sec) and small apertures.
It has to do with the geometry of a leaf shutter, which opens from the
center first. This means you have to increase the exposure when using
high shutter speeds and large apertures.

I quote:

"No mechanical shutter will have 100% efficiency at any speed since it
takes the blades a finite time to open and close. For most modern high
speed shutters the opening and closing times are about 1/2000th each.
The effective time is measured at the half open points for the size of
aperature involved. Marked speeds are for the full open apertur of the
shutter. The idea is that mostly the lens will be wide open when the
highest speed is used.

For most shutters the efficiency is around 80%. Of course, for small
openings the opening and closing times become a smaller part of the
total open time, effectively the efficiency goes up so the speed is
slower. The main thing is to know what it is and whether its
consistent. Even old Compur shutters are pretty consistent although
the highest speed may never have been more than wishful thinking.

The service manual for the Synchro-Compur used in Rollei E's and F's
gives a speed of around 1/380 as the target speed for 1/500th when
measuring total open time.

For slower speeds the error becomes much less since the opening and
closing times remain constant."

----
Richard Knoppow
Los Angeles,Ca.
"

http://medfmt.8k.com/mf/shutters.html

Michael Scarpitti wrote:
: Frank Pittel wrote in message ...

:
: I know a lot of things. One of the things I do know for a fact from personal experience
: is that leaf shutters work well at their full range of speeds (I have yet to see one
: that will go faster then 1/500) even with the aperature wide open.

: In addition to being unable to spell, here's the point you missed: The
: shutter works just fine, but at high speeds (intervals shorter than
: 1/50 sec) and large apertures the efficiency of a leaf shutter is
: lower than at lower speeds (longer than 1/50 sec) and small apertures.
: It has to do with the geometry of a leaf shutter, which opens from the
: center first. This means you have to increase the exposure when using
: high shutter speeds and large apertures.

Bull!!
--




Keep working millions on welfare depend on you
-------------------

"Frank Pittel" wrote in message
...
Michael Scarpitti wrote:
: Frank Pittel wrote in message
...

:
: I know a lot of things. One of the things I do know for a fact from
personal experience
: is that leaf shutters work well at their full range of speeds (I have
yet to see one
: that will go faster then 1/500) even with the aperature wide open.

: In addition to being unable to spell, here's the point you missed: The
: shutter works just fine, but at high speeds (intervals shorter than
: 1/50 sec) and large apertures the efficiency of a leaf shutter is
: lower than at lower speeds (longer than 1/50 sec) and small apertures.
: It has to do with the geometry of a leaf shutter, which opens from the
: center first. This means you have to increase the exposure when using
: high shutter speeds and large apertures.

Bull!!

One would think it should be easily possible to account for the aperture
size in the shutter timing, since both mechanisms are in the same housing. I
think I read in Stroebel's book that they do indeed do so, or it might be
that he wrote that few or none do so. I don't recall. The difference would
be either very small in normal lighting, or large enough to measure in very
extreme lighting.

To put numbers on it: Uncorrected, the error is twice the time the shutter
leafs take to sweep from 71% of the smaller aperture to 71% of wide open
(half the square root of 2, for half the exposure). The shutter has to fully
open in less than 2 milliseconds to allow for a 1/500 speed. If the
acceptable error in exposure is 1/3 stop, half my bracketing interval, I
come up with the following for a 210mm f/5.6 lens:

1/3 stop is log 0.10. For 1/500, the acceptable time error is 0.52
milliseconds. For 1/250, the acceptable error is 1.04 ms.

Wide open, 210mm f/5.6, the aperture is 37.5 mm. The shutter has to sweep
half that distance in 2 ms, giving an average speed of 9.38 mm/ms.

In 0.52 ms, the shutter leaf sweeps radially 4.88 mm; 9.76 mm in 1.04 ms.
These distances correspond to 1/500 and 1/250 respectively.

Exposure time "starts" at the point that the shutter reveals half the
aperture, or at 71% of the wide open radius: 37.5mm * .71 / 2 = 13.26mm.

To produce a noticeable error, the selected aperture must be smaller than:

For 1/500: (13.26 - 4.88) / .71 = 11.9 mm === f/17.7.
For 1/250: (13.26 - 9.76) / .71 = 4.95 mm === f/42.2.
For 1/125 (13.26 - 19.52) .... not meaningful.

Thus, the exposure error is less than 1/3 stop for apertures larger than the
following at the listed speed:

f/16 @ 1/500
f/45 @ 1/250.
.... any size at 1/125 and slower.

Shorter lenses will have an easier time of it. Longer lenses will have a
harder time of it.

