A trillion is a big number

[Pete]

Most of the time a camera is mounted on Wishing Star Observatory’s 14” scope. Celestial viewing is about light and not magnification. The 14” collects 350,000 times more light than the human dilated pupil. Since you have 2 eyes, say only 175,000 times. The eye works at 30 frames/second – like a movie camera. But a film camera can capture photons with long exposures. A one minute exposure captures 1800 times more light than the same aperture at 30 fps. And my SBIG ST-8XME camera is far more sensitive than film and can expose for a quarter of an hour easy. So it's 1000 times better than film. Putting all these numbers together the scope/camera setup is 3,160,000,000 (over 3 trillion) times more sensitive than naked eye viewing.

Thoughts do wander on a cloudy nite.....

Pete

[bluemax]

Stop it Pete! My head is swimming

[NGC7000]

Your thoughts do wander wondrously, Pete, and I am a grateful beneficiary of your enlightening ruminations.

Tom

[Bruce D]

I remember Commander Cosmos stacked almost 500 hours of images taken through a 66 mm refractor and got down to better than mag 19... I wonder what would happen if you did the same with your scope Pete- !

[Pete]

Hi Bruce,

Near Earth asteroids have an apparent motion and as you know I'm limited to short exposures (can't accurately measure the position of a streak as a dot). But sometimes on a clear winter night when the motion is slow and the object is 19th magnitude I will expose as long as 5 minutes and stack multiple frames. Since the camera keeps running as I work the asteroid by the time I'm done I've got more frames to stack and if Guide 9 shows that there's a slightly dimmer asteroid in the FOV I'll go after that using the additional frames that have collected while working asteroid #1. Sometimes there are several dimmer asteroids within the FOV and I repeat the process as photons collect through even more images. One night there were 6 or 7 really dim asteroids and over the course of an hour I worked down to 20.7 magnitude. Since 3 positions are required by the Minor Planet Center these may have been 30 minute stacks - can't find the data now.

One thing to note. The 14" is configured for utmost sensitivity. Adaptive optics to keep the Full-Width-Half-Max minimized. No filters as even a neutral density filter cuts light throughput by 50%. Camera with a CCD sensitivity exceeding 80%. And the chip's a blooming configuration so that there's minimal spacing between pixels.

For a while I was chasing really dim quasars to see how far back in time the scope could go. Seem to recall working 20th magnitude there too.

Pete

[Bruce D]

I wonder if there's a formula that would predict what magnitude you could reach if you were to take a 500 hour exposure with your setup

[TimW]

Stars are pretty.

[Pete]

I wonder if there's a formula that would predict what magnitude you could reach if you were to take a 500 hour exposure with your setup

Wouldn't attempt to calculate this one Bruce. It wouldn't be linear as I seem to recall that S/N deteriorates as you stack. (A single 5-minute long exposure's supposed to be better than stacking 5 one-minute exposures. And the maximum length of a single exposure depends upon many factors.)

[Bruce D]

well- here's my guestimate-

Obviously the Commander stacked his images to get 500 hours of data, else he put his scope in orbit and didn't tell any of us! I don't know whether he stacked 500 hours worth of 1 hour exposures or 5 minute exposures but- assuming Pete stacked the same number of images at the same exposure the Commander used:

Pete's 356mm scope has roughly 27 times the light gathering power of the Commander's 66mm scope. A difference of 1 magnitude is 250% increase in brightness so divide 27/2.5 = 10 or 11 magnitudes deeper than the Commander's 19.5 mag so I'm thinking Pete would come darn close to mag 29 or 30 by stacking 500 hours of images.

Sounds perposterous at first, but, Pete has hit almost mag 21 with a 30 minute stack so who knows what 1000 times more imaging time would do?

Or, maybe I am remembering the Commander's story wrong! (or my methodology is all off)

[Pete]

Pete's 356mm scope has roughly 27 times the light gathering power of the Commander's 66mm scope. A difference of 1 magnitude is 250% increase in brightness so divide 27/2.5 = 10 or 11 magnitudes deeper than the Commander's 19.5 mag so I'm thinking Pete would come darn close to mag 29 or 30 by stacking 500 hours of images.

Well, area is a function of the square of the diameter, so actually my 3550mm scope has 2893X the "light gathering power" of a 66mm scope.

And since the magnitude thing is also non-linear I need a 22" scope to delve a full magnitude deeper

Pete