Re: Regarding exposure times


Nov 20, 2005

 


----------------------------

#21667 Nov 20, 2005

Is it better to take fewer, but longer exposures rather than more, but

shorter exposures? I'm using an SBIG ST10XE and it doesn't take more

than a couple of minutes in some regions of the sky to get some pretty

serious blooming started. Am I better off limiting the size of the

blooms by taking 60 2 minute exposures, or ignoring the blooming by

taking 4 30 minute exposures, then eliminating them later in Maxim

DL? Thanks for your help.



Rob



----------------------------

#21669 Nov 20, 2005

It all comes down to s/n, and you've presented two ends of the extreme

in terms of exposure times for your subs. The major noise factor to

overcome with "each" exposure is the camera's read noise. I'd be more

concerned about this than any blooming issues...there's pretty good

bloom removal software available (although all come at a price of some

loss of data).



Without getting into the math, Stan Moore has determined that if you

expose long enough to end up with a background adu count of around 800

to 1000 adu, you will have "swamped" the read noise with the "sky"

noise (light pollution, etc). At that point, you have overcome one of

the major noise sources, and exposing longer vs more exposures at

that "optimum" time are very close in terms of end results.



Thus, try to find the optimum time for each sub exposure that produces

that 1000 minimum adu background count...then you can stop there and

just take as many of those as reasonably possible.



Bottom line...too short a subexposure and read noise will

dominate....too long a subexposure and you open yourself up to a

greater likelyhood of sattelites, airplanes, guiding glitches, field

rotation due to non-perfect polar alignment, etc)....The compromise

scenario I presented above will give you the best of both worlds for

most targets.



Since you indicated you have taken 2 minute exposures already, it

should be an easy task to calculate at what point you will reach a

background count of around 1000 adu....measure your background count

with some of your images and divide by two...that's your accumulated

background count per minute...then just figure out how many minutes to

reach the target adu count. CAVEAT: if you're imaging from extremely

dark skies, it may take quite a long exposure to overcome the read

noise with the "sky" noise....however, for most of us in visual Mag 4

to 5 skies, the subexposures aren't that long...for me it's around 10

minutes minimum with a STL6303 on a 12.5 RC at F9....I usually go 15

minutes as a norm.



Hope this helps,



Randy Nulman



--- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...> wrote:

>

> Is it better to take fewer, but longer exposures rather than more,

but

> shorter exposures? I'm using an SBIG ST10XE and it doesn't take more

> than a couple of minutes in some regions of the sky to get some

pretty

> serious blooming started. Am I better off limiting the size of the

> blooms by taking 60 2 minute exposures, or ignoring the blooming by

> taking 4 30 minute exposures, then eliminating them later in Maxim

> DL? Thanks for your help.

>

> Rob

>



----------------------------

#21672 Nov 20, 2005

hi randy - i thought this was very sage advice. in order to measure

for 1000 adu background should i stretch the image or just let the

image download with a low or medium stretch setting and click on the

background using maxim's pointer and info screen.

once i know the method for measuring adu's i could adjust my exposure

times, please advise.

best,

david

peterborough ontario



----------------------------

#21673 Nov 20, 2005

Thanks, Randy. I appreciate your help on this. I've spent some

time trying to understand ADU and *think* I've got it. I do almost

all of my CCD work from the Tucson foothills, north of the city,

shooting thru a lot of light pollution. So I get a lot of *noise*

in my images right from the start. Even though the location is far

from ideal, I see a number of astrophotographers in the same

situation doing awfully good work, so I'm encouraged.



As far as the practical aspect of measuring ADU, I'm under the

impression that MaximDL's Information window is where I can do

that, by looking at the "BgdAvg" number as I pass the cursor over

the darkest part of an image. Correct? If so, that helps a great

deal.



Thanks for the explanation. More than I expected.



Rob







--- In MaxImDL@yahoogroups.com, "Randy Nulman" rj.nulman@v...>

wrote: >

> It all comes down to s/n, and you've presented two ends of the

extreme > in terms of exposure times for your subs. The major noise factor

to > overcome with "each" exposure is the camera's read noise. I'd be

more > concerned about this than any blooming issues...there's pretty

good > bloom removal software available (although all come at a price of

some > loss of data).

