ASTRO: Suburban dew-drop flatfield blues

I have been having fun with a new Proline 9000 for the past month or so.
Mostly I have been making various measurements and assessing data but I have
had a few nights under the stars as well. What I don't have are a bunch of
pretty pictures to show for the effort but I do have some teasers of what
will come pretty soon.

The key issue I have been grappling with has been the issue of flats. We are
in galaxy season and nebulae are rising later than I have time to deal with
on work nights. So I have mostly been shooting RGB in Globs.

Shooting sky flats of RGB around sunset is a hurried affair: trying to get a
set of even 10 uniformly lit/ constant DN level exposures is not easy with a
large sensor such as a KAF09000 if you are attempting to keep minimum
shutter-open periods of 3 to 4 seconds to avoid the shutter transit-shading
problem.

Well with the big sensor and the Uniblitz shutter it appears a minimum
shutter open time of about 8 seconds may be a better choice: I'm seeing
significant shutter shading artifacts toward the edge of the flats with a 3
sec min with the big sensor. Not so with the PL3200 using the smaller
KAF3200 sensor, but it is a different matter with the '09000 sensor.

My typical imaging sessions during the week are unattended ones: queuing up
a sequence and going to bed with the automation software parking the scope
after completion. usually I then have it finish up the night with darks and
keep the cooler running so I can shoot flats if I get up early enough.
Lately I haven't been getting up early enough so I just turn things off in
the morning and wait until that evening to continue taking flats.

Well that's not working so well and now I know why.

The big sensor needs a big window in the camera. The thermal conductivity of
glass isn't as good as aluminum so when this big sensor is close to a big
window the middle of the window gets colder than the outer parts of the
window: more so than in smaller sensor cameras with their smaller windows.

So there's a larger temperature drop from center of window to camera case
than there is for my '6303 or CM10

What ends up happening is by morning I am having dew form on my camera
window. We've had humid nights as of late and when the dew dries by the next
afternoon, it is leaving water spots on the window. Then when I shoot my
flats I have differences in my flats now than when I shot the images.

the result are colored spots in the calibrated and combined color images
that don't look very good.

The heaters are the solution and some are in transit as I type this. But in
the meantime I took a short set of flats last night to test out the theory,
but they are noisier than I would normally use but at least they match the
window "cleanliness" state when the images were shot.

So here is the result but I had some shutter transit shading in my blue and
green flats so I had to make the background darker than I would have liked
to hide it.

http://www.narrowbandimaging.com/m17...r_rgb_page.htm

besides a lot of interesting data on RBI, I also have concluded the spider
webs were in fact the source of the spikes in my stars in the '180EDT so
that is also fixed. This has been a busy month of discovery :-)

apologies to Bob Dylan for changed name of his classic tune as the subject
of my posting :-)

nice job Richard!
I had to make a heater for my camera because of this very problem. Mine
is on the draw tube of the focuser so when I remove the camera it stays.

Richard Crisp wrote:
I have been having fun with a new Proline 9000 for the past month or so.
Mostly I have been making various measurements and assessing data but I have
had a few nights under the stars as well. What I don't have are a bunch of
pretty pictures to show for the effort but I do have some teasers of what
will come pretty soon.

The key issue I have been grappling with has been the issue of flats. We are
in galaxy season and nebulae are rising later than I have time to deal with
on work nights. So I have mostly been shooting RGB in Globs.

Shooting sky flats of RGB around sunset is a hurried affair: trying to get a
set of even 10 uniformly lit/ constant DN level exposures is not easy with a
large sensor such as a KAF09000 if you are attempting to keep minimum
shutter-open periods of 3 to 4 seconds to avoid the shutter transit-shading
problem.

Well with the big sensor and the Uniblitz shutter it appears a minimum
shutter open time of about 8 seconds may be a better choice: I'm seeing
significant shutter shading artifacts toward the edge of the flats with a 3
sec min with the big sensor. Not so with the PL3200 using the smaller
KAF3200 sensor, but it is a different matter with the '09000 sensor.

My typical imaging sessions during the week are unattended ones: queuing up
a sequence and going to bed with the automation software parking the scope
after completion. usually I then have it finish up the night with darks and
keep the cooler running so I can shoot flats if I get up early enough.
Lately I haven't been getting up early enough so I just turn things off in
the morning and wait until that evening to continue taking flats.

Well that's not working so well and now I know why.

The big sensor needs a big window in the camera. The thermal conductivity of
glass isn't as good as aluminum so when this big sensor is close to a big
window the middle of the window gets colder than the outer parts of the
window: more so than in smaller sensor cameras with their smaller windows.

