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Flashlight dimmer for cave photography?

B

BrianP

Jan 1, 1970
0
Hi,

I have a harebrained scheme to create a 12 Volt, wide angle flashlight
with a dimmer. I want to be able to go from the glow of a firefly to
that of an aircraft landing by adjusting a dial or slider.

I am a Scientist (mechanical engineer) and Photographer and am often
called upon to shoot in cave dark conditions. In bright light
conditions, my camera (Nikon D100) uses the old subtract and add
algorithm to find the point of maximum contrast to focus. In dark
conditions, it falls back on the much less accurate infrared beam trick
and the results are noticeably less consistent and accurate.

I want to put a 12 Volt, wide angle, halogen bulb on a dimmer and be
able to illuminate my subject(s) with or without blinding them in the
process. It will also give me a second, offset light source to reduce
shadows and shine from the flash. I need power in roughly the 10 - 100
Watt range.

Another, extremely useful feature would be to have the lights
automatically turn off as soon as the main flash strobes. I have a
photoelectric flash attachment which flashes a slave flash when it sees
the main flash go off (or when you pass your hand in front of the
detector and it senses a spike in illumination). This apparatus sends a
voltage telling the slave flash to flash. Surely, this same signal could
be used to turn a circuit off.

Ideally, I would get ready to take a picture, press a button to turn the
secondary light(s) on, dial in the desired illumination, take the flash
photo and have the light of the main flash turn off the secondary lighting.

I checked Radio Shack and all they have are either 120 V AC dimmers or a
3 W, DC rheostat. I want a time division switch which keeps the
connection closed for between 1% and 99% of the time. Ideally, it would
run off of the 12 V supply it is controlling and not use the same amount
of power all of the time by burning some of the juice off as heat and
the rest as light. I am thinking about a time division circuit
connected to a capacitor to cushion the sudden blasts of on-time voltage.

Any brilliant ideas?

Brian
 
R

Rich Grise

Jan 1, 1970
0
BrianP said:
Hi,

I have a harebrained scheme to create a 12 Volt, wide angle flashlight
with a dimmer. I want to be able to go from the glow of a firefly to
that of an aircraft landing by adjusting a dial or slider.
...
Ideally, I would get ready to take a picture, press a button to turn the
secondary light(s) on, dial in the desired illumination, take the flash
photo and have the light of the main flash turn off the secondary lighting.
...
Any brilliant ideas?

With a micro and power FET, this is almost trivial. It's a natural
for PWM (pulse-width modulation) - your steady-state is a stream
of pulses with a duty cycle proportional to your desired light
level (roughly - your eye/hand would be in the feedback loop)
and when you press the "secondary lights on" you just go to
full brightness until you sense the "the flash just flashed"
signal, then go back to idle.

Nothing to it - you might not even need to do any programming -
somebody will probably do this with a 556 and a couple of
gates.

Cheers!
Rich
 
J

JeffM

Jan 1, 1970
0
create a 12 Volt, wide angle flashlight with a dimmer
...to go from the glow of a firefly to
that of an aircraft landing by adjusting a dial or slider.
BrianP

Grise covered the PWM part.
Have you considered chromatic response over the range?
 
J

John Muchow

Jan 1, 1970
0
Have you considered chromatic response over the range?

That's what I was thinking (the bulb would definitely go "red" as the
brightness was reduced). In addition, halogens hate being dimmed.
OK, they don't hate it, but the bulb life is significantly reduced.

But, if I read the post correctly, the halogen light is to be turned
off before the picture is taken (and back on again after the "shutter"
has closed). It's primarily being used to allow the auto-focus to
operate more accurately.

John
John Muchow
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R

Rich Grise

Jan 1, 1970
0
John Muchow said:
That's what I was thinking (the bulb would definitely go "red" as the
brightness was reduced). In addition, halogens hate being dimmed.
OK, they don't hate it, but the bulb life is significantly reduced.

But, if I read the post correctly, the halogen light is to be turned
off before the picture is taken (and back on again after the "shutter"
has closed). It's primarily being used to allow the auto-focus to
operate more accurately.