>

> Without getting into the math, Stan Moore has determined that if

you > expose long enough to end up with a background adu count of around

800 > to 1000 adu, you will have "swamped" the read noise with the "sky"

> noise (light pollution, etc). At that point, you have overcome

one of > the major noise sources, and exposing longer vs more exposures at

> that "optimum" time are very close in terms of end results.

>

> Thus, try to find the optimum time for each sub exposure that

produces > that 1000 minimum adu background count...then you can stop there

and > just take as many of those as reasonably possible.

>

> Bottom line...too short a subexposure and read noise will

> dominate....too long a subexposure and you open yourself up to a

> greater likelyhood of sattelites, airplanes, guiding glitches,

field > rotation due to non-perfect polar alignment, etc)....The

compromise > scenario I presented above will give you the best of both worlds

for > most targets.

>

> Since you indicated you have taken 2 minute exposures already, it

> should be an easy task to calculate at what point you will reach a

> background count of around 1000 adu....measure your background

count > with some of your images and divide by two...that's your

accumulated > background count per minute...then just figure out how many

minutes to > reach the target adu count. CAVEAT: if you're imaging from

extremely > dark skies, it may take quite a long exposure to overcome the read

> noise with the "sky" noise....however, for most of us in visual

Mag 4 > to 5 skies, the subexposures aren't that long...for me it's around

10 > minutes minimum with a STL6303 on a 12.5 RC at F9....I usually go

15 > minutes as a norm.

>

> Hope this helps,

>

> Randy Nulman

>

>

> --- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...>

wrote: > >

> > Is it better to take fewer, but longer exposures rather than

more, > but

> > shorter exposures? I'm using an SBIG ST10XE and it doesn't take

more > > than a couple of minutes in some regions of the sky to get some

> pretty

> > serious blooming started. Am I better off limiting the size of

the > > blooms by taking 60 2 minute exposures, or ignoring the blooming

by > > taking 4 30 minute exposures, then eliminating them later in

Maxim > > DL? Thanks for your help.

> >

> > Rob

> >

>







----------------------------

#21675 Nov 21, 2005

David,

By "stretch", I assume you mean adjusting the "screen stretch"

settings? This is not necessary, and remember that it doesn't affect

the image data anyway...just the way the image displays.



All you need to do to measure the background adu is open the "info"

screen and put the curser over a background area that's void of stars

or nebula...just background. You can then look at the adu counts for

that area (or just look at the avg background reading also available on

the info screen)....no need or value in adjusting the screen stretch

settings prior to doing this...the readings will be the same regardless

of what screen stretch setting you have.



Hope this helps,

Randy Nulman



--- In MaxImDL@yahoogroups.com, "dhersey0308" dhersey1@c...> wrote:

>

> hi randy - i thought this was very sage advice. in order to measure

> for 1000 adu background should i stretch the image or just let the

> image download with a low or medium stretch setting and click on the

> background using maxim's pointer and info screen.

> once i know the method for measuring adu's i could adjust my exposure

> times, please advise.

> best,

> david

> peterborough ontario

>



----------------------------

#21676 Nov 21, 2005

Rob,



You absolutely "got it" G>. Remember that your camera is linear

for quite some time, so you don't need to take a bunch of different

exposures to figure out at what point you reach the desired

background count. Just take, say a 3 minute unbinned exposure and

measure the background adu...then divide by 3 and you will know how

much "sky noise" accumulates per minute...then figure out how many

minutes to reach you target background adu. Do the test near the

zenith with no moon out to get the best "test" results.



Regards,

Randy Nulman



--- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...> wrote:

>

> Thanks, Randy. I appreciate your help on this. I've spent some

> time trying to understand ADU and *think* I've got it. I do

almost

> all of my CCD work from the Tucson foothills, north of the city,

> shooting thru a lot of light pollution. So I get a lot of *noise*

> in my images right from the start. Even though the location is

far

> from ideal, I see a number of astrophotographers in the same

> situation doing awfully good work, so I'm encouraged.

>

> As far as the practical aspect of measuring ADU, I'm under the

> impression that MaximDL's Information window is where I can do

> that, by looking at the "BgdAvg" number as I pass the cursor over

> the darkest part of an image. Correct? If so, that helps a great

> deal.

>

> Thanks for the explanation. More than I expected.

