Light Panel

[Fay]

Can the brightness of a light panel be reduced?

Thanks

[Mac]

Yes,

you need to build a pwm (pulse width modulated) power supply.

Basically the same as a dimmer switch,

The light panel sheet is switched on and off say 500 times a second.
all you do is to change the length of the on time,
this will adjust the brightness.



in the top one the pannel will be 50% as bright as its only on for half the time
and in the bottom one it will only be 12.5% as bright for the same reason.

Mac.

[Fay]

well thanks Mac. Can I buy one?

[mickw]

Or
Reduce the exposure time

[Fay]

my flat exposures are minute anyway.

[mickw]

Why one minute ? they can be any length you like.

Or you could just get a dimmer switch (suitable for fluorescent lights) like you would use indoors about £20

[Fay]

No i may have misspelt that, I mean minute as in in very small. I am thinking Mike may have something , it is in his field of expertise or Maplins

[mickw]

Nope, I misread it 

Define minute - 1/1000 sec ?

Duncan uses one of these, I don't think he dims it.

[The Thing]

you need to build a pwm (pulse width modulated) power supply.

Not sure if this would work, the power unit that comes with the ELP makes a high pitched buzz just like a dimmer switch and it takes a visible amount of time to make the ELP achieve its usual brightness. I suspect there may be odd results if you try to switch it on and off quickly with a PWM.


Yes I do have one of these, but I also have a slow f10 scope. I use exposures of 1/200s with the Canon 350Da at iso800 with the Astronomik CLS-CCD clip filter and the Baader Telecompressor (about f5 according to Maxim DL). With that set up I get a nice unsaturated histogram. I also rotate the ELP a small amount between exposures to even out defects in its surface (averaging the flats removes the moving blemishes, leaving the ones stuck to the optics etc. I believe).

[Mike]

PWM won't work on ELP's. ELP's need an AC current and high voltage (at least 100VAC), hence the buzzing sound from the PSU. PWM is only for DC circuits. The panel works almost exactly the same as a capacitor. It needs AC as the illuminescence is created by generating an electric field by building up a charge across two surfaces. Light will only be output if the voltage is oscillating. Changing the frequency or amplitude of the AC will not change the brightness, but will change the colour.

In other words, there is nothing you can do about the brightness, it's fixed. As Mick says, adjust your exposure time instead.

[Fay]

Thanks Mike, saved the first explosion of 2011     

[RobertM]

Well you certainly can't dim them but you can reduce the light level by putting something opaque in front of it like a white sheet.  If it's a DSLR then you can reduce the exposure time down to 1/2000 or 1/4000th second, your Atik can probably go down to exposures of 1/1000th second so there's plenty of range.  If that isn't fast enough to get flats even with something in front of it then I would exchange that ELP - they must have sent you a floodlight by mistake.

Robert

[Fay]

 

[The Thing]

Damien Peach puts white paper over his... or so I've read.