So there's a larger temperature drop from center of window to camera case
than there is for my '6303 or CM10

What ends up happening is by morning I am having dew form on my camera
window. We've had humid nights as of late and when the dew dries by the next
afternoon, it is leaving water spots on the window. Then when I shoot my
flats I have differences in my flats now than when I shot the images.

the result are colored spots in the calibrated and combined color images
that don't look very good.

The heaters are the solution and some are in transit as I type this. But in
the meantime I took a short set of flats last night to test out the theory,
but they are noisier than I would normally use but at least they match the
window "cleanliness" state when the images were shot.

So here is the result but I had some shutter transit shading in my blue and
green flats so I had to make the background darker than I would have liked
to hide it.

http://www.narrowbandimaging.com/m17...r_rgb_page.htm

besides a lot of interesting data on RBI, I also have concluded the spider
webs were in fact the source of the spikes in my stars in the '180EDT so
that is also fixed. This has been a busy month of discovery :-)

apologies to Bob Dylan for changed name of his classic tune as the subject
of my posting :-)




--
John N. Gretchen III
N5JNG NCS304
http://www.tisd.net/~jng3

Richard Crisp wrote:
I have been having fun with a new Proline 9000 for the past month or so.
Mostly I have been making various measurements and assessing data but I have
had a few nights under the stars as well. What I don't have are a bunch of
pretty pictures to show for the effort but I do have some teasers of what
will come pretty soon.

The key issue I have been grappling with has been the issue of flats. We are
in galaxy season and nebulae are rising later than I have time to deal with
on work nights. So I have mostly been shooting RGB in Globs.

Shooting sky flats of RGB around sunset is a hurried affair: trying to get a
set of even 10 uniformly lit/ constant DN level exposures is not easy with a
large sensor such as a KAF09000 if you are attempting to keep minimum
shutter-open periods of 3 to 4 seconds to avoid the shutter transit-shading
problem.

Well with the big sensor and the Uniblitz shutter it appears a minimum
shutter open time of about 8 seconds may be a better choice: I'm seeing
significant shutter shading artifacts toward the edge of the flats with a 3
sec min with the big sensor. Not so with the PL3200 using the smaller
KAF3200 sensor, but it is a different matter with the '09000 sensor.

My typical imaging sessions during the week are unattended ones: queuing up
a sequence and going to bed with the automation software parking the scope
after completion. usually I then have it finish up the night with darks and
keep the cooler running so I can shoot flats if I get up early enough.
Lately I haven't been getting up early enough so I just turn things off in
the morning and wait until that evening to continue taking flats.

Well that's not working so well and now I know why.

The big sensor needs a big window in the camera. The thermal conductivity of
glass isn't as good as aluminum so when this big sensor is close to a big
window the middle of the window gets colder than the outer parts of the
window: more so than in smaller sensor cameras with their smaller windows.

So there's a larger temperature drop from center of window to camera case
than there is for my '6303 or CM10

What ends up happening is by morning I am having dew form on my camera
window. We've had humid nights as of late and when the dew dries by the next
afternoon, it is leaving water spots on the window. Then when I shoot my
flats I have differences in my flats now than when I shot the images.

the result are colored spots in the calibrated and combined color images
that don't look very good.

The heaters are the solution and some are in transit as I type this. But in
the meantime I took a short set of flats last night to test out the theory,
but they are noisier than I would normally use but at least they match the
window "cleanliness" state when the images were shot.

So here is the result but I had some shutter transit shading in my blue and
green flats so I had to make the background darker than I would have liked
to hide it.

http://www.narrowbandimaging.com/m17...r_rgb_page.htm

besides a lot of interesting data on RBI, I also have concluded the spider
webs were in fact the source of the spikes in my stars in the '180EDT so
that is also fixed. This has been a busy month of discovery :-)

apologies to Bob Dylan for changed name of his classic tune as the subject
of my posting :-)

Ditto here. I solved the shutter problem by using something akin to T
shirt flats. My wife made a cover for the scope out of three layers of
fine thread muslin, the middle one is dark gray. This allows me to
shoot flats by day even with the sun out. I point the scope such that
no sunlight falls on the cover but it is pointed at a bright spot in the
sky. Average exposure time for Lum is 10 seconds. It goes up to over a
minute for narrow band so there I use a three layer white cover that
brings it back down to about 7 seconds. RGB run about 35 seconds which
is manageable as I can just set it and let it run. This works well with
my closed tube. Not so sure it would with your open truss.

