Skyglow Calibration Pictures

[PokemonMazter]

Hi,
I took my calibration pictures as suggested. When I started analyzing my pictures in ImageJ at 1/1000 exposure point the mean pixel value started with 219.044; at 1/500 it was 253.56 and at 1/250 it became 255. And thereafter for all exposure time points it is 255 (which is the saturation point probably). Please suggest what should I change to take calibration pictures. I'll really appreciate quick help to resolve this issue.

Thanks

[PharmaMan]

Hello,

If all of your calibration values are relatively close to one another, I would wonder if the relative brightness of the area where you took your photos is too much. I would think that that might be why all of your readings are close to the saturation point. What was the setting like where you took your pictures?

Let us know and we'll be happy to help you further,
Pharma

[PokemonMazter]

Hello thanks for your prompt response,

I took the pictures around 2:30 pm, the sunlight was not too bright, the only issue I could think could be that the sunlight wasn't coming behind me but to the left of me and I wasn't sure if that it would be considered direct or indirect sunlight. Also, one more question, my camera was very close to the paper so that the whole paper would be on the camera screen,could that effect the results? Today I took pictures indoors in my brightly light basement,​ I could see the gradation in the mean pixel intensity. My next question is, can I use artificially illuminated pictures taken in my basement for making the calibration curve? Will it effect my results?

​Thanks Once Again​​

​Regards

PokemonMazter​

[PharmaMan]

Hello,

I think that the sunlight coming in not directly behind you should still be ok, as long as it was not shining directly onto the paper. To address your second question, I think the paper being close to the camera should also be ok, because the intensity of the light in the room will determine how quickly your saturation will be reached in your measurements.

For your last question, even if it is an artificial light, I also think that this should be ok. This is because you are comparing all of your experimental (skyglow pictures) to your calibration curve. As long as everything is being compared to these standards, it should work fine. Glad to hear that you got a nice calibration curve using this method!

Let us know if you have any further questions, and I apologize for the delayed response.

Best,
Pharma