>

> Rob

>

>

>

> --- In MaxImDL@yahoogroups.com, "Randy Nulman" rj.nulman@v...>

> wrote:

> >

> > It all comes down to s/n, and you've presented two ends of the

> extreme

> > in terms of exposure times for your subs. The major noise

factor

> to

> > overcome with "each" exposure is the camera's read noise. I'd

be

> more

> > concerned about this than any blooming issues...there's pretty

> good

> > bloom removal software available (although all come at a price

of

> some

> > loss of data).

> >

> > Without getting into the math, Stan Moore has determined that if

> you

> > expose long enough to end up with a background adu count of

around

> 800

> > to 1000 adu, you will have "swamped" the read noise with

the "sky"

> > noise (light pollution, etc). At that point, you have overcome

> one of

> > the major noise sources, and exposing longer vs more exposures

at

> > that "optimum" time are very close in terms of end results.

> >

> > Thus, try to find the optimum time for each sub exposure that

> produces

> > that 1000 minimum adu background count...then you can stop there

> and

> > just take as many of those as reasonably possible.

> >

> > Bottom line...too short a subexposure and read noise will

> > dominate....too long a subexposure and you open yourself up to a

> > greater likelyhood of sattelites, airplanes, guiding glitches,

> field

> > rotation due to non-perfect polar alignment, etc)....The

> compromise

> > scenario I presented above will give you the best of both worlds

> for

> > most targets.

> >

> > Since you indicated you have taken 2 minute exposures already,

it

> > should be an easy task to calculate at what point you will reach

a

> > background count of around 1000 adu....measure your background

> count

> > with some of your images and divide by two...that's your

> accumulated

> > background count per minute...then just figure out how many

> minutes to

> > reach the target adu count. CAVEAT: if you're imaging from

> extremely

> > dark skies, it may take quite a long exposure to overcome the

read

> > noise with the "sky" noise....however, for most of us in visual

> Mag 4

> > to 5 skies, the subexposures aren't that long...for me it's

around

> 10

> > minutes minimum with a STL6303 on a 12.5 RC at F9....I usually

go

> 15

> > minutes as a norm.

> >

> > Hope this helps,

> >

> > Randy Nulman

> >

> >

> > --- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...>

> wrote:

> > >

> > > Is it better to take fewer, but longer exposures rather than

> more,

> > but

> > > shorter exposures? I'm using an SBIG ST10XE and it doesn't

take

> more

> > > than a couple of minutes in some regions of the sky to get

some

> > pretty

> > > serious blooming started. Am I better off limiting the size

of

> the

> > > blooms by taking 60 2 minute exposures, or ignoring the

blooming

> by

> > > taking 4 30 minute exposures, then eliminating them later in

> Maxim

> > > DL? Thanks for your help.

> > >

> > > Rob

> > >

> >

>







----------------------------

#21677 Nov 21, 2005

hi randy - i have it now - thanks for your help. looking forward to

using this method.



david



----------------------------

#21679 Nov 21, 2005

Hi Rob



If you load an image, (or capture one), run your curser over the dark

areas of the image and look at the bottom right of MaxIm.



You'll see the image size, pixel location and ADU count. In a run I

did Saturday night, (10 min. subs on M33), my ADU averages in the

dark areas, 15770. Divide by 10 gives me a sky count of 1,500

approximately per minute.



Considering I am shooting from the heart of the city, (3.2 mag

skies), not bad.



Hope this helps.



Bob



--- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...> wrote:

>

> Thanks, Randy. I appreciate your help on this. I've spent some

> time trying to understand ADU and *think* I've got it. I do almost

> all of my CCD work from the Tucson foothills, north of the city,

> shooting thru a lot of light pollution. So I get a lot of *noise*

> in my images right from the start. Even though the location is far

> from ideal, I see a number of astrophotographers in the same

> situation doing awfully good work, so I'm encouraged.

>

> As far as the practical aspect of measuring ADU, I'm under the

> impression that MaximDL's Information window is where I can do

> that, by looking at the "BgdAvg" number as I pass the cursor over

> the darkest part of an image. Correct? If so, that helps a great

> deal.

>

> Thanks for the explanation. More than I expected.

>

> Rob

>

>

>

> --- In MaxImDL@yahoogroups.com, "Randy Nulman" rj.nulman@v...>

> wrote:

> >

> > It all comes down to s/n, and you've presented two ends of the

> extreme

> > in terms of exposure times for your subs. The major noise factor

> to

> > overcome with "each" exposure is the camera's read noise. I'd be

> more

> > concerned about this than any blooming issues...there's pretty

> good

> > bloom removal software available (although all come at a price of

> some

> > loss of data).

