Telescope Reviews: 5 or 30 minute exposures for narrowband?

That's the thing, if the models are correct and the only thing that prevents us from using more short subs, is read noise, the better calibration should eliminate much of that issue.

If we go back to the dart example, it's sort of like throwing the darts, at a bar, with your friends. Intuitively, you can get the same result whether you throw lots of darts at once, or stop and start again latter. However, read noise is like the friends you brought along. Every time you stop, they decide it will be fun to spin you around. Now, when you go back, you are dizzy, so your throws become more variable and you still feel like your spinning in one direction, so, there is a "bias" added as your throws tend to drift I one direction.

However, you may realize that your friends calm down after some number of beers, but they get more rowdy if they have too many. So, you can use the same principles used to find the bullseye, to find the optimal amount of beer, so that your friends have less of an effect. The problem is you get diminishing returns as you try to further refine your estimation of the optimal amount of beer. If you try to measure this 16 times, there is still around 25% variation in your ability to determine the correct amount of beer. If you do 20 measures, you should still have a 22% variation in your certainty of the correct amount. So, it seems like there is no real gain. However, I you went to 400 measures, your guess would now be accurate to within 5% of the optimal level. If your estimation of the bullseye location is mainly limited by your friends, you've now effectively reduced they influence by 95% compared to 75% with just 16 measures. And if the bullseye is really small, that little percentage may make a huge improvement in your ability to find it. It may still not be enough enough of a reduction though, to make shorter throwing sessions equivalent to longer ones, but it gets you closer. You can now go much shorter than before calibration and achieve the same result.

If you further and further improve your calibration of your friends (read noise) at some point, other, more nominal sources of error may become a bigger proportion of the remaining limitation for further accuracy. Perhaps now that your friends are not bothering you, the drunks at the bar are becoming more noticeable (think of them as sky noise, cosmic rays, or passing clouds, or periods of poor "seeing" etc...). So, perhaps it is beneficial to pause and deal with you now mellow friends a little more, so that you can redo these sets of throws. Or perhaps, you want to do this because you are out of shape and your muscles are getting tired (think poor polar alignment. Or equipment limitations). Then though, a narrow band filter is sort of like some headphones, you can put on some nice soothing music and forget all about the drunks and just carry on

however, this doesn't help your muscles and unfortunately the headphones aren't perfect, so, at some point we may still want to retry some sets do to other although more nominal influence of the drunks....

Edited by Inverted (02/01/13 10:32 AM)