shutter speed

Hi,
any ideas how I can figure out my shutter speeds. Do I need more than a
recording CRO and a photo electric cell?

Is the speed measured from just open to fully closed or fully open to start
of closing.

Thanks
David

"Michele Smith" wrote in message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I need more than a
recording CRO and a photo electric cell?
Is the speed measured from just open to fully closed or fully open to
start
of closing.
Thanks
David

I assume you're measuring between lens type shutters. I think it's normal
to measure from half-way open to half-way closed. Measurements at different
apertures will show significant variations, particularly at the higher
speeds. Have fun, and let us know the results! The slow speeds on one of my
shutters can be measured with a s l o w stop watch - I really must get
it cleaned.
--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

"Michele Smith" wrote in message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I need more than a
recording CRO and a photo electric cell?
Is the speed measured from just open to fully closed or fully open to
start
of closing.
Thanks
David

I assume you're measuring between lens type shutters. I think it's normal
to measure from half-way open to half-way closed. Measurements at different
apertures will show significant variations, particularly at the higher
speeds. Have fun, and let us know the results! The slow speeds on one of my
shutters can be measured with a s l o w stop watch - I really must get
it cleaned.
--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

"Michele Smith" wrote in message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I
need more than a
recording CRO and a photo electric cell?

Is the speed measured from just open to fully closed or
fully open to start
of closing.

Thanks
David

Calibrations are generally made at the halfway points to
give the "effective" speed for the full shutter aperture.
The speed at small stops will be pretty much the total open
time of the shutter. Most shutter testers measure the total
open time and a correction is used for the effective time.
For Compur shutters the opening and closing times are about
1/2000 sec. The total open time for 1/500th second is around
1/400th.
The ideal way to measure the shutter is to use a linear
photo detector and an oscilloscope. Since the detector sees
only a small spot a lens is required to focus the light onto
the detector. The light will vary in intensity as the
shutter opens and closes, the scope trace will show the
actual transmission curve of the shutter.
The effective time can also be measured with a simple
shutter tester like the Calumet tester by a similar method
where a spot of ligth is focused on the detector. The
aperture blades are adjusted so that the cut-off of the
tester is 2 stops down from maximum, which is the equivalent
of the halfway points of the shutter. When the aperture is
opened full this will also give you the effective exposure
time although it won't show the opening and closing times as
does the scope trace.
This method can also be used to measure the effective
times of focal plane shutters.
It is also possible to measure the open time at the
periphery of the shutter aperture and compare it to the
interval at the center.
The Calumet shutter tester is a very useful instrument. I
think they are now selling for around $80. This will check
both speeds and consistency of shutters and measure the
dwell time of strobe flash. As indicated above it will also
give effective speed measurements of both leaf and focal
plane shutters.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Michele Smith" wrote in message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I
need more than a
recording CRO and a photo electric cell?

Is the speed measured from just open to fully closed or
fully open to start
of closing.

Thanks
David

Calibrations are generally made at the halfway points to
give the "effective" speed for the full shutter aperture.
The speed at small stops will be pretty much the total open
time of the shutter. Most shutter testers measure the total
open time and a correction is used for the effective time.
For Compur shutters the opening and closing times are about
1/2000 sec. The total open time for 1/500th second is around
1/400th.
The ideal way to measure the shutter is to use a linear
photo detector and an oscilloscope. Since the detector sees
only a small spot a lens is required to focus the light onto
the detector. The light will vary in intensity as the
shutter opens and closes, the scope trace will show the
actual transmission curve of the shutter.
The effective time can also be measured with a simple
shutter tester like the Calumet tester by a similar method
where a spot of ligth is focused on the detector. The
aperture blades are adjusted so that the cut-off of the
tester is 2 stops down from maximum, which is the equivalent
of the halfway points of the shutter. When the aperture is
opened full this will also give you the effective exposure
time although it won't show the opening and closing times as
does the scope trace.
This method can also be used to measure the effective
times of focal plane shutters.
It is also possible to measure the open time at the
periphery of the shutter aperture and compare it to the
interval at the center.
The Calumet shutter tester is a very useful instrument. I
think they are now selling for around $80. This will check
both speeds and consistency of shutters and measure the
dwell time of strobe flash. As indicated above it will also
give effective speed measurements of both leaf and focal
plane shutters.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Michele Smith" wrote in message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I need more than a
recording CRO and a photo electric cell?