> >

> > Without getting into the math, Stan Moore has determined that if

> you

> > expose long enough to end up with a background adu count of

around

> 800

> > to 1000 adu, you will have "swamped" the read noise with

the "sky"

> > noise (light pollution, etc). At that point, you have overcome

> one of

> > the major noise sources, and exposing longer vs more exposures at

> > that "optimum" time are very close in terms of end results.

> >

> > Thus, try to find the optimum time for each sub exposure that

> produces

> > that 1000 minimum adu background count...then you can stop there

> and

> > just take as many of those as reasonably possible.

> >

> > Bottom line...too short a subexposure and read noise will

> > dominate....too long a subexposure and you open yourself up to a

> > greater likelyhood of sattelites, airplanes, guiding glitches,

> field

> > rotation due to non-perfect polar alignment, etc)....The

> compromise

> > scenario I presented above will give you the best of both worlds

> for

> > most targets.

> >

> > Since you indicated you have taken 2 minute exposures already, it

> > should be an easy task to calculate at what point you will reach

a

> > background count of around 1000 adu....measure your background

> count

> > with some of your images and divide by two...that's your

> accumulated

> > background count per minute...then just figure out how many

> minutes to

> > reach the target adu count. CAVEAT: if you're imaging from

> extremely

> > dark skies, it may take quite a long exposure to overcome the

read

> > noise with the "sky" noise....however, for most of us in visual

> Mag 4

> > to 5 skies, the subexposures aren't that long...for me it's

around

> 10

> > minutes minimum with a STL6303 on a 12.5 RC at F9....I usually go

> 15

> > minutes as a norm.

> >

> > Hope this helps,

> >

> > Randy Nulman

> >

> >

> > --- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...>

> wrote:

> > >

> > > Is it better to take fewer, but longer exposures rather than

> more,

> > but

> > > shorter exposures? I'm using an SBIG ST10XE and it doesn't

take

> more

> > > than a couple of minutes in some regions of the sky to get some

> > pretty

> > > serious blooming started. Am I better off limiting the size of

> the

> > > blooms by taking 60 2 minute exposures, or ignoring the

blooming

> by

> > > taking 4 30 minute exposures, then eliminating them later in

> Maxim

> > > DL? Thanks for your help.

> > >

> > > Rob

> > >

> >

>







----------------------------

#21686 Nov 21, 2005

Thanks, Bob--



This is helpful also. Using this method, I ran the cursor over some

15 minute sub frames of the Pelican region I took last night, but

through a Hydrogen alpha filter. I come up with an average ADU in

the dark areas of about 300. Based on this method, I could shoot

*much* longer and still be OK using the Ha filter.



Rob





--- In MaxImDL@yahoogroups.com, "Robert Anderson" bob@t...> wrote:

>

> Hi Rob

>

> If you load an image, (or capture one), run your curser over the

dark

> areas of the image and look at the bottom right of MaxIm.

>

> You'll see the image size, pixel location and ADU count. In a run

I

> did Saturday night, (10 min. subs on M33), my ADU averages in the

> dark areas, 15770. Divide by 10 gives me a sky count of 1,500

> approximately per minute.

>

> Considering I am shooting from the heart of the city, (3.2 mag

> skies), not bad.

>

> Hope this helps.

>

> Bob

>

>

> --- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...>

wrote:

> >

> > Thanks, Randy. I appreciate your help on this. I've spent some

> > time trying to understand ADU and *think* I've got it. I do

almost

> > all of my CCD work from the Tucson foothills, north of the city,

> > shooting thru a lot of light pollution. So I get a lot of

*noise*

> > in my images right from the start. Even though the location is

far

> > from ideal, I see a number of astrophotographers in the same

> > situation doing awfully good work, so I'm encouraged.

> >

> > As far as the practical aspect of measuring ADU, I'm under the

> > impression that MaximDL's Information window is where I can do

> > that, by looking at the "BgdAvg" number as I pass the cursor

over

> > the darkest part of an image. Correct? If so, that helps a

great

> > deal.

> >

> > Thanks for the explanation. More than I expected.

