Measuring Skyglow; HELP PLEASE

[Karmas]

I am a bit confused about the procedure. To those who have done this project, how far did you put the sheet away from the camera? Did all of you take these photos in different areas?

[deleted-71724]

Dear KARMAS,

If you would describe the project you are having trouble with, we will be glad to help you.
Please briefly describe what information you are given, what procedure you will follow and what tools you are using to perform sky glow measurement.

Science Buddies provides project instructions to make a photometer for such observations...

--fred wetzler

[deleted-71447]

Hi Karmas,
Is this the project you are describing?
https://www.sciencebuddies.org/science- ... p022.shtml
Chris

[Karmas]

Use the following procedure to measure your camera's dynamic range (its range of response to different light levels).

1. Set up a piece of white paper so that it is uniformly illuminated by indirect sunlight.
2. Set up the camera so that the paper fills the field of view. Mount the camera on a tripod, if you have one. Otherwise, place the camera on a solid support. (Many of the exposures you will take will be too long for hand-holding the camera.)

Confused about that bit.

[deleted-71588]

Use the following procedure to measure your camera's dynamic range (its range of response to different light levels).

1. Set up a piece of white paper so that it is uniformly illuminated by indirect sunlight.
2. Set up the camera so that the paper fills the field of view. Mount the camera on a tripod, if you have one. Otherwise, place the camera on a solid support. (Many of the exposures you will take will be too long for hand-holding the camera.)

Confused about that bit.
Use the following procedure to measure your camera's dynamic range (its range of response to different light levels).

1. Set up a piece of white paper so that it is uniformly illuminated by indirect sunlight.
2. Set up the camera so that the paper fills the field of view. Mount the camera on a tripod, if you have one. Otherwise, place the camera on a solid support. (Many of the exposures you will take will be too long for hand-holding the camera.)

Confused about that bit.

Measuring the dynamic range of a film (or digital sensor) is an exercise in determining how reactive the recording media (film or digital sensor) is. This is typically done by altering only one control (independent variable) that affects exposure and measuring the result.

how far did you put the sheet away from the camera? Did all of you take these photos in different areas?
I am a bit confused about the procedure. To those who have done this project, how far did you put the sheet away from the camera? Did all of you take these photos in different areas?

As to how far away to put the sheet of paper, that is up to you. Any distance will do so long as it meets the constraint "that the paper fills the <entire> field of view". In order to eliminate distance and illumination differences, you need to NOT CHANGE distance, zoom control, angles, or anything else that will affect the geometry or the illumination of the paper during the entire test over a range of different shutter speeds (with a constant aperature) or over a range of different aperatures (with a constant shutter speed). I didn't check this proceedure to know which of these was recommended.

In order to perform a dynamic exposure range experiment on a digital camera, you must have one that you can manually control the exposure which means that you can set the aperature and the shutter speed.

[Karmas]

So I should find an area without a street light? Set up the tripod and the camera, set up the settings, and take pictures of a white paper that covers the whole view of the camera that I am holding up. "1. Set up a piece of white paper so that it is uniformly illuminated by indirect sunlight. " ?? Still a bit confused about that. I'm very sorry about this. I'm kind of a slow learner and I just want to get an clearer understanding of all of this.

[deleted-71588]

So I should find an area without a street light?...

NO!
There are at least two independent steps to measuring skyglow. The first step is to "calibrate" your test setup which involved figuring out the dynamic range of your digital camera. For this step, you do it in the daytime with "indirect sunlight" as the light source. By taking multiple exposures of the white piece of paper at different shutter speeds, you will be able to determine how many f-stops or shutter speed stops it takes to go from fully saturated (pixels are all 255 values) to the noise floor (say most pixels are less than 10 values). Carefully re-read this calibration proceedure for specific instructions. Ask a parent, grandparent, teacher, your advisor to help you work through it if you are still having difficulties.

[StudyFalcon]

Why do I need to complete the callibration steps?

[deleted-71588]

Why do I need to complete the callibration steps?

Try researching "calibration" in general, here is one article http://en.wikipedia.org/wiki/Calibration. Why was it important in the Civil War to calibrate artillary?

There is a wide variation in the response of the image sensors in digital cameras, particularly at low light levels and long exposures. The calibration steps in this experiment should be designed to determine the charateristics of your particular camera for scientific use.

Most people who buy a digital camera just want to capture "good" images. What constitutes a "good" image is highly subjective. Raw sensor images in low light tend to be very "noisy" so camera manufacturers have invented software algorithms to do noise reduction and sharpen edges eliminate red-eye and lots of other image clean up. The calibration steps should be designed to determine over what range of light a camera will maintain a linear raw image response and without these image processing algorithms getting in the way of collecting scientific data.