I made one of this and it works fine for my purposes
http://www.geocities.com/Yosemite/2131/shspeed.html

and this is a web page of a guy that also made the above:
http://open.hr/~dpleic/photo/Shutter.html

Guillermo

"Michele Smith" wrote in message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I need more than a
recording CRO and a photo electric cell?

I made one of this and it works fine for my purposes
http://www.geocities.com/Yosemite/2131/shspeed.html

and this is a web page of a guy that also made the above:
http://open.hr/~dpleic/photo/Shutter.html

Guillermo

"f/256" wrote in message
...

"Michele Smith" wrote in
message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I
need more than a
recording CRO and a photo electric cell?

I made one of this and it works fine for my purposes
http://www.geocities.com/Yosemite/2131/shspeed.html

and this is a web page of a guy that also made the above:
http://open.hr/~dpleic/photo/Shutter.html

Guillermo

This is a perfectly good way to test shutter speeds but
it tests total open time just as does the Calumet tester I
mentioned. By using an oscilloscope as Michele Smith
suggested the actual shutter curve can be seen. This is
sometimes useful since it makes it easy to calculate the
shutter efficiency at any f/stop. The scheme will also work
with focal plane shutters. While there is a popular myth
that FP shutters are 100% efficient they are far from that.
The efficiency varys with the distance the slit is from the
film, with the f/stop, and with the focal length of the
lens. A perfectly efficient FP shutter would have to be
essentially in contact with the film and have infintessimal
thickness. The effective shutter speed for FP shutters can
be substantially less than the speed measured with a total
open time meter. That is why Speed Graphic FP shutters often
have the spring wound way up. Measured for total open time
1/1000 may measure around 1/750th but the exposure will
still be 1/1000. A scope trace will show the effect of the
penumbra of the curtain slit so the effecive speed will be
easy to determine.
Nonetheless, a sound card meter of the sort described in
the links can be built for a few dollars and works fine.


--
---
Richard Knoppow
Los Angeles, CA, USA

"f/256" wrote in message
...

"Michele Smith" wrote in
message
...
Hi,
any ideas how I can figure out my shutter speeds. Do I
need more than a
recording CRO and a photo electric cell?

I made one of this and it works fine for my purposes
http://www.geocities.com/Yosemite/2131/shspeed.html

and this is a web page of a guy that also made the above:
http://open.hr/~dpleic/photo/Shutter.html

Guillermo

This is a perfectly good way to test shutter speeds but
it tests total open time just as does the Calumet tester I
mentioned. By using an oscilloscope as Michele Smith
suggested the actual shutter curve can be seen. This is
sometimes useful since it makes it easy to calculate the
shutter efficiency at any f/stop. The scheme will also work
with focal plane shutters. While there is a popular myth
that FP shutters are 100% efficient they are far from that.
The efficiency varys with the distance the slit is from the
film, with the f/stop, and with the focal length of the
lens. A perfectly efficient FP shutter would have to be
essentially in contact with the film and have infintessimal
thickness. The effective shutter speed for FP shutters can
be substantially less than the speed measured with a total
open time meter. That is why Speed Graphic FP shutters often
have the spring wound way up. Measured for total open time
1/1000 may measure around 1/750th but the exposure will
still be 1/1000. A scope trace will show the effect of the
penumbra of the curtain slit so the effecive speed will be
easy to determine.
Nonetheless, a sound card meter of the sort described in
the links can be built for a few dollars and works fine.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Richard Knoppow" wrote in message
...

The ideal way to measure the shutter is to use a linear
photo detector and an oscilloscope. Since the detector sees
only a small spot a lens is required to focus the light onto
the detector. The light will vary in intensity as the
shutter opens and closes, the scope trace will show the
actual transmission curve of the shutter.
The effective time can also be measured with a simple
shutter tester like the Calumet tester by a similar method
where a spot of ligth is focused on the detector. The
aperture blades are adjusted so that the cut-off of the
tester is 2 stops down from maximum, which is the equivalent
of the halfway points of the shutter. When the aperture is
opened full this will also give you the effective exposure
time although it won't show the opening and closing times as
does the scope trace.

So a scope and a linear photo detector could potentially be used to
calibrate the apertures of a lens, correct? You'd measure the amplitude of
the signal at an specific f-number of a known well calibrated lens with the
shutter fully open, then set the lens being calibrated with the shutter
fully open and play with the aperture opening until we get the same
measurement of the known well calibrated lens. Then is just a matter of
finding the other f-numbers by halving or doubling the amplitude of the
measured signal (for full stops. And in general, multiplying or dividing by
2^n, where n=stops or fraction of stops of difference). Anybody done this
before?

Guillermo