> >

> > Rob

> >

> >

> >

> > --- In MaxImDL@yahoogroups.com, "Randy Nulman" rj.nulman@v...>

> > wrote:

> > >

> > > It all comes down to s/n, and you've presented two ends of the

> > extreme

> > > in terms of exposure times for your subs. The major noise

factor

> > to

> > > overcome with "each" exposure is the camera's read noise. I'd

be

> > more

> > > concerned about this than any blooming issues...there's pretty

> > good

> > > bloom removal software available (although all come at a price

of

> > some

> > > loss of data).

> > >

> > > Without getting into the math, Stan Moore has determined that

if

> > you

> > > expose long enough to end up with a background adu count of

> around

> > 800

> > > to 1000 adu, you will have "swamped" the read noise with

> the "sky"

> > > noise (light pollution, etc). At that point, you have

overcome

> > one of

> > > the major noise sources, and exposing longer vs more exposures

at

> > > that "optimum" time are very close in terms of end results.

> > >

> > > Thus, try to find the optimum time for each sub exposure that

> > produces

> > > that 1000 minimum adu background count...then you can stop

there

> > and

> > > just take as many of those as reasonably possible.

> > >

> > > Bottom line...too short a subexposure and read noise will

> > > dominate....too long a subexposure and you open yourself up to

a

> > > greater likelyhood of sattelites, airplanes, guiding glitches,

> > field

> > > rotation due to non-perfect polar alignment, etc)....The

> > compromise

> > > scenario I presented above will give you the best of both

worlds

> > for

> > > most targets.

> > >

> > > Since you indicated you have taken 2 minute exposures already,

it

> > > should be an easy task to calculate at what point you will

reach

> a

> > > background count of around 1000 adu....measure your background

> > count

> > > with some of your images and divide by two...that's your

> > accumulated

> > > background count per minute...then just figure out how many

> > minutes to

> > > reach the target adu count. CAVEAT: if you're imaging from

> > extremely

> > > dark skies, it may take quite a long exposure to overcome the

> read

> > > noise with the "sky" noise....however, for most of us in

visual

> > Mag 4

> > > to 5 skies, the subexposures aren't that long...for me it's

> around

> > 10

> > > minutes minimum with a STL6303 on a 12.5 RC at F9....I usually

go

> > 15

> > > minutes as a norm.

> > >

> > > Hope this helps,

> > >

> > > Randy Nulman

> > >

> > >

> > > --- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...>

> > wrote:

> > > >

> > > > Is it better to take fewer, but longer exposures rather than

> > more,

> > > but

> > > > shorter exposures? I'm using an SBIG ST10XE and it doesn't

> take

> > more

> > > > than a couple of minutes in some regions of the sky to get

some

> > > pretty

> > > > serious blooming started. Am I better off limiting the size

of

> > the

> > > > blooms by taking 60 2 minute exposures, or ignoring the

> blooming

> > by

> > > > taking 4 30 minute exposures, then eliminating them later in

> > Maxim

> > > > DL? Thanks for your help.

> > > >

> > > > Rob

> > > >

> > >

> >

>







----------------------------

#21720 Nov 23, 2005

Hi Rob



Yes, sounds like you could go quite a bit longer. Obviously, the

bandwidth of the Ha filter has a major bearing on the length of time

as well as the fear of ruining a shot with a plane running through. I

had planes ruin two X 10 minute subs Saturday night.



For Ha, 1/2 hour seems to be a normal period but in this hobby,

nothing is normal!



Cheers and good luck!



Bob



--- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...> wrote:

>

> Thanks, Bob--

>

> This is helpful also. Using this method, I ran the cursor over

some

> 15 minute sub frames of the Pelican region I took last night, but

> through a Hydrogen alpha filter. I come up with an average ADU in

> the dark areas of about 300. Based on this method, I could shoot

> *much* longer and still be OK using the Ha filter.

>

> Rob

>

>

>

> --- In MaxImDL@yahoogroups.com, "Robert Anderson" bob@t...> wrote:

> >

> > Hi Rob

> >

> > If you load an image, (or capture one), run your curser over the

> dark

> > areas of the image and look at the bottom right of MaxIm.

> >

> > You'll see the image size, pixel location and ADU count. In a run

> I

> > did Saturday night, (10 min. subs on M33), my ADU averages in the

> > dark areas, 15770. Divide by 10 gives me a sky count of 1,500

> > approximately per minute.

> >

> > Considering I am shooting from the heart of the city, (3.2 mag

> > skies), not bad.

> >

> > Hope this helps.