Ah! Then just a Watson Name flashlight with a pot or 555 PWM, and
just a "bright-<~.5s>-Shoot-Off" sequence sounds like it would
work. :)

Cheers!
Rich
 
B

barryn56

Jan 1, 1970
0
Hi,

if your main requirements are to a) not alert your subject and b) use
mainly in dark environments, why not just build an infra-red light
source (IR LED array) and turn that on to help your camera focus in
the dark?

You would not need to switch off during exposure.
 
J

JeffM

Jan 1, 1970
0
if your main requirements are to a) not alert your subject and b) use
mainly in dark environments, why not just build an infra-red light
source (IR LED array) and turn that on to help your camera focus in
the dark?
You would not need to switch off during exposure.
barryn56

I presume that this is in response to
Flashlight dimmer for cave photography.

Some newsreaders (and certainly the Google archive)
lose track of the thread when you change the Subject line.

If you still feel the need to change it,
at least blockquote a bit of the original post.
 
B

BrianP

Jan 1, 1970
0
Rich, Jeff, John,
PWM (pulse-width modulation) - your steady-state is a stream
of pulses with a duty cycle proportional to your desired light
level

This is exactly what I was thinking. It's just like pinching a garden
hose periodically to govern the water flow. How about a capacitor
(expandable rubber section in-line to absorb the inrush volume) in-line
to avoid jarring and fatiguing the filament?
just go to full brightness until you sense the "the flash just flashed"
signal, then go back to idle.

Simple photoelectric effect generates a voltage which energizes an
electromagnetic which opens a rotating switch stopping the current.
That's how my old Mustang's alternator knew when it was done charging my
battery (substituting battery voltage for photoelectric effect). Isn't
that how an old fashioned volt meter works?
Have you considered chromatic response over the range?
It would get redder as the filament got cooler ( blackbody response to
lower 4th power K temperature). Actually, I was thinking of having 2,
one on each side of the camera to give me offset lighting to reduce
reflection and glare. I could turn one off rather than running 2 at half
power.

But, at sunset, you get a much redder light than at noon with a lower
color temperature and that is often the best time to shoot. It's much
better than shooting in a shadow with a white balance set for direct
sunlight and getting blue skin.

Or, have one of those blinding blue LEDs which would kick in in some
sort of inverse proportion to the halogen power!
halogens hate being dimmed.OK, they don't hate it, but the bulb life
is significantly reduced.
Get out of town?! One would think it would last noticeably longer at 75%
power than at full power. Is it possible that the Wolfram gas would not
be redeposited on the hot spot at lower temperatures? But, it's got a
boiling point of 10,000 degrees F. There can't be much of it
evaporating. How hot is a filament?
But, if I read the post correctly, the halogen light is to be turned
off before the picture is taken
Actually, it is the flash signal which would turn it off. This secondary
light would help focusing and also reduce the power of the central
flash reducing the dreaded white spot on people's foreheads, noses and
cheeks, especially at night time, summer parties!

I want to have 2 of these mounted on flexible "eye stalks" which I could
point where needed for the shot. Attach them to a plate planted on the
bottom of the camera. Perhaps wear them like antennae so you wouldn't
need to have a wire from the battery (belt) to the camera. Hmmm.
Ah! Then just a Watson Name flashlight with a pot or 555 PWM, and just
a "bright- said:

Huh?

Where can I find the parts to build a pair of these? Radio shack didn't
seem to have anything of the sort online.

Thank you,

Brian
 
J

John Muchow

Jan 1, 1970
0
PWM (pulse-width modulation) - your steady-state is a stream
This is exactly what I was thinking. It's just like pinching a garden
hose periodically to govern the water flow. How about a capacitor
(expandable rubber section in-line to absorb the inrush volume) in-line
to avoid jarring and fatiguing the filament?

Something like a sine-wave would treat the filament better than a
simple full-on/full-off square wave. Another way is to just bring the
bulb down a few volts. Not turning it off (so it starts cooling), but
just down enough to reduce its brightness enough (but still stay hot).
I guess a square wave could work here since it would get averaged out
to pulsating DC by the slow response time of the filament.
Get out of town?! One would think it would last noticeably longer at 75%
power than at full power. Is it possible that the Wolfram gas would not
be redeposited on the hot spot at lower temperatures? But, it's got a
boiling point of 10,000 degrees F. There can't be much of it
evaporating. How hot is a filament?

