"Ken Hart" <kwhart1@[EMAIL PROTECTED]
> wrote in message
news:fq9g84$v50$1@[EMAIL PROTECTED]
>
> "Richard Knoppow" <dickburk@[EMAIL PROTECTED]
> wrote in
> message news:13sfg5amptadv36@[EMAIL PROTECTED]
>>
>> <jjs> wrote in message
>> news:13seve6aqb88of8@[EMAIL PROTECTED]
>>>
>>> "Richard Knoppow" <dickburk@[EMAIL PROTECTED]
> wrote in
>>> message news:13serbt1qjvdl5c@[EMAIL PROTECTED]
>>>
>>>> Just never fire a bulb off in your face... YIKES!!
>>>> I agree about using solenoids for remote tripping.
>>>> Silent and no limit on distance. Some shutters,
>>>> particularly the Kodak Supermatic and Flash Supermatic,
>>>> will not trip at 1/400 with just two batteries and
>>>> sometimes not with three. This was a problem in the old
>>>> days and extra-high-voltage photoflash batteries were
>>>> made for just this purpose.
>>>
>>> Yup! I know. Radio-Shack, still offer the old 22.5V
>>> batteries that those units used. This link shows a
>>> camera that used the same.
>>> http://www.digoliardi.net/ks6/
>>>
>>> I had that set since 1968, and later sold that for a
>>> bloody fortune. Sometimes life it good. :)
>>>
>> The 22.5V batteries were used in several BC type
>> flashguns including one of the Rolleiflash units. I don't
>> think they were ever used for solenoid flash. The "high
>> voltage" batteries I was talking about were standard
>> Size-D cells with something special about the mix. They
>> were enough higher than the standard 1.5V so that three
>> of them in a standard flashgun would have enough extra
>> oomph to deal with hard to trip shutters. I don't think
>> these have been made for decades. I don't know what was
>> done to them to increase the voltage but they had a
>> reputation for having short life.
>> When Wollensak came out with the Rapax shutter it was
>> designed to eliminate this problem by having a constant
>> and relatively low "trigger pull" at all speeds. Although
>> Wollensak made some flakey lenses their shutters were
>> always excellent.
>>
>>
> Begging your pardon, Richard, but I think a solenoid would
> require high current (amperes), while a flash bulb would
> require votage. I'd venture to guess that a couple of
> old-style 1.5V dry cells (about 2" diameter and 6" high
> with screw cap connections, originally used as "talk
> batteries" in telephone systems) would pull in most
> solenoids. Generally with batteries, size/bulk equals
> current. The larger the cell, the more current it can
> source, generally.
>
> How big a solenoid would it take to trip the old wind-up
> focal plane shutters in the press cameras?! (The shutter
> curtain had four different size slits and the was a
> tension setting to control how fast the slit moved.)
Well, you are right that the solenoid draws some current
and that minimum voltage is needed to reliably fire the
bulb. The problem was that the batteries could not supply
enough current for the solenoid when it was used with some
hard to trip shutters. This would result in the synch delay
being wrong, the shutter not tripping at all or the bulb not
firing. What was needed was somewhat greater current
capability rather than higher voltage but the pulling power
of the electromagnet is the result of both current and
voltage. If the supply voltage is increased the current
drawn by the soleniod is greater and its pulling force is
greater. A problem remains that the delay may ****ft for the
highest speed where the solenoid must work harder to trip
the shutter. Generally, I set up solenoids for the highest
speed and then check at lower speeds to see if the synch is
within the window.
Large, high current, batteries, like the No.6 cells you
mention might help but would be impractical due to size.
Also, keep in mind that there were more than one kind of
cell of this type. Telephone batteries were intended for
long life where the current draw would be low. Similar
batteries were made for ignition of model airplane motors,
these were capable of higher current supply where high
current but intermittant use was desired. There were also
versions made for electric lanterns.
I am not sure what a 22.5 volt battery would do to a
synchronizer solenoid. If the battery supplies enough
currrent it would probably burn it out.
BTW, the method I use for setting up solenoids is to use
an oscilloscope and watch the trace through the shutter
without any lens in it. The scope is set for single sweep
and triggered by the trip button, which is what would
normally fire the bulb. I use a calibrated sweep and mark
the scope face with something to indicate the right delay. I
then adjust the solenoid plunger and overall position to
give the right delay and strongest force on the trip lever.
Two kinds of bulbs were used, Class-F, and Class-M.
There were also Class-S bulbs but they were meant for use
with open flash, not with synchronizers.
Class-F bulbs need a 5 millisecond delay and Class-M
bulbs need about a 20 ms delay. The actual delay may vary
slightly from this since the ideal is to have the shutter
just at its maximum opening when the bulb reaches peak light
output.
Solenoids were never used for focal plane shutters.
There were external synchronizers available "aftermarket"
for these. The ones I am familiar with are mechanical and
fit over the winding knob on Speed Graphic or Graflex FP
shutters. These provide a contact closure. Special, very
long duration, bulbs were made for focal plane use, called
Class-FP. The duration of the flash was long enough to use
with short travel shutters on 35mm cameras but would work on
a 4x5 Speed Graphic only at the highest speed (1/1000
second) where the slit travel time was minimum. Another
arrangement is used on the Super-D Graflex. This has a
built-in flash contact mounted on the shutter curtain. The
system can be used with Class-FP bulbs at the highest speed
(but has problems when the rotating back is set for
"****trait", or, it can be used for strobe using what Graflex
called "drop curtain" where the mirror is used as the
opening part of the shutter, comes completely open, at which
point the flash is fired, and then the FP shutter curtain
caps the path. The system has an open time of a bit less
than 1/10th second so some care must be used about ambient
light. Again, this is completely manual, no solenoid
involved. This system works, I've used it for ****traiture
especially for kids.
Even though shutters with built-in synchronization
became available around the late 1940's many press cameras
still had solenoids installed. This was partly because the
solenoid provides a convenient method of remote tripping and
partly because its use doesn't require the second cocking
operation required by the Kodak and Ilex synch shutters
which were common on a lot of Speed Graphics. When I was
first introduced to the Speed Graphic back in highschool I
often used the solenoid strictly for tripping the shutter
but connected the bulb through the shutter contacts. All of
the late Graflex flashguns allow this arrangement.
Press photographers may not be very welcome now but at
least people don't have to deal with fried and broken
flashbulbs all over the place. Pop, sizzle, crunch...
--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@[EMAIL PROTECTED]
|
