Picture file size not making any sense

[Curiositykat]

My Panasonic FZ-28 has been uncooperative the last couple nights. I've been trying to take pictures of the moon at full 18x zoom. While I am getting good results, my camera is messing with my mind. Its set for 10MP images. Normally when I am shooting I get a 3-4MB file size when shooting .jpeg only. I'm sure my camera has a reason for what its doing, I just can't seem to figure it out. So shooting the moon at 18X zoom in 10MP JPEG only, I get a image only 200-300KB in size. Its something about the moon at night only. I can take pictures of the moon when its out during the day and it works properly. Anyone know what the issue is here?

thanks!

 

[Bitter Jeweler]

Does the zoom actually just crop the image?

 

[MissCream]

Is it 18x digital zoom or optical? If it's digital then the camera is just taking the picture and zooming in on it (I'm bad at explaining things), it would be like if you took a picture, put it in photoshop and cropped out the moon and zoomed in on it. It will be bad quality and not as high resolution.

I could be wrong though.

 

[Bitter Jeweler]

Oh wait! Don't jpegs size vary with the amount of detail/variation in it? Meaning, all black image will be smaller than a pic with detail in it?

 

[Boutte]

Oh wait! Don't jpegs size vary with the amount of detail/variation in it? Meaning, all black image will be smaller than a pic with detail in it?

I think you have the answer.

 

[Curiositykat]

It is x18 optical zoom.

Bitterjeweler that does make sense. I never noticed the file size until I upload it, meaning I don't see obvious lack of detail where their is detail. So it must be the fact that the image is mostly black. Here is one of my results from last night.

 

[Forkie]

Oh wait! Don't jpegs size vary with the amount of detail/variation in it? Meaning, all black image will be smaller than a pic with detail in it?

This with knobs on.

 

[Judobreaker]

Yes, jpg is very good in compressing large areas of a single color so large black areas or plain white areas (as may appear on the moon depending on your shot) are compressed really well.
As there's probably hardly any other details around besides a tiny star or some craters on the moon a photo like this will most definitely be compressed a lot while you won't notice much quality loss.

 

[KmH]

Oh wait! Don't jpegs size vary with the amount of detail/variation in it? Meaning, all black image will be smaller than a pic with detail in it?

Ding! Ding! Ding! (Raw files too!)

Ah, the mysteries of digital photography.