I don't understand it completely (but I'm sure there is a lot of data
on the WWW), but my understanding is that at less than full voltage,
the evaporated metal gets deposited on the inside of the glass bulb
and not back onto the filament, causing premature failure of the
filament.
Actually, it is the flash signal which would turn it off. This secondary
light would help focusing and also reduce the power of the central
flash reducing the dreaded white spot on people's foreheads, noses and
cheeks, especially at night time, summer parties!

I'm not sure the timing works here. The flash fires when the
"shutter" is already open and then the lamp circuit receives a signal
to turn off. Problem is that the lamp takes a while to turn off, up
to several hundred milliseconds. This might affect the image.

But, reading your response above, it sounds like you want some of the
lamp light to hit the subject to balance out the flash. Those
reflections you mention are often highlights due to reflections from
skin oils. No matter what your light source is, it will reflect more
from those body "high points" than from others. Not sure if having
some of the lamp light mixed in with the flash will work.
Huh?

Where can I find the parts to build a pair of these? Radio shack didn't
seem to have anything of the sort online.

Rich's idea will definitely work

A standard 555 timer chip would work, or a 556 (dual-555's) might be
needed. Probably the easiest thing to do would be to have the 555 run
in "astable mode", that is creating a series of square waves with an
"on" time and "off" time (thus the frequency too) adjustable by you.

The 555 would trigger a MOSFET that is rated to handle the voltage and
current of your lamp (with a good 50% safety margin) and be set to
give you the "idling" brightness you need. I'd then have a pushbutton
switch that triggered another 555 timer (or the second timer in the
556 timer chip) in "monostable mode" to create a pulse that turns on
the MOSFET full (no square wave going on/off) to give you the high
brightness you want. The pulse from this second 555 would be set to
what ever length of time you felt you'd need for this high-brightness
mode. If you needed it on for longer, the monostable can be set to
stay high whenever the button is held down. Otherwise, the lamp would
go back to the idling brightness after this second 555 timer's pulse
had ended.

This doesn't automatically bring the light back down to idle when the
flash fires but it is a simpler circuit to build and can be modified
later to add that "auto-idling" function if you want.

John
John Muchow
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J

JeffM

Jan 1, 1970
0
PWM (pulse-width modulation) - your steady-state is a stream of
This is exactly what I was thinking. It's just like pinching a garden
hose periodically to govern the water flow.
Brian
Only if you can pinch and release VERY quickly. :cool:
PWM works by integration at the load.
How about a capacitor
(expandable rubber section in-line to absorb the inrush volume) in-line
to avoid jarring and fatiguing the filament?
If you mean ramping up the duty cycle to its final value, OK.
Doubt it would have much effect.
halogens hate being dimmed.
OK, they don't hate it, but the bulb life is significantly reduced.

Get out of town?!
Agreed.
But, if I read the post correctly,
the halogen light is to be turned off before the picture is taken

Actually, it is the flash signal which would turn it off.
This secondary light would help focusing
and also [sic] reduce the power of the central flash
Ah! Then just a Watson Name flashlight with a pot or 555 PWM,
and just a "bright-<~.5s>-Shoot-Off" sequence sounds like it would
work. :)

Huh?
A reference to Watt Sun.
http://groups.google.com/groups?q=Watson-a-Name+LEDs+flashlight

Take a FET that will handle the current of your bulb,
with its gate driven by the 555 astable.
A photosensitive latching circuit could reset the PWM.

555 basics
http://groups.google.com/groups?&[email protected]
 
J

John Muchow

Jan 1, 1970
0
halogens hate being dimmed.

That halogens hate being dimmed, or that I should get out of town?
:)


John Muchow
-- remove SPAMMENOT for e-mail responses --
 
J

JeffM

Jan 1, 1970
0
halogens hate being dimmed.
That halogens hate being dimmed, or that I should get out of town? :)
John Muchow

and the halogen you rode in on. :cool:
 
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