> >

> > Bob

> >

> >

> > --- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...>

> wrote:

> > >

> > > Thanks, Randy. I appreciate your help on this. I've spent

some

> > > time trying to understand ADU and *think* I've got it. I do

> almost

> > > all of my CCD work from the Tucson foothills, north of the

city,

> > > shooting thru a lot of light pollution. So I get a lot of

> *noise*

> > > in my images right from the start. Even though the location is

> far

> > > from ideal, I see a number of astrophotographers in the same

> > > situation doing awfully good work, so I'm encouraged.

> > >

> > > As far as the practical aspect of measuring ADU, I'm under the

> > > impression that MaximDL's Information window is where I can do

> > > that, by looking at the "BgdAvg" number as I pass the cursor

> over

> > > the darkest part of an image. Correct? If so, that helps a

> great

> > > deal.

> > >

> > > Thanks for the explanation. More than I expected.

> > >

> > > Rob

> > >

> > >

> > >

> > > --- In MaxImDL@yahoogroups.com, "Randy Nulman" rj.nulman@v...>

> > > wrote:

> > > >

> > > > It all comes down to s/n, and you've presented two ends of

the

> > > extreme

> > > > in terms of exposure times for your subs. The major noise

> factor

> > > to

> > > > overcome with "each" exposure is the camera's read noise.

I'd

> be

> > > more

> > > > concerned about this than any blooming issues...there's

pretty

> > > good

> > > > bloom removal software available (although all come at a

price

> of

> > > some

> > > > loss of data).

> > > >

> > > > Without getting into the math, Stan Moore has determined that

> if

> > > you

> > > > expose long enough to end up with a background adu count of

> > around

> > > 800

> > > > to 1000 adu, you will have "swamped" the read noise with

> > the "sky"

> > > > noise (light pollution, etc). At that point, you have

> overcome

> > > one of

> > > > the major noise sources, and exposing longer vs more

exposures

> at

> > > > that "optimum" time are very close in terms of end results.

> > > >

> > > > Thus, try to find the optimum time for each sub exposure that

> > > produces

> > > > that 1000 minimum adu background count...then you can stop

> there

> > > and

> > > > just take as many of those as reasonably possible.

> > > >

> > > > Bottom line...too short a subexposure and read noise will

> > > > dominate....too long a subexposure and you open yourself up

to

> a

> > > > greater likelyhood of sattelites, airplanes, guiding

glitches,

> > > field

> > > > rotation due to non-perfect polar alignment, etc)....The

> > > compromise

> > > > scenario I presented above will give you the best of both

> worlds

> > > for

> > > > most targets.

> > > >

> > > > Since you indicated you have taken 2 minute exposures

already,

> it

> > > > should be an easy task to calculate at what point you will

> reach

> > a

> > > > background count of around 1000 adu....measure your

background

> > > count

> > > > with some of your images and divide by two...that's your

> > > accumulated

> > > > background count per minute...then just figure out how many

> > > minutes to

> > > > reach the target adu count. CAVEAT: if you're imaging from

> > > extremely

> > > > dark skies, it may take quite a long exposure to overcome the

> > read

> > > > noise with the "sky" noise....however, for most of us in

> visual

> > > Mag 4

> > > > to 5 skies, the subexposures aren't that long...for me it's

> > around

> > > 10

> > > > minutes minimum with a STL6303 on a 12.5 RC at F9....I

usually

> go

> > > 15

> > > > minutes as a norm.

> > > >

> > > > Hope this helps,

> > > >

> > > > Randy Nulman

> > > >

> > > >

> > > > --- In MaxImDL@yahoogroups.com, "Rob Buehler" rbuehler@a...>

> > > wrote:

> > > > >

> > > > > Is it better to take fewer, but longer exposures rather

than

> > > more,

> > > > but

> > > > > shorter exposures? I'm using an SBIG ST10XE and it doesn't

> > take

> > > more

> > > > > than a couple of minutes in some regions of the sky to get

> some

> > > > pretty

> > > > > serious blooming started. Am I better off limiting the

size

> of

> > > the

> > > > > blooms by taking 60 2 minute exposures, or ignoring the

> > blooming

> > > by

> > > > > taking 4 30 minute exposures, then eliminating them later

in

> > > Maxim

> > > > > DL? Thanks for your help.

> > > > >

> > > > > Rob

> > > > >

> > > >

> > >

> >

>







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