At 100 EI, this is equivalent to 18 EV for Zone V at 1/500; EV 22 for 1/250.
Both are unrealistically high for natural lighting. Even at 400 EI, you
would have to meter 14 EV in deep shadow to run into problems.

So, yes, it can be a problem. And, no, it isn't a problem you're likely to
run into.

MikeWhy wrote:
: "Frank Pittel" wrote in message
: ...
: Michael Scarpitti wrote:
: : Frank Pittel wrote in message
: ...
:
: :
: : I know a lot of things. One of the things I do know for a fact from
: personal experience
: : is that leaf shutters work well at their full range of speeds (I have
: yet to see one
: : that will go faster then 1/500) even with the aperature wide open.
:
: : In addition to being unable to spell, here's the point you missed: The
: : shutter works just fine, but at high speeds (intervals shorter than
: : 1/50 sec) and large apertures the efficiency of a leaf shutter is
: : lower than at lower speeds (longer than 1/50 sec) and small apertures.
: : It has to do with the geometry of a leaf shutter, which opens from the
: : center first. This means you have to increase the exposure when using
: : high shutter speeds and large apertures.
:
: Bull!!

: One would think it should be easily possible to account for the aperture
: size in the shutter timing, since both mechanisms are in the same housing. I
: think I read in Stroebel's book that they do indeed do so, or it might be
: that he wrote that few or none do so. I don't recall. The difference would
: be either very small in normal lighting, or large enough to measure in very
: extreme lighting.

I'm looking that the timing numbers I got a few monthes ago for my rodenstock
lens in a Copal shutter. It does appear that there is an amount of compensation
occuring. At 1/500 of a second or 2.0 milliseconds and the actual time is 3.6ms.
at 1/250 or 4.0 ms the actual is 4.9. Going through the rest of the speeds I see
that the shift in time is non linear. Which is consistant with at least an attempt
to compensate. If the error was purly the result of an error in the timing mechanism
the error would track in a much more linear manner.


: To put numbers on it: Uncorrected, the error is twice the time the shutter
: leafs take to sweep from 71% of the smaller aperture to 71% of wide open
: (half the square root of 2, for half the exposure). The shutter has to fully
: open in less than 2 milliseconds to allow for a 1/500 speed. If the
: acceptable error in exposure is 1/3 stop, half my bracketing interval, I
: come up with the following for a 210mm f/5.6 lens:

: 1/3 stop is log 0.10. For 1/500, the acceptable time error is 0.52
: milliseconds. For 1/250, the acceptable error is 1.04 ms.

: Wide open, 210mm f/5.6, the aperture is 37.5 mm. The shutter has to sweep
: half that distance in 2 ms, giving an average speed of 9.38 mm/ms.

: In 0.52 ms, the shutter leaf sweeps radially 4.88 mm; 9.76 mm in 1.04 ms.
: These distances correspond to 1/500 and 1/250 respectively.

: Exposure time "starts" at the point that the shutter reveals half the
: aperture, or at 71% of the wide open radius: 37.5mm * .71 / 2 = 13.26mm.

: To produce a noticeable error, the selected aperture must be smaller than:

: For 1/500: (13.26 - 4.88) / .71 = 11.9 mm === f/17.7.
: For 1/250: (13.26 - 9.76) / .71 = 4.95 mm === f/42.2.
: For 1/125 (13.26 - 19.52) .... not meaningful.

: Thus, the exposure error is less than 1/3 stop for apertures larger than the
: following at the listed speed:

: f/16 @ 1/500
: f/45 @ 1/250.
: ... any size at 1/125 and slower.

: Shorter lenses will have an easier time of it. Longer lenses will have a
: harder time of it.

: At 100 EI, this is equivalent to 18 EV for Zone V at 1/500; EV 22 for 1/250.
: Both are unrealistically high for natural lighting. Even at 400 EI, you
: would have to meter 14 EV in deep shadow to run into problems.

: So, yes, it can be a problem. And, no, it isn't a problem you're likely to
: run into.

My point exactly!! I understand that there is always going to be an error in
timing. That's true with leaf shutters, curtain shutters, etc. The point I've
been trying to make is that the error is small enough to be discounted. While
I've never done the math as you've done here. I've spent a number of years using
leaf shutters on my LF camera shoting everything from B&W to C41 and E6. I can't
say that I've ever noticed a need to make exposure compensation at higher shutter
speeds on a properly working shutter.


--




Keep working millions on welfare depend on you
-------------------

"MikeWhy" wrote in message m...

So, yes, it can be a problem. And, no, it isn't a problem you're likely to
run into.

Kodak published the correction tables in one of their books, so it was
at least enough that it would affect critical work.