Photometer for measuring light intensity

[dhumpie]

Hey good people of ISS,

I have a question that maybe some of you might have experience with. My PhD supervisor is looking for a way to measure light from glowworms. Since they glow rather dimly, it would be similar to light from the stars and that is why he asked me if there was a way to measure light intensity under dim conditions. Any suggestions would be greatly appreciated.

Darren

[janoskiss (Steve H)]

That's what the Sky Quality Meter does. Accuracy is claimed to be about +/- 10% (+/- 0.1 mag) which is excellent considering the huge dynamic range (90dB+).

[[1ponders] (Paul)]

Are you trying to measure the collective light or the light from each worm?

If the second, you could try taking an Avi of them and instead of averaging the frames, add them. That should get them bright enough to take a reading you can work with. You might have to buy a 16" dob to shoot through though, to get enough light catching power. Seriously though you never know with the right gain and exposure my may be able to do it with a ToUcam and still average them by stacking in registax. There are plenty of programs around that will then measure the brightness.

[74tuc]

A few questions:

0. What does the supervisor want to find out?
... Do glow worms get into sync? Like synchronised fire flys.

1. Do yo want to measure the light from a single glow worm?
... Intensity vs time plot?

2. All the glow worms in a view?
... estimate of surface magnitude?


3. How far from the glow worms is the sensor to be?

Use a web cam? Start of a good idea! - CCD camera seems good. You may need a reference glow worm (calibration source)

Alot of answers are needed before good advice can be given - the web cam idea is brilliant. Use of a large light collector? thats what one ends up using.


Jerry.

[Dennis]

Hi Darren

Here are a couple of screen prints of a 3 min raw exposure of M83 from the software applications MIRA AP and CCDSoft. There are a lot of measurement tools available in these apps, most of them are a mystery to me, but if you want to take it any further, you are most welcome to drop by and explore their potential.

The important thing about the raw file is that it has not been modified in a non-linear manner, so absolute measurements can be taken after darks and flats are applied.

Cheers

Dennis

[dhumpie]

Thanks for all the input guys. I will show all the post to my supe and see what he says. From memory the detector would be quite a distance from the glow worms as they are found hanging from the top of caves. Also I assume they will be measuring the intensity from a group of glowworms as opposed to individuals. Will keep you updated....

Cheers,
Darren

[74tuc]

Hi Darren,

1. Judging by the last post:

- Your supervisor's instrument needs a wide FoV.
- It does not need to form a good image
... F1 optics? ... see the physics dept!!

- Needs a large area and sensitive photo-detector.
... 12 - 15 dynode photomultiplier comes to mind.

Jerry.