I have the same dew problem but only in winter when it is frost.
Wrapping heat tape about the camera does the trick. Since I run
unattended and that cable could snag I do have a quick disconnect power
connector on both ends of the power cord in case it snags. So far that
hasn't happened except in a test. They released without even the
slightest glitch to tracking. SBIG sent me a heater for the optical
window but that didn't help much and did cut down my cooling by about
3C. It was quickly disconnected. Heat tape doesn't bother the cooling
that I can detect. I leave it on constantly as the warmth seems to
drive out any condensation by day which also helps a lot. Being a
closed tube moisture is slow to reenter once driven off. I keep the
corrector dew heater running constantly as well for this same reason.
Otherwise by night I can find frost on the inside of the corrector. Not
a good place for it!

52 days of overcast nights and counting. It is supposed to be partly
cloudy night for Monday through Wednesday. Yep full moon time. But I
only have less than 2 hours to image a night up here so hardly worth the
effort.

M17 shows the same slightly blue color toward the brighter regions I got
when processing it. I don't usually see that in other photos but
nothing I did could get rid of it. Now I'm seeing a few like yours that
show it is real. It's just too low for a good shot from my latitude
however.

Rick

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

"Rick Johnson" wrote in message
. com...


Richard Crisp wrote:
I have been having fun with a new Proline 9000 for the past month or so.
Mostly I have been making various measurements and assessing data but I
have had a few nights under the stars as well. What I don't have are a
bunch of pretty pictures to show for the effort but I do have some
teasers of what will come pretty soon.

The key issue I have been grappling with has been the issue of flats. We
are in galaxy season and nebulae are rising later than I have time to
deal with on work nights. So I have mostly been shooting RGB in Globs.

Shooting sky flats of RGB around sunset is a hurried affair: trying to
get a set of even 10 uniformly lit/ constant DN level exposures is not
easy with a large sensor such as a KAF09000 if you are attempting to keep
minimum shutter-open periods of 3 to 4 seconds to avoid the shutter
transit-shading problem.

Well with the big sensor and the Uniblitz shutter it appears a minimum
shutter open time of about 8 seconds may be a better choice: I'm seeing
significant shutter shading artifacts toward the edge of the flats with a
3 sec min with the big sensor. Not so with the PL3200 using the smaller
KAF3200 sensor, but it is a different matter with the '09000 sensor.

My typical imaging sessions during the week are unattended ones: queuing
up a sequence and going to bed with the automation software parking the
scope after completion. usually I then have it finish up the night with
darks and keep the cooler running so I can shoot flats if I get up early
enough. Lately I haven't been getting up early enough so I just turn
things off in the morning and wait until that evening to continue taking
flats.

Well that's not working so well and now I know why.

The big sensor needs a big window in the camera. The thermal conductivity
of glass isn't as good as aluminum so when this big sensor is close to a
big window the middle of the window gets colder than the outer parts of
the window: more so than in smaller sensor cameras with their smaller
windows.

So there's a larger temperature drop from center of window to camera case
than there is for my '6303 or CM10

What ends up happening is by morning I am having dew form on my camera
window. We've had humid nights as of late and when the dew dries by the
next afternoon, it is leaving water spots on the window. Then when I
shoot my flats I have differences in my flats now than when I shot the
images.

the result are colored spots in the calibrated and combined color images
that don't look very good.

The heaters are the solution and some are in transit as I type this. But
in the meantime I took a short set of flats last night to test out the
theory, but they are noisier than I would normally use but at least they
match the window "cleanliness" state when the images were shot.

So here is the result but I had some shutter transit shading in my blue
and green flats so I had to make the background darker than I would have
liked to hide it.

http://www.narrowbandimaging.com/m17...r_rgb_page.htm

besides a lot of interesting data on RBI, I also have concluded the
spider webs were in fact the source of the spikes in my stars in the
'180EDT so that is also fixed. This has been a busy month of discovery
:-)

apologies to Bob Dylan for changed name of his classic tune as the
subject of my posting :-)

Ditto here. I solved the shutter problem by using something akin to T
shirt flats. My wife made a cover for the scope out of three layers of
fine thread muslin, the middle one is dark gray. This allows me to shoot
flats by day even with the sun out. I point the scope such that

That has been one of the things I have done for some time with the emission
line filters. I use what amounts to an attenuator and diffuser

It works better when I am certain I have no light leaks.

but it is a pretty good scheme. I need to get set up for that again Rick, if
I keep shooting RGB

Richard Crisp wrote:

"Rick Johnson" wrote in message
. com...


