- If you have a set of RGB filters that a G2V star calibration gave you

the following weights,R= 1.2, G=1, B=1.8, which of the following would

be the preferred senerio for data collection and stacking? Maybe it

makes no difference which senerio is chosen although it would be easier

to maintain a dark calibration library with senerio A or B.

A. Take 10 ten minute images of each R,G,B and combine them using

the 1.2:1: 1.8 weights

B. Take 12 ten minute R images, 10 ten minute G images, and 18 ten B

images and combine them using 1:1:1 weights

C. Take 10 twelve minute R images, 10 ten minute G images, and 10

eighteen G images and combine them using 1:1:1 weights

Joe - Wow that's a good Q and I think I've tried all of the below options.

My current MO is method #C

-Paul in San Diego

>

> If you have a set of RGB filters that a G2V star calibration gave you

> the following weights,R= 1.2, G=1, B=1.8, which of the following would

> be the preferred senerio for data collection and stacking? Maybe it

> makes no difference which senerio is chosen although it would be easier

> to maintain a dark calibration library with senerio A or B.

>

> A. Take 10 ten minute images of each R,G,B and combine them using

> the 1.2:1: 1.8 weights

>

> B. Take 12 ten minute R images, 10 ten minute G images, and 18 ten B

> images and combine them using 1:1:1 weights

>

> C. Take 10 twelve minute R images, 10 ten minute G images, and 10

> eighteen G images and combine them using 1:1:1 weights

>

> Joe

> - If you use dark frame scaling, all three options work well enough.

But if you want to use darks that are exactly the same length as your

exposures, then options A and B certainly are easier.

Options B and C tend to equalize the amount of shot noise in all

three channels, so I would probably not use option A. (Actually

truth be known, I use option A all the time because it's easier on my

brain!)

With option C, you equalize the read noise better than option B. My

gut feeling is that read noise isn't an issue, but your mileage might

vary.

With option B, you have to be careful how you combine the images. If

you average them, then the weights will be 1.2:1: 1.8, but if you sum

them, then the weights will be 1:1:1.

There's a caveat that you probably only have a certain amount of time

available to do your exposures; so if the total time is 300 minutes,

option C would actually use 9, 7.5, and 13.5 minute exposures, while

option B might require 9, 8, and 13 exposures, depending on how you

want to round the numbers. I haven't figured out if this has any

real bearing on the question you asked, but I thought I would mention

it anyhow.

Hilary

--- In ccd-newastro@yahoogroups.com, "Joe Morris" <joemorris@...>

wrote:>

you

> If you have a set of RGB filters that a G2V star calibration gave

> the following weights,R= 1.2, G=1, B=1.8, which of the following

would

> be the preferred senerio for data collection and stacking? Maybe

it

> makes no difference which senerio is chosen although it would be

easier

> to maintain a dark calibration library with senerio A or B.

using

>

> A. Take 10 ten minute images of each R,G,B and combine them

> the 1.2:1: 1.8 weights

B

>

> B. Take 12 ten minute R images, 10 ten minute G images, and 18 ten

> images and combine them using 1:1:1 weights

>

> C. Take 10 twelve minute R images, 10 ten minute G images, and 10

> eighteen G images and combine them using 1:1:1 weights

>

> Joe

> - Hi Hilary -- Yes, I was asking the question to find the most time

efficient way to collect the data if in fact it makes no difference in

the final quality of the combined data. It seems to me that with "A",

one is throwing out some data just to equalize the filter differences.

"B" looks like the best in order to make life easier with the dark

library. I usually use one of the statistical combining methods like

SD Mask or sigma clip. Using method "B" with one of these, would the

combine ratio be 1:1:1?

Joe

--- In ccd-newastro@yahoogroups.com, "Hilary Jones" <hilaryyahoo3@...>

wrote:>

> If you use dark frame scaling, all three options work well enough.

> But if you want to use darks that are exactly the same length as your

> exposures, then options A and B certainly are easier.

>

> Options B and C tend to equalize the amount of shot noise in all

> three channels, so I would probably not use option A. (Actually

> truth be known, I use option A all the time because it's easier on my

> brain!)

>

> With option C, you equalize the read noise better than option B. My

> gut feeling is that read noise isn't an issue, but your mileage might

> vary.

>

> With option B, you have to be careful how you combine the images. If

> you average them, then the weights will be 1.2:1: 1.8, but if you sum

> them, then the weights will be 1:1:1.

>

> There's a caveat that you probably only have a certain amount of time

> available to do your exposures; so if the total time is 300 minutes,

> option C would actually use 9, 7.5, and 13.5 minute exposures, while

> option B might require 9, 8, and 13 exposures, depending on how you

> want to round the numbers. I haven't figured out if this has any

> real bearing on the question you asked, but I thought I would mention

> it anyhow.

>

> Hilary

>

> --- In ccd-newastro@yahoogroups.com, "Joe Morris" <joemorris@>

> wrote:

> >

> > If you have a set of RGB filters that a G2V star calibration gave

> you

> > the following weights,R= 1.2, G=1, B=1.8, which of the following

> would

> > be the preferred senerio for data collection and stacking? Maybe

> it

> > makes no difference which senerio is chosen although it would be

> easier

> > to maintain a dark calibration library with senerio A or B.

> >

> > A. Take 10 ten minute images of each R,G,B and combine them

> using

> > the 1.2:1: 1.8 weights

> >

> > B. Take 12 ten minute R images, 10 ten minute G images, and 18 ten

> B

> > images and combine them using 1:1:1 weights

> >

> > C. Take 10 twelve minute R images, 10 ten minute G images, and 10

> > eighteen G images and combine them using 1:1:1 weights

> >

> > Joe

> >

> - SD Mask and sigma clipping are just fancy ways of doing averages, so

the weights should be 1.2:1: 1.8.

Hilary

--- In ccd-newastro@yahoogroups.com, "Joe Morris" <joemorris@...>

wrote:>

in

> Hi Hilary -- Yes, I was asking the question to find the most time

> efficient way to collect the data if in fact it makes no difference

> the final quality of the combined data. It seems to me that

with "A",

> one is throwing out some data just to equalize the filter

differences.

> "B" looks like the best in order to make life easier with the dark

the

> library. I usually use one of the statistical combining methods like

> SD Mask or sigma clip. Using method "B" with one of these, would

> combine ratio be 1:1:1?

enough.

>

> Joe

>

> --- In ccd-newastro@yahoogroups.com, "Hilary Jones" <hilaryyahoo3@>

> wrote:

> >

> > If you use dark frame scaling, all three options work well

> > But if you want to use darks that are exactly the same length as

your

> > exposures, then options A and B certainly are easier.

on my

> >

> > Options B and C tend to equalize the amount of shot noise in all

> > three channels, so I would probably not use option A. (Actually

> > truth be known, I use option A all the time because it's easier

> > brain!)

My

> >

> > With option C, you equalize the read noise better than option B.

> > gut feeling is that read noise isn't an issue, but your mileage

might

> > vary.

images. If

> >

> > With option B, you have to be careful how you combine the

> > you average them, then the weights will be 1.2:1: 1.8, but if you

sum

> > them, then the weights will be 1:1:1.

time

> >

> > There's a caveat that you probably only have a certain amount of

> > available to do your exposures; so if the total time is 300

minutes,

> > option C would actually use 9, 7.5, and 13.5 minute exposures,

while

> > option B might require 9, 8, and 13 exposures, depending on how

you

> > want to round the numbers. I haven't figured out if this has any

mention

> > real bearing on the question you asked, but I thought I would

> > it anyhow.

> >

> > Hilary

> >

>