Richard Crisp wrote:

I have been having fun with a new Proline 9000 for the past month or so.
Mostly I have been making various measurements and assessing data but I
have had a few nights under the stars as well. What I don't have are a
bunch of pretty pictures to show for the effort but I do have some
teasers of what will come pretty soon.

The key issue I have been grappling with has been the issue of flats. We
are in galaxy season and nebulae are rising later than I have time to
deal with on work nights. So I have mostly been shooting RGB in Globs.

Shooting sky flats of RGB around sunset is a hurried affair: trying to
get a set of even 10 uniformly lit/ constant DN level exposures is not
easy with a large sensor such as a KAF09000 if you are attempting to keep
minimum shutter-open periods of 3 to 4 seconds to avoid the shutter
transit-shading problem.

Well with the big sensor and the Uniblitz shutter it appears a minimum
shutter open time of about 8 seconds may be a better choice: I'm seeing
significant shutter shading artifacts toward the edge of the flats with a
3 sec min with the big sensor. Not so with the PL3200 using the smaller
KAF3200 sensor, but it is a different matter with the '09000 sensor.

My typical imaging sessions during the week are unattended ones: queuing
up a sequence and going to bed with the automation software parking the
scope after completion. usually I then have it finish up the night with
darks and keep the cooler running so I can shoot flats if I get up early
enough. Lately I haven't been getting up early enough so I just turn
things off in the morning and wait until that evening to continue taking
flats.

Well that's not working so well and now I know why.

The big sensor needs a big window in the camera. The thermal conductivity
of glass isn't as good as aluminum so when this big sensor is close to a
big window the middle of the window gets colder than the outer parts of
the window: more so than in smaller sensor cameras with their smaller
windows.

So there's a larger temperature drop from center of window to camera case
than there is for my '6303 or CM10

What ends up happening is by morning I am having dew form on my camera
window. We've had humid nights as of late and when the dew dries by the
next afternoon, it is leaving water spots on the window. Then when I
shoot my flats I have differences in my flats now than when I shot the
images.

the result are colored spots in the calibrated and combined color images
that don't look very good.

The heaters are the solution and some are in transit as I type this. But
in the meantime I took a short set of flats last night to test out the
theory, but they are noisier than I would normally use but at least they
match the window "cleanliness" state when the images were shot.

So here is the result but I had some shutter transit shading in my blue
and green flats so I had to make the background darker than I would have
liked to hide it.

http://www.narrowbandimaging.com/m17...r_rgb_page.htm

besides a lot of interesting data on RBI, I also have concluded the
spider webs were in fact the source of the spikes in my stars in the
'180EDT so that is also fixed. This has been a busy month of discovery
:-)

apologies to Bob Dylan for changed name of his classic tune as the
subject of my posting :-)

Ditto here. I solved the shutter problem by using something akin to T
shirt flats. My wife made a cover for the scope out of three layers of
fine thread muslin, the middle one is dark gray. This allows me to shoot
flats by day even with the sun out. I point the scope such that


That has been one of the things I have done for some time with the emission
line filters. I use what amounts to an attenuator and diffuser

It works better when I am certain I have no light leaks.

but it is a pretty good scheme. I need to get set up for that again Rick, if
I keep shooting RGB

The multi port system on the back of my scope does leak light in
daylight conditions with such long exposures for the flats. She also
made me a black bag that covers the camera and ports preventing the
light leaks. Cooling is reduced as the hot air builds in the bag.
Still I usually can get the flats taken before the cooling hits 80% due
to the heat build up. On the few occasions it was a problem I just
stopped, opened the bag to release the air and after a couple minutes
could finish the series. Sure beats trying to get something at dusk
before the stars come out too strongly. I gave up on that ages ago.

Rick

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

"Rick Johnson" wrote in message
. com...


That has been one of the things I have done for some time with the
emission line filters. I use what amounts to an attenuator and diffuser

It works better when I am certain I have no light leaks.

but it is a pretty good scheme. I need to get set up for that again Rick,
if I keep shooting RGB

The multi port system on the back of my scope does leak light in daylight
conditions with such long exposures for the flats. She also made me a
black bag that covers the camera and ports preventing the light leaks.
Cooling is reduced as the hot air builds in the bag. Still I usually can
get the flats taken before the cooling hits 80% due to the heat build up.
On the few occasions it was a problem I just stopped, opened the bag to
release the air and after a couple minutes could finish the series. Sure
beats trying to get something at dusk before the stars come out too
strongly. I gave up on that ages ago.



I use aluminum foil to cure the light leaks but is sure is ugly. It's gotten